Geological characteristics and main challenges of onshore deep oil and gas development in China

More than 30 years of continuous development has made onshore deep and ultra-deep conventional and unconventional oil and gas become an integral part of increasing the energy reserves and output by China’s petroleum industry. Based on the deep oil and gas geological conditions in the country, the present study finds that paleo stratum and deep burial are the two basic geological characteristics of deep oil and gas. Furthermore, we put forward the notion that it is necessary to strengthen the fundamental research of theories in four aspects and the core technology in five aspects of deep oil and gas. It is suggested that it is of special importance to promote the scientific and technological research of deep oil and gas through the scientific exploration of “myriameter deep” wells as the starting point, so as to boost the development of deep oil and gas field in China.Cited as: Yang, Z., Zou, C., Gu, Z., Yang, F., Li, J., Wang, X. Geological characteristics and main challenges of onshore deep oil and gas development in China. Advances in Geo-Energy Research, 2022, 6(3): 264-266. https://doi.org/10.46690/ager.2022.03.0

Basic properties and exploitation strategies of source rock strata

Source rock strata are filled and aggregated with large-scale continuous hydrocarbon resources, including significant volumes of in-place retained, short-distance migrated and potentially generated hydrocarbons. Source rock strata simultaneously possess the properties of reservoirs and hydrocarbon source rocks, known as source-reservoir coexisting systems. Reservoir properties refer to the physical properties concerning the storage and transmission of oil and gas, while hydrocarbon source rock properties refer to the physicochemical properties related to governing the generation, retention and expulsion of oil and gas in the source rock strata. These properties fundamentally determine the technical path for the successful exploitation of petroleum and natural gas in the source rock strata. With regard to reservoir properties, in-depth research and development of the advanced energy-storing fracturing technology can aid the construction of complex fracture networks to overcome the limitations in the connectivity properties of source rock strata. Focusing on the hydrocarbon source rock properties, an underground in-situ conversion technology should be created and developed to alleviate the shortcomings of organic matter quantity and maturity properties of the source rock strata. Furthermore, selecting the appropriate exploitation path based on the property characteristics can promote the achievement of commercial and sustainable development of oil and gas in the source rock strata.Document Type: PerspectiveCited as: Yang, Z., Zou, C., Fan, Y., Wu, S., Liu, H., Wei, Q. Basic properties and exploitation strategies of source rock strata. Advances in Geo-Energy Research, 2023, 10(2): 77-83. https://doi.org/10.46690/ager.2023.11.0

Sequence Stratigraphy of Fine-Grained “Shale” Deposits: Case Studies of Representative Shales in the USA and China

The fine-grained “shale” deposits host a vast amount of unconventional oil and gas resources. This chapter examines the variations in lithofacies, patterns of well logs, geochemistry, and mineralogy in order to construct a sequence stratigraphic framework of the representative marine Barnett, Woodford, Marcellus, Mowry, and Niobrara fine-grained “shales” (USA) and the marine Longmaxi shale and lacustrine Chang7 lacustrine shale (China). Practical methods are proposed in order to recognize the sequence boundaries, the flooding surfaces, the parasequences and parasequence sets, the system tracts, and variation patterns of facies and rock properties. The case studies for the sequence stratigraphy in the USA and China have revealed that the transgressive systems tract (TST) and the early highstand systems tract (EHST, if identifiable) of fine-grained “shales” have been deposited in anoxic settings. TST and EHST of the siliciclastic “shales” are characterized by high gamma ray, high TOC, and high quartz content, while TST and EHST of the carbonate-dominated fine-grained “shales” are characterized by low gamma ray, organic lean, and carbonate rich fine-grained deposits. The lithofacies, geochemistry, mineralogy, depositional evolution, and reservoir development have been predicted and correlated within a sequence stratigraphic framework for the suggested cases. The best reservoir with the best completion quality is developed in TST and HST in both siliciclastic-dominated and carbonate-dominated fine-grained “shales.

Suggestions on the development strategy of shale gas in China

AbstractFrom the aspects of shale gas resource condition, main exploration and development progress, important breakthrough in key technologies and equipment, this paper systematically summarized and analyzed current situation of shale gas development in China and pointed out five big challenges such as misunderstandings, lower implementation degree and higher economic uncertainty of shale gas resource, and still no breakthrough in exploration and development core technologies and equipment for shale gas buried depth more than 3500 m, higher cost and other non-technical factors that restrict the development pace. Aiming at the above challenges, we put forward five suggestions to promote the shale gas development in China: (1) Make strategies and set goals according to our national conditions and exploration and development stages. That is, make sure to realize shale gas annual production of 20 × 109 m3, and strives to reach 30 × 109 m3. (2) Attach importance to the research of accumulation and enrichment geological theory and exploration & development key engineering technologies for lower production and lower pressure marine shale gas reservoir, and at the same time orderly promote the construction of non-marine shale gas exploration & development demonstration areas. (3) The government should introduce further policies and set special innovation funds to support the companies to carry out research and development of related technologies and equipment, especially to strengthen the research and development of technology, equipment and process for shale gas bellow 3500 m in order to achieve breakthrough in deep shale gas. (4) Continue to promote the geological theory, innovation in technology and management, and strengthen cost control on drilling, fracturing and the whole process in order to realize efficient, economic and scale development of China's shale gas. (5) Reform the mining rights management system, establish information platform of shale gas exploration and development data, and correctly guide the non-oil and gas companies to participate in shale gas exploration and development

“Exploring petroleum inside source kitchen”: Connotation and prospects of source rock oil and gas

Based on the transitional background of the global energy structure, exploration and development of unconventional oil and gas, and investigation of key basins, the unconventional oil and gas resources are divided into three types: source rock oil and gas, tight oil and gas, and retention and accumulated oil and gas. Source rock oil and gas resources are the global strategic supplies of oil and gas, the key resource components in the second 150-year life cycle of the future petroleum industry, and the primary targets for “exploring petroleum inside source kitchen”. The geological connotation of source rock oil and gas was proposed, and the models of source rock oil and gas generation, expulsion and accumulation were built, and five source rock oil and gas generation sections were identified, which may determine the actual resource potential under available technical conditions. The formation mechanism of the “sweet sections” was investigated, that is, shale oil is mainly accumulated in the shale section that is close to the oil generation section and has higher porosity and permeability, while the “sweet sections” of coal-bed methane (CBM) and shale gas have self-contained source and reservoir and they are absorbed in coal seams or retained in the organic-rich black shale section, so evaluation and selection of good “sweet areas (sections)” is the key to “exploring petroleum inside source kitchen”. Source rock oil and gas resources have a great potential and will experience a substantial growth for over ten world-class large “coexistence basins” of conventional-unconventional oil and gas in the future following North America, and also will be the primary contributor to oil stable development and the growth point of natural gas production in China, with expected contribution of 15% and 30% to oil and gas, respectively, in 2030. Challenges in source rock oil and gas development should be paid more attention to, theoretical innovation is strongly recommended, and a development pilot zone can be established to strengthen technology and promote national support. The source rock oil and gas geology is the latest progress of the “source control theory” at the stage of unconventional oil and gas. It will provide a new theoretical basis for the new journey of the upstream business in the post-industry age. Key words: source rock oil and gas, shale gas, shale oil, coal-bed methane, sweet section, sweet area, source control theory, man-made oil and gas reservoir, unconventional oil and gas revolution, large “coexistence basins” of conventional-unconventional oil and ga

History, achievements and significance of scientific exploration wells: For the 30th anniversary of the Scientific Exploration Well Program

Thirty years have past since the “scientific exploration well” program (1986−2000) was initiated in 1986. Review and summary of the exploration history, achievements and management experiences are significant for directing future onshore exploration. The program aimed to address critical and fundamental geological challenges and achieve breakthroughs through scientific exploration in new basins, new strata and new regions, on the basis of new geologic cognitions obtained by PetroChina Research Institute of Petroleum Exploration & Development (RIPED). During 15 years of efforts, 14 wells were drilled, of which Well Taican 1 and Well Shaancan 1 contributed to the discovery of Tuha Oilfield and Jingbian giant gas field, opening the prelude to large-scale natural gas exploration in the Jurassic System in northwest China and the Ordos Basin. Several wells (e.g. Gaoke 1, Jiucan 1, and Qincan 1) produced low-yield oil and gas flows, laying the foundation for later large discoveries. Moreover, a series of strategic domains and targets have been ascertained. In program management, a scientific and rational exploration procedure has been established: the PetroChina headquarter assumes investment risks, RIPED proposes domains/targets, and oilfields undertake specific tasks under the supervision of RIPED, following the rules of “intensive and thorough explorations”. The significance of the “scientific exploration well” program is manifested in transforming scientific achievements into productivity, guiding and driving oil and gas exploration to achieve strategic breakthroughs, and accumulating valuable experiences for PetroChina to carry out risk exploration. Key words: scientific exploration well, “three new” fields, Tuha Basin, Ordos Basin, Shanshan Oilfield, Jingbian gas field, Well Taican 1, Well Shaancan

Geological exploration theory for large oil and gas provinces and its significance

In the period of “11th Five-year Plan” (2006-2010), PetroChina proposed and developed a geological exploration theory for large oil and gas provinces, under which a group of major discoveries have been achieved. Large oil and gas provinces are large oil/gas-bearing areas consisting of several groups or belts of reservoirs (oil/gas fields) under the same large structural setting. These are determined by similar accumulation conditions, dominated by a certain type of hydrocarbon reservoir and overlaid vertically and connected horizontally. The combination of the large structural setting, favorable source rock and widely distributed heterogeneous reservoir is essential for development of large oil and gas provinces. Large oil and gas provinces are mainly developed in large structures such as continental depressions, foreland and marine craton basins, with large oil/gas-bearing areas and considerable reserves. Reservoirs are widely distributed, with low porosity and low permeability and high heterogeneity. Hydrocarbon distribution is not controlled by local structures and there is no uniform oil/gas/water contact but varying proportions of oil, gas and water. Based on the reservoir lithology, large oil and gas provinces are divided into clastics, carbonates and volcanic, which are subdivided into five sub-large oil and gas provinces, i.e. low porosity and permeability clastic; complex, steep and deep foreland structural; carbonate karst stratigraphic; carbonate platform margin reefal; and volcanic stratigraphic. Moreover, key technologies integrating seismic surveys, drilling, logging and formation tests have been developed. The exploration in large oil and gas provinces stresses the concept of “overall study, overall exploration and overall control”, and the evaluation method of “integrating exploration and development, and integrating production expansion and reserve growth”, to maximize the benefits of both exploration and development. Key words: litho-stratigraphic hydrocarbon reservoir, large oil and gas province, accumulation mechanism, geological characteristics, exploration concept, exploration metho

Energy revolution: From a fossil energy era to a new energy era

This paper aims to predict the future situation of global energy development. In view of this, we reviewed the history of energy use and understood that new energy sources will usher in a new era following oil & gas, coal and wood one after another in the past time. Although the fossil energy sources are still plenty in the world, great breakthroughs made in some key technologies and the increasing demand for ecological environmental protection both impel the third time of transformation from oil & gas to new energy sources. Sooner or later, oil, gas, coal and new energy sources will each account for a quarter of global energy consumption in the new era, specifically speaking, accounting for 32.6%, 23.7%, 30.0% and 13.7% respectively. As one of the largest coal consumer, China will inevitably face up to the situation of tripartite confrontation of the coal, oil & gas and new energy. The following forecasting results were achieved. First, the oil will be in a stable period and its annual production peak will be around 2040, reaching up to 45 × 108 t. Second, the natural gas will enter the heyday period and its annual production peak will be around 2060, reaching up to 4.5 × 1012 m3, which will play a pivotal role in the future energy sustainable development. Third, the coal has entered a high-to-low-carbon transition period, and its direct use and the discharged pollutants will be significantly reduced. In 2050, the coal will be dropped to 25% of the primary energy mix. Last, the development and utilization of new energy sources has been getting into the golden age and its proportion in the primary energy mix will be substantially enhanced. On this basis, we presented some proposals for the future energy development in China. At first, we should understand well that China's energy production and consumption has its own characteristics. Under the present situation, we should strengthen the clean and efficient use of coal resources, which is the key to solving our energy and environmental issues. Then, under the low oil price circumstance, we should keep 200 million tons of annual oil production as “the bottom line” so as to ensure national energy security and to accelerate tight gas, shale gas and other unconventional resources development. In 2030, the annual natural gas production will reach up to more than 300 Bcm. Finally, the development and utilization of new energy resources should be further strengthened and non-fossil energy sources will be expected to reach as high as 20% of the primary energy consumption by 2030

Characteristics and controlling factors of fractures in igneous rock reservoirs

Based on the updated exploration and research achievements, this paper studies the types and controlling factors of the fractures in Carboniferous igneous rocks of Northern Xinjiang, and their influences on the high-quality reservoir and high production of oil and gas. Fractures with different occurrences (oblique fracture, net fracture, horizontal fracture and vertical fracture) and geneses (autoclasic fracture, contraction fracture, dissolved fracture, joint fracture and structural fracture) were developed in igneous rocks. The ability of fluid flow and seepage radius were different in various fractures. The development degree of fractures was controlled by lithology, tectonic movement, early and late diagenesis. It was controlled mainly by lithology in the areas of weak tectonic movement; it varied in different lithologic igneous rocks with the same tectonic background. The main controlling factors of forming fractures in igneous rocks were tectonic movement, late and early diagenesis, especially tectonic movement and hypergenesis during the stage of late diagenesis. Various lithologic igneous rocks undergoing intense tectonic movement and long-time weathering developed fractures and favorable volcanic reservoirs that were concentrated in the area no more than 3 km away from the main fault zone. The closer to the fault the well is located, the easier it gains high and stable production of oil and gas. 摘要: 基于新疆北部石炭系火成岩的最新勘探和研究成果 研究火成岩-发育的裂缝类型、控制因素 及裂缝对优质储集层发育和油气高产的控制作用。火成岩-发育不同产状 斜交缝、网状缝、水平缝、直劈缝和成因裂缝 自碎缝、收缩缝、溶蚀缝、节理缝、构造缝 不同类型裂缝的流体渗流能力和渗流半径存在差异。裂缝发育程度受岩性、构造、早期成岩和后期成岩作用控制 在构造作用较弱地区 火成岩裂缝发育程度受岩性控制 在相同构造背景下不同岩性火成岩-裂缝发育程度不同 构造、早期成岩和后期成岩作用是火成岩成缝的主要控制因素 构造作用和后期成岩-的表生作用对火成岩成缝的贡献最大 构造作用强、风化淋滤时间长的区域 不同岩性火成岩-均发育裂缝 并能形成有利储集层 距主断裂带3 km范围是裂缝和有利储集层的集-发育区 油井离断裂越近越易高产、稳产。图10参20 关键词火成岩 有利储集层 裂缝 控制因素 石炭系 新疆北部-图分类号TE121.1 文献标识码A Key words: igneous rock, favorable reservoir, fracture, controlling factor, Carboniferous, Northern Xinjian