Low permeability tight oil and gas in Yanchang area, Ordos Basin: Advances in accumulation theory and exploration practice

doi:10.13745/j.esf.sf.2022.8.30

Abstract

Abstract:

Petroleum resources (oil, natural gas, shale gas) exploration and development in the Ordos Basin has achieved remarkable results owing to the coordinated resources development as well as theoretical and technical researches promoted by the Shaanxi Yanchang Petroleum (Group) Co., Ltd. In petroleum exploration, a “alternate accumulation of ultra-low permeability oil” theory is proposed, and a new model for Mesozoic multi-stage differential accumulation is establishment, which leads to the discovery of ultra-low permeability oil reserves exceeding 1×10⁸ t per year for the last 10 years. In tight oil discovery, the “sand control by storm and earthquake” theory is proposed for fine-grained sedimentary areas, along with a “sweet spot” prediction method, which leads to the discovery of tight oil reserves totaling 2.1×10⁸ t. In tight gas exploration, the genetic mechanism of sand bodies in tight gas fields and the law of natural gas migration and accumulation are unclear. To overcome this problem a new theory is proposed which considers sand-body distribution is controlled by frequent shoreline migration in shallow water environment, and a formation model for high-quality tight sandstone gas reservoir is established. It is found that pure quartz sandstone and quartz-rich low-plastic granular lithic sandstone are tight-gas “sweet spots”, and a target optimization technique is developed based on multi-element, whole-process natural gas migration and accumulation simulation, which leads to the discovery of the Yan’an gas field with 7635×10⁸ m³ natural gas in reserves. In shale gas exploration, a “ternary accumulation and enrichment of continental shale gas” theory is proposed, which considers that the high-quality lacustrine shale is the material basis for shale gas enrichment and high production, the multi-type, multi-scale complex pore network determines the occurrence conditions of shale gas, and the self-sealing ability and high pressure of thick shale are the keys to gas storage. In the future, the Yanchang Petroleum Group will continue to adhere to the strategy “stabilize oil production, boost gas production, strengthen unconventional resources development”, and ensure sustainable enterprise development by promoting “integrated geological engineering” in resources exploration and development.

Key words: Yanchang Petroleum Group, Ordos Basin, alternate accumulation of oil, Yan’an gas field, continental shale gas

CLC Number:

TE122.1

WANG Xiangzeng. Low permeability tight oil and gas in Yanchang area, Ordos Basin: Advances in accumulation theory and exploration practice[J]. Earth Science Frontiers, 2023, 30(1): 143-155.

Figures/Tables 10

Fig.1 Relationship between diagenetic evolution and hydrocarbon charging in ultra-low permeability reservoirs

Fig.2 Asphalt fluorescence statistics for typical well

Fig.3 Physical simulation of petroleum migration

Fig.4 Seismic sedimentary model of Chang 6-Chang 8 in Ordos Basin

Fig.5 Storm sedimentary model of Chang 6-Chang 8 in Ordos Basin

Fig.6 Variation of source-rock generated gas, oil mass percentage and gas-oil ratio in different evolutionary stages

Fig.7 Flowchart for deltaic sedimentation simulation experiment under water level fluctuation in the Shanxi Formation, Yanchang oil field

Fig.8 Coupling relationship between densification process of different rock facies and gas charging

Fig.9 Gas generation intensity contour plot for mud shale in Chang 7 member of Yan’an exploration area

Fig.10 Gas content in shales of different phases under different pore sizes

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