23 June 2016, Volume 43 Issue 3
    

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  • Key geological issues and main controls on accumulation and enrichment of Chinese shale gas
    GUO Tonglou
    . 2016, 43(3): 317-326. https://doi.org/10.11698/PED.2016.03.01
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    By analyzing geological characteristics of shale gas in Southern China and the United States, main factors controlling the accumulation and key issues in the exploration and development of shale gas in China have been examined. The geological characteristics of shale gas in China include multi-stages of tectonic evolution, complex structure types, abundant faults, small continuous distribution area of shale formations, and no corresponding relationship between current thermal evolution degree and current burial depth of two main sets of shale formations (the Cambrian and Silurian). According to the analysis of the factors affecting shale gas enrichment such as fracture, tectonic type, shale gas migration, and gas content etc, the enrichment mechanisms of shale gas in China are: “sedimentary facies and preservation condition” are the main reservoir-controlling factors affecting the accumulation of shale gas, and “structure types and tectonism” are the main factors controlling the enrichment of shale gas in China; the former factors define shale gas plays, and the latter ones determine the position of sweet spots. The future research directions of shale gas in China are: firstly, contrary to the shale gas development in the United States, shale gas exploration and development in China should extend from the overpressure to normal pressure, and even low pressure areas; secondly, shale gas exploration in the Sichuan basin should extend from middle-deep to deep formations, studies should be done on the shale gas enrichment mechanism and accumulation models in formations more than 4 000 m deep, and horizontal well fracturing technology for these formations; thirdly, the development of transitional facies and continental facies shale gas should be brought along by drawing on exploration and development experience of marine shale gas.
  • Accumulation conditions and play targets of oil and gas in the Cambrian subsalt dolomite, Tarim Basin, NW China
    DU Jinhu, PAN Wenqing
    . 2016, 43(3): 327-339. https://doi.org/10.11698/PED.2016.03.02
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    Based on seismic, well drilling and crop data in the Tarim Basin, the accumulation conditions including source rock, reservoir, caprock and paleouplift of the Cambrian subsalt dolomites have been investigated, and favorable exploration areas have been selected. The research results reveal: there are two sets of source rock, the excellent Cambrian Yuertusi Formation source rock and the potential Nanhua-Sinian source rock, in the Tarim Basin. The dolomite reservoir of platform mound-shoal and platform margin reef-shoal facies is extensive in the Lower Cambrian Xiaoerbulake Formation in Taixi terrace area. The Middle Cambrian high quality gypsum-salt caprock has an area of about 11×104 km2; three inherited paleouplifts control the distribution of reservoirs and development of lithology stratigraphic traps and hydrocarbon accumulation, therefore, there are very good geologic conditions for the formation of large oil and gas fields in the Tarim Basin. Five oil and gas plays, namely, Tazhong-Badong intra-platform shoal, Tabei platform margin-reef bank, Keping platform margin-reef bank, Yulong-Moyu evaporative dolomite flat and Lunnan-Gucheng platform margin have been picked out, which provides a scientific basis for the oil and gas exploration and development in the Lower Cambrian dolomite.
  • Characteristics, origin and distribution of dolomite reservoirs in Lower-Middle Cambrian, Tarim Basin, NW China
    SHEN Anjiang, ZHENG Jianfeng, CHEN Yongquan, NI Xinfeng, HUANG Lili
    . 2016, 43(3): 340-349. https://doi.org/10.11698/PED.2016.03.03
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    Based on cores, thin sections and drilling data of 18 wells and two outcrop profiles of the Lower-Middle Cambrian in the Tarim Basin, geochemical analysis of multi-parameters in micro-area (the same type of diagenetic minerals formed in different diagenetic events) and reservoir dissolution modeling were carried out to find out the types, origin and distribution of Lower-Middle Cambrian dolomite reservoirs. There develop three types of dolomite reservoirs, margin reef-shoal reservoir, platform interior mound-shoal reservoir and platform interior gypsodolomite reservoir. The rock types include algae dolomite, grain dolomite, and gypsodolomite; the pore types in them include algae framework pores in algae dolomite; intergranular pores, intra-granular dissolved pores, inter-crystalline dissolved pores in grain dolomite and gypsum-dissolved pore gypsodolomite. The primary pores in sediments of reef-shoal facies and gypsodolomite flat are the key to the development of the dolomite reservoirs, some aragonite and calcite are the material basis of dissolution in early supergene stage, and the dolomite formed in penecontemporaneous dolomitization acts as strong rock skeleton to protect the primary pores from destructive effect in burial stage. The margin reef-shoal reservoirs, large in scale and good in physical properties, are the most practical exploration targets; furthermore, the platform interior reef-shoal reservoirs in Lower Cambrian Xiaoerbulake Formation and platform interior gypsodolomite reservoir in the Middle-Lower Cambrian have higher oil and gas potential.
  • Shale gas enrichment pattern and exploration significance of Well Wuxi-2 in northeast Chongqing, NE Sichuan Basin
    LIANG Feng, BAI Wenhua, ZOU Caineng, WANG Hongyan, WU Jin, MA Chao, ZHANG Qin, GUO Wei, SUN Shasha, ZHU Yanming, CUI Huiying, LIU Dexun
    . 2016, 43(3): 350-358. https://doi.org/10.11698/PED.2016.03.04
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    The shale gas enrichment pattern of Well Wuxi-2 in northeast Chongqing was studied, based on the data of the drilling, graptolite biostratigraphy, geochemistry, rock minerals, microscopic characteristics of reservoir beds and tectonic conditions, etc. The organic-rich shale of Upper Ordovician Wufeng Formation—Lower Silurian Longmaxi Formation is 89.8 m thick in Well WX-2. The graptolite biozonations are completely developed in this well, and the organic-rich shale intervals extend upward from the late Katian of the Ordovician to the early Telychian of the Lower Silurian. The deposition time of the organic-rich shale is far longer and the thickness is larger than those in other areas of the Sichuan Basin. The highest measured gas content exceeded 8 m3/t in Well WX-2, and the gas content is mainly controlled by TOC. The organic nano-pores are the main storage space, and the minerals contribute less to the storage space. The organic pores larger than 50 nm are well-developed and those less than 10 nm are the main reservoir space of adsorbed gas. The target intervals of Well WX-2 are located under the neutral surface of compressional Tianba anticline. Two vertical fracture (cleavage) development zones, which are beneficial for shale gas storage and complex fracture network formation during later fracturing, were formed in brittle layers of this organic-rich shale. Compressional faults existed in two limbs of the Tianba anticline, with non-permeable shale developing on both sides of fault planes and development of clay smear, which shows that the faults have good sealing properties, and are favorable for shale gas preservation. Thus the good match between the above various accumulation conditions forms the “tectonic sweet-spot” of shale gas in this study area.
  • Hydrothermal fluid activity and the quantitative evaluation of its impact on carbonate reservoirs: A case study of the Lower Paleozoic in the west of Dongying sag, Bohai Bay Basin, East China
    LI Jiyan, WANG Yongshi, LIU Chuanhu, DONG Dawei, GAO Zhiqiang
    . 2016, 43(3): 359-366. https://doi.org/10.11698/PED.2016.03.05
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    By integrating the analyses of core samples, thin sections, homogenization temperature measurement of inclusions, stable isotopic compositions of carbon & oxygen, trace element composition, and conventional physical properties, this research identifies the evidence of Lower Paleozoic hydrothermal fluid activity in the western Dongying sag of Bohai Bay Basin, quantitatively evaluates the hydrothermal dissolution strength in various carbonate reservoirs, and analyzes the longitudinal distribution of effective fractures in reservoirs. The markers of hydrothermal dissolution in the study area include the typical hydrothermal mineral combinations such as fluorite-anhydrite-authigenic quartz combination, the homogenization temperature of inclusions in fracture fillings related to hydrothermal fluid of up to 150 ℃-210 ℃, and the high FeO, high SiO2, high MnO and low Na2O features of carbonate in hydrothermal fluid karst area. Dissolution of hydrothermal fluid can produce not only new fluorite mineral, but also many pores, micropores, small fractures and micro-fractures, which significantly improve the quality of carbonate reservoirs. During the process of hydrothermal fluid dissolution, calcite precipitated and filled structural fractures as the hydrothermal fluid dissolved host rock. As the hydrothermal fluid went up along faults, its velocity and temperature dropped gradually, the intensity of dissolution and calcite filling differ significantly in different formations of the Lower Paleozoic, for example, the Fengshan and Yeli-Liangjiashan Formations have low fracture filling degree and highly developed dissolved fractures and pores, whereas the Majiagou Formation has high fracture filling degree and poorly developed dissolved fractures and pores.
  • Geological features of grain bank reservoirs and the main controlling factors: A case study on Cretaceous Mishrif Formation, Halfaya Oilfield, Iraq
    WANG Jun, GUO Rui, ZHAO Limin, LI Wenke, ZHOU Wen, DUAN Tianxiang
    . 2016, 43(3): 367-377. https://doi.org/10.11698/PED.2016.03.06
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    The geological features and distribution regularity of the grain bank reservoirs of the Cretaceous Mishrif Formation in Halfaya Oilfield and their main controlling factors were analyzed based on coring data, 302 pieces of thin sections and 2507 experiment data points. Various types and multiple phases of grain bank reservoirs are developed in Mishrif Formation, which are dominated by grainstone, followed by wackestone packstone. The formation and distribution of grain bank reservoirs are mainly controlled by relative sea level change, paleogeomorpholoy and contemporaneous-penecontemporaneous dissolution. Relative sea level change controls the types and development phases of grain banks. When the sea level falls, rudists, coquina, arene and pelletoids are extensively deposited, among which, rudists clastic bank and coquina bank that are deposited at the lowest sea level have the best reservoir properties, with a maximum porosity of 33.94%, maximum permeability of 764.571×10-3 μm2 and an average permeability of 45.81×10-3 μm2. Paleogeomorpholoy controls high-energy facies belt and the dissolution of meteoric water. The submarine paleohigh controls the formation and distribution of high-energy facies belt during depositional period. However, during uplifting and denudation period, the reservoirs in paleohigh are intensively dissolved and represent good reservoir properties, with an average porosity of 14.78% and permeability of 7.849×10-3 μm2. Contemporaneous-penecontemporaneous dissolution results in the formation of most effective pores, which is the key factor for the formation of grain bank reservoirs in the study area.
  • Influencing factors of micropores in the graptolite shale of Ordovician Pingliang Formation in Ordos Basin, China
    DENG Kun, ZHOU Wen, ZHOU Lifa, WAN Yanzhou, DENG Hucheng, XIE Runcheng, CHEN Wenling
    . 2016, 43(3): 378-385. https://doi.org/10.11698/PED.2016.03.07
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    A variety of tests were conducted on graptolite shale samples from Middle Ordovician Pingliang Formation in three typical areas in Ordos Basin to find out the relationship between micro-nano pore structure, graptolite content, rock composition, TOC, maturity, main and trace elements and gas content. The graptolite of Pingliang Formation concentrates in the black shale at the lower section of this layer. Pores in the shale are diverse in types, including extracellular polymeric substance (EPS) pore, pore in bio-graptolite body, clay mineral inter-granular pore, intra-granular pore, interstitial pores between mineral crystals, micro-fractures, and intra-granular dissolution pores etc. Test analysis shows graptolite has some effect on sedimentary environment and shale gas accumulation; graptolites content is positively correlated with TOC, in a certain range, specific surface area is positively correlated with TOC and maturity; the main reason is related to lithology, inorganic minerals and organic matter. The rare earth elements (REE) patterns of the three areas are similar, indicating the same provenance. Rare earth amount, Fe, Al and Ti content are negatively correlated with TOC, indicating the high REE content is not caused by organic matter enrichment, but related to minerals REE adsorbed to. Gas content is positively correlated with specific surface area, TOC and maturity. The above factors have significant effects on micro-nano pores in shale, so TOC and maturity should be taken into consideration in pore structure study.
  • Hydrocarbon migration caused by rupture of pressure compartment in south Liaozhong sag, Bohai Bay Basin, Offshore China
    PENG Jingsong, XU Changgui, WEI Ajuan, WANG Yuechuan, WANG Bingjie, GUO Yonghua, ZHANG Jiangtao, WANG Xin
    . 2016, 43(3): 386-395. https://doi.org/10.11698/PED.2016.03.08
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    Based on the study of the abnormal pressure of mudstone and reservoirs of south Liaozhong sag, Bohai Bay Basin, the structure of the abnormal pressure compartment in the Paleogene of south Liaozhong sag and its impact on oil and gas migration have been analyzed. The pressure compartment in the study area has a “sandwich structure”, with the mudstone of Paleogene Dongying Formation as cap rock, the reservoirs of the upper Shahejie Formation of the Paleogene as the transport interlayers, and the mudstone from the lower Shahejie Formation as the hydrocarbon source rock. Based on overpressure formation mechanism and basin-modeling, the pre-neotectonic movement pressure of the transport interlayers was reconstructed, then the rupture of the pressure compartment and pressure differentiation caused by Tanlu fault zone during the neo-tectonic movement were investigated. The hydrocarbon migration was simulated under different pressure conditions before and after the neo-tectonic movement, to find out the relationship between the neo-tectonic movement of Tanlu fault, abnormal pressure and oil and gas migration. The simulation results show that the differential activity within Tanlu fault zone caused the differentiation of pressure and increase of fluid potential gradient; and the strike-slip pull-apart area with low potential caused by pump-sucking effect became the main direction of hydrocarbon migration in Tanlu fault zone. The comprehensive research of the late-stage hydrocarbon accumulation shows that, there are inner and outer compartment hydrocarbon accumulation systems in the south Liaodong sag, and the transport interlayer in the inner compartment is the “hydrocarbon transfer station” of the shallow outer compartment, and determines the hydrocarbon plane distribution.
  • Gas and water distribution of Ordovician Majiagou Formation in northwest of Ordos Basin, NW China
    YU Hongyan, WEI Li, QIN Xiaoyan, WANG Zhenliang, CHENG Hao, WANG Aiguo, WANG Dongxu, FENG Qianghan, LAN Yifei, WANG Yong
    . 2016, 43(3): 396-402. https://doi.org/10.11698/PED.2016.03.09
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    Based on the geologic background and reservoir characteristics, the characteristics and controlling factors of gas and water distribution of the carbonate reservoir in the 5th member of Ordovician Majiagou Formation in Northwest Ordos Basin have been examined from macro and micro aspects using data of structure, deposition, diagenesis, paleotopography, physical property, mercury injection, well logs and core observation. The 5th member of Majiagou Formation in the study area shows very complex gas and water distribution pattern: the gas layer is distributed uniformly across the whole area in 2D horizontal map, while the water layer is scattered and concentrates in small area, appearing in discontinuous distribution; there is no gas and water interbeds in vertical direction, making it difficult to develop the gas reservoir efficiently. The gas and water distribution is controlled by paleogeomorphology and diagenesis macroscopically, and is controlled by pore-throat structure, connectivity and the transportation relation between source rock and reservoir microscopically. The gas largely concentrates in and around the ancient grooves and low hill regions in the paleokast slope where the reservoirs have good physical properties and good pore - throat connectivity, and there is no bauxite between source rock and reservoir, making it easy for gas to charge and accumulate.
  • Application of multi-point geostatistics in deep-water turbidity channel simulation: A case study of Plutonio oilfield in Angola
    ZHANG Wenbiao, DUAN Taizhong, LIU Zhiqiang, YUAN Shujin, LIN Yu, XU Huaming
    . 2016, 43(3): 403-410. https://doi.org/10.11698/PED.2016.03.10
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    In order to simulate the deep water channel distribution of the Oligocene O73 sand layers in the Plutonio oilfield in Angola of west Africa. Based on the shallow high frequency seismic data, the morphology and quantitative scale of shallow channel were studied. By analogy, this study was used as guidance for the scale statistics of single deep channel sandstone, and a three dimensional quantitative training image was created. On this basis, the deep water channel distribution was simulated using multi-point geo-statistics Snesim algorithm and tested by real drilling. The results show that the width and depth of shallow single channel are in linear correlation, while the tortuosity is negatively correlated with the slope gradient exponentially. The average depth of single channel sandstone was 13 meters and the average width was 162 meters. It is concluded that the deep water channel distribution simulation results consist with well data obtained through high resolution gradient impedance inversion, extraction of shallow channel geologic body as 3-D quantitative training image and simulation using Snesim algorithm. The spatial morphology and size of different channels are constrained by the quantitative characteristics of training image, and can reproduce geometric characteristics and spatial structure of deep water channels and levees.
  • Radiogenic heat and hydrocarbon generation potential of sediments, Gongola Basin, Nigeria
    OYEBANJO O M, AJAYI T R, TCHOKOSSA P
    . 2016, 43(3): 411-416. https://doi.org/10.11698/PED.2016.03.11
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    Samples taken from Well Kolmani-1 in the Gongola Basin in the Upper Benue Trough of Nigeria were studied to estimate the radiogenic heat generated and to analyze the possible impact of radiogenic heat on hydrocarbon generation potential of the sediments. Thirty-eight samples taken from the different formations at intervals of 73.2 m including sand, shale, coaly shale, sandy shale, and shaly sand were analyzed for 40K, 238U, and 232Th using the well calibrated NaI (Tl) Gamma Ray detector System. The results showed that the activity concentrations of the radio-nuclides varied significantly within the sediments. The 40K concentrations were the highest. The radiogenic heat produced ranges widely from 228.44 pW/kg to 1 412.82 pW/kg. In Well Kolmani-1, sands and sandy shale are low heat production sediments, while the shale, coaly shale and silty sands are medium heat production sediments, the potential source rock (shale and coaly shale) medium in heat production (750 pW/kg to 1 500 pW/kg), can produce liquid and gaseous hydrocarbons. It is estimated that the radiogenic heat from the sediments contributed about 10.9% to 20.9% to the total surface heat flux in the basin. Therefore, the radiogenic heat generated by the sediments contributed significantly to the total surface heat flux, and should be taken into consideration in the simulation of basin thermal evolution.
  • Quantitative evaluation of rock brittleness and fracability based on elastic-wave velocity variation around borehole
    TANG Xiaoming, XU Song, ZHUANG Chunxi, SU Yuanda, CHEN Xuelian
    . 2016, 43(3): 417-424. https://doi.org/10.11698/PED.2016.03.12
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    Brittleness and fracability are two important rock properties in hydraulic fracturing of unconventional reservoirs. Based on the variation of compressional and shear velocity around borehole using acoustic measurement, an effective technique is developed to estimate these parameters to guide reservoir-fracturing. During drilling, when the rock is broken, a significant amount of drilling induced cracks will occur in the formation around the borehole, resulting in the drop of radial elastic wave velocity and the wave velocity variation from low to high in radial direction. The radial variation of compressional and shear velocities of formation rocks surrounding a borehole were respectively obtained from P-wave travel time tomography and dipole shear-wave dispersion inversion. By integrating the two variation profiles along the radial direction, the brittleness-fracability index is obtained to estimate the brittleness and fracability of formation rocks. The index shows fairly good consistency and correlation with rock brittleness and fracability, which demonstrates the practicability and effectiveness of the proposed approach. Well log data analysis examples are presented to demonstrate the effectiveness of our technique.
  • Quantitative fracture evaluation method based on core-image logging: A case study of Cretaceous Bashijiqike Formation in ks2 well area, Kuqa depression, Tarim Basin, NW China
    QU Haizhou, ZHANG Fuxiang, WANG Zhenyu, YANG Xiangtong, LIU Hongtao, BA Dan, WANG Xi
    . 2016, 43(3): 425-432. https://doi.org/10.11698/PED.2016.03.13
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    A quantitative evaluation method of fracture is established based on core observation and image logging, and is used to characterize the distribution feature of fractures in Bashijiqike Formation of ks2 well area. This method gets the empirical corrections of fracture parameters between cores and image logging in the same depth, and these empirical values will be used in other depth where cores are not acquired to obtain all the fracture parameters per meter of the target layer. The study shows the fractures in ks2 well area are mainly high angle structural fractures between 45°-75°, and their strikes are near SN or near EW. The fracture linear density values are 0.11-1.30/m, the fracture area ratio is 0.027%-0.130%, the average fracture width is 0.13-0.55 mm, and the fracture length is 0.39-1.20 m. The development of fracture is divided into three levels (Ⅰ-developed, Ⅱ- relatively developed, Ⅲ-poorly developed) based on the linear density value and surface area ratio. Fractures in this well area are most abundant in sandstones of 1st and 2nd members of Bashijiqike Formation, forming 4-6 fracture segments with good continuity. The thicknesses, development levels, parameters of fracture segments decrease exponentially with the increase of distance to fault and to anticline axis. The most favorable area (Ⅰ-Ⅱ) is within 800 m from the fault, or within 1 800 m from the anticlinal axis. It is predicted the fractures in ks2 well area, are more developed in the eastern area than the middle-western area, and more developed in the southern area than the northern area, and that the linear fracture density can be up to 1.0 /m around Well ks201, Well ks207-ks2-12, Well ks203 and areas near faults.
  • Relationship between sandstone architecture and remaining oil distribution pattern: A case of the Kumkol South oilfield in South Turgay Basin, Kazakstan
    ZHAO Lun, LIANG Hongwei, ZHANG Xiangzhong, CHEN Li, WANG Jincai, CAO Haili, SONG Xiaowei
    . 2016, 43(3): 433-441. https://doi.org/10.11698/PED.2016.03.14
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    Taking the Kumkol South oilfield in South Turgay Basin, Kazakstan as an example, this article summarizes the controlling pattern of different types of sandstone architecture on remaining oil distribution through examining architecture characteristics, development effect and remaining oil distribution characteristics of meandering river sandstone, braided river sandstone and delta sandstone. The braided river sandstone has simple architecture which is extensive connecting body with horizontal mud-interlayers. The water flooding sweeps evenly and the edge-bottom water drives quickly in braid river sandstone. And the remaining oil distribution pattern of braid river sandstone is the vertical blocking pattern controlled by the horizontal mud-interlayers at the high water cut stage. The meandering river sandstone is a half connecting body with abandoned channels and the lateral accretion mud-interlayers, so the injected water sweeps through the middle and lower parts of point bar sandstone, and its remaining oil distribution pattern is the horizontal blocking pattern controlled by abandoned channels and the lateral accretion mud-interlayers. The delta sandstone has a complex architecture of mosaic structure with abundant horizontal and vertical mud-interlayers and mud-interbeds, in which the injected water sweeps along preferential path, with low sweeping efficiency, and the remaining oil distribution pattern is the complex blocking pattern controlled by horizontal and vertical mud-interlayers and mud-interbeds. The results show that different techniques should be used to enhance the remaining oil recovery because of the different remaining oil distribution patterns in different kind of sand bodies.
  • An improved vdW-type component mixing-rule applied in CO2-crude system
    YANG Siyu, LIAN Liming, LI Shi, YANG Yongzhi, CHEN Xinglong
    . 2016, 43(3): 442-447. https://doi.org/10.11698/PED.2016.03.15
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    A new vdW-type mixing-rule has been proposed considering the interaction among the affecting factors of temperature, pressure and non-hydrocarbon components, through analysis of equation of state and theory of interaction among molecules. By the derivation of the formulation at reduced state, a new mixing-rule has been established for the conditions of high pressure and high temperature. The theoretical strictness of the rule has been demonstrated through reducing to the dependency relationship of second virial coefficients. With the in situ petroleum samples data of vapor and liquid phase components from actual measurement, comparison has been taken between the calculation precisions of components and densities parameters calculated by the new rule and the old one. The new mixing-rule has a better accuracy to meet the industrial requirement, and its calculation is also simplified. The weighted mean error of components calculation declines from 15% to 4% and that of density calculation from 10% to 3%.
  • Determination of dynamic reserves of fractured horizontal wells in tight oil reservoirs by multi-region material balance method
    WEI Yi, RAN Qiquan, LI Ran, YUAN Jiangru, DONG Jiaxin
    . 2016, 43(3): 448-455. https://doi.org/10.11698/PED.2016.03.16
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    To overcome the deficiencies of the material balance method, according to strong heterogeneity of tight oil reservoirs, the flow region of fractured horizontal well is divided into high permeable zone and low permeable zone, which are equivalent to radial composite percolation model. Based on parallel plane theory, multiple media of each zone are equivalent as a continuous medium, and with the integral method, the multi-region material balance to calculate the dynamic reserves for the fractured horizontal well of tight oil reservoirs is proposed base on the nonlinear seepage mechanism of tight oil reservoirs, and the corresponding pressure distribution equation and material balance equation for the two zones have been established. In view of the actual production performance, this method considers the pressure mutation and fluid exchange at the interface of two zones. The computational results of an example show that this method can work out the dynamic reserves within a single well control, the dynamic reserves of high permeable zone and low permeable zone, and the recharge rate from the low permeable zone to the high permeable zone in different production time accurately, which provides a basis for selection of well production and appropriate working system, and deployment and adjustment of development well pattern.
  • Experiments on CO2 foam seepage characteristics in porous media
    DU Dongxing, WANG Dexi, JIA Ninghong, LYU Weifeng, QIN Jishun, WANG Chengcheng, SUN Shengbin, LI Yingge
    . 2016, 43(3): 456-461. https://doi.org/10.11698/PED.2016.03.17
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    Simulative experiments were carried out for CO2 foam flooding process in homogeneous porous media prepared with the sand packing method, and the CO2 foam seepage characteristics in porous media were studied with CT technology. CO2 foam flooding experiments were carried out under different packing sand sizes, different surfactant concentrations and different gas-liquid ratios. CT technology was employed to visualize the displacement process and to obtain the water saturation data along the sample, and the pressure distribution in the sample during the foam seepage process was measured at the same time. Experimental results show that, CO2 foam flooding has higher pressure drop and lower water saturation entrance effect in the porous media with lower average grain sizes; when surfactant concentrations are higher than CMC (Critical Micelle Concentration), the generated foam is stable, without showing obvious difference for the foam displacement efficiency in the sample, and water saturation entrance effect gradually decreases with increase of surfactant concentrations; improving gas-liquid ratio can lead to higher foam seepage pressure drop, but has little effect on residue water saturation after foam displacement.
  • Through-wall yield collapse pressure of casing based on unified strength theory
    LIN Yuanhua, DENG Kuanhai, SUN Yongxing, ZENG Dezhi
    . 2016, 43(3): 462-468. https://doi.org/10.11698/PED.2016.03.18
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    The unified algorithm of through-wall yield collapse pressure for casing with due consideration of strength differential (SD), yield-to-tensile strength ratio, material hardening and intermediate principal stress, which is suitable to calculate collapse strength of all casing has been obtained based on unified strength theory, and four classical through-wall yield collapse formulas of casing have been presented based on the L.Von Mises, TRESCA, GM and twin yield strength criterion. The calculated value is maximum based on the twin yield strength criterion, which can be used as upper limit of through-wall yield collapse pressure, and the calculated value is minimum based on the TRESCA strength criterion, which can be used as lower limit of through-wall yield collapse pressure in the design process. Numerical and experimental comparisons show that the equation proposed by this paper is much closer to the collapse testing values than that of other equations.
  • Cement bond quality evaluation based on acoustic variable density logging
    TANG Jun, ZHANG Chengguang, ZHANG Bixing, SHI Fangfang
    . 2016, 43(3): 469-475. https://doi.org/10.11698/PED.2016.03.19
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    A new method of cement bond quality evaluation was proposed by combining numerical simulation and calibrated cased hole acoustic logging data. The effects of the cement channel angle and the quality of the second bond interface (the interface of cement with formation) on acoustic variable density logging data were analyzed. Based on the analysis result, a new cement bond evaluation standard was presented after revising the traditional CBL/VDL method. The axisymmetric acoustic field was simulated by real axis integral method, while the non-axisymmetric acoustic field was simulated by 2.5-D finite differential method. After comparing with the calibrated cased hole acoustic logging data, the research has the below results: the numerical simulation result matches with the calibrated well logging data very well and the new method is reliable; the amplitude of the first acoustic arrival in the case hole decreases as the angle of cement channel decreases, and the denser the cement is, the faster the amplitude of cased hole acoustic waveform decays; the lower limit of cement channel angle is around 45 degrees which can be detected by acoustic logging; the formation acoustic waveform is not easy to be detected in time domain, however it is easy to be detected in frequency domain, especially in limestone formation, the first arrival only can be detected when the annulus width of the second bond interface is small. According to the research result of the numerical simulation of cased hole acoustic field and acoustic variable density logging data, new evaluation criteria of cement bound quality were presented.
  • Inhibition performance and mechanism of Horsetail extract as shale stabilizer
    BARATI Pezhman, KESHTKAR Sadegh, AGHAJAFARI Amirhossein, SHAHBAZI Khalil, MOMENI Ali
    . 2016, 43(3): 476-481. https://doi.org/10.11698/PED.2016.03.20
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    The Horsetail extract was used as shale stabilizer, its inhibition performance was stuided by laboratory experiments and compared with potassium chloride and polyamine, and its anti-swelling mechanism was analyzed. Bentonite inhibition test, sodium bentonite sedimentation test, dynamic linear swelling test, and hot rolling cutting dispersion test were employed. The results show that: the bentonite is not capable of being hydrated or dispersed in solution with the Horsetail extract; the Horsetail extract can resuce the swelling of the bentonite and prevent disintegration and dispersion of cuttings in aqueous medium; the extract is well comparable and competitive with potassium chloride and polyamine in inhibition performance. The constituents of the Horsetail extract have active hydroxyls which are capable of forming hydrogen bounding with surfaces of bentonite particles, leading to decrease of the water absorption on bentonite particles’ surfaces which results in bentonite swelling reduction. Besides having good anti-swelling ability, Horsetail extract is ecofriendly, readily available and inexpensive.
  • Braided river delta outcrop architecture: A case study of Triassic Huangshanjie Formation in Kuche depression, Tarim Basin, NW China
    ZHU Weihong, WU Shenghe, YIN Zhijun, HAN Tao, WU Yiming, LIU Yong, FENG Wenjie, LUO Ya’ nan, CAO Cen
    . 2016, 43(3): 482-489. https://doi.org/10.11698/PED.2016.03.21
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    Guided by the theory of reservoir architecture, the architecture of braided river delta of Triassic Huangshanjie Formation in Kuche depression of Tarim Basin was studied using cycle constraints and hierarchical dissection analysis method. According to sedimentary cycle and lithofacies assemblage characteristics, two types (distributary channel and distributary bar) of fourth level architectural units and their boundaries were identified on outcrops. Vertically, the reservoir sand bodies overlay in the three patterns, distributary channel-distributary bar, distributary bar-distributary bar, and distributary channel- distributary channel. Laterally, the architecture units stitching in four patterns, distributary channel-distributary channel intersecting and stacking, distributary channel-distributary bar intersecting and stacking, distributary bar-distributary bar and distributary bar-distributary channel intersecting and stacking. The fourth level units overlay and joint together, forming complex fifth level architectural units of channel filling divided by architectural boundaries of different levels. The fourth and fifth level boundaries reduce the vertical connectivity and enhance the heterogeneity of the reservoir. Through field measurement, profile architecture element database,was established and the quantitative relationship among the parameters was characterized. The research results provide a geological basis for the characterization of fine reservoir architecture of the similar sedimentary conditions in the Tarim Basin.
  • Three dimensional characterization and quantitative connectivity analysis of micro/nano pore space
    SUN Liang, WANG Xiaoqi, JIN Xu, LI Jianming, WU Songtao
    . 2016, 43(3): 490-498. https://doi.org/10.11698/PED.2016.03.22
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Evaluation is performed on pore connectivity of unconventional reservoirs using 3-D FIB-SEM imaging characterization and digital rock techniques. 3-D images are first obtained by FIB-SEM device and then transformed into digital pore structure model through shape correction, brightness correction, depth-of-field correction and phase distinguishing. Based on this model, a new connectivity evaluation method for micro/nano pores in unconventional reservoirs is proposed. This method differentiates dead and live pore space, grades live connected domains (1-grade is the worst and 3-grade is the best) and calculates the connectivity rates of all grades. Selected connected domains can be quantitatively characterized through statistical analysis of connected domain distribution, volume and shape. The applications on nano material, shale and carbonate get distinctive connectivity rates (96%, 22% and 82%) and characteristic differences on connected domain distribution, volume and shape. Through these statistical parameters (connectivity rate, connected domain distribution, volume and shape), the three demonstrated materials and reservoirs are quantitatively characterized and differentiated. Thus, validity of the proposed connectivity method in this paper is proved.
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