Theory, Technology and Practice of Unconventional Petroleum Geology

0 INTRODUCTION The breakthroughs in unconventional petroleum have a great impact on world petroleum industry and innovation in petroleum geology(Dou et al,2022;Jia,2017;Zou et al.,2015b,2014a;Yerkin,2012;Pollastro,2007;Schmoker,1995).The exploration and development evolution from conventional petroleum to unconventional petroleum and more and more frequent industrial activities of exploring petroleum inside sources kitchen have deepened theoretical understanding of unconventional petroleum geology and promoted technical research and development(Jia et al.,2021,2017;Jin et al.,2021;Zhao W Z et al.,2020;Ma Y S et al.,2018,2012;Zou et al.,2018b,2016,2009;Dai et al.,2012).We have introduced and extended the theory of continuous hydrocarbon accumulation since 2008 and published several papers/books(in Chinese and English)with respect to unconventional petroleum geology since 2009,basically forming the theoretical framework for this discipline(Yang et al.,2022a,2021a,2019a,,2015a;Zou et al.,2019c,2017b,2014a,,2013a).In this paper,we present the background of unconventional petroleum geology,review the latest theoretical and technological progress in unconventional petroleum geology,introduce relevant thinking and practices in China,and explore the pathway of unconventional petroleum revolution and multi-energy coordinated development in super energy basins,hopefully to promote the unconventional petroleum geology and industry development.

Progress in China's Unconventional Oil & Gas Exploration and Development and Theoretical Technologies

The new century has witnessed a strategic breakthrough in unconventional oil ＆ gas.Hydrocarbon accumulated in micro-/nano-scale pore throat shale systems has become an important domain that could replace current oil ＆ gas resources.Unconventional oil ＆ gas plays an increasingly important role in our energy demand.Tight gas,CBM,heavy oil and asphaltic sand have served as a key domain of exploration ＆ development,with tight oil becoming a ＇bright spot＇ domain and shale gas becoming a ＇hotspot＇ domain.China has made great breakthroughs in unconventional oil ＆ gas resources,such as tight gas,shale gas,tight oil and CBM,and great progress in oil shale,gas hydrate,heavy oil and oil sand.China has an estimated（223-263）×10~8t of unconventional oil resources and（890-1260）×l0^（12）m^3 of gas resources.China has made a breakthrough for progress in unconventional oil ＆ gas study.New progress achieved in fine-grained sedimentary studies related to continental open lacustrine basin large-scale shallow-water delta sand bodies,lacustrine basin central sandy clastic flow sediments and marine-continental fine-grained sediments provide a theoretical basis for the formation and distribution of basin central reservoir bodies.Great breakthroughs have been made in unconventional reservoir geology in respect of research methodology ＆ technology,multi-scale data merging and physical simulation of formation conditions.Overall characterization of unconventional reservoirs via multi-method and multi-scale becomes increasingly popular and facilitates the rapid development of unconventional oil ＆ gas geological theory,method and technology.The formation of innovative,continuous hydrocarbon accumulation theory,the establishment of the framework of the unconventional oil ＆ gas geological theory system,and the determination of the implications,geological feature,formation mechanism,distribution rule and core technology of unconventional oil＆ gas geological study lays a theoretical foundation for extensive unconventional oil ＆ gas exploration and development.Theories and technologies of unconventional oil ＆ gas exploration and development developed rapidly,including some key evaluation techniques such as ＇sweet spot zone＇ integrated evaluation and a six-property evaluation technique that uses hydrocarbon source,lithology,physical property,brittleness,hydrocarbon potential and stress anisotropy,and some key development ＆engineering technologies including micro-seismic monitoring,horizontal drilling ＆ completion and ＂factory-like＂ operation pattern, ＂man-made reservoir＂ development,which have facilitated the innovative development of unconventional oil ＆ gas.These breakthroughs define a new understanding in four aspects：①theoretical innovation;② key technologies;③ complete market mechanism and national policy support;and ④ well-developed ground infrastructure,which are significant for prolonging the life cycle of petroleum industry,accelerating the upgrade and development of theories and technologies and altering the global traditional energy structure.

Development of Petroleum Geology in China:Discussion on Continuous Petroleum Accumulation

Petroleum exploration targets are extending gradually from the single conventional trap reservoirs to the large-scale unconventional continuous accumulations. Oil and gas reservoirs have been divided into two types based on the trapping mechanism and distribution of oil and gas： conven- tional single-trap reservoirs, such as the Daqing oil field in Songliao Basin and the Kela-2 gas field in Tarim Basin; and unconventional continuous petroleum accumulation, such as Upper Paleozoic tight gas and Mesozoic tight oil in Ordos Basin, and Upper Triassic tight gas in Sichuan Basin. Two typical geologic characteristics of continuous petroleum accumulation involve： （1） coexisting source and reser- voir, petroleum pervasive throughout a large area tight reservoirs, and no obvious traps or well-defined water-oil and gas contracts; （2） non-buoyancy accumulation, continuous petroleum charge, and no sig- nificant influence by buoyancy. Continuous petroleum accumulation generally have nm-scale pore throats, and the diameters range of 10-500 nm. The geometry and connectivity of these pore throats has significant impact on the migration and distribution of oil and gas in continuous petroleum accu- mulation. China has numerous continuous petroleum accumulation containing various petroleum de- posits, and the exploration of continuous resources is very promising. Unconventional petroleum geol- ogy will become an important new subject in petroleum geology in future, and the nano-technology will function greatly on research, exploration and development of the hydrocarbon accumulation in nano-pore-throats.