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Most Cited Petroleum Exploration and Development Articles

The most cited articles published since 2014, extracted from Scopus.

Formation and enrichment mode of Jiaoshiba shale gas field, Sichuan Basin

Volume 41, Issue 1, 二月 2014, Pages 31-40
Guo Tonglou | Zhang Hanrong

The Silurian Longmaxi shale gas play in Jiaoshiba Structure in the southeast margin of the Sichuan Basin is studied to discuss the key controlling factors of shale gas enrichment in complex tectonic zone with high evolution. Jiaoshiba Structure is a faulted anticline which experienced multiphase tectonic movements. The Longmaxi Formation has high thermal evolution degree with Romore than 2.2%, 35-45 meters thick high-quality shale (TOC > 2%) in its lower part. The reservoir is overpressure with a pressure coefficient of 1.55, and the shale gas production and pressure are stable. Structure type, evolution and geochemical analyses show that there are several stages of hydrocarbon generation, migration and accumulation in the Longmaxi Formation. The joint action of two groups (two stages) of fault systems and the detachment surface at the bottom of the Longmaxi Formation control the development of reticular cracks and overpressure preservation, and it is the key to the shale gas accumulation and high yield. The sealed box-like system in the Longmaxi Formation ensures the gas reservoir dynamic balance. The model of high yield and enrichment of Jiaoshiba shale gas play is "ladder migration, anticline accumulation, fault-slip plane controlling fractures, and box shape reservoiring". Like in conventional gas plays, good preservation and tectonic conditions are also required to form high yield shale plays in areas which have complex structures, multi-stage tectonic movements, and have high evolution shale. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Formation mechanism, geological characteristics and development strategy of nonmarine shale oil in China

Volume 40, Issue 1, 二月 2013, Pages 15-27
Caineng Zou | Zhi Yang | Jingwei Cui | Rukai Zhu | Lianhua Hou | Shizhen Tao | Xuanjun Yuan | Songtao Wu | Senhu Lin | Lan Wang | Bin Bai | Jingli Yao

As an important type of " conventional-unconventional orderly accumulation" , shale oil is mature oil stored in organic-rich shales with nano-scale pores. This paper analyzes and summarizes elementary petroleum geological issues concerning continental shale oil in China, including sedimentary environment, reservoir space, geochemical features and accumulation mechanism. Mainly deposited in semi-deep to deep lake environment, shale rich in organic matter usually coexists with other lithologies in laminated texture, and micron to nano-scale pores and microfractures serve as primary reservoir space. Favorable shale mainly has type I and IIAkerogens with a Roof 0.7%-2.0%, TOC more than 2.0%, and effective thickness of over 10 m. The evolution of shale pores and retained accumulation pattern of shale oil are figured out. Reservoir space, brittleness, viscosity, pressure, retained quantity are key parameters in the " core" area evaluation of shale oil. Continuously accumulated in the center of lake basins, continental shale oil resources in China are about 30×108-60×108t by preliminary prediction. Volume fracturing in horizontal wells, reformation of natural fractures, and man-made reservoir by injecting coarse grains are some of the key technologies for shale oil production. A three step development road for shale oil is put forward, speeding up study on " shale oil prospective area" , stepping up selection of " core areas" , and expanding " test areas" By learning from marine shale breakthroughs in North America, continental shale oil industrialization is likely to kick off in China. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Characteristics of tight oil in Triassic Yanchang Formation, Ordos Basin

Volume 40, Issue 2, 四月 2013, Pages 161-169
Jingli Yao | Jingli Yao | Xiuqin Deng | Xiuqin Deng | Yande Zhao | Yande Zhao | Tianyou Han | Tianyou Han | Meijuan Chu | Meijuan Chu | Jinlian Pang | Jinlian Pang

By comprehensive study of reservoir and source rock distribution, petrology and geochemistry, the tight oil and its exploration potential was analyzed in the Triassic Yanchang Formation, Ordos Basin. The Triassic Yanchang Formation is rich in low permeability reservoirs. The proved geological reserves of tight oil, with the permeability less than 2×10-3μm2, is about two billion tons by now. The tight oil mainly occurs in tight sandstone reservoirs of Chang6-Chang8 oil-bearing members which are close to or interbedded with the oil shale layers, without long-distance migration. The large-scale gravity flow sandstone reservoirs of Chang7 and Chang6 oil-bearing members in the center of the lacustrine basin are particularly tight, with the permeability less than 0.3×10-3μm2in general. The tight oil in the Yanchang Formation features large scale in sand body complex, tight reservoir, complicated pore throat structure, high content of rigid components, abundant fractures and saturation, good crude property, low fluid pressure and low oil yield. The formation of large-scale superimposed tight oil reservoirs is controlled by the interbeded lithologic combination of extensive source rocks and reservoirs and the strong hydrocarbon generation and expulsion during geological history. This type of pools is an important potential resource for future oil exploration and development. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Formation, distribution, resource potential, and discovery of Sinian-Cambrian giant gas field, Sichuan Basin, SW China

Volume 41, Issue 3, 一月 2014, Pages 306-325
Caineng Zou | Jinhu Du | Chunchun Xu | Zecheng Wang | Baomin Zhang | Guoqi Wei | Tongshan Wang | Genshun Yao | Shenghui Deng | Jingjiang Liu | Hui Zhou | Anna Xu | Zhi Yang | Hua Jiang | Zhidong Gu

The Anyue Sinian-Cambrian giant gas field was discovered in central paleo-uplift in the Sichuan Basin in 2013, which is a structural-lithological gas reservoir, with 779.9 km2proven gas-bearing area and 4 403.8×108m3proven geological reserves in the Cambrian Longwangmiao Formation in Moxi Block, and the discovery implies it possesses trillion-cubic-meter reserves in the Sinian. Cambrian Formations in Sichuan Basin. The main understandings achieved are as follows: (1) Sinian-Cambrian sedimentary filling sequences and division evidence are redetermined; (2) During Late Sinian and Early Cambrian, "Deyang-Anyue" paleo-taphrogenic trough was successively developed and controlled the distribution of source rocks in the Lower-Cambrian, characterized by 20-160 m source rock thickness, TOC 1.7%-3.6% and Ro2.0%-3.5%; (3) Carbonate edge platform occurred in the Sinian Dengying Formation, and carbonate gentle slope platform occurred in the Longwangmiao Formation, with large-scale grain beach near the synsedimentary paleo- uplift; (4) Two types of gas-bearing reservoir, i.e. carbonate fracture-vug type in the Sinian Dengying Formation and dolomite pore type in the Cambrian Longwangmiao Formation, and superposition transformation of penecontemporaneous dolomitization and supergene karst formed high porosity-permeability reservoirs, with 3%-4% porosity and (1-6)×10-3μm2permeability in the Sinian Dengying Formation, and 4%-5% porosity and (1-5)×10-3μm2permeability in the Cambrian Longwangmiao Formation; (5) Large paleo-oil pool occurred in the core of the paleo-uplift during late Hercynian-Indosinian, with over 5 000 km2and (48-63)×108t oil resources, and then in the Yanshanian period, in-situ crude oil cracked to generate gas and dispersive liquid hydrocarbons in deep slope cracked to generate gas, both of which provide sufficient gas for the giant gas field; (6) The formation and retention of the giant gas field is mainly controlled by paleo-taphrogenic trough, paleo-platform, paleo-oil pool cracking gas and paleo-uplift jointly; (7) Total gas resources of the Sinian-Cambrian giant gas field are preliminarily predicted to be about 5×1012m3, and the paleo-uplift and its slope, southern Sichuan Basin depression and deep formations of the high and steep structure belt in east Sichuan, are key exploration plays. The discovery of deep Anyue Sinian-Cambrian giant primay oil-cracking gas field in the Sichuan Basin, is the first in global ancient strata exploration, which is of great inspiration for extension of oil & gas discoveries for global middle-deep formations from Lower Paleozoic to Middle-Upper Proterozoic strata. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Theoretical and technical innovations in strategic discovery of a giant gas field in Cambrian Longwangmiao Formation of central Sichuan paleo-uplift, Sichuan Basin

Volume 41, Issue 3, 一月 2014, Pages 294-305
Jinhu Du | Caineng Zou | Chunchun Xu | Haiqing He | Ping Shen | Yueming Yang | Yalin Li | Guoqi Wei | Zecheng Wang | Yu Yang

Since 2011, huge gas fields have been discovered in the Sinian and Cambrian strata in Moxi-Gaoshiti region, central Sichuan paleo-uplift, with the geological reserves reaching more than one trillion cubic meters. The main gas-bearing layers include Deng 2 Member, Deng 4 Member and Longwangmiao Formation. Based on brief review of the exploration history of large gas province in central Sichuan paleohigh, the paper systematically describes the formation conditions and petroleum accumulation patterns of huge gas fields there, and points out the large ancient uplift background, huge net of hydrocarbon supply system, large-scale grain shoal reservoirs and regional reservoir-cap combinations are important material conditions for the formation of large gas fields. In view of the huge depth, high temperature, high pressure and some other complex formation conditions, a lot of efforts have been put into the research on logging, seismic, drilling, reservoir stimulation etc, and a series of accomplishments have been achieved, which work well in the exploration and development of gas in Sichuan Basin. The Sinian and Cambrian strata in the Sichuan Basin have a great potential for petroleum exploration. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Multi-scale method of Nano(Micro)-CT study on microscopic pore structure of tight sandstone of Yanchang Formation, Ordos Basin

Volume 40, Issue 3, 六月 2013, Pages 354-358
Bin Bai | Bin Bai | Rukai Zhu | Rukai Zhu | Songtao Wu | Songtao Wu | Wenjing Yang | Jeff Gelb | Allen Gu | Xiangxiang Zhang | Xiangxiang Zhang | Ling Su | Ling Su

Multi-scale (nano-to-micro) three-dimensional CT imaging was used to characterize the distribution and texture of micro-scale pore throats in tight sandstone reservoirs of the Triassic Yanchang Formation, Ordos Basin. First, the low-resolution Micro-CT was used to reflect the micro-pore texture of the core column with a diameter of 2.54 cm. Then, some samples with a diameter of 65 μm was derived from different areas according the different characteristics of micro-pore texture of the core scanned by low-resolution Micro-CT and scanned by high-resolution Nano-CT. Thus, a three-dimensional texture model of nano-scale micro-pores was reestablished and the permebility and porosity data of the sample could be obtained. On a micrometer scale, the size of the micro-pores varies, and their diameters range from 5.4 to 26.0 μm. The micro-pores are isolated, locally in the shape of a band. On a nanometer scale, the quantity of nanoscale micropores increases, the diameter of which ranges from 0.4 to 1.5 μm. The pore throats are arranged in the shape of tube and ball inside or on the surface of mineral particles(crystals). The ball-shaped micropores in nanoscale, often isolated in the three-dimensional space, show the poor connectivity and consequently act as the reservoir space. By contrast, the tube-shaped micropores in nanoscale show certain connectivity with micro-scale tube-shaped micropores and adjacent isolated ball-shaped micropores in nanoscale. Therefore, these tube-shaped micropores in nanoscale serve as throats and pores. Based on the calcution, the permeability of the samples is 0.843×10-3μm2and porosity is 10%. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Shale gas in China: Characteristics, challenges and prospects (I)

Volume 42, Issue 6, 十二月 2015, Pages 753-767
Caineng Zou | Dazhong Dong | Dazhong Dong | Yuman Wang | Xinjing Li | Jinliang Huang | Shufang Wang | Quanzhong Guan | Chenchen Zhang | Hongyan Wang | Hongyan Wang | Honglin Liu | Wenhua Bai | Feng Liang | Wen Lin | Qun Zhao | Dexun Liu | Zhi Yang | Pingping Liang | Shasha Sun | Zhen Qiu

© 2015 Research Institute of Petroleum Exploration & Development, PetroChina. The main factors controlling the enrichment and high yield of shale gas were analyzed based on the recent research progress of depositional model and reservoir characterization of organic-rich shale in China. The study determines the space-time comparison basis of graptolite sequence in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation and proposes the important depositional pattern of marine organic-rich shale: stable ocean basin with low subsidence rate, high sea level, semi-enclosed water body, and low sedimentation rate. Deposited in the stage of Late Ordovician-Early Silurian, the superior shale with thickness of 20-80 m and total organic carbon (TOC) content of 2.0%-8.4% was developed in large deep-water shelf environment which is favorable for black shale development. Based on the comparison among the Jiaoshiba, Changning and Weiyuan shale gas fields, it is believed that reservoirs of scale are mainly controlled by shale rich in biogenic silica and calcium, moderate thermal maturity, high matrix porosity, and abundant fracture. The shales in the Wufeng and Longmaxi formations are characterized by porosity of 3.0%-8.4%, permeability of 0.000 2×10-3-0.500 0×10-3μm2, stable areal distribution of matrix pore volume and their constituents, great variation in fracture and pore characteristics among different tectonic regions as well as different well fields and different intervals in the same tectonic. The Cambrian Qiongzhusi shale features poor physical properties with the porosity of 1.5%-2.9% and the permeability of 0.001×10-3-0.010×10-3μm2, resulted from the carbonization of organic matter, high crystallinity of clay minerals and later filling in bioclastic intragranular pores. Four factors controlling the accumulation and high production of shale gas were confirmed: depositional environment, thermal evolution, pore and fracture development, and tectonic preservation condition; two special features were found: high thermal maturity (Roof 2.0%-3.5%) and overpressure of reservoir (pressure coefficient of 1.3-2.1); and two enrichment modes were summarized: "structural sweet spots" and "continuous sweet area".

New perspectives on deep-water sandstones: Implications

Volume 40, Issue 3, 六月 2013, Pages 316-324
G. Shanmugam

The emerging new concepts of sandy mass-transport deposits (SMTD) and bottom-current reworked sands (BCRS) have made a big impact on conventional turbidite concepts. Sediment failures near the shelf edge are the common cause of gravity-driven downslope processes. Mass-transport processes, which include slide, slump, and debris flow, exhibit elastic and plastic behaviors due to high sediment concentration (25-100% by volume). Turbidity currents which represent viscous fluid behavior with low sediment concentration (1-23% by volume) are not mass-transport processes. Four common bottom currents are thermohaline, wind-driven, deep tidal, and baroclinic types. A distinctive attribute of BCRS is their traction structures. However, depositional aspects of baroclinic currents associated with internal waves and tides are poorly understood. Seismic facies and geometries are unreliable for distinguishing types of SMTDs and BCRS in the ancient record. The only reliable method of distinguishing a specific depositional facies is by detailed bed-by-bed examination of sedimentological features in core and outcrop. Short-term events that represent only a matter of hours or days (e.g., earthquakes, tsunamis, tropical cyclones, etc.) are more important in triggering sediment failures than periods of sea-level lowstands that represent thousands of years. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Effect of pore structure on methane sorption potential of shales

Volume 41, Issue 2, 一月 2014, Pages 272-281
Yuguang Hou | Sheng He | Jizheng Yi | Baiqiao Zhang | Xuehui Chen | Xuehui Chen | Yi Wang | Jiankun Zhang | Chunyang Cheng

Samples from the lower Paleozoic marine shale and Mesozoic continental shale in the west of middle Yangtze region were taken to investigate the effect of pore structure characteristics on the methane sorption of shale using field emission scanning electron microscope (FE-SEM), low pressure N2isotherm analysis and high pressure methane sorption analysis. A mass of organic matter pores (mostly with pore diameter less than 50 nm) have been found in the high thermal evolution marine shale rich in organic matter. The positive correlation between TOC, N2BET surface areas and sorption capacity in shale indicate that micro-porosity associated with organic matter is the key factor controlling methane sorption capacity of high thermal maturity shale rich in organic matter. The development of organic matter pores was limited in the organically lean marine shale and continental shale due to the lower TOC content and lower thermal maturity respectively, and their reservoir space is composed of inorganic matter pores in 30 nm to 4.5 μm diameter. Providing bigger specific surface area for methane sorption, the pores within or between clay particles is an important factor to affect methane sorption capacity. With the increase of thermal maturity, the major pore system of shale reservoir changes from inorganic matter pores to organic matter pores, favorable for the improvement of methane sorption capacity of shale. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Evolution of overmature marine shale porosity and implication to the free gas volume

Volume 40, Issue 6, 十二月 2013, Pages 819-824
Feiyu Wang | Feiyu Wang | Jing Guan | Weiping Feng | Linyan Bao

The porosities of the Lower Cambrian shale and Upper Ordovician-Lower Silurian marine shale from the Sichuan Basin were analyzed using He-Hg porosimetry and field-emission scanning electron microscopy, to discuss the relationship of porosity to the organic matter maturity, total organic carbon (TOC) and free gas volume. Overmature (Rogreater than 2%) shale samples with a TOC less than 5% display a positive correlation between TOC and porosity, but samples with a TOC greater than 5% display a limited increase in porosity with increasing TOC. The porosity of shale decreases generally with increasing maturity in the overmature stage. The free gas in porosity is the key factor for successful development of shale gas, and free gas volumes are controlled by porosity and gas saturation. Higher TOC shale has higher porosity and gas saturation. The Lower Silurian Longmaxi Formation shale has a higher TOC, Roranging from 2.0% to 2.3%, its porosity and gas saturation are significantly higher than the Lower Cambrian shale. The high free gas volume results in high production in the Lower Silurian Longmaxi Formation shale pay. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Geological features of Mesozoic lacustrine shale gas in south of Ordos Basin, NW China

Volume 41, Issue 3, 一月 2014, Pages 326-337
Xiangzeng Wang | Shengli Gao | Chao Gao

The geological characteristics of Mesozoic lacustrine shale gas are summarized from the following aspects: distribution of shale, geochemistry of shale gas, characteristics of shale reservoir, enrichment form of shale gas etc, based on the lacustrine shale gas exploration research and practices in southeast of the Ordos Basin. The geochemical characteristics and thermal evolution degree of shale gas source rocks are controlled by the evolution of lacustrine basin in the early and middle stages of late Triassic Period, and the main hydrocarbon-generation rocks are shale from the Chang 7 and Chang 9 members of the Triassic Yanchang Formation, with high abundance of organic matter and in the mature to wet gas stage. The most mineral compositions are quartz, feldspar and clay mineral in shale gas reservoir, and the primary intergranular pores and secondary dissolution pores are the main pore types. The shale gas in the study area is oil-type gas, dominantly wet gas. The shale gas occurs mostly in the adsorption state, the free state and the dissolved state. Estimated by the volumetric method, the total shale gas resources of Chang 7 is 5 318.27×108m3, and the total shale gas resources of Chang 9 is 3 067.29×108m3. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Concepts, characteristics, potential and technology of unconventional hydrocarbons: On unconventional petroleum geology

Volume 40, Issue 4, 八月 2013, Pages 413-428
Caineng ZOU | Guosheng ZHANG | Zhi YANG | Shizhen TAO | Lianhua HOU | Rukai ZHU | Xuanjun YUAN | Qiquan RAN | Denghua LI | Zhiping WANG

Petroleum geology is evolving into two branches, conventional petroleum geology and unconventional petroleum geology, with the latter becoming a new theoretical frontier in the petroleum industry. The core of conventional hydrocarbon geological study is based on identifying the match between source rock, reservoir, caprock, migration, trap, preservation and timing; the core of unconventional hydrocarbon geological study evaluates if the oil and gas is part of a continuous accumulation, where stress is placed on the evaluation of "lithology, physical properties, brittleness, oiliness, source rock features, stress anisotropy" and their configuration. The oil and gas accumulation mode and theoretical formula at various low limits of pore throat diameter have been established, as well as the "L" type production curve. Theoretical production prediction models for unconventional oil and gas, and formation mechanism and development patterns for unconventional oil and gas are being revealed. The connotation, characteristics, potential and technology for unconventional oil and gas have been observed, and two key marks to identify unconventional hydrocarbon have been put forward: (1) continuous distribution of hydrocarbon-bearing reservoirs over a large area, with no obvious trap boundary; and (2) no natural stable industrial production, and no obvious Darcy flow. Systematic research shows that the proportion of global unconventional to conventional hydrocarbon resources is 8:2, in which the unconventional oil is almost equal to conventional oil, and the unconventional gas is about 8 times that of conventional gas. In China, unconventional oil resources are about 240×108t and unconventional gas resources are about 100×1012m3. In recent years the development of tight gas and tight oil should be strengthened to realize industrial reserves and increase production. Construction of shale gas pilot plants and shale oil research should be strengthened. Unconventional oil and gas industrial systems and research should be set up, including unconventional hydrocarbon geology, fine particle sedimentology, unconventional reservoir geology, seismic reservoir prediction, massive fracturing of horizontal wells, "factory-like" operation, low cost management and subsidy policy and personnel training. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Lacustrine fine-grained sedimentary features and organicrich shale distribution pattern: A case study of Chang 7 Member of Triassic Yanchang Formation in Ordos Basin, NW China

Volume 42, Issue 1, 一月 2015, Pages 37-47
Xuanjun Yuan | Senhu Lin | Qun Liu | Jingli Yao | Lan Wang | Hao Guo | Xiuqin Deng | Dawei Cheng

© 2015 Research Institute of Petroleum Exploration & Development, PetroChina. The Chang 7 Member of Triassic Yanchang Formation in Ordos Basin is taken as an example to study the distribution rule and major controlling factors of the fine-grained sedimentary system by core description, thin section observation, X-ray diffraction, geochemical testing and TOC well logging quantitative calculation. The main sedimentary pattern of organic-rich shale in Chang 7 Member is transgression-water stratification. The sedimentary facies, water depth, anoxic condition and lacustrine flow are the major controlling factors for the formation and distribution of organic-rich shale. During the deposition of the Chang 73Member, lake water invaded rapidly, lake depth and scope sharply increased. Because of the temperature difference, the circulation between upper surface water and lower water in deep lake was restrained, then large-area anoxic environment was formed in deep lake, which was favorable for the development of organic-rich shale. In silent deep lake where is far away from the delta front, organic-rich shale well developed, with high organic carbon content and mainly type I kerogen. In deep lake where sandy debris flows developed, organic-rich shale was inter-bedded with sandstone, which contains high organic carbon content, mainly with type I-II1kerogen. In semi-deep lake close to the delta front, wavy-massive silty mudstone developed, mainly with type II kerogen.

Current development and application of chemical combination flooding technique

Volume 40, Issue 1, 二月 2013, Pages 96-103
Youyi Zhu | Youyi Zhu | Qingfeng Hou | Qingfeng Hou | Guoqing Jian | Guoqing Jian | Desheng Ma | Desheng Ma | Zhe Wang | Zhe Wang

Great progress and success have been achieved in the fundamental study and field test of chemical combination flooding in recent years. In China, a low concentration ASP formula is employed to achieve ultra-low interfacial tension by the synergistic effect of alkali and surfactant. The viscosity of polymer solution prepared from produced water can meet the technological requirement when salt tolerance polymer is applied. ASP or SP flooding can increase both oil displacement efficiency and sweep volume. ASP pilot tests and industrial field tests in Daqing Oilfield have resulted in an oil recovery increase of 18.5%-26.5%. The chemical combination flooding has entered into the industrial promotion and application stage, with a series of supporting techniques formed in the field tests. The main challenges in this technique include short pump-checking period and difficulty in produced liquid handling and high cost. Micelle-polymer flooding as the major chemical combination flooding technique was applied abroad in the early stage of chemical flooding tests. However, the micelle-polymer flooding has not been applied widely due to its high cost. With the rise of oil price in recent years, low concentration chemical combination flooding has drawn more attention. Because of high temperature and high salinity in most reservoirs abroad where chemical combination flooding is used, high performance temperature and salt tolerance oil displacement agents are the bottleneck for future chemical flooding. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Study of meso-damage characteristics of shale hydration based on CT scanning technology

Volume 41, Issue 2, 一月 2014, Pages 249-256
Tianshou Ma | Ping Chen

In view of the shale hydration problem in wellbore stability analysis during drilling in shale formation, a quantitative evaluation method based on CT scanning technology was proposed to research the meso-damage characteristics of shale hydration, and the CT scanning tests for shale samples in stages of shale hydration were conducted. The analysis results of CT images and their gray-level histograms show that the early period of soaking is the main period of meso-damage in shale samples, and as the soaking time increases, the meso-damage propagates slowly; the mark of meso-damage increasing dramatically is that the gray-level histogram of the CT image changes from unimodal style to bimodal style. The visual resolutions of CT images can be improved by the pseudocolor enhancement technique, and the integrity and damage degrees of CT images provide a convenient way for quantitative analysis. The relationship between damage variable and soaking time was obtained based on the segmentations of CT images, which shows that the meso-damage of shale hydration mainly occurs in the early stage of soaking, which is the initial stage and rapid evolution stage of meso-damage, from then on, as the damage variable increases continuously and slowly, the macro-damage of shale sample occurs. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Propagation area evaluation of hydraulic fracture networks in shale gas reservoirs

Volume 41, Issue 6, 一月 2014, Pages 833-838
Bing Hou | Mian Chen | Zhimeng Li | Yonghui Wang | Ce Diao

© 2014 Research Institute of Petroleum Exploration & Development, PetroChina. Based on hydraulic fracturing experiments in laboratory, the hydraulic fracture propagation in shale is analyzed, a method for evaluating the fracture propagation extent is proposed, and the effects of geological factors and engineering factors on fracture propagation are studied. "Stimulated Rock Area (. SRA)" is proposed as an evaluation index for the hydraulic fracturing results. By analyzing the experiment results, it is found that hydraulic fracturing in shale reservoirs can generate a complex fracture network; a lower stress difference in brittle shale formation and a shorter distance between hydraulic fracture and bedding plane lead to a larger SRA and more complex fracture geometry; a fracture network is more likely to generate in the case that the angle between horizontal maximum stress direction and bedding plane is 90° or large enough, or the approaching angle between hydraulic fracture and well-opened natural fracture is close to 90° a higher brittle mineral content leads to better fracturing ability; low fluid viscosity and high flow rate lead to a large SRA; a variable flow rate increases the possibility that the hydraulic fracture communicates with bedding planes and natural fractures.

Prediction model of casing annulus pressure for deepwater well drilling and completion operation

Volume 40, Issue 5, 十月 2013, Pages 661-664
Jin Yang | Haixiong Tang | Zhengli Liu | Liping Yang | Xiaolong Huang | De Yan | Ruirui Tian

Casing collapse and fracture may be caused by the rise of casing annulus temperature and pressure in the initial stage of production and testing of deepwater wells. Based on the casing program and wellbore heat transfer process, a pressure calculation model for casing annulus was established, which provides basis for annulus pressure control. With the annulus between testing string and production casing as an example, a casing annulus temperature calculation method was derived according to the principle of conservation of energy and wellbore heat transfer analysis. The casing annulus pressure prediction model was established for typical deepwater wells according to the volume change of casing annulus fluid with temperature and pressure, and in combination of the casing annulus PVT equation and annulus temperature equation. The casing annulus temperature and pressure calculation methods were successfully applied in the casing annulus temperature and pressure management operation in 7 deepwater wells in West Africa, and the predicted temperature and pressure were compared with the actual ones, which indicates that casing annulus temperature and pressure prediction methods have good accuracy, with the relative error below 10%. © 2013 Research Institute of Petroleum Exploration & Development, PetroChina.

Shale gas in China: Characteristics, challenges and prospects (II)

Volume 43, Issue 2, 四月 2016, Pages 182-196
Caineng Zou | Dazhong Dong | Dazhong Dong | Yuman Wang | Xinjing Li | Jinliang Huang | Shufang Wang | Quanzhong Guan | Chenchen Zhang | Hongyan Wang | Hongyan Wang | Honglin Liu | Wenhua Bai | Feng Liang | Wen Lin | Qun Zhao | Dexun Liu | Zhi Yang | Pingping Liang | Shasha Sun | Zhen Qiu

© 2016 Research Institute of Petroleum Exploration & Development, PetroChina. This paper mainly discusses the industrialization progress, "sweet spot" evaluation criterion, E&P technologies, success experiences, challenges and prospects of China's shale gas. Based on the geologic and engineering parameters of the Fuling, Changning and Weiyuan shale gas fields in the Sichuan Basin, this paper points out that China's shale gas has its particularity. The discoveries of super-giant marine shale gas fields with high evolution degree (Ro=2.0%-3.5%) and ultrahigh pressure (pressure coefficient=1.3-2.1) in southern China is of important scientific significance and practical value to ancient marine shale gas exploration and development to China and even the world. It's proposed that shale gas "sweet spots" must be characterized by high gas content, excellent frackability and good economy etc. The key indicators to determine the shale gas enrichment interval and trajectory of horizontal wells include "four highs", that is high TOC (>3.0%), high porosity (>3.0%), high gas content (>3.0 m3/t) and high formation pressure (pressure coefficient>1.3), and "two well-developed" (well-developed beddings and well-developed micro-fractures). It's suggested that horizontal well laneway be designed in the middle of high pressure compartment between the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation. The mode of forming "artificial shale gas reservoir" by "fracturing micro-reservoir group" is proposed and the mechanisms of "closing-in after fracturing, limiting production through pressure control" are revealed. Several key technologies (such as three-dimensional seismic survey and micro-seismic monitoring of fracturing, horizontal wells, "factory-like" or industrialized production mode, etc.) were formed. Some successful experiences (such as "sweet spot" selection, horizontal well laneway control, horizontal length optimization and "factory-like" production mode, etc.) were obtained. The four main challenges to realize large-scale production of shale gas in China include uncertainty of shale gas resources, breakthroughs in key technologies and equipment of shale gas exploration and development below 3 500 m, lower cost of production, as well as water resources and environment protection. It is predicted that the recoverable resources of the Lower Paleozoic marine shale gas in southern China are approximately 8.8×1012m3, among which the recoverable resources in the Sichuan Basin are 4.5×1012m3in the favorable area of 4.0×104km2. The productivity of (200-300)×108m3/a is predicted to be realized by 2020 when the integrated revolution of "theory, technology, production and cost" is realized in Chinese shale gas exploration and development. It is expected in the future to be built "Southwest Daqing Oilfield (Gas Daqing)" in Sichuan Basin with conventional and unconventional natural gas production.

Calculation model for on-way parameters of horizontal wellbore in the superheated steam injection

Volume 43, Issue 5, 十月 2016, Pages 798-805
Zifei FAN | Congge HE | Anzhu XU

© 2016 Research Institute of Petroleum Exploration & Development, PetroChina Due to superheated steam as a pure gas, the ordinary steam model for the calculation of horizontal well-bore parameters based on two phases flow theory isn't applicable to the superheated steam injection process. According to the conservation of mass, conservation of momentum and conservation of energy, a calculation model for on-way parameters of horizontal well-bore in the superheated steam injection considering the steam phase changing is set up. The on-way parameters of temperature, pressure and dryness of a horizontal well injected superheated steam from Kazakhstan Kumsai oilfield is calculated using the model, and the calculation result of the new model is in good agreement with that of the field data, which verifies the effectiveness of the model. Sensitivity analysis indicates that the length to the heel of horizontal well undergoing the steam phase state changing increases as the injection rate or the degree of superheat increases, but the increase extent is not significant when the injection rate is larger than 8 t/h or the degree of superheat is larger than 80 °C. In the permeability distribution pattern that the permeability increases along the horizontal well-bore, steam temperature is decreased at the lowest rate and the length to the heel of horizontal well undergoing the steam phase changing is the longest.

Fracturing with carbon dioxide: Application status and development trend

Volume 41, Issue 4, 一月 2014, Pages 513-519
He Liu | Feng Wang | Jin Zhang | Siwei Meng | Yongwei Duan

Stimulation principles, construction techniques, equipment requirements and technical features of liquid carbon dioxide fracturing were summarized, and the existing problems and development trend of this technology were discussed. Compared with the conventional hydraulic fracturing technology, it has several advantages including high flowback, small damage in reservoir, outstanding stimulation effect and so on. There are five main problems existing in this technology: friction of liquid carbon dioxide is very high; liquid carbon dioxide has an extremely low viscosity, poor proppant carrying ability and a large amount of fluid loss, thus behaves poorly in fracturing; the phase behavior of carbon dioxide is very complex in the process of fracturing, it is hard to realize accurate prediction and control for phase transition of carbon dioxide; fracturing equipments, especially blenders have obvious defects and should be improved further; computational methods for operation parameters in liquid carbon dioxide fracturing is still lacking. Supercritical carbon dioxide fracturing technology succeeds almost all the advantages of traditional liquid carbon dioxide fracturing technology, and has a better stimulation effect, smaller pump pressure and fewer requirements for blenders, thus is the trend in carbon dioxide fracturing. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

A comprehensive review of polyacrylamide polymer gels for conformance control

Volume 42, Issue 4, 一月 2015, Pages 525-532
Baojun Bai | Jia Zhou | Mingfei Yin

© 2015 Research Institute of Petroleum Exploration & Development, PetroChina. Polymer gels have been designed and successfully applied to improve sweep efficiency and to reduce excessive water production by minimizing reservoir heterogeneity. Based on their compositions and application conditions, polyacrylamide polymer gels can be classified into three types: in-situ monomer-based gel, in-situ polymer-based gels, and preformed particle gels. Initially, in-situ monomer gels which are mainly composed of acrylamide were developed for water shutoff. Conventional in-situ polymer gels include metal-cross linked polyacrylamide gels and organic-cross linked polyacrylamide gels. Preformed gels include preformed particle gels, pH sensitive microgels, and micro- and nano-gels. A few directions are suggested for future research on novel gels, such as gels used for in-depth fluid diversion and gels for severe reservoir environments.

Movability of lacustrine shale oil: A case study of Dongying Sag, Jiyang Depression, Bohai Bay Basin

Volume 41, Issue 6, 一月 2014, Pages 703-711
Linye Zhang | Linye Zhang | Youshu Bao | Juyuan Li | Zheng Li | Zheng Li | Rifang Zhu | Jingong Zhang

© 2014 Research Institute of Petroleum Exploration & Development, PetroChina. Taking the Paleogene Shahejie Formation lacustrine shale in Dongying Sag, Jiyang Depression, Bohai Bay Basin, as an example, this paper makes a systematic study on the properties of shale of lower part of Sha-3 Member (Es3x) and upper part of Sha-4 Member (Es4s), including porosity, compressibility, mechanical properties, oil saturation, gas-oil ratio and oil saturation pressure by lab analysis and well log data of shale cores taken from different depths. On this basis, the movability of shale oil is discussed in terms of formation energy. According to the study results, both the elastic movable oil ratios and the solution gas driving movable oil ratios of Es3xand Es4sincrease with the shale burial depth increasing, and both ratios of Es4sare generally higher than that of Es3xat the same depth. Within the depth of 2 800 - 4 000 m, the total movable oil ratio of Es3xvaries from 8% to 28%, while the total movable oil ratio of Es4svaries from 9% to 30%. Combining with the profiles of oil saturation and movable oil ratio of shale, a conclusion is made that the shale of Es3xand Es4sdeeper than 3 400 m in the study area are favorable objects for shale oil exploration.

Conventional and unconventional petroleum "orderly accumulation": Concept and practical significance

Volume 41, Issue 1, 二月 2014, Pages 14-30
Zou Caineng | Yang Zhi | Zhang Guosheng | Hou Lianhua | Zhu Rukai | Tao Shizhen | Yuan Xuanjun | Dong dazhong | Wang Yuman | Guo Qiulin | Wang Lan | Bi Haibin | Li Denghua | Wu Na

Based on the latest global conventional-unconventional petroleum development situation and the conclusion of petroleum geology theory and technology innovation in recent 10 years, the connotation of conventional and unconventional petroleum "orderly accumulation" connotation is formulated. This concept indicates that, unconventional petroleum occurs in the hydrocarbon supply direction of conventional petroleum, and conventional petroleum may appear in the outer space of unconventional petroleum. Proper evaluation methods and engineering technology are important to push the conventional-unconventional petroleum co-development, and the petroleum finding thought from outer-source into inner-source. Unconventional petroleum evaluation focuses on source rocks characteristics, lithology, physical property, brittleness, oil-gas possibility and stress anisotropy. Taking shale gas for examples, in China, these six properties are TOC>2%, laminated silicious calcareous shale or calcareous silicious shale, porosity 3%-8%, brittle minerals content 50%-80%, gas content 2.3-4.1 m3/t, pressure coefficient 1.0-2.3, natural fractures; in north America, these six properties are TOC>4%, silicious shale or calcareous shale or marl, porosity 4%-9%, brittle minerals content 40%-70%, gas content 2.8-9.9 m3/t, pressure coefficient 1.3-1.85, natural fractures. "Sweet spot area" assessment, "factory-like" operation pattern and other core evaluation methods and technologies are discussed. And 8 key elements of unconventional "sweet spot area" are proposed, 3 of them are TOC>2% (for shale oil S1>2 mg/g), higher porosity (for tight oil & gas >10%, shale oil & gas >3%), and microfractures. Multiple wells "factory-like" operation pattern is elaborated, and its implementation needs 4 elements, i.e. batch well spacing, standard design, flow process, and reutilization. Through horizontal well volume fractures in directions, "man-made reservoirs" with large-scale fracture systems can be formed underground. For "shale oil revolution" in future, non-water "gas in critical state" and etc. fracturing fluid and matching technology should be stressed to be industrially tested and encouraged to be low cost developed. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Discussion on effective development techniques for continental tight oil in China

Volume 41, Issue 2, 一月 2014, Pages 217-224
Jinhu Du | He Liu | He Liu | Desheng Ma | Desheng Ma | Jinhua Fu | Yuhua Wang | Tiyao Zhou | Tiyao Zhou

Based on the main geological features and technical breakthroughs made in tight oil exploration, the major challenges facing tight oil development are analyzed, and the key technical trend for tight oil development is discussed in this paper. Mainly found in continental deposits, tight oil reservoirs in China feature small area, poor physical properties, big differences in geological characteristics between different basins, but low porosity, low permeability and pressure in general. In contrast to marine tight oil, tight oil in continental deposits faces such challenges as low production and recovery, and poor economics. Through nearly three years of research and pilot test, an integrated development mode with repeated fracturing of horizontal wells as the principal technique has been proposed, which includes integrated design, platform long horizontal well drilling, massive volume fracturing, re-fracturing stimulation, controlled production, factory-like operation, concentrated surface construction etc. It is recommended that study be strengthened on basic tight oil development theory, practical development technologies, and economic evaluation of tight oil development over the whole life cycle. © 2014 Research Institute of Petroleum Exploration & Development, PetroChina.

Characteristics of lacustrine shale porosity evolution, Triassic Chang 7 Member, Ordos Basin, NW China

Volume 42, Issue 2, 一月 2015, Pages 185-195
Songtao Wu | Songtao Wu | Songtao Wu | Rukai Zhu | Rukai Zhu | Rukai Zhu | Jinggang Cui | Jinggang Cui | Jinggang Cui | Jingwei Cui | Jingwei Cui | Jingwei Cui | Bin Bai | Bin Bai | Bin Bai | Xiangxiang Zhang | Xiangxiang Zhang | Xiangxiang Zhang | Xu Jin | Xu Jin | Xu Jin | Desheng Zhu | Desheng Zhu | Desheng Zhu | Jianchang You | Jianchang You | Jianchang You | Xiaohong Li | Xiaohong Li | Xiaohong Li

© 2015 Research Institute of Petroleum Exploration & Development, PetroChina. With low mature Triassic Chang 7 Member shale samples from the Ordos Basin as study object, the 3-D porosity evolution with temperature increase and its main controlling factors are analyzed based on the physical modeling under high temperature & pressure and nano-CT scanning data. More and more nano-pores were developed in Chang 7 Member organic-rich shale with the increase of maturity. The porosity calculated from the nano-CT scanning model increased from 0.56% to 2.06%, more than 250% times larger, when temperature increased from 20 °C to 550 °C. The process of porosity evolution can be divided into three phases. Firstly, porosity decreased rapidly from immature to low mature stage because of weak hydrocarbon generation and strong compaction; Secondly, porosity increased rapidly when the maturity increased from low mature stage to mature and post-mature stage, organic matter cracked into hydrocarbon (HC) massively, and clay minerals transformed intensively; Thirdly, porosity system kept stable when the shale entered into post-mature stage and the intensity of both HC generation and clay mineral transformation decreased. Organic matter thermal evolution, clay mineral transformation and brittle mineral transformation make different contribution to the porosity of shale, and the ratio is 6:3:1 respectively. It is inferred abundant organic matter pores occur when Ro is over 1.2%.

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