The secondary development of mature oilfields with high water cut is a revolution in the history of oilfield development and also a strategic systematic project. It plays an irreplaceable role in maintaining long-term stable oil production. From the aspects of intelligent decision-making, intelligent planning, intelligent operation, intelligent monitoring, and intelligent evaluation, and within the framework of the policies for carbon peaking and carbon neutrality, the prospects for the secondary development of mature oilfields in China were discussed. It is indicated that the secondary development of mature fields should be implemented by reconstructing underground understanding system, well pattern, and surface process, and technically by way of overall control, stratigraphic subdivision, plane reorganization, three-dimensional optimization, and deep profile control, ensuring the smooth integration of secondary development and tertiary development.
To further understand the petroleum resources/reserves classification system and its development trend, China’s petroleum resources/reserves classification system is reviewed with respect to its development history and characteristics, and compared with the Petroleum Resources Management System (PRMS) and the United States Securities and Exchange Commission’s standard classification system. The research reveals that the three systems are significantly different in evaluation purpose, reserves definition, and evaluation approach. China’s classification system focuses on the discovered petroleum originally-in-place, emphasizes the total quantity of resources, and serves for the overall benefits and long-term planning of petroleum exploration and development. PRMS, a project-based classification system, facilitates international communication and cooperation, and considers the attributes of petroleum as both resource and asset. It centers on the remaining commercially recoverable reserves and emphasizes the commercial value of resources. The SEC standard classification system provides a benchmarking platform for petroleum companies, and ensures consistent disclosure of reserves information to the public. It also centers on remaining economically recoverable reserves, paying more attention to the attribute of petroleum as asset. These classification systems maintain their distinct features while borrowing from and integrating with each other.
As the measures are taken against global climate issues, more than 120 countries/regions have set the goal of “carbon neutrality”. The global energy transition is progressing rapidly, and the oil companies mainly engaged in traditional oil and gas businesses are facing pressures from both multiple environmental protection regulations and carbon emission reduction. Therefore, the low-carbon transition strategy has received extensive attention. On the basis of analyzing the global energy transition under the background of “carbon peaking and carbon neutrality”, the current situation and trend of the global oil and gas development were investigated from several aspects such as supply-demand pattern, exploration and development trends, business structure, international oil prices, and geopolitics. Finally, relevant countermeasures for the development of China’s oil and gas industry were put forward: (1) take both oil and gas as the main energy sources, put more efforts in exploration and development, and attach equal importance to “unconventional and conventional resources, offshore and onshore resources, deep and shallow resources”, in order to increase reserves, stabilize oil production and enhance gas production for purpose of national energy security; (2) combine carbon emission reduction with carbon utilization, and accelerate energy conservation and emission reduction, in order to realize green and low-carbon development; (3) keep the integrated development of oil, gas, and new energy, and promote the development of new energy step by step with a clear strategy by relying on the advantages (e.g. funds, technologies and talents) of oil/gas exploration and development; (4) follow the technological innovation strategy centered on theory/technology research, key technology R&D and supporting technology applications, in order to drive the oil and gas industry to achieve green transition and high-quality development
In order to understand the growth trend of proven oil and natural gas geological reserves in China, this paper analyzes the distribution and change of the incremental proven oil and natural gas geological reserves discovered from 2010 to 2019 in China. The results show that the incremental proven oil reserves are mainly distributed in the areas such as Ordos basin, Bohai Bay basin, and Junggar basin, and accumulated in the middle-shallow to middle-deep formations in these basins; the incremental proven natural gas reserves are mainly distributed in the areas such as Ordos basin, Sichuan basin, Tarim basin, and East China Sea Shelf basin, and accumulated in middle-deep to ultra-deep formations; the quality of the incremental oil and gas reserves become worse, the abundance goes lower and the burial depth is deeper and deeper; and incremental proven oil and gas reserves are mainly preserved in lithologic oil and gas reservoirs, unconventional oil and gas reservoirs and deep oil and gas reservoirs.
We reviewed the geological features, reserves, production, drilling activities and progress of development technology in major shale oil zones in the Permian basin, the Bakken area in the Williston basin and the Eagle Ford area in the Gulf of Mexico basin, analyzed the development trend of shale oil in the USA, and summarized the experience and enlightenment from the USA, with the intent to provide a reference to the development of shale oil in China. The results show that the Permian basin has the highest reserves and production of shale oil in the USA, which is mainly produced from the Spraberry zone and the Wolfcamp zone, and they will also be of great importance in the future. In 2020, influenced by COVID-19, the amount of drilling rigs and the oil production in the three major shale oil zones mentioned above first declined and then increased, and the ultra-low oil prices drove a new round of technological innovation and cost-cutting measures to increase well production in oil companies. By referring to the experiences in shale oil exploration and development in the USA, to develop shale oil in China, priority should be given to highly matured light oil and condensate oil, and the advanced development technologies of condensate oil reservoirs in the USA should be studied and followed. Grading evaluation of sweet spot is the basis of efficient development of shale oil in the USA, and plays a particularly significant role at low oil prices. There is a long way to go to get profitable development of shale oil in China. Technological progress is the key to reducing cost and enhancing profit. Technological researches should be paid attention to in early exploration and development. Life-cycle and geological-engineering integration management is recommended. This may be a new way for efficient shale oil development and rapid cost reduction in China.
This paper reviews field test cases for enhancing oil recovery in tight oil reservoirs at home and abroad in recent years, analyzes the effects of various development methods, and points out the problems arising out of and the enlightenment obtained from the field tests. According to the results of field tests at home and abroad, we conclude that gas injection (CO2 and natural gas) is a popular development method at present; most pilot tests are successful with the oil recovery improved by 3% to 30%; the laboratory models are too ideal and quite different from or even contrary to the field test results; fracture interference and channeling result in uneven energy spread, which is the fundamental cause for the failure of some pilot tests. Therefore, how to balance “utilization and treatment” of fractures, clarify the “ substantial” exchange mechanism between tight matrix and fractures, and guide and optimize laboratory research through field experience are key issues to resolve in tight oil development in China. In addition, it is necessary to further optimize the methods for tight oil resource evaluation, increase policy support to oil and gas industry and promote the leapfrog development of the theory and technology for enhancing tight oil recovery.
Two conclusions have been existent about the crude oil of the Lucaogou formation in the Jimsar sag, Junggar basin. One conclusion classifies the crude oil as tight oil, and the other as shale oil. According to two national standards - Geological Evaluation Method for Tight Oil and Geological Evaluation Method for Shale Oil, the classification of the crude oil in the Lucaogou formation is determined. The studies show that, based on the source-reservoir relationship and layer thickness statistics, the crude oil in the Lucaogou formation of the Jimsar sag is shale oil; based on the occurrence, source-reservoir relationship and oil accumulation model, the oil is determined as shale oil which accumulates between layers. In terms of the geochemical parameters of the source rock, the lithology and physical properties of the reservoir, the parameters of the oil reservoir, fracture development and brittleness, this study investigates how the characteristics of the shale oil in the Lucaogou formation are different from the typical shale oil at home and abroad. The results show that the shale oil in the Lucaogou formation is of low to middle maturity, but a large amount of hydrocarbons have been generated and expelled in the early stage; the reservoir has high porosity, but its permeability is obviously low; the oil saturation of the reservoir is high and the oil is characterized by high density, high viscosity, low gas-oil ratio and poor fluidity. Natural fractures in the reservoir are not developed, and the brittleness calculated with the rock mechanical method is poor.
Multi-cluster fracturing technology in horizontal well is one of key technologies to stimulate shale reservoirs efficiently, which can increase hydraulic fracture complexity and enhance pay-gross ratio among clusters. In this paper, the application status of multi-cluster fracturing technology in the shale reservoirs in North America and southern Sichuan basin is stated and some opinions are presented by combing with its mechanism. Multi-cluster fracturing technology should match with well spacing, diversion technology and limited-entry perforation technology should be used to improve cluster efficiency and promote fracture propagation evenly so as to increase multi-cluster fracturing effectiveness. Multi-cluster fracturing has been extensively applied in the shale areas in North America to enhance production and realize efficient development, but the technology in the shale area in the southern Sichuan basin started relatively late and at present field tests of the hydraulic fracturing technology with 6-8 clusters in horizontal sections have been conducted in horizontal wells with the well spacing of 300-400 m. In order to reduce cost and improve operation efficiency, long horizontal section multi-cluster fracturing is considered as a promising trend for efficient development. However, with the increase of cluster number, the matching of perforation technology, diversion technology, cluster number with operation parameters is facing challenges, and a multi-cluster fracturing technology suitable for different geological and engineering characteristics of the target areas needs to be further studied.
