10 August 2018, Volume 45 Issue 4
    

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    PETROLEUM EXPLORATION
  • Connotation and strategic role of in-situ conversion processing of shale oil underground in the onshore China
    ZHAO Wenzhi, HU Suyun, HOU Lianhua
    Petroleum Exploration and Development, 2018, 45(4): 537-545. https://doi.org/10.11698/PED.2018.04.01
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    In-situ conversion processing (ICP) of shale oil underground at the depth ranging from 300 m to 3 000 m is a physical and chemical process caused by using horizontal drilling and electric heating technology, which converts heavy oil, bitumen and various organic matter into light oil and gas in a large scale, which can be called “underground refinery”. ICP has several advantages as in CO2 capture, recoverable resource potential and the quality of hydrocarbon output. Based on the geothermal evolution mechanism of organic materials established by Tissot et al., this study reveals that in the nonmarine organic-rich shale sequence, the amount of liquid hydrocarbon maintaining in the shale is as high as 25% in the liquid hydrocarbon window stage (Ro less than 1.0%), and the unconverted organic materials in the shale interval can reach 40% to 100%. The conditions of organic-rich shale suitable for underground in-situ conversion of shale oil should be satisfied in the following aspects, TOC higher than 6%, Ro ranging between 0.5% and 1%, concentrated thickness of organic-rich shale greater than 15 meters, burial depth less than 3 000 m, covering area bigger than 50 km2, good sealing condition in both up- and down-contacting sequences and water content smaller than 5%, etc. The shale oil resource in China’s onshore region is huge. It is estimated with this paper that the technical recoverable resource reaches 70-90 billion tons of oil and 60-65 trillion cubic meters of gas. The ICP of shale oil underground is believed to be a fairway to find big oil in the source kitchen in the near future. And it is also believed to be a milestone to keep China long-term stability of oil and gas sufficient supply by putting ICP of shale oil underground into real practice in the future.
  • Significant progress of continental petroleum geology theory in basins of Central and Western China
    JIA Chengzao, ZOU Caineng, YANG Zhi, ZHU Rukai, CHEN Zhuxin, ZHANG Bin, JIANG Lin
    Petroleum Exploration and Development, 2018, 45(4): 546-560. https://doi.org/10.11698/PED.2018.04.02
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    China’s continental oil and gas geology theory occupies an important academic position in the world's academic circle of petroleum geology. China’s oil and gas resources are dominated by continental resources. Chinese geologists have successfully explored and developed complex continental oil and gas, and developed a continental oil and gas geological theory system. This paper summarizes the development history and theoretical achievements of continental oil and gas geological theory since the 1940s and proposes that the development of this theory should be divided into three stages (i.e., proposal, formation and development). The China’s continental oil and gas geology theory has formed a basically perfect theoretical system consisting of five parts, i.e., continental basin structure, continental lake basin sediments and reservoirs, continental oil generation, continental basin oil and gas accumulation, and continental sandstone oil and gas field development geology. As an advanced geological theory, it has a universal significance globally. This paper focuses on the major discoveries of oil and gas exploration and development and the production growth in the basins of the Central and Western China in the past 30 years as well as the major advances in the continental oil and gas geological theory, including the continental basin tectonics of Central and Western China under the compression background, special reservoir geology such as various types of lake basin sedimentary systems and deep conglomerate, new fields of continental hydrocarbon generation such as coal-generated hydrocarbons, continental oil and gas enrichment regularity such as foreland thrust belts and lithologic-stratigraphic reservoirs, continental unconventional oil and gas geology and continental low-permeability oil and gas development geology. These major advances have greatly developed and enriched the continental oil and gas geology theory and become an important part of it.
  • China’s shale gas exploration and development: Understanding and practice
    MA Yongsheng, CAI Xunyu, ZHAO Peirong
    Petroleum Exploration and Development, 2018, 45(4): 561-574. https://doi.org/10.11698/PED.2018.04.03
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    Through detailed analyses of the distribution characteristics of organic-rich shale, appearance features of high-quality shale, microscopic characteristics of shale reservoir rocks, fracturabilities, and the relationship between preservation conditions and shale gas enrichment in Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Sichuan Basin, theoretical understandings and specific suggestions with respect to the exploration and development of shale gas in China are summarized and proposed respectively. Successful experiences in the exploration and development of shale gas of the Wufeng Formation-Longmaxi Formation in the Sichuan Basin can be summarized into the following aspects: depositional environment and depositional process control the distribution of organic-rich shale; high quality shale in “sweet spot segments” are commonly characterized by high content of organic carbon, high brittleness, high porosity and gas content; organic pores are important storage space for the enrichment of shale gas; preservation conditions are the key factor for the geological evaluation of shale gas in structurally complex regions; shale gas can be considered as “artificial gas reservoirs” and the fracturability assessment is essential for high-production; nanoscale storage space and the mode of occurrence control the special seepage characteristics of shale gas. The following suggestions are proposed for the development of China’s shale gas industry: (1) focus more on fundamental research to achieve new breakthrough in the geological theory of shale gas; (2) emphasize exploration practices to have all-round discoveries in multiple strata; (3) study the regularities of development and production to establish new models of shale gas development; (4) think creatively to invent new technologies to tackle key problems; (5) explore the management innovation to create new mechanisms in shale gas development.
  • Theory, technology and prospects of conventional and unconventional natural gas
    ZOU Caineng, YANG Zhi, HE Dongbo, WEI Yunsheng, LI Jian, JIA Ailin, CHEN Jianjun, ZHAO Qun, LI Yilong, LI Jun, YANG Shen
    Petroleum Exploration and Development, 2018, 45(4): 575-587. https://doi.org/10.11698/PED.2018.04.04
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    The development of natural gas in China has entered a golden and leap-forward stage, which is a necessary bridge to clean energy. This in-depth study on the status quo, theory, technology and prospect of natural gas development shows: (1) The global remaining proven recoverable reserves of natural gas are 186×1012 m3, and the reserves-production ratio is 52.4, indicating a solid resource base for long-term and rapid development. (2) Ten formation and distribution laws of conventional and unconventional natural gas reservoirs have been proposed. In terms of exploration geology, the theory of conventional “monolithic” giant gas fields with different gas sources, and an unconventional gas accumulation theory with continuous distribution of “sweet spots” in different lithologic reservoirs have been established; in terms of development geology, a development theory of conventional structural gas reservoirs is oriented to “controlling water intrusion”, while a development theory of unconventional gas is concentrated on artificial gas reservoirs. (3) With the geological resources of 210×1012 m3 (excluding hydrates) and the total proven rate of the resources less than 2% at present, the natural gas in China will see a constant increase in reserve and production; by 2030, the proven geological reserves of natural gas are expected to reach about (6 000-7 000)×108 m3, the production of conventional and unconventional natural gas each will reach about 1 000×108 m3, and the gas consumption will reach 5500×108 m3. The dependence on imported natural gas may be 64% by 2030, and 70% by 2050. (4) Ten measures for future development of natural gas have been proposed, including strengthening exploration in large-scale resource areas, increasing the development benefits of unconventional gas, and enhancing the peak adjusting capacity of gas storage and scale construction of liquified natural gas.
  • Geochemical characteristics of ultra-deep natural gas in the Sichuan Basin, SW China
    DAI Jinxing, NI Yunyan, QIN Shengfei, HUANG Shipeng, PENG Weilong, HAN Wenxue
    Petroleum Exploration and Development, 2018, 45(4): 588-597. https://doi.org/10.11698/PED.2018.04.05
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    The natural gas components and geochemistry of 50 ultra-deep gas wells (buried depth greater than 6000 m) in the Sichuan Basin were analyzed to determine the genesis of ultra-deep natural gas in the basin. The natural gas components of the basin have the following characteristics: Methane has an absolute advantage, which can be up to 99.56% with an average of 86.6%; ethane is low, with an average of 0.13%; there is nearly no propane and butane. So it is dry gas at over-mature thermal stage. The content of H2S can be up to 25.21%, with an average of 5.45%. The alkane gas isotopes are: The carbon isotope varies from -32.3‰ to -26.7‰ for methane and from -32.9‰ to -22.1‰ for ethane. There is nearly no carbon isotopic reversal among methane and its homologues. Hydrogen isotope varies from -156‰ to -114‰ for methane, and from -103‰ to -89‰ for some ethane. The carbon isotope of CO2 varies from -17.2‰ to 1.9‰ and most of them fall within the range of 0±3‰. According to the δ13C1-δ13C2-δ13C3 plot, except some wells, all other ultra-deep gas wells are dominated by coal-derived gas. Based on the CO2 origin distinguishing plot and δ13CCO2, except individual wells, most of the ultra-deep CO2 are of carbonate metamorphic origin. H2S in the ultra-deep layer of Longgang and Yuanba gas fields belongs to thermochemical sulfate reduction (TSR), while H2S from Well Shuangtan belongs to thermal decomposition of sulfides (TDS).
  • Synthetic well logs generation via Recurrent Neural Networks
    ZHANG Dongxiao, CHEN Yuntian, MENG Jin
    Petroleum Exploration and Development, 2018, 45(4): 598-607. https://doi.org/10.11698/PED.2018.04.06
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    To supplement missing logging information without increasing economic cost, a machine learning method to generate synthetic well logs from the existing log data was presented, and the experimental verification and application effect analysis were carried out. Since the traditional Fully Connected Neural Network (FCNN) is incapable of preserving spatial dependency, the Long Short-Term Memory (LSTM) network, which is a kind of Recurrent Neural Network (RNN), was utilized to establish a method for log reconstruction. By this method, synthetic logs can be generated from series of input log data with consideration of variation trend and context information with depth. Besides, a cascaded LSTM was proposed by combining the standard LSTM with a cascade system. Testing through real well log data shows that: the results from the LSTM are of higher accuracy than the traditional FCNN; the cascaded LSTM is more suitable for the problem with multiple series data; the machine learning method proposed provides an accurate and cost effective way for synthetic well log generation.
  • A global satellite survey of density plumes at river mouths and at other environments: Plume configurations, external controls, and implications for deep-water sedimentation
    SHANMUGAM G
    Petroleum Exploration and Development, 2018, 45(4): 608-625. https://doi.org/10.11698/PED.2018.04.07
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    The U. S. National Aeronautics and Space Administration (NASA) has archived thousands of satellite images of density plumes in its online publishing outlet called 'Earth Observatory' since 1999. Although these images are in the public domain, there has not been any systematic compilation of configurations of density plumes associated with various sedimentary environments and processes. This article, based on 45 case studies covering 21 major rivers (e.g., Amazon, Betsiboka, Congo [Zaire], Copper, Hugli [Ganges], Mackenzie, Mississippi, Niger, Nile, Rhone, Rio de la Plata, Yellow, Yangtze, Zambezi, etc.) and six different depositional environments (i.e., marine, lacustrine, estuarine, lagoon, bay, and reef), is the first attempt in illustrating natural variability of configurations of density plumes in modern environments. There are, at least, 24 configurations of density plumes. An important finding of this study is that density plumes are controlled by a plethora of 18 oceanographic, meteorological, and other external factors. Examples are: 1) Yellow River in China by tidal shear front and by a change in river course; 2) Yangtze River in China by shelf currents and vertical mixing by tides in winter months; 3) Rio de la Plata Estuary in Argentina and Uruguay by Ocean currents; 4) San Francisco Bay in California by tidal currents; 5) Gulf of Manner in the Indian Ocean by monsoonal currents; 6) Egypt in Red Sea by Elian dust; 7) U.S. Atlantic margin by cyclones; 8) Sri Lanka by tsunamis; 9) Copper River in Alaska by high-gradient braid delta; 10) Lake Erie by seiche; 11) continental margin off Namibia by upwelling; 12) Bering Sea by phytoplankton; 13) the Great Bahama Bank in the Atlantic Ocean by fish activity; 14) Indonesia by volcanic activity; 15) Greenland by glacial melt; 16) South Pacific Ocean by coral reef; 17) Carolina continental Rise by pockmarks; and 18) Otsuchi Bay in Japan by internal bore. The prevailing trend in promoting a single type of river-flood triggered hyperpycnal flow is flawed because there are 16 types of hyperpycnal flows. River-flood derived hyperpycnal flows are muddy in texture and they occur close to the shoreline in inner shelf environments. Hyperpycnal flows are not viable transport mechanisms of sand and gravel across the shelf into the deep sea. The available field observations suggest that they do not form meter-thick sand layers in deep water settings. For the above reasons, river-flood triggered hyperpycnites are considered unsuitable for serving as petroleum reservoirs in deep-water environments until proven otherwise.
  • Production characteristics and sweet-spots mapping of the Upper Devonian-Lower Mississippian Bakken Formation tight oil in southeastern Saskatchewan, Canada
    CHEN Zhuoheng, YANG Chao, JIANG Chunqing, KOHLRUSS Dan, HU Kezhen, LIU Xiaojun, YURKOWSKI Melinda
    Petroleum Exploration and Development, 2018, 45(4): 626-635. https://doi.org/10.11698/PED.2018.04.08
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    A workflow that helps identify potential production sweet spots in the Middle Bakken tight oil play is proposed based on analysis of large amounts of production data. The proposed approach is a multivariate statistical model that extracts relevant information from a training dataset of production wells to facilitate geological similarity comparison between economic and sub-economic production wells. The model is applied to the Middle Bakken tight oil play in southeastern Saskatchewan. Data screening for diagnostic geological indicators for sweet spots reveals that several geological factors indicative for conventional oil reservoirs seem to work for the Middle Bakken tight oil play as well. These factors include: a) the NE trend Torqunay-Rocanville structural belt serving as a preferred regional migration path for connecting mature source rock in southern Williston Basin and the Middle Bakken tight reservoir in southeastern Saskatchewan; b) the oils in the Bakken tight reservoirs along the U.S. and Canada border are more likely from local matured Bakken source rocks; c) subtle structural components enhancing the convergence of dispersed hydrocarbons over a large area; d) top seal and lateral barrier improving preservation, thus favouring oil productivity; e) orientation of maximum horizontal stress coincident with the direction of the variogram spatial continuity in ultimate recoverable reserves, so the direction of horizontal well has a significant impact on the oil productivity.
    • OIL AND GAS FIELD DEVELOPMENT
  • Technologies of enhancing oil recovery by chemical flooding in Daqing Oilfield, NE China
    SUN Longde, WU Xiaolin, ZHOU Wanfu, LI Xuejun, HAN Peihui
    Petroleum Exploration and Development, 2018, 45(4): 636-645. https://doi.org/10.11698/PED.2018.04.09
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    By tracking and analyzing the research and practices of chemical flooding carried out in the Daqing Oilfield, NE China since the 1970s, the chemical flooding theory, technology adaptability and existing problems were systematically summarized, and directions and ideas of development in the future were proposed. In enhanced oil recovery by chemical flooding, the Daqing Oilfield developed theories related to compatibility between crude oil and surfactant that may form ultra-low interfacial tensions with low-acidity oil, and a series of surfactant products were developed independently. The key technologies for chemical flooding such as injection parameter optimization and numerical simulation were established. The technologies of separation injection, cleansing and anti-scaling, preparation and injection, and produced liquid processing were developed. The matching technologies of production engineering and surface facilities were formed. Through implementation of chemical flooding, the Daqing Oilfield achieved outstanding performances with enhanced recovery rate of 12% in polymer flooding and with enhanced recovery rate of 18% in ASP flooding. To further enhance the oil recovery of chemical flooding, three aspects need to be studied: (1) fine characterization of reservoirs; (2) smart and efficient recovery enhancement technologies; (3) green, high-efficiency and smart matching processes.
  • Development of the theory and technology for low permeability reservoirs in China
    HU Wenrui, WEI Yi, BAO Jingwei
    Petroleum Exploration and Development, 2018, 45(4): 646-656. https://doi.org/10.11698/PED.2018.04.10
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    The development theories of low-permeability oil and gas reservoirs are refined, the key development technologies are summarized, and the prospect and technical direction of sustainable development are discussed based on the understanding and research on developed low-permeability oil and gas resources in China. The main achievements include: (1) the theories of low-permeability reservoir seepage, dual-medium seepage, relative homogeneity, etc. (2) the well location optimization technology combining favorable area of reservoir with gas-bearing prediction and combining pre-stack with post-stack; (3) oriented perforating multi-fracture, multistage sand adding, multistage temporary plugging, vertical well multilayer, horizontal and other fracturing techniques to improve productivity of single well; (4) the technology of increasing injection and keeping pressure, such as overall decreasing pressure, local pressurization, shaped charge stamping and plugging removal, fine separate injection, mild advanced water injection and so on; (5) enhanced recovery technology of optimization of injection-production well network in horizontal wells. To continue to develop low-permeability reserves economically and effectively, there are three aspects of work to be done well: (1) depending on technical improvement, continue to innovate new technologies and methods, establish a new mode of low quality reservoir development economically, determine the main technical boundaries and form replacement technology reserves of advanced development; (2) adhering to the management system of low cost technology & low cost, set up a complete set of low-cost dual integration innovation system through continuous innovation in technology and management; (3) striving for national preferential policies.
  • New progress and prospect of oilfields development technologies in China
    YUAN Shiyi, WANG Qiang
    Petroleum Exploration and Development, 2018, 45(4): 657-668. https://doi.org/10.11698/PED.2018.04.11
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    As technologies advance in oilfield development, mature oilfields are able to keep sustainable production and complex oilfields difficult to produce in the past are put into production efficiently. In this work, new progresses of main development technologies for medium-high permeability and high water cut, low permeability, heavy oil, complex faulted block and special lithology reservoirs in the past decade, especially those international achievements made in enhanced oil recovery, were summarized, the key problems and major challenges that different oilfields are facing were analyzed, and the development route and direction of three-generation technologies were proposed as “mature technology in industrialized application, key technology in pilot test and innovative technology for backup”. The key research contents should focus on: (1) Fine water flooding and chemical flooding for mature oilfields, improving oil recovery after chemical flooding, and gas flooding for low permeability reservoirs must be researched and tested in field further. (2) Study on subversive technologies like nanometer smart flooding, in-situ upgrading and injection and production through the same well should be strengthened. (3) EOR technologies for low oil price, new fields (deep sea, deep layer, unconventional reservoirs etc.) and highly difficult conditions (the quaternary recovery after chemical flooding, tertiary recovery in ultra-low permeability reservoirs) should be stocked up in advance. The development cost must be lowered significantly through constant innovation in technology and reservoir management to realize sustainable development of oilfields.
  • Theories and practices of carbonate reservoirs development in China
    LI Yang, KANG Zhijiang, XUE Zhaojie, ZHENG Songqing
    Petroleum Exploration and Development, 2018, 45(4): 669-678. https://doi.org/10.11698/PED.2018.04.12
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    Carbonate reservoirs in China have the characteristics of diversified accumulation pattern, complex structure and varying reservoir conditions. Concerning these characteristics, this article tracks the technical breakthroughs and related practices since the 1950s, summarizes the developed theory and technologies of carbonate reservoir development, analyzes their adaptability and problems, and proposes their development trend. The following theory and technologies have come into being: (1) carbonate reservoir formation mechanisms and compound flow mechanisms in complex medium; (2) reservoir identification and description technologies based on geophysics and discrete fracture-vuggy modeling method; (3) well testing analysis technology and numerical simulation method of coupling free flow and porous media flow; (4) enhanced oil recovery techniques for nitrogen single well huff and puff, and water flooding development techniques with well pattern design in spatial structure, changed intensity water injection, water plugging and channel blocking as the core; (5) drilling and completion techniques, acid fracturing techniques and its production increasing techniques. To realize the efficient development of carbonate oil and gas reservoirs, researches in four aspects need to be done: (1) complex reservoir description technology with higher accuracy; (2) various enhanced oil recovery techniques; (3) improving the drilling method and acid fracturing method for ultra-deep carbonate reservoir and significantly cutting engineering cost; (4) strengthening the technological integration of information, big data, cloud computation, and artificial intelligence in oilfield development to realize the smart development of oilfield.
  • Optimum development options and strategies for water injection development of carbonate reservoirs in the Middle East
    SONG Xinmin, LI Yong
    Petroleum Exploration and Development, 2018, 45(4): 679-689. https://doi.org/10.11698/PED.2018.04.13
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    Through the research on several carbonate reservoirs developed in the Middle East, the basic characteristics of different types of carbonate reservoirs are determined, and a set of high-efficiency water injection development options and strategies are presented. Hidden baffles and barriers exist in carbonate reservoirs in the Middle East, so the reservoirs could be divided into different separated development units based on the baffles and barriers characteristics. Flexible and diverse profile control techniques such as high angle wells and intelligent zonal water injection have been introduced to improve the control and development degree of reservoirs. Three principal water injection development methods suitable for different carbonate reservoirs in the Middle East are proposed, including the combination of crestal gas injection and peripheral water injection, bottom interval injection and top interval production (buoyancy underpinning), and “weak point and strong plane” area well pattern. Based on the characteristics of very low shale content, fast and far pressure transmission in the Middle East carbonate reservoirs, a large well-spacing flood pattern is recommended, and reasonable development strategies have been made such as moderate water injection rate and maintaining reasonable production pressure drawdown and voidage replacement ratio, so as to maximize the recovery of reservoirs in the none or low water cut period.
  • Development characteristics, models and strategies for overseas oil and gas fields
    MU Longxin, FAN Zifei, XU Anzhu
    Petroleum Exploration and Development, 2018, 45(4): 690-697. https://doi.org/10.11698/PED.2018.04.14
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    Based on about 20 years of accumulated experience and knowledge of oil and gas field development in overseas countries and regions for China’s oil companies, the development features, ideas, models and plan designing strategies of overseas oil and gas fields were comprehensively summarized. Overseas oil and gas field development has ten major features, such as non-identity project resource, diversity of contract type, complexity of cooperation model, and so on. The overseas oil and gas field development aims at the maximization of production and benefit during the limited contract period, so the overseas oil and gas field development models are established as giving priority to production by natural energy, building large-scale production capacity, putting into production as soon as possible, realizing high oil production recovery rate, and achieving rapid payback period of investment. According to the overseas contract mode, a set of strategies for overseas oil and gas field development plans were made. For tax systems contracts, the strategy is to adopt the mode of “first fat and then thinner, easier in the first and then harder”, that is, early investment pace, production increase rate, development workload and production were decided by the change of tax stipulated in the contract. For production share contracts, the strategy is to give priority to high production with a few wells at a high production recovery rate to increase the cost-oil and shorten the period of payback. For technical service contracts, the strategy is that the optimal production target and workload of the project were determined by the return on investment, so as to ensure that the peak production and stable production periods meet the contract requirements.
    • PETROLEUM ENGINEERING
  • Potential application of functional micro-nano structures in petroleum
    LIU He, JIN Xu, ZHOU Dekai, YANG Qinghai, LI Longqiu
    Petroleum Exploration and Development, 2018, 45(4): 698-704. https://doi.org/10.11698/PED.2018.04.15
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    This paper takes micro-nano motors and metamaterials as examples to introduce the basic concept and development of functional micro nano structures, and analyzes the application potential of the micro-nano structure design and manufacturing technology in the petroleum industry. The functional micro-nano structure is the structure and device with special functions prepared to achieve a specific goal. New functional micro-nano structures are classified into motor type (e.g. micro-nano motors) and fixed type (e.g. metamaterials), and 3D printing technology is a developed method of manufacturing. Combining the demand for exploration and development in oil and gas fields and the research status of intelligent micro-nano structures, we believe that there are 3 potential application directions: (1) The intelligent micro-nano structures represented by metamaterials and smart coatings can be applied to the oil recovery engineering technology and equipment to improve the stability and reliability of petroleum equipment. (2) The smart micro-nano robots represented by micro-motors and smart microspheres can be applied to the development of new materials for enhanced oil recovery, effectively improving the development efficiency of heavy oil, shale oil and other resources. (3) The intelligent structure manufacturing technology represented by 3D printing technology can be applied to the field of microfluidics in reservoir fluids to guide the selection of mine flooding agents and improve the efficiency of mining.
  • Introduction to the theory and technology on downhole control engineering and its research progress
    SU Yinao
    Petroleum Exploration and Development, 2018, 45(4): 705-712. https://doi.org/10.11698/PED.2018.04.16
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    On the basis of reviewing the development history of drilling engineering technology over a century, this paper describes the technical and scientific background of downhole control engineering, discusses its basic issues, discipline frame and main study contents, introduces the research progress of downhole control engineering in China over the past 30 years, and envisions the development direction of downhole control engineering in the future. The author proposed the study subject of well trajectory control theory and technology in 1988, and further proposed the concept of downhole control engineering in 1993. Downhole control engineering is a discipline branch, which applies the perspectives and methods of engineering control theory to solve downhole engineering control issues in oil and gas wells; meanwhile, it is an application technology field with interdisciplinarity. Downhole control engineering consists of four main aspects; primarily, investigations about dynamics of downhole system and analysis methods of control signals; secondly, designs of downhole control mechanisms and systems, research of downhole parameters collections and transmission techniques; thirdly, development of downhole control engineering products; fourthly, development of experimental methods and the laboratories. Over the past 30 years, the author and his research group have achieved a number of progress and accomplishments in the four aspects mentioned above. As a research field and a disciplinary branch of oil and gas engineering, downhole control engineering is stepping into a broader and deeper horizon.
  • Development of key additives for organoclay-free oil-based drilling mud and system performance evaluation
    SUN Jinsheng, HUANG Xianbin, JIANG Guancheng, LYU Kaihe, LIU Jingping, DAI Zhiwen
    Petroleum Exploration and Development, 2018, 45(4): 713-718. https://doi.org/10.11698/PED.2018.04.17
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    Traditional oil-based drilling muds (OBMs) have a relatively high solid content, which is detrimental to penetration rate increase and reservoir protection. Aimed at solving this problem, an organoclay-free OBM system was studied, the synthesis methods and functioning mechanism of key additives were introduced, and performance evaluation of the system was performed. The rheology modifier was prepared by reacting a dimer fatty acid with diethanolamine, the primary emulsifier was made by oxidation and addition reaction of fatty acids, the secondary emulsifier was made by amidation of a fatty acid, and finally the fluid loss additive of water-soluble acrylic resin was synthesized by introducing acrylic acid into styrene/butyl acrylate polymerization. The rheology modifier could enhance the attraction between droplets, particles in the emulsion via intermolecular hydrogen bonding and improve the shear stress by forming a three-dimensional network structure in the emulsion. Lab experimental results show that the organoclay-free OBM could tolerate temperatures up to 220 ℃ and HTHP filtration is less than 5 mL. Compared with the traditional OBMs, the organoclay-free OBM has low plastic viscosity, high shear stress, high ratio of yield point to plastic viscosity and high permeability recovery, which are beneficial to penetration rate increase, hole cleaning and reservoir protection.
  • The “fracture-controlled reserves” based stimulation technology for unconventional oil and gas reservoirs
    LEI Qun, YANG Lifeng, DUAN Yaoyao, WENG Dingwei, WANG Xin, GUAN Baoshan, WANG Zhen, GUO Ying
    Petroleum Exploration and Development, 2018, 45(4): 719-726. https://doi.org/10.11698/PED.2018.04.18
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    To solve the problems facing the economic development of unconventional oil and gas, a new concept and corresponding technology system of reservoir stimulation based on “fracture-controlled reserves” are put forward. The “fracture-controlled reserves” stimulation technology is to realize the three-dimensional producing and economic and efficient development of unconventional hydrocarbon resources by forming a fracture system that well matches “sweet spots” and “non-sweet spots”. The technical route of the stimulation technology is “three optimizations and controls”, that is, control the scope of sand body through optimizing well spacing, control the recoverable reserves through optimizing fracture system, and control the single well production reduction through optimizing energy complement method. The “fracture-controlled reserves” stimulation emphasizes the maximization of the initial stimulation coefficient, the integration of energy replenishment, stimulation and production, and prolonging the re-fracturing cycle or avoiding re-fracturing. It aims at realizing the three-dimensional full producing and efficient development of reservoir in vertical and horizontal directions and achieving the large-scale, sustainable and high profitable development of unconventional oil and gas resources. The stimulation technology was used to perform 20 pilot projects in five typical tight-oil, shale gas blocks in China. The fracturing and producing effects of tight oil improved and the commercial development for shale gas was realized.
    • COMPREHENSIVE RESEARCH
  • Distribution and potential of global oil and gas resources
    TONG Xiaoguang, ZHANG Guangya, WANG Zhaoming, WEN Zhixin, TIAN Zuoji, WANG Hongjun, MA Feng, WU Yiping
    Petroleum Exploration and Development, 2018, 45(4): 727-736. https://doi.org/10.11698/PED.2018.04.19
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    Using conventional and unconventional oil and gas resource evaluation methods with play as a unit, this study evaluates the oil and gas geology and resource potential of conventional oil and gas resources and seven types of unconventional resources in the global major oil and gas basins (excluding China). For the first time, resource evaluation data with independent intellectual property rights has been obtained. According to evaluation and calculation, the global recoverable conventional oil resources are 5 350.0×108 t, the recoverable condensate oil resources are 496.2×108 t, and the recoverable natural gas resources are 588.4×1012 m3. The remaining oil and gas 2P recoverable reserves are 4 212.6×108 t, the reserve growth of oil and gas fields are 1 531.7×108 t. The undiscovered oil and gas recoverable resources are 3 065.5×108 t. The global unconventional oil recoverable resources are 4 209.4×108 t and the unconventional natural gas recoverable resources are 195.4×1012 m3. The evaluation results show that the global conventional and unconventional oil and gas resources are still abundant.
    • ACADEMIC DISCUSSION
  • Profitable exploration and development of continental tight oil in China
    HU Suyun, ZHU Rukai, WU Songtao, BAI Bin, YANG Zhi, CUI Jingwei
    Petroleum Exploration and Development, 2018, 45(4): 737-748. https://doi.org/10.11698/PED.2018.04.20
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    Based on the investigation of tight oil exploration and development in North America, the successful cases of tight oil exploration and development in North America under the background of low oil price are summarized. The geological differences between continental tight oil in China and marine tight oil in North America is analyzed to explore the technical strategies for the industrial development of continental tight oil in China. The experiences of large-scale exploration and profitable development of tight oil in North America can be taken as references from the following 6 perspectives, namely exploring new profitable strata in mature exploration areas, strengthening the economic evaluation of sweet spots and focusing on the investment for high-profitability sweet spots, optimizing the producing of tight oil reserves by means of repetitive fracturing and 3D fracturing, optimizing drilling and completion technologies to reduce the cost, adopting commodity hedging to ensure the sustainable profit, and strengthening other resources exploration to improve the profit of whole project. In light of the high abundance of tight oil in China, we can draw on successful experience from North America, four suggestions are proposed in sight of the geological setting of China’s lacustrine tight oil: (1) Evaluating the potential of tight oil resources and optimizing the strategic area for tight oil exploration; (2) selecting “sweet spot zone” and “sweet spot interval” accurately for precise and high efficient development; (3) adopting advanced tight oil fracturing technology to realize economic development; (4) innovating management system to promote the large-scale profitable development of tight oil.
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