Deep and ultra-deep marine carbonates have abundant oil and gas resources and are very important for the discovery of oil and gas. They have been considered as a realistic field to achieve energy replacement in China ^[1,2]. In the past 20 years, many large and medium-sized oil and gas fields have been discovered in deep marine carbonates in the Tarim Basin and the Sichuan Basin. Examples include the Ordovician karst fracture-cavity reservoirs represented by Tahe-Lunnan and Tazhong oil and gas fields in the Tarim Basin ^[3,4,5], Upper Permian-Lower Triassic reef/shoal reservoirs represented by Puguang, Yuanba and Longgang gas fields in the Sichuan Basin ^[6], and shoal rock reservoirs in Sinian-Lower Cambrian represented by Anyue gas field ^[7,8,9]. Recently, carbonate tidal flat lithologic gas reservoirs have been discovered in the Triassic Leikoupo Formation in front of the Longmen Mountain in the Sichuan Basin. Carbonate reservoirs controlled by coupled fault-fluid modification have been discovered in the Permian Maokou Formation and Qixia Formation ^[10]. Potential microbial carbonate reservoirs in the ancient Precambrian strata have been gaining more and more attention ^[11,12].

In the recent ten years, through continuing research on the geological theories, seismic processing methods and drilling technologies, a major exploration discovery has been achieved in ultra-deep carbonates in the Shunbei area located between the Tazhong and Tabei uplifts in the Tarim Basin. In the Shunbei area, high production of light oil below the depth of 7000 m refreshes the conventional understanding of petroleum geology. The discovery and successful production capacity construction of the Shunbei oil and gas field can be considered as a milestone achievement in the history of exploration and development in the deep and ultra-deep marine carbonates. This article reviews the exploration and development history of the Shunbei ultra-deep carbonate oil and gas field in the Tarim Basin, summarizes the advances in exploration and development technologies during the National 13^th Five-Year Plan Period of China, and points out challenges and key research directions in the National 14^th Five-Year Plan Period of China. This study can further enrich the theory and technology of exploration and development in deep and ultra-deep carbonates in China, providing important guidance for the exploration and development of ultra-deep carbonate reservoirs in other basins in general.

The Shunbei oil and gas field is located in the Shuntuoguole Low Uplift at the center of the Tarim Basin. This low uplift is adjacent to the Shaya Uplift in the north and the Katake Uplift in the south. It is located between the Awati Depression and the Manjiaer Depression in the east-west direction in a relatively low “saddle” position (Fig. 1a). After the stable tectonic subsidence with weak extension in the Early Caledonian, the Shuntuoguole Low Uplift was formed and developed under regional compression in the Middle-Late Caledonian-Early Hercynian. The adjustment and modification of the Shuntuoguole Low Uplift occurred since the Middle-Late Hercynian and the Indosinian, when the present pattern of the Shuntuoguole Low Uplift was formed ^{[13,14,15,16]}. Compared with the Shaya and Katake paleo-uplifts, the Shuntuoguole Low Uplift is structurally stable with weak tectonic deformation, but with multi-stage activated strike-slip faults formed therein ^[15,16]. In this region, the stratum is relatively complete with only a few sections missing.

Controlled by tectonic and sedimentary evolution, a series of high-quality source rocks of slope facies (Yurtus Formation) were developed in the Early Cambrian. During the Cambrian-Middle Ordovician, carbonate strata with a thickness of about 3000 m were formed. Under the modification of strike-slip faults, large-scale fault-controlled reservoirs formed ^[17]. In the Late Ordovician, the continental shelf facies mudstone with a thickness of about 500-2500 m was deposited in this area. Together with the underlying fault-controlled reservoirs in the carbonates, a good reservoir-cap combination was formed (Fig. 1). It has been the main subject for exploration and development in the Shunbei oil and gas field ^[17,18].

Up to present, the discovered oil and gas reservoirs in the Shunbei oil and gas field are mainly embedded in the Ordovician Yingshan Formation-Yijianfang Formation with a burial depth of 7200-8800 m. Drilling practices have revealed that oil and gas reservoirs are mainly distributed along the major strike-slip faults. The reservoir spaces are fracture-cavity systems formed under structural deformation ^{[17, 19-20]}. In the oil and gas field, the hydrocarbon phase varies significantly. Oil is distributed in the north and the west, whereas the gas is distributed in the east and the south (Fig. 2). The target layers in the western part of the Shunbei oil and gas field are buried deeper than 7000 m, with mainly light oil reservoirs. The target layers in the middle and eastern parts of the Shunbei oil and gas field are buried deeper than 6500 m, mainly with condensate and dry gas reservoirs. By the end of 2021, the Shunbei oil and gas field has proved reserves more than 2×10⁸ t (oil equivalent). A production capacity field of one million tons has been built therein. It is estimated that the oil and gas resources distributed along the 18 major strike-slip faults in the Shunbei oil and gas field reach 17×10⁸ t (oil equivalent).

The discovery of the Shunbei oil and gas field went through a difficult process. In 1984, oil and gas discovery has been achieved in Ordovician marine carbonate rocks by Well Shacan 2 in the Tarim Basin. After more than 10 years of exploration in the Shaya uplift, a typical unconformity karst-controlled fracture-cavity large oil field, Tahe oil field, was discovered in 1997. Since then, China Petroleum & Chemical Corporation (Sinopec) has learned the successful experience of the Tahe oil field and adhered to the exploration idea of ​​"approaching to the main source rocks, focusing on large paleo-uplifts and paleo-slopes" in order to discover large oil and gas fields in the Katake Uplift, the Bachu Uplift and Hetian paleo uplift. However, no large-scale oil and gas field was discovered. Since 2010, Sinopec has further carried out research on the dynamic evolution of "source-reservoir-cap- accumulation", and has gradually recognized that high quality source rocks and thick layers of argillaceous caprocks are developed in the middle and lower Cambrian in the slope areas of the Shaya and Katake paleo-uplifts, forming excellent "source-cap" assemblage. Meanwhile, the exploration and development practices in the Tahe oil field and its periphery have demonstrated that the strike-slip faults with multi-stage activities have important controls on reservoir formation and hydrocarbon accumulation ^[21,22]. This led to the notion that strike-slip faults in the slope regions in structural low areas might be favorable exploration domains, which are worth for further investigations.

From 2011 to 2014, the Yuejin area and the Shunnan area with relatively shallow buried depth of the target layer in the north and southeast of the Shuntuoguole Low Uplift, respectively, have been firstly explored. Wells, Shunnan 1, Yuejin 1X, Shunnan 4, Shunnan 5, etc., have been drilled. Drilling results confirmed that fault-controlled carbonate reservoirs were developed in the northern and southeastern parts of the Shuntuoguole Low Uplift. Oil and gas have been accumulated and enriched along the strike-slip faults. Important natural gas discoveries have also been achieved in the Shunnan area, and high-yield industrial gas flows have been obtained from wells Shunnan 4 and Shunnan 5 (Table 1). However, due to high formation temperature (generally greater than 170 °C) and high pressure (over 120 MPa in some wells) of the target formation in the Shunnan area, it was difficult to implement drilling, well completion and testing. Consequently, the exploration was shifted to the central and northern parts of the Shuntuoguole Low Uplift.

In 2015, high-yield industrial oil and gas flows have been obtained from Well Shuntuo 1 near the Shunbei No. 8 fault in the central part of the Shuntuoguole Low Uplift and Well Shunbei 1-1H in the north of the Shunbei No. 1 fault, successively (Table 1). Meanwhile, research and drilling practices have further confirmed that although the oil and gas resources were deeply buried in the northern part of the Shuntuoguole low uplift, the geothermal gradient was low with mainly light oil and condensed oil accumulated. From 2015 to 2016, all the 6 wells drilled on the Shunbei No. 1 fault have obtained high-production industrial oil and gas flow, announcing the successful discovery of the Shunbei oil and gas field ^{[17, 21]}. Since then, exploration has expanded to multiple strike- slip faults in the west, the south and the east of the Shunbei oil and gas field. From 2018 to 2020, wells Shunbei 5X and Shunbei 53X drilled on the Shunbei No. 5 fault obtained industrial oil and gas flows. Well Shunbei 7X in the Shunbei No. 7 fault has also obtained oil and gas. Since 2021, five wells, including Shunbei 41X, deployed in Shunbei No. 4 and No. 8 faults have obtained 1000 tons (oil and gas equivalent) of oil and gas flows per day (Table 1). Oil and gas shows from wells Shunbei 11 and Shunbei 111 deployed in Shunbei No. 11 fault further confirmed that the Ordovician carbonate rocks in the Shunbei oil and gas field contained oil and gas, and strike-slip fault zones are favorable locations for oil and gas accumulation.Since the discovery of the Shunbei oil and gas field in 2016, the integrated evaluation of exploration and development has been improved continuously. The wells drilled in the Shunbei No. 1 fault, its branch fault and the northern segment of the Shunbei No. 5 fault have successively yielded high production oil and gas flows. Since 2019, with the exploration and discovery in the southern segment of the Shunbei No. 5 fault and the Shunbei No. 4 and No. 8 faults, the integrated evaluation of exploration and development has further expanded to the south and the east. In development, the plan has been continuously adjusted and optimized according to the characteristics of oil and gas reservoirs in different fault zones, so as to improve the drilling and reservoir improving technologies. By the end of 2021, in Shunbei No. 1 district, a production capacity of one million tons has been achieved with more than 50 production wells in operation, with 317×10⁴ t of crude oil and 13.8×10⁸ m³ of natural gas produced accumulatively. In total, more than 30 wells have been drilled in the southern segment of the Shunbei No. 5 fault zone and the Shunbei No. 4 fault zone, leading to the complete control on these two faults.The process of exploration and quick production capacity construction of the Shunbei oil and gas field has been accompanied by advances in geological theoretical understanding and improvements of geophysical and engineering technologies.

2.1.1. Development of major source rocks and hydrocarbon generation

The geochemical characteristics of crude oil from the Ordovician oil and gas reservoirs discovered in the Shunbei area were similar to those of the Tahe Oilfield crude oil, with C₂₁TT<C₂₃TT, low gamma cerane, and a "V"-shaped distribution of C₂₇-C₂₈-C₂₉ααα20R regular steranes. The regular steranes content is relatively higher than rearranged steranes content. The carbon isotopic composition of crude oil is light. Up to date, researches suggest that major source rocks were developed in the Lower Cambrian Yuertusi Formation ^{[17, 21, 23]}.Since the 13^th Five-Year Plan Period of China, significant effort has been taken to understand the development and distribution model of the Yuertusi Formation. Based on detailed studies of outcrops, drilling and seismic data, a gentle-slope deposition model has been established ^{[21, 24-25]} (Fig. 3). During the deposition of the Yuertusi Formation, inner, middle and outer gentle-slope depositions occurred surrounding the “central archicontinent”. The abundance of organic matter of the tidal flat clastic rocks on the inner gentle slope drilled by Xiahe 1 and Fang 1 wells ranges from 0.04% to 0.38% with an average of 0.22%. In contrast, wells Batan 5 and Mabei 1 have not revealed Yuertusi Formation ^[25-26]. The organic matter abundance in black shale and siliceous shale on the outer gentle slope of Wells Yuli 1, Kongtan 1 and Tadong 2 is 1.64%-33.1%, with an average of 11.8% ^[27]; the organic matter abundance in the siliceous rock and black shale on the gentle slope revealed by Well Xinghuo 1 ranges from 1.00% to 9.43% with an average value of 4.71% ^[28]. Although no wells have been drilled through the Yuertusi Formation in the Shunbei area, it is inferred that the Yuertusi Formation of middle and outer gentle slope facies developed therein with high-quality source rocks. This provides ideal geological conditions for massive liquid hydrocarbon accumulation and the formation of large oil and gas field.

2.1.2. Paleotemperature field and hydrocarbon generation of source rocks

As shown in Fig. 2, the oil and gas distribution in the Ordovician in the Shunbei oil and gas field is characterized by that gas reservoirs are distributed in the south and the east, whereas the oil reservoirs are distributed in the west and the north. In the Shunbei area, light liquid oil has been well kept below the depth of more than 8000 m. This is due to lower paleo-geothermal gradient and slow hydrocarbon generation under high pressure in the ultra-deep strata ^[19,20].The Tarim Basin has gone through four major tectonic evolution stages, including: Cambrian-Silurian-Devonian, Carboniferous-Permian, Triassic-Jurassic and Cretaceous- Cenozoic. The paleo-geothermal field has changed significantly across four different evolution stages, including high heat flow ("hot" basin) during the Sinian-Ordovician, thermal attenuation in the Silurian-Late Paleozoic (transition from a "hot" basin to a "cold" basin), and stable thermal evolution in the Mesozoic (low heat flow "cold" basin stage), and Cenozoic lithospheric flexural thermal evolution ^[29,30]. Studies have shown that the paleotemperature of the source rocks in the Yuertusi Formation in the Shunbei area during the Late Ordovician was 120-125 °C, the paleotemperature of the source rock in the Late Hercynian was about 150-160 °C, and the current temperature is 185 °C. The geothermal field in the Shunnan area is significantly hotter than that in the central and western of the Shunbei area. The paleotemperature of the source rocks in the Yuertusi Formation in the Shunnan area during the Late Ordovician was 180- 190 °C, and that in the Late Hercynian period was about 200-210 °C. The current temperature therein is 235 °C ^[20].The Shunbei oil and gas field is located in a tectonically stable and subsidence environment for a long time, characterized by continuing low geothermal background. The Lower Cambrian source rocks have a long liquid oil generation period under the conditions of low geothermal background, large burial depth and high pressure. They were in the stages of generating high-mature oil and condensated oil and gas in the late Hercynian period and the Yanshanian-Himalayan Period, respectively (Fig. 4a). The Lower Cambrian source rocks in the east of the Shunbei oil and gas field are characterized by high geothermal and high degree of geothermal evolution. Generation of highly mature oil and condensated oil and gas occurred in the late Hercynian period, whereas generation of condensated oil and gas occurred in the Yanshanian-Himalayan period (Fig. 4b).

2.1.3. Hydrocarbon phases and their distribution in the Shunbei oil and gas field

The hydrocarbon phase of the Shunbei oil and gas field is controlled not only by the history of hydrocarbon generation of the Lower Cambrian source rocks but also by the adjustment reconstruction of the hydrocarbon after their accumulation. Studies on hydrocarbon accumulation have shown that the Shunbei area has experienced multiple stages of hydrocarbon accumulation, including the late Caledonian, late Hercynian and Yanshanian-Himalayan stages ^{[17, 19-20, 31]}. The process of hydrocarbon accumulation differs among distinct strike-slip faults in various regions. Recent studies suggest that oil reservoirs in the middle and the east of the Shunbei oil and gas field have experienced thermal cracking and sulfate thermochemical reduction modification (TSR) to different extent^[32,33,34]. According to the studies on the paleo-geothermal history of the Shunbei oil and gas field, hydrocarbon generation of the major source rocks and the adjustment reconstruction of oil reservoirs, the hydrocarbon phase distribution of the Shunbei oil and gas field has been predicted (Fig. 5). The predicted phase distribution laid the foundation for determining the exploration directions.

2.2.1. Development characteristics of strike-slip faults

During the 12th Five-Year Plan Period of China, a few geologists believed that the strata were continuously deposited on the slope regions of the Tazhong and Tabei uplifts with little tectonic deformation, whereas the multi-stage active strike-slip faults played important roles on reservoir formation and hydrocarbon accumulation in carbonate rocks in this region ^[35,36]. This idea provided important theoretical support for the discovery of the Shunbei oil and gas field. Compared with large-scale strike-slip faults (e.g. plate boundary transform faults and indent-linked strike-slip faults) with displacements reaching several hundred to several thousand km ^[37,38], the displacements of strike-slip faults in the Shunbei area are commonly smaller than 2 km ^[39], also known as intracratonic strike-slip faults ^[40,41,42].Since the “13th Five-Year Plan” period, based on the interpretation of 2D and 3D seismic data, the overall distribution and development characteristics of the intracratonic strike-slip fault system in the Shunbei area and its surroundings have been studied. These strike-slip faults are characterized by regional differences ^{[15, 20]}, particularly in their distributions in the east and west regions (Fig. 1). For instance, the No. 4, No. 8, No. 12, No. 14 faults located to the east of the Shunbei No. 5 fault are striking 30° from the north to the east, forming a sub-parallel northeast- oriented strike-slip fault system. In contrast, the No. 7, No. 9, No. 11, No. 13 faults located to the west of the Shubei No. 5 fault area striking 20° from the north to the west, forming a northwest-oriented strike-slip fault system. No. 1 and No. 2 faults conjoin with No. 5 fault, forming its branch faults. Because Shunbei No. 5 fault and the branch faults are located between the northeast-oriented and northwest-oriented faults, they might be formed as transition structures. A few “X-shaped” apparent conjugate faults are distributed between No. 5 and No. 1 faults adjacent to the Shaya Uplift. Detailed seismic and geological interpretation on layered structures and movement period of strike-slip faults suggest that differences exist among various strike-slip fault arrays. The above- mentioned strike-slip faults were mainly formed during the III phase of the Middle Caledonian (in the Late Ordovician) ^{[16, 41]}. The northeast-oriented strike-slip faults were later reactivated in the Late Caledonian-Early Hercynian, and Middle to Late Hercynian. In contrast, reactivation of the northwest-oriented strike-slip faults after the Late Caledonian are not shown by seismic data^[20].The strike-slip faults in the Shunbei area are characterized by “layered deformation” in profile. They display subvertical segments as “principal displacement zone” at depth and en echelon normal fault zones where relatively shallow as a result of superposition of multi-stage movements. Major strike-slip faults in the Shunbei area cut through the Cambrian and downward to the basement. They propagated upward to the Carboniferous and Permian (Fig. 6). At the top of carbonates of the Middle to Lower Ordovician, the strike-slip faults display four structural styles along their strike, e.g., pull-aparts, push-ups, strike-slip segments and composite structures^{[20, 41]}.

2.2.2. Controls of strike-slip faults on reservoir formation

The fracture-cavity reservoirs controlled by ultra-deep faults in the Shunbei oil and gas field were formed along with the movement of the strike-slip faults in the Shunbei oil and gas field. The reservoir spaces are mainly fault controlled fracture-cavity systems, including caves, fractures, fault breccia and a few dissolution pores distributed along fractures (Fig. 7, Table 2). Drilling practices have demonstrated that the main target layers (Ordovician Yingshan Formation-Yijianfang Formation) have very strong spatial heterogeneity in the reservoir rocks distributed along strike-slip faults. The physical properties also vary significantly (Table 2). The reservoir spaces are mainly distributed along the strike-slip faults, which commonly cause drilling breaks and drilling fluid loss of horizontal and sidetracking wells when drilling into strike-slip fault zones. The thicknesses of drilling breaks are generally smaller than 5 m and mostly about 2 m ^[17]. In contrast to wells traversing strike-slip faults, the wells located more than a hundred meters away from the strike-slip faults rarely had drilling breaks and mud loss occur, suggesting that rock matrix developed between strike-slip faults are tight and have nearly no reservoir spaces developed ^[43,44].

During the "13th Five-Year Plan Period of China, based on exploration practices in the Shunbei area and comprehensive studies on outcrop description of strike-slip faults in carbonates, it is confirmed that the strike-slip faults in the Shunbei oil and gas field played an important role in the formation of ultra-deep carbonate reservoirs ^{[17, 20, 43]}.

Strike-slip faults developed in tight carbonates in the Middle-Lower Ordovician have fault core-damage zone structures, which are three dimensional geological bodies characterized by complex internal architectures ^[45]. The outcrop studies and detailed description of strike-slip faults in the Ordovician carbonates in the Aksu area of the Tarim Basin suggest that fault breccias develop in fault core. Cavities are commonly developed among fault breccias ^[41]. The image log interpretation of Well Shunbei 7X which drilled through strike-slip faults also show the presence of fault breccias and damage zones. Fault breccias in the image log are characterized by “gravel-like bright spots” with high porosities and permeabilities ^{[44, 46]}. Recently, Well Shunbei 41X drilled through Shunbei No. 4 fault further revealed the transverse and vertical heterogeneities. In transverse direction, the fault zone is characterized by clustered core-damage zone structures ^[47]. The thickness of brecciated zones ranges from 3.48 m to 8.45 m, and the fracture zone thickness is 2.98 m (Fig. 8) In vertical direction, the heterogeneities of fault controlled reservoir rocks are characterized by various types and volumes, which are presumably controlled by mechanical stratigraphy ^[48].

The scale of fault controlled reservoirs in the Shunbei area is controlled by the segmentation styles and movement intensity. There are three common types of segments: push-ups, pull-aparts and strike-slip segments. Push-ups and pull-aparts are commonly developed at step-over areas. The widths of push-ups and pull-aparts are generally controlled by the distance between the two adjacent segments. Therefore, their widths are commonly larger than that of strike-slip segment ^[49]. The corresponding scale of reservoir rocks is also larger ^[18]. Under the same conditions, the more intensive a fault segment moves, the volume of fault controlled reservoir rocks becomes larger. For instance, wells Shubei 7 and Shunbei 5 are drilled on the push-ups of Shunbei No. 7 fault and No. 5 fault, respectively ^[49]. These two faults are both northwest-oriented strike-slip faults. The push-ups are both characterized by left-stepping and right lateral strike-slip. However, Shunbei No. 7 fault has a smaller length and movement intensity than those of Shunbei No. 5 fault. The former is limited within the northwest region of the Shunbei area, whereas the latter traverses the Tabei Uplift, the Shuntuoguole Low Uplift, and the Tazhong Uplift. The scale of reservoir revealed by Well Shunbei 7 is also smaller than that of Well Shunbei 5.

2.2.3. Controls of strike-slip faults on hydrocarbon accumulation

The ultra-deep fault-controlled fracture-cavity reservoirs in the Shunbei area are characterized by a “steeply-dipping plate” shape. They have large oil columns and high productivity. Differences in hydrocarbon phases and abundances occur among different strike-slip faults. This is closely related to the development characteristics of reservoir rocks and fault-source connectivity ^[17,18,19].

The major strike-slip faults in the Shunbei area cut down to the basement and cut into Cambrian source rocks at depth. The structural styles in profile control the fault-source connectivity, causing differences in conducting abilities, and further control the degree of hydrocarbon accumulation. On one hand, as vertical migration conduits, the strike-slip faults cut into the Lower Cambrian source rocks and Middle-Lower Ordovician reservoir rocks. In pathway of migration, the faults developed through the Middle-Lower Cambrian gypsum layers. When the thickness of gypsum layers is large, the overlying target layer is commonly drilled with water or oil reservoirs with high water content ^[18]. On the other hand, high-production oil and gas are commonly discovered along the middle strike-slip segment of the composite structures developed on the southern segment of the Shunbe No. 5 fault. Because the central strike-slip segment cut through the Cambrian strata and cut into the Yuertusi source rocks, whereas the graben fault planes propagate from the above down to the Middle-Upper Ordovician and die out, i.e., not connected with source rocks, the hydrocarbon accumulation rarely occurred on graben faults ^[41].

Because the segmentation structural styles of strike- slip faults control the size and spatial distribution of fault controlled reservoir rocks, they also control the segmentation of reservoirs.

Taking the northwest-oriented Shunbei No. 1 fault as an example, detailed structural interpretation suggest that it is composed of 8 left-stepping segments. Pull-part structures occur at the stepovers ^[41]. The interference well tests show that four well groups on the Shunbei No. 1 fault are connected, which are consistent with the geometries of the segments. Wells located on different segments, even closely located, are not connected. Distant wells located on the same segment can be well-connected. Therefore, oil and gas reservoirs are distributed along strike-slip faults and showing “one segment, one reservoir” characteristics.

As summarized above, strike-slip faults in the Shunbei oil and gas field control the formation of fracture-cavity reservoir rocks and the distribution of oil and gas reservoirs. The development of strike-slip faults and their controls on reservoir formation and hydrocarbon accumulation are illustrated in a schematic model in Fig. 9. Steeply-dipping strike-slip faults have multi-episode activities. Under structural deformation, fault-fracture systems were formed. Though rock-fluid interaction and modification, the “plate-shape” fault controlled fracture- cavity rocks were formed. Meanwhile, strike-slip faults developed downward to Lower Cambrian high-quality source rocks. Along with multi-phase fault movement, oil and gas were accumulated, forming fault controlled fracture-cavity oil and gas reservoirs with large oil and gas column (max. height reaching 580 m). The differences in segmentation, sectional structural styles and movement intensities of strike-slip faults control the variations in reservoir sizes among different parts of a single strike-slip fault and among distinct strike-slip faults.

During the 13th Five-Year Plan Period of China, in order to solve key technical problems such as the imaging and detailed description of the ultra-deep strike-slip fault zones and the fault-controlled reservoirs in the desert, through continuous studies on the integration of acquisition-processing-interpretation and the integration of geological and geophysical research, a series of technologies were innovatively integrated, including ultra-deep carbonate seismic acquisition, three-dimensional imaging of strike-slip faults and fracture-cavity bodies, detailed analysis on strike-slip fault zones, characterization and quantitative description of fault-controlled fracture-cavity bodies, geophysical description of fault-controlled traps and target selection. These technologies provided important support for the exploration and development of the Shunbei oil and gas field.

3.1.1. 3D seismic acquisition technology of ultra-deep carbonate rocks

The ground surface in the Shunbei area is covered by mostly large sand dunes, the Middle-Lower Ordovician steeply-dipping strike-slip faults are deeply buried (average greater than 7300 m). The vertical and horizontal heterogeneities are strong with significant seismic wave energy attenuation. As a result, effective signals from the seismic data of the target layer are usually weakened with complex wave field, low signal-to-noise ratio, and low imaging accuracy for strike-slip faults and fault controlled fracture-cavity bodies ^[50].

The on-site test on the critical seismic problems of the Shunbei ultra-deep fault controlled fracture-cavity bodies showed that the key acquisition factors that affected the imaging accuracy of the reservoirs were energy, signal-to-noise ratio and spatial sampling rate. Therefore, 5-7 m below the water table and 16-22 kg of explosive excitation can be used to increase the wave energy of deep weak reflection and diffraction. With 3 strings of 36 multi-detectors forming a particular pattern of reception area and high coverage number of 300-400, the signal-to-noise ratio of the target layer can be improved. With the three-dimensional observation system of 25 m × 25 m acquisition panel, wide azimuth with aspect ratio greater than 0.5, maximum offset greater than 7000 m, and high density of 0.6-1 million artillery channels/km², the spatial sampling density of ultra-deep steeply dipping faults can be significantly improved.

Through the exploration, a set of cost-effective 3D seismic acquisition technology for ultra-deep, steeply- dipping strike-slip faults in desert has been formed. With the control on the firing interval to reduce the impact of environmental noise, the point-by-point video recording to control the construction quality on the field operation site, the real-time monitoring software with more than ten thousand collection channels to carry out real-time quality monitoring on the construction quality of each shot in the field, the basic on-site tracking and monitoring data from the third party, it is guaranteed that the seismic data obtained in the field are comprehensive, accurate and reliable. The signals of strike-slip faults and fracture-cavity bodies can be enhanced and the signal-to-noise ratio can be improved.

3.1.2. 3D imaging technology for ultra-deep strike-slip fault zones and fracture-cavity bodies

Because the main frequency of the seismic data on the target layer is low (17-18 Hz) with a narrow frequency band ranging from 5 to 55 Hz, the seismic response of strike-slip faults and fracture-cavity bodies is weak with low imaging accuracy. The Permian volcanic rocks are well developed in the whole area with diverse lithofacies and significant variation in thicknesses and velocities, which cause pseudo-structures within the time domain and interlayer multiples. These affect the imaging accuracy of strike-slip faults and fracture-cavity bodies.

With accurate imaging of geological target as the goal, the dune fitting method is used to improve the static correction boundary effect, and the structural artifacts caused by the tomographic static correction of the dune boundaries are eliminated. With high-precision pre-stack and pre-processing technology which preserve low frequency and diffraction, the “point-line-surface-body” four-level quality control is used to optimize the imaging processing parameters of the fault control reservoirs. With combined methods for suppressing multiples, including reverse scattering series method and generalized free surface multiples removal method, multiples caused by intrusive rocks can be eliminated. With Gaussian beam velocity modeling, five-dimensional velocity modeling technology, high wave number velocity fields of inversion igneous rocks and fracture zones, the velocity model accuracy is improved. With the broad band Reverse Time Migration (RTM) imaging technology, low-frequency effective signals are preserved. With special imaging methods such as diffraction wave imaging technology and frequency-divided imaging technology, the imaging accuracy of fault controlled fracture and cavity bodies can be further improved.

Through exploration and practice, the optimization of important pre-stack and pre-processing parameters, including the preservations of low frequency, diffraction waves and amplitude and the test of pre-stack time migration parameter are performed. The 3D imaging technology and workflow for strike-slip faults and fracture-cavity bodies have been established with high-precision velocity modeling of the Permian volcanic rocks, Ordovician strata, Cambrian strata and strike-slip faults as the main content (Fig. 10). When the main frequency of the target is increased by 2 Hz and the frequency band is widened by 7 Hz, the imaging accuracy of ultra-deep strike-slip faults can be improved from 20 m to 15 m, the seismic response of the fracture-cavity bodies are also significantly improved ^[51].

3.1.3. Technologies for characterization and quantitative description of fault-controlled fracture-cavity bodies

The development of fault-controlled fracture-cavity bodies is controlled by steeply dipping strike-slip fault zones with strong internal heterogeneities. The drilling practices suggest that the development of fracture-cavity bodies varies significantly. Therefore, accurate characterization of fracture-cavity bodies and the quantification of their sizes have been the main challenges for the exploration and development.

According to outcrop studies and analyses of drilling, well-logging and well-testing, the reservoir space of fault-controlled fracture-cavity bodies can be divided into three types: cave, pore and fracture. Forward modeling and drilling practices have demonstrated that the main seismic facies are "beaded" reflection phase, irregular reflection phase and linear weak reflection phase ^[52,53,54]. The corresponding sensitive attributes are instantaneous amplitude, discontinuity and AFE attributes ^[55,56]. Drilling and well-logging data incorporated with structure tensor attributes are used to describe the configurations of fault-controlled fracture-cavity bodies. Integrated with low-frequency information, the initial inversion model can be established to carry out the phase-controlled wave impedance inversion of the well-seismic combined fracture-cavity bodies. The spatial distribution of reservoirs can be determined. Applying the relationship between porosities and wave impedance of well-logging, a wave impedance-porosity fitting equation has been established. It can be used to convert the inverted wave impedance volume into a porosity volume. The fault-controlled reservoirs can thus be characterized in 3D and quantitatively described.

The established technology series for characterization and quantitative description of fault-controlled fracture- cavity bodies have efficiently supported the prediction of reservoirs and the submission of proved reserves ^{[50, 56-57]}. During the 13th Five-Year Plan Period, the drilling accuracy in the major strike-slip faults t in the Shunbei area has been increased from 75% to 85%.

3.1.4. Characterization of fault-controlled trap and target optimization technology

Fault-controlled fracture-cavity traps are controlled by fault damage zones, which went through rock-fluid interaction and modification. They are special lithological traps sealed by tight rock layers developed above and sideway.

Due to the particularity of fault-controlled fracture- cavity traps ^[17], segmental structural styles of strike-slip faults have been studied. Together with high-precision mapping using coherence maps, the configurations of faults are determined. Through studies on the seismic phase prediction of the three types (caves, pores and fractures) of reservoirs, the outer boundary of the fault- controlled reservoirs can be determined. Through the physical property analysis on mudstone caprock and tight limestone under the weathering crust, the distribution of efficient caprock can be predicted. Incorporated with the range of top seal, side seal and reservoirs, the boundary of the trap can be determined ^{[50, 54]}. The spatial characterization of fault-controlled fracture-cavity traps can thus be carried out (Fig. 11a, 11b). Based on the evaluation of fault zones and trap description, quantitative characterization and spatial positioning of major fault planes and reservoirs can be carried out to optimize favorable targets. Integrated with drilling practices of strike-slip faults of different structural styles, well trajectory designs including the "anchor" style for push-ups, "hook" style for strike-slip segments, "sickle" style for pull-aparts and "shovel" style for composite structures have been proposed (Fig. 11c).

Through explorations and practices, technologies of characterization of fault controlled fracture-cavity traps, target optimazation and well-trajectory design have been established. These technologies greatly supported the exploration and development of the Shunbei oil and gas field. In the meantime, 57 well targets have been seleced, with the drilling success rate of the major strike-slip fault zones reaching 83%. A field with a million-ton production capacity has been constructed. Two strike-slip faults (No. 4 and No. 8 faults) with potential reservoirs of more than 100 million-tons have been discovered.

During the 13th Five-Year Plan Period, in response to the practical needs for exploration and development of ultra-deep strike-slip fault-controlled fracture-cavity reservoirs, through the deep integration of geology and engineering, the well trajectory space optimization, optimal and fast drilling, highly efficient well completion and testing in fault-controlled oil and gas reservoirs have been achieved. These technologies have provided important support for the exploration and development of the Shunbei oil and gas field.

3.2.1. 3D well trajectory optimization technology

The reservoirs in the Shunbei area are deeply buried and the overlying strata have complicated lithologies. Drilling in the Permian volcanic rocks, Silurian en echelon faults and Upper Ordovician intrusive rocks are prone to leakage and drilling bit jamming. Because the fault- controlled reservoirs are distributed along steeply dipping strike-slip faults, the success rate of drilling into reservoirs at a single time was initially low. The horizontal wells have been used mostly. Due to the damaged strata and high degree of heterogeneities, well wall collapse and jamming often occurred.

Through the integration of geology and engineering, the optimization technology of 3D well trajectory in fault-controlled fracture-cavity reservoirs has been established (Fig. 12). According to the analysis on Permian volcanic rocks and seismic phases of intrusive rocks, seismic inversion prediction, coherence mapping and interpretation of Silurian faults of different scales ^[58], the identification accuracy of intrusive rocks has become no less than 10 m. 3D visualization technology has been used to avoid faults and fractures, the mud loss has been significantly reduced. Through 3D characterization of faults in the target layer, reservoir space of "caves, pores and fractures" has been characterized and visualized. The target hit rate of 3D optimized well trajectory of large-scale reservoirs has been improved ^[59]. Meanwhile, based on the 3D seismic data information, a geological horizon model has been established. Incorporated with well-log information, a 3D regional geological model and a collapse pressure risk analysis model around the fracture zone can be constructed. Through the simulation of well wall-stability risk at different levels and under various conditions with different well deviations and drilling azimuths, the 3D optimization technology of the well trajectory in the fractured formation has been formed. This technology ensured safe and efficient drilling of directional wells in the Shunbei area.

3.2.2. Technology of fast drilling of ultra-deep wells

The reservoirs in the Shunbei oil and gas field are deeply buried, with a large burial depth ranging from 7200 m to 8800 m under ultra-high pressure (89-129 MPa) and high temperature (160-209 °C). The drilling engineering have been confronted with many challenges, such as complex pressure systems, coexistences of overflow and leakage, steeply dipping structures and bedding layers, damaged strata, severe mud losses, and difficulties in well structure design ^[60]. With the well-seismic integrated technology, in-depth analysis on the formation pore pressure, collapse pressure and fracture pressure profiles combined with drilling practice, an optimized sequence of well structures in the Shunbei oil and gas field has been formed ^[61]. Through the studies on Paleozoic stratigraphic characteristics and rock mechanics parameters, customized development has been carried out to optimize and formed the drilling speed increase technology for Paleozoic strata ^[62]. Based on integrated studies on structural characteristics, fracture development and the infilling degree, and well wall rock stress, the reason for well wall collapse has been well understood. The anti- collapse drilling fluid technology of fractured formations has been proposed. This technology generally solved the problem of well wall collapse in fractured formations^[63]. Meanwhile, based on the studies on rock mineral composition, microstructures and their damage factors, temporary plugging system composed of acid-soluble fiber for filling and elastic graphite has been generated. A reservoir protection technology of "drilling fluid performance control and acid-soluble temporary plugging system" ^[64] has been established. The technology can solve the fractured reservoir leakage and reservoir pollution problems.

With the continuing exploration and development of the Shunbei oil and gas field, new technologies have been promoted. For instance, the "drilling tools and high torque screw" speed-up technology has been applied in steeply dipping and easy-to-tilt formations. The test of rotation steering one trip drilling technique in the directional well section has also been developed. Through continuing research, the Shunbei ultra-deep well rapid drilling technology has been formed and the drilling cycle has been shortened from 460 days in the early stage to less than 200 days at the current stage. This has greatly supported the efficient exploration and development of the Shunbei oil and gas field.

3.2.3. Safe and efficient whole well testing technology

The Ordovician oil and gas reservoirs in the Shunbei oil and gas field are ultra-deep, high temperature, high fracture pressure and highly corrosive fault-controlled fracture-cavity oil and gas reservoirs. The well completion has been facing many challenges, such as the easy collapse of open hole wall, the high temperature and highly corrosive environment, and ultra-deep well-logging with tremendous difficulties. In order to solve the problem of easy collapse of open hole wall, the open hole wall supporting technology has been applied. The acid-resistant and easy-to-drill aluminum alloy liner pipes have been used to effectively support the wall and facilitate the later side drilling. The stable well hole has effectively guaranteed the smooth transportation of oil and gas during production. In order to overcome the poor protection effect of the traditional CaCl₂ salt-water system when temperature is over 130 °C, a new type of NaCl-NaBr protection fluid suitable at 130-210 °C under acidic conditions has been developed. The indoor corrosion rate was less than or equal to 0.05 mm/a, which effectively ensure the safety of the tube in the high-temperature CO₂-H₂S environment. Additionally, in order to overcome the difficulties in normal production logging operations in ultra-deep horizontal wells and highly tilted wells, ultra-long (9000 m) and continuous oil tubes have been brought in. This solved the instruments transportation problem. With upgraded well-logging tools which can function under high temperature and high pressure, the maximum measurement depth has been increased up to 8808 m. The application of these well-logging tools can provide important scientific support for next measurement decisions of wells and the evaluation of dynamic reserve. In order to overcome the difficulties in conventional well testing of the Shunbei fault-controlled fracture-cavity oil reservoirs, the establishment of well-testing new models of fractured-cavity reservoirs ^[65] has enable the volume prediction of fracture-cavity bodies and the prediction of productivity, providing efficient methods for reserve evaluation and data interpretation.

3.2.4. Technology to improve ultra-deep fault-controlled fracture-cavity reservoirs

Because the Shunbei fault-controlled fracture-cavity reservoirs are characterized by strong vertical and horizontal compartmentalization, conventional well completion can hardly build the production capacity. Based on the geological characteristics of fault-controlled fracture-cavity reservoirs, targeted transformation technologies have been formed: (1) In order to solve the problems of heavy mud loss and well pollution in fractured reservoirs, based on the mathematical model of acid-etched wormhole expansion ^[66] and the corresponding optimal injection rate ^[67], the gelling acid for removing near-well plugging and cross-linked acid for reducing remote pressure technics has been established. With acid-etched wormholes penetrating the contaminated zones quickly, high-viscosity cross-linked acid are injected through a large discharge pump to form a channel with higher conductivity to dredge the remote well. The dredging range is 30-60 m, which effectively solved the problems of leaky and contaminated wells in reproduction and production increase. (2) “Main fracture and complex fractures” acid fracturing technology. Due to the poor connectivity of fractures developed in the fracture-cavity bodies, based on the theory of rock brittleness and the theory of weakening of rock strength by acid ^[68], the “main fracture and complex fracture” acid fracturing technology has been established. The fracturing fluid is used to create the main fracture, acid and slick water are used to create branch fractures to expand the scope of transformation and to activate more natural fractures. Efficient production of reservoir bodies with poor internal connectivity can be achieved. (3) Temporary plugging and segmented acid fracturing technology for fault-controlled fracture-cavity reservoirs. Due to multiple reservoirs developed around the well in the fault-controlled fracture-cavity reservoirs, general acid fracturing can hardly meet the need of high-efficiency production. According to the theory of compound temporary plugging and turning layer ^[69,70], the temporary plugging and sectional acid fracturing technology of horizontal wells has been formed. With the acid fracturing technology, the temporary plugging capacity reaches 20 MPa, and the temporary plugging of 2 to 3 soft segments can be implemented. This has increased the production capacity of the unconnected reservoirs around the well and improved the production.

The exploration and development of the Shunbei oil and gas field during the "13th Five-Year Plan" period showed that in the western margin of the Manjiaer Depression, an overall contiguous hydrocarbon-bearing belts of Tabei-Shunbei-Shunnan has been formed with significant exploration and development potentials. Improving basic geological research, continuing to evaluate the resources scale, expanding exploration areas, promoting geophysical technology research, continuously improving the prediction accuracy of ultra-deep complex geological targets, and improving the development of oil and gas reservoirs under the conditions of ultra-deep, ultra-high-temperature and ultra-high pressure can provide important guarantee for sustainable increase in reserves and production of the Shunbei oil and gas field during the 14th Five-Year Plan Period.

The ultra-deep source rock and reservoirs in the Shunbei area and the patterns of hydrocarbon accumulation and enrichment, the characterization of the internal architecture of the major strike-slip faults, the imaging and characterization of minor faults and fractured-cavity bodies are important problems to solve for determining the amount of resources and for the expansion of the exploration area.

Previous studies on high-quality source rocks of Yuertusi Formation and multi-stage active strike-slip faults in the Shunbei area suggested that the kinematic characteristics of faults largely controlled the size and the architecture of the reservoir rocks in the Shunbei region^[17,18,19]. With the exploration and development engaged in multiple fault zones in the Shunbei area, drilling practices have revealed large variations in the hydrocarbon phases and enrichment extent. In different parts of the same strike-slip fault, hydrocarbon-water characteristics and productivity vary. This suggests that the development conditions of source-reservoir rocks and the pattern of hydrocarbon accumulation and enrichment are worth for further investigations. The lithofacies, organic facies and differential hydrocarbon generation processes of the source rocks of the Yuertusi Formation, as well as the differential hydrocarbon accumulation and secondary conversion processes among different fault zones should be further studied. Whether the deep-water source rocks in Middle-Lower Ordovician have the capacity to generate hydrocarbon remains an important question ^{[24, 71]}. On the other hand, the distribution pattern of fault related fracture systems of different faults, fault-fluid coupling mechanism and the variation of reservoir properties under different stress fields are not clear yet. Drilling has also revealed that reservoirs of other types occur in the Cambrian-Ordovician strata in the Shunbei area. The genesis, distribution pattern and appraisal of these reservoirs should be further studied.

Based on the understanding of the development characteristics of faults and reservoirs, a series of applicable geophysical methods and technologies have been established, which have effectively supported the exploration and development in the previous stage ^[50]. However, there are still many technical problems limiting further exploration and evaluation. Currently, the identification and prediction of minor faults and the related fracture-cavity reservoirs between the major strike-slip fault zones are not clear. To the west of the Shunbei No. 5 fault, due to the shielding effect of Permian volcanic rocks and intrusive rocks in the Middle-Upper Ordovician, accurate identification and prediction of strike-slip faults and fracture-cavity reservoirs are difficult to implement. To the east of Shunbei No. 12 fault, due to large variations of surface dunes, the signal-to-noise ratio of previous seismic data is low. The imaging of the internal architecture of the major strike-slip faults and minor faults in between can hardly be used to accurately predict and evaluate the reservoirs. Incorporated with the exploration and development, continuing improvement on the characterization technology of the internal architecture of the strike-slip faults and reservoir heterogeneities are important for improving the accuracy of target prediction and the efficiency of exploration and development.

Because different blocks of the Shunbei oil and gas field are at different stages of exploration and development, the problems and challenges they face with differ.

In the Shunbei No.1 block, although one million tons of production capacity has been built, in order to improve the development and maintain a stable production level, there are many problems and challenges, such as low reserve production, low energy retention, difficulties in water injection, and low wellbore integrity. It is necessary to further study the oil reservoirs, promote the research on fracture-cavity characterization and internal structural connectivity to find out the state of available reserves, optimize the construction of injection and production well patterns, optimize water injection plans, accelerate the drilling of new wells (mainly sidetrack wells) to increase the production to reservoir ratio, and to maintain a stable production level.

In the Shunbei No. 2 block, Shunbei No. 4 and No. 8 faults have been discovered with great hydrocarbon potentials. However, how to efficiently promote the integrated evaluation of exploration and development and achieve the goal of "sparse wells, high production, multiple controls and long-term stability" remains the main challenge. According to the characteristics of fault structures and their control on reservoir formation and hydrocarbon accumulation, it is very important to find out the development of fracture-cavity bodies in different segments, to carry out basic research on fluid phase behavior of condensate gas reservoirs, to carry out studies on unstable well test, productivity evaluation and development methods. Plane segmentation, vertical combination of depth and shallow injection well networks for optimization, exploring multiple targets in one well, increasing reserve to production ratio and single well productivity, optimizing development plans, and accelerate the appraisal on the distribution of oil and gas reservoirs and the volume of the reserves ^[72].

In the Shunbei No.3 block, composite structures occurred on the southern segment of the Shunbei No. 5 fault ^{[16, 20]}. Through continuing research and exploration practices, it has been believed that the characteristics of near-well fracture flow are significant, the physical properties of the remote end are deteriorated and the supply capacity is insufficient. These are the main factors causing the difficulties in obtaining stable production. In order to increase the production to reserve ratio, studies on the kinematic characteristics of fault structures and their control on reservoir formation and hydrocarbon accumulation, the distribution pattern of large-scale reservoirs and oil, gas and water, the improved characterization of the internal connectivity of fracture-cavity bodies, and detailed design of well trajectories are important to carry on.

Since the 13th Five-Year Plan Period, the easy collapse of fractured Ordovician strata, the insufficient temperature resistance of directional wells, and the leakage and contamination problem of reservoirs have not been fully solved. In the next step, the supporting engineering technology research, development of ultra-deep, ultra-high temperature, ultra-high pressure wells should be promoted. Accelerating one way drilling speed, increasing and controlling pressure during the drilling process should be carried out to further shorten the drilling cycle. Well control risks should be reduced, and the pace of exploration should be accelerated, so that the engineering cost can be reduced. With the exploration and development of the Shunbei oil and gas field approaching to deeper layers, it is necessary to develop supporting technologies to simplify the Shunbei well body structure, drilling and completion technologies for branch wells in the Shunbei ultra-deep fault controlled reservoirs, anti-gas invasion drilling fluid technologies, and protection technologies of ultra-deep fault controlled reservoirs, lightweight tubing and casing, etc. The technology for well body structure simplification should meet the need of drilling of 7000 m, with single well productivity no less than 100 t/d, and the drilling cycle in the Shunbei gas area shortened by 50%.

The stratigraphic conditions (ultra-deep, high pressure, and high temperature) among different fault zones differ. Basic researches on engineering technologies supporting efficient exploration and development are lacking. It is urgent to carry out formation pressure prediction and researches on reservoir stress distribution, reservoir damage mechanism, and engineering-geology integrated risk prediction. Understanding the in-situ stress characteristics of each strike-slip fault, the vertical and horizontal distribution of three pressures (formation pore pressure, collapse pressure and fracture pressure), the main controlling factors of reservoir damage, improvement of the integrated risk prediction technology are important for engineering technology optimization and for supporting the efficient exploration and development of oil and gas reservoirs.

The discovery and efficient production of the Shunbei oil and gas field have provided important guidance for deep and ultra-deep exploration and development practices.

Continuing basic geological research lays a solid theoretical foundation for breakthroughs in exploration. In order to solve basic geological problems such as hydrocarbon generation and reservoir formation in the ultra- deep marine carbonate formations, continuing researches based on outcrop data, drilling, seismic data have been carried out to determine the distribution of main source rock distribution and hydrocarbon generation evolution. These provide important basis for selecting the exploration area. With exploration practices, it is proposed that large-scale reservoirs are developed along fault zones. Improving basic research on strike-slip fault geometries and kinematics has provided new understanding on the control of strike-slip fault zones on reservoir formation and hydrocarbon accumulation. This has promoted the exploration focus to transit from unconformity karst- controlled carbonate oil and gas reservoirs in large paleo-uplifts to strike-slip fault zones in structural low areas with in-situ source rocks developed. As a result, discoveries of Shunbei ultra-deep fault-controlled fracture-cavity oil and gas reservoirs have been made.

Integration and collaborative innovation are the keys to achieving effective production of deep and ultra-deep oil and gas reservoirs. The burial depth of the reservoirs in the Shunbei oil and gas field is 7200-8800 m under conditions of ultra-high pressure (89-129 MPa) and high temperature (160-209 °C). Through the integration, multi-discipline incorporated research including geology, geophysics and reservoir engineering has formed a four- level "belt-fault-plane-target" exploration and evaluation method. The 3D seismic acquisition, processing and interpretation have been improved, and the high-accuracy imaging and fine description technology is established for desert area, desertmulti-layer intrusive rock development area and ultra-deep fault-controlled fracture-cavity bodies. Through the researches and practices on exploration and development integration, the understanding of reservoir characteristics and enrichment patterns has been improved continuously. A deep exploration target selection and appraisal decision-making system based on the integration of geology, engineering and economics has been established. This system improves the success rate of exploration and development. Through the geology- engineering integration during the whole process, ultra- deep, high temperature, high pressure drilling, well-logging and well completion technology series has been created. This system has effectively solved the problems including poor drillability, high temperature, high pressure, and high breaking pressure in the upper stratum of the target. Drilling cycle has been shortened from 460 days to about 200 days. In 2021, a number of "thousand-ton wells" have been drilled. In the Shunbei oil and gas field, a million- ton production capacity field has been built, achieving efficient production of ultra-deep oil and gas reservoirs.