, Volume 38 Issue 3

    

• Select all
  |

油气勘探
• Select
  Paleokarst and reservoirs of the Huanglong Formation in eastern Sichuan Basin

  Zhang Bing; Zheng Rongcai; Wang Xuben; Li Wei; Wen Huaguo and Hu Zhonggui

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  According to the combination of surficial geology, drilling data, and the isotope geochemical characteristics of carbon, oxygen and strontium, the identification markers of paleokarst were described in detail, and the relationships between the vertical zoning, plane distribution and karstification degree of paleokarst and the reservoir development were further analyzed. The study shows that karst breccias are the direct sign of paleokarst. Karst of different genetic types and dissolution intension have different stable isotope geochemical characteristics from the cements, and their formation and evolution are significantly influenced by fluid sources, fluid nature and isotope fractionation. The identification markers of small scale pinholes are quite different from that of large scale holes. The development and evolution law of palaeokarst are mainly controlled by structure, palaeoclimate and lithology. The best lithology for the development of reservoirs is dolomite in the C2hl2, the best zone for the development of reservoir is located in the upper and lower dissolution sections of C2hl2, and the best position for the development of reservoir is located in the karst highland, remnant hills and sloping fields in the karst slope.
• Select
  Jia-2 Member doloarenite reservoir in the Moxi gas field, middle Sichuan Basin

  Tan Xiucheng; Luo Bing; Li Zhuopei; Ding Xiong; Nie Yong; Wu Xingbo; Zou Juan and Tang Qingsong

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  Based on analysis on the macroscopic and microcosmic features of doloarenite in C layer, Sub-member 2, Jia-2 Member of the Jialingjiang Formation in the Moxi gas field, the genetic mechanism of favorite reservoirs in beach facies carbonate rock is established. Primary inter-granular pores are the main reservoir spaces in the beach facies carbonates, which have the following key characteristics and identification signs: the reservoir development was strictly controlled by the depositional microfacies; the main pore types are residual inter-granular pores and dissolved-enlarged residual inter-granular pores; only submarine cement existed in the grain contact; initial compaction led to grains under framework support in line-concavo-convex contact and the burial cement in some separate inter-granular pores being not dissolved. The conservation mechanism of primary inter-granular pores is described as follows: after submarine cementation, the initial compaction made grains with early rim cement under framework support and the throats decrease accordingly; the compaction fluid cementation compressed the beach body’s margin, the limited shallow burial cementation in inter-granular pores plugged the throats, and the cementation terminated after the diagenetic fluid reached dissolution-cementation balance; late burial-dissolution mainly adjusted and optimized early porous strata, which only played a secondary role in increasing the reservoir space of single reservoir permeable body and didn’t change the spatiotemporal distribution of this kind of reservoir.
• Select
  Characteristics and main controlling factors of porous carbonate reservoirs: A case from the Jia 5 Member of the Jialingjiang Formation, southwest Sichuan Basin

  Liu Hong; Tan Xiucheng; Li Ling; Luo Bing; Ma Changlin and Yang Ligen

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  With the help of core observation, conventional and cast slice, physical property analysis and mercury penetration, this paper studies the reservoir characteristics and main controlling factors of the Jia 5 Member, Triassic Jialingjiang Formation, and identifies two types of reservoir rocks, silt-sized crystalline dolomite and calcarenite, which are different in forming environment, reservoir space, poroperm characteristics, and pore throat structure. The silt-sized crystalline dolomite reservoir developed in the dolomite-flat microfacies has a good pore/throat configuration with intercrystalline pores and dissolved pores as reservoir space. It has excellent permeability and is the best reservoir in the region of interest. The calcarenite reservoir developed in the microfacies of arenite bank has the reservoir space of isolated intragranular dissolved pores and moldic pores; the mesoporosity and micro-throat configuration makes the reservoir characterized by high porosity and low permeability. Research on the main controlling factors of the reservoirs indicated that they are typically facies-controlled reservoirs. Microreliefs inside the carbonate platform lead to high heterogeneity of the reservoirs. Dolomitization and the leaching of syngenesis meteoric water are the key factors for forming good porous carbonate reservoirs.
• Select
  Reservoir Heterogeneities between structural positions in the anticline: A case study from Kela-2 gas field in the Kuqa Depression, Tarim Basin, NW China

  Han Denglin; Li Zhong and Shou Jianfeng

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  There are strong heterogeneous characteristics of reservoir property between the core and limbs of the Kela-2 anticline, although they are in the same structure. The heterogeneity of “small-scale and east-west” cannot be explained by the distribution mode of compressional stress “large-scale and south-north” proposed by previous scholars. Statistics of rock constituents and characteristics shows that the differentiation of reservoir compaction between the anticlinal core and limbs of the Kela-2 anticline is clear, which is controlled by the difference of tensile stress suffered by strata over the neutral plane during fold modification. The tensile stress suffered by strata in the anticlinal core is stronger than that in the anticlinal limbs. In the Kela-2 anticline, the difference of tensile stress between the anticlinal core (Kela-201) and limbs (Kela-203 & Kela-204) is obvious. The tensile stress offsets the compaction effect caused by vertical and lateral (south-north) stress, and it is constructive to reservoir properties. It is the major factor controlling the differentiation of reservoir compaction.
• Select
  Organic matter in deep carbonate rocks of the Tarim Basin, NW China

  Zhou Shixin; Song zhengxiang; Wang Baozhong; Jia Xingliang and Li Jing

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  Compositions of free and inclusion organic matter and the individual hydrocarbon isotopic compositions of n-alkanes and isoalkanes were investigated in deep carbonate rocks from the Tacan 1 well of the Tarim Basin. The comparison reveals that there are different evolutional trends for biomarker maturity parameters in different occurrences of organic matter at the high- and over-mature stage. The biomarker thermal maturity parameters of Ts/Tm for C27 hopanes and tricyclics/hopanes ratio can still be used to estimate the maturity of source-rock extracts when Ro is in the range of 1.0–1.3％. Whereas, these biomarker parameters showed reverse trends and are not useful for maturity assessment wehn Ro over 1.3%. The two ratios of C29 sterane isomerization, 20S/20S+20R and ββ/ββ+αα , also showed reverse change trends and can not be used to indicate the level of maturity when Ro is more than 1.1%. Although there are obvious different molecular compositions between free organic matter (chloroform bitumen A) and inclusion organic matter (chloroform bitumen C) in the deep carbonate rocks, the carbon isotopic values of n-alkanes and isoalkanes have similar values for the same samples with two different existence states, which indicates that the organic matters in the two existence states are derived from the same precursor, and their differences in molecular composition characteristics are due to the difference in thermal maturity.
• Select
  Relations of overpressure and hydrocarbons in the Mesozoic of western Mahuangshan, Ordos Basin

  Li Xingwen; Li Zhongdong; Guo Min; Hui Kuanyang and Ding Xiaoqi

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  The mudstone compaction research, in combination with hydrocarbon distribution, reveals that the Mesozoic overpressure in western Mahuangshan is horizontally distributed in the eastern stable belt and the central depression belt, vertically mainly in the Chang 7 and Yan 7 members in western Mahuangshan. Oil source faults and deeply undercut river valleys act as migration pathways for the discharge and accumulation of oil and gas in the Yan'an Formation. The Yan'an Formation regional overpressure belt strengthens the sealing ability of the regional cap rock, preventing upward migration or dissipation of the oil and gas, and the oil and gas can only accumulate below the overpressure area. Minor faults and the crack system have a certain decompression function to the Yan'an Formation overpressure area, and this is the reason why some oil is currently discovered above the overpressure's region of the Yan'an Formation in the eastern stable belt. Three patterns of oil and gas distribution associated with overpressure are developed in the Mesozoic in the eastern stable belt; they are lower combination, middle combination and upper combination. The middle combination pattern is developed in the central depression belt and western fracture belt.
• Select
  Petroleum migration and accumulation of the Yanchang Formation in the Zhenbei oil field, Ordos Basin

  Wang Xuejun; Wang Zhixin; Chen Jie and Zeng Jianhui

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  The Yanchang Formation in the Ordos Basin is a typical low permeability reservoir, and a critical problem of the hydrocarbon accumulation research in this area is the petroleum migration and accumulation mechanism in the low permeability reservoir. This paper studies the characteristics of the petroleum migration and accumulation in the Yanchang Formation by means of nitrogen compounds analysis of crude oil, organic inclusion analysis, fluorescent thin slice analysis of oil-bearing sandstone, in combination with physical properties of crude oil, the correlation between oil-bearing characters and physical property changes of sandstones, and so on. Late Jurassic – Early Cretaceous is the main accumulation period of petroleum in the Yanchang Formation. The hydrocarbon generation is a continuous process and there are not multiple periods of accumulation. The petroleum of the Yanchang Formation is of episodic and rapid migration under overpressure; cracks and microcracks are the main passage of oil migration, and the distance of petroleum lateral migration is short; buoyancy of oil is minor compared to the capillary resistance, so the oil can not produce secondary migration. At present, petroleum accumulation remains being injected into reservoirs under abnormal pressure, repeated high-pressure charges makes reservoirs located in the passage of cracks connecting oil sources infilled again and again, so that valid accumulations of petroleum are generated.
• Select
  Late-stage hydrocarbon accumulation and enrichment in the Huanghekou sag, southern Bohai Sea

  Sun Hefeng; Zhou Xinhuai; Peng Wenxu; Zou Huayao; Yang Bo; He Dianbo and Zeng Xuan

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  The Huanghekou sag is one of the major oil-bearing areas in the offshore Bohai Bay Basin and is characterized by late-stage accumulation. The easy Ro% model is used to simulate the hydrocarbon generation time of source rocks, showing that the major source rock has matured since 5.1Ma. The analysis of the migration system reveals that hydrocarbons in the Huanghekou sag migrate through faults and fractures which are the main pathways. The analysis of reservoir inclusions shows that the main charge time is 5.1Ma or later. The late-stage accumulation in the Huanghekou sag is characterized by late quick hydrocarbon generation, late vertical migration through faults, near-source accumulation and late charge. The main factors controlling the hydrocarbon enrichment are the regional reservoir-cap assemblage of the Shahejie formation and lower member of the Minghuazhen formation, dominant migration pathways, and traps formed by Neotectonic movement. Paleogene overpressured reservoirs with near source rocks and Neogene shallow water deltaic reservoirs are the most important hydrocarbon accumulation models in the Huanghekou sag.
• Select
  Control of Paleogene structural slope-break on lithologic-stratigraphic traps in the Qibei Sag，Bohai Bay Basin

  Xiang Xuemei; Wang Hua; Wang Jiahao; Xiao Dunqing and Pu Xiugang

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  The study of sequence stratigraphy is carried out in central Huanghua Depression using 3D seismic data, drilling, and well logging data. The Paleogene of the studied area can be divided into 3 second-order sequences, and 11 third-order sequences. Two kinds of structural slope-break are developed in the Qibei slope: faulted slope-break and flexural slope-break. The development and evolution of the slope-breaks are episodic and successive: in early period, it is faulted slope-break; in later period, it is flexural slope-break. Different kinds of slope-breaks have different sequence stratigraphic patterns and inner systems tracts. The faulted slope-breaks control the development of lowstand fan delta sandbodies and combination structural-lithologic traps, while the flexural slope-breaks not only control the development of sandbodies, but more apparently control the development of stratigraphic overlap and lithologic traps. The surrounding areas of the slope-breaks are favorable for the development of lithologic-stratigraphic traps，and have great potential for exploration.
• Select
  Chen Xuehai, Lu Shuangfang, Xue Haitao, Li Junhui, Liu Qiuhong, Hu Shoumei，Huang Wenbiao

  Chen Xuehai; Lu Shuangfang; Xue Haitao; Li Junhui; Liu Qiuhong; Hu Shoumei and Huang Wenbiao

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  The petroleum exploration in the Huhehu Depression has become a new area for searching reserves in the Daqing Oilfield, but no great breakthrough has been made owing to the lower study degree. According to the seismic reflection termination relationship and the regional geological background, the Cretaceous in the Huhehu Depression can be divided into eight seismic sequences, Sq1—Sq8. According to the internal reflection texture and external geometric configuration and in combination with the parameters of amplitude and continuity, eight seismic facies are identified in the target sequences of the study area, including parallel sheet, sub-parallel sheet, prograding, filling, wedge shaped, moundy, chaotic and wave-hummocky seismic facies. And their characteristics are described in detail. These seismic facies show differentiation in horizontal distribution and are successive and evolutionary vertically. Seismic facies are transformed into sedimentary facies through a comprehensive interpretation. The seismic – sedimentary facies model of each sequence is established according to the lacustrine sedimentary theory. The results show that the target sequences develop the sedimentary systems of alluvial fan, fan delta, braided river delta, lake and sublacustrine fan.
• Select
  Design and implementation of the high-efficiency data operation cache on the Java well logging software platform

  Liu Yingming; Li Ning; Xia Shouji; Wang Caizhi and Zhang Ling

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  The integrated well logging network platform is a large comprehensive system of well logging processing and interpretation that is the first in the world to totally adopt Java Language development and support running in different systems. Because the platform achieves integration on the underlying data based on the broad sense logging curve theory, other non-Java logging systems can be effectively integrated and redeveloped with little change on original programming codes and minimal workloads on the integration platform. For the common features of interactive processing and interpretation modules with different languages, the article proposes an advanced mode of cache based on proxy curve, and implements in Java language. The results of the large-scale integration testing and the interpretation of water-flooded layers in the Daqing Oilfield show that, this proxy mode effectively solves the technical difficulty that the original cache function cannot be reused in the cross-platform integrating of different-language interactive processing software. The interactive cache processing efficiency of the original system can be further improved as the case may be.
油气田开发
• Select
  Physical modeling of the horizontal well “gel dam” in-depth fluid diversion

  Liu Yuzhang; Lü Jing; Wang Jialu; Gao Jian and Li Yikun

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  In view of the ineffective cycling problem for injected water along bottom high permeability layers during the development process of positive rhythm reservoirs by water flooding, the horizontal well “gel dam” in-depth fluid diversion technique is proposed. The technique involves the injection of gel throughout a horizontal or sidetracking well drilled in the more permeable and strong water flooded zone in the bottom of thick positive rhythm reservoirs, then the injected water will bypass the gel dam and divert into the upper unswept or poorly swept low permeable zones. So the sweep efficiency and oil recovery of the upper low permeable zone can be both increased. A 2D visible sandpack physical model was set up, and a video camera was used to visualize the fluid diversion effects of gel dams. The results of the experiments indicate that, with one or two “gel dams” set up, the ultimate oil recovery and sweep efficiency are increased significantly, and the ascending velocity of water cut is slowed down. Compared with the physical model without gel dam, the ultimate oil recovery of physical model with one “gel dam” increased by 17.6%, and the ultimate recovery of the physical model with two “gel dams” increased by 27.3%. The horizontal well “Gel dam” in-depth fluid diversion technique breakthrough the bottleneck of the in-depth placement of plugging agents, which can greatly enhance the water swept degree of positive rhythm reservoirs.
• Select
  Characteristics of micro scale nonlinear filtration

  Li Yang; Lei Qun; Liu Xiangui and Xiao Hanmin

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  Take the flow characteristics of fluid in micro tube as the object, the characteristics of nonlinear filtration in low permeability reservoirs were studied using micro scale method by simulating the micro pore throat of reservoir with the micro tube which has the similar scale pore throat of low permeability reservoirs. The flow characteristics of de-ionized water flowing through fused silica capillary tubes with radius of 10.0 μm, 7.5 μm, 5.0 μm and 2.5 μm were investigated in experiments. Relationship between average flow rate and pressure gradient, effect of pressure gradient on fluid boundary layer, and relationships between flow resistance coefficient and Reynolds number were analyzed respectively in these experiments with different micro tubes. The flow of fluid through micro tubes with low velocity has nonlinearity, and the extent of nonlinearity increases with the tube radius decreasing. Nonlinear flow experimental points can be matched by quadratic curve. In micro flow, the percentage of effective fluid boundary layer thickness to micro tube radius decreases with the pressure gradient increasing. Research results indicated that Reynolds number can be used as the criteria of nonlinear flow. Flows with Reynolds number less than 10－3 have nonlinear features.
• Select
  Development characteristics of low saturated-oil reservoirs

  Liu Bolin and Wang Youqi

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  The filtration of low saturated-oil reservoirs are obviously different from that of conventional reservoirs. This paper studied the development performance and the influence factors for low saturated-oil reservoirs by using laboratory large model physical modeling and reservoir numerical simulation, to match and establish the empirical formula of water cut variation. In the numerical stimulation process, the effect of threshold pressure on filtration for low permeability reservoirs was considered, which made the results more realistic. There wasn’t a period of oil recovery without water for low saturated-oil reservoirs; the water cut increased rapidly at the beginning, and dropped slightly before the period of oil production with stable water cut. The higher the initial water saturation, the shorter the production time with stable water cut. Recovery changes greatly with the injection/production pressure gradient when the injection/production pressure gradient closed to the pseudo threshold pressure gradient. Recovery changed little, even no change, with the injection/production pressure gradient when the injection/production pressure gradient was far larger than the pseudo threshold pressure gradient. There was a positive correlation between recovery degree and water injection rate when the injection/production pressure gradient less than the pseudo threshold pressure gradient.
• Select
  Identifying water flooded layers based on the domain-driven data mining technique

  Li Xiongyan; Li Hongqi; Zhou Jinyu; Tan Fengqi; He Xu and Chen Yihan

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  To identify water flooded layers and determine the flooded degree of reservoirs, the data mining technique is introduced and an efficient predictive model, combining with the relative knowledge of evaluating water flooded layers, is established to identify water flooded layers from the view of domain-driven. With the sedimentary facies characteristics of the study area, this paper uses the cluster analysis, association rule and decision tree to mine the logging data of the flooded layers and reservoir derived parameters by sedimentary microfacies and parameter combinations. As a result, the predictive models of the entire region and small layers are obtained. And the sensitivity of the parameters in identifying the water flooded layers is given, proving that different sedimentary microfacies have parameters sensitive to flooded conditions. After the predictive models of the small layers are programmed, they are used to evaluate the 180 old wells and 10 new wells; the accuracy is 91.03 percent, which proved the reliability of this method.
石油工程
• Select
  Law and countermeasures for the casing damage of oil wells and water injection wells in Tarim Oilfield

  Wang Tao; Yang Shenglai; Zhu Weihong; ian Wanjiang; Liu Min; Lei Yu; Zhang Yuan; Zhao Wei; Chen Lan; Zhou Xiaoping and Liao Jianhua

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  Based on the analyses of the situation and distribution of casing damage in the Tarim Oilfield, it was considered that there are six major factors causing the casing damage: (1) There are flowing rock or high permeable formation around the casing; (2) The well bore structure is unreasonable; (3) The up hole elevation of cement in the drilling design is not high enough, or the cementing quality does not conform to the rules; (4) The quality of casing grading hoop is not up to the required standard; (5) Collapse resistance decreased due to the corrosion, wear, etc. from special down hole operation; (6) The unreasonable development factors. According to the present situation of the casing damage, the comprehensive countermeasures of "defense", "diagnosis", "treatment" for repairing the casing-damaged wells were developed. For the casing-damaged wells, 3 ways, taking underground work sit sealing to suppress, engineering logging and static temperature gradient, were used to find a leak. During 1998-2009, casing damages happened in 71 wells, and 87 places were damaged in total. After determining the position of the casing damages, 3 ways were employed to repair the casing-damaged wells, cement squeezing, using packer to the selected segement, tube expanding subsidies. 57 casing-damaged wells were repaired, of which, 46 wells were recovered on production. The success ratio is 80.7%.
• Select
  Influences of formation water invasion on the well bore temperature and pressure in supercritical CO2 drilling

  Wang Haizhu; Shen Zhonghou and Li Gensheng

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  Aiming to study the influence of formation water invasion on the well bore temperature and pressure in SC-CO2 (supercritical CO2) drilling with coiled tubing, this paper builds up a wellbore flow model with formation water invasion in SC-CO2 drilling with coiled tubing, based on the comprehensive investigation of the influence of viscosity, density, thermal conductivity, isobaric heat capacity and Joule-Thompson coefficient of SC-CO2. The wellbore temperature and pressure distribution were calculated by the method of coupling among these parameters. The results show that the bigger the rate of invaded formation water and the bigger the density of mixed fluid, the bigger the convective heat transfer coefficient in the annulus. Because of the Joule-Thompson cooling effect caused by nozzle throttling, the annulus mixture fluid density increased abruptly and the convective heat transfer coefficient decreased abruptly at the well depth of about 1 900 m (about 10 m to bottom hole). Meanwhile the wellbore fluid temperature increased with the invasion rate of formation water, and the same Joule-Thompson cooling effect caused the wellbore fluid temperature to decrease abruptly at the well depth of about 1 900 m. Moreover, the wellbore annulus pressure increased with the increasing of invaded formation water quantity. but the amplitude is not obvious.
综合研究
• Select
  Study and application of an environmental drilling fluid system

  Xie Shuixiang; Jiang Guancheng; Chen Mian; Deng Hao; Liu Guangquan; Xu Yu; Wang Jianhua and Qiu Kang

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  Based on numerous laboratory studies, an environmental drilling fluid system is developed. The formula is 4% bentonite＋0.3%IND-30＋1.5%NAT-20＋3%FXJS＋2%NFT-25. By adopting environmental additives, the system has good temperature resistance (up to 150 ℃) and excellent contamination resistance (30% saturated salt tolerance and 8% bentonite tolerance). It can also effectively protect reservoir and achieve more than 81.5% of permeability recovery. When spreading on land surface with thickness of 0-20 cm, all the indexes of the soil environmental quality are above the second degree of the national standard. Meanwhile, it can improve the water content and fertility of sandy land. And this drilling fluid system was successfully used in 15 wells of the Tarim Oilfield, Karamay Oilfield and Jiangsu Oilfield and got satisfactory results in environmental protection and reservoir protection. After this environmental drilling fluid is abandoned, the contents of organic matter, active nitrogen, active phosphorus and active potassium in the soil around wells are increased. 40.87×104 Yuan of comprehensive cost per well was saved and the total saved cost of the 15 wells was 613.05×104 Yuan.
学术讨论
• Select
  Conditions for the saturation pressure method in identifying oil accumulation periods

  Bao Youshu; Zhang Linye; Li Juyuan; Zhang Shouchun and Wang Ru

  . 2011, 38(3): 2-0.

  Abstract ( ) Download PDF ( ) Knowledge map Save

  There have been arguments on the principle and method of oil saturation pressure for determining the accumulation period of oil reservoirs. The application of the method in the high-exploration-degree depression, Jiyang Depression, shows that the method is not fit for many reservoirs, the inferred depths and periods of the oil accumulation do not match the actual conditions. Based on the study of the oil saturation pressures in the reservoirs and the change of the oil saturation pressures in the oil generation and migration stage, this paper analyzes the reason why the method is not working for many reservoirs in the Jiyang Depression. In the Jiyang Depression, the viscosities of saturated oil are not necessarily the lowest and easiest to migrate in formation conditions. Most oils generated and expelled from the Paleogene source rocks of the Jiyang Depression are unsaturated. The oils migrating and accumulating in an unsaturated state are the main reason why the oil saturation pressure does not work in the area. Oils can accumulate in a large scale both in a saturation state and in an unsaturated state. So, the saturation pressure method cannot be used to determine the accumulation period of a reservoir before it is that the oils in the reservoir accumulated in a saturated state.