Xinjiang Petroleum Geology ›› 2025, Vol. 46 ›› Issue (6): 712-722.doi: 10.7657/XJPG20250607

• RESERVOIR ENGINEERING • Previous Articles     Next Articles

Potential of Replacement Areas for Shale Oil Development in the Lucaogou Formation, Jimsar Sag

LI Qing1a(), LUO Gang1b, LI Yingyan1b, DENG Yuan1b, XIAO Dianshi2(), XIE Xiaoquan2   

  1. 1. PetroChina a.Xinjiang Oilfield Company; b.Research Institute of Exploration and Development, Xinjiang Oilfield Company, Karamay, Xinjiang 834000, China
    2. School of Geosciences, China University of Petroleum (East China), Qingdao, Shandong 266580, China
  • Received:2025-04-30 Revised:2025-07-12 Online:2025-12-01 Published:2025-12-05
  • Contact: XIAO Dianshi E-mail:liqing688@petrochina.com.cn;xiaods@upc.edu.cn

Abstract:

In the Jimsar sag, the replacement areas for shale oil development in the Lucaogou formation contain abundant resources, but exhibit small reservoir thickness and heterogeneous sweet spot distribution. Through experimental tests involving organic geochemistry, petrology, pore structure, and hydrocarbon occurrence/mobility, a comprehensive evaluation was conducted on the source rock, crude oil property, reservoir lithology, pore type, and shale oil occurrence/mobility in the replacement areas. The results show that the replacement areas have favorable source rock conditions, and have generally experienced two oil-generating peaks, with significantly lower crude oil density and viscosity and a higher proportion of light components, as compared with the primary zones. The reservoirs in the replacement areas are characterized by small thickness and fine grain size, with underdeveloped intergranular pores but relatively developed dissolution pores and intercrystalline pores, demonstrating a similar pore size range to the primary zones but smaller pore-throat radii than the latter. Both the replacement areas and primary zones hold oil in multiple types of pores, with similar shale oil occurrence patterns. The lower limit of pore size for free hydrocarbon occurrence in the replacement areas is 40-60 nm, which is smaller than that in the primary zones. Crude oil viscosity has a significant control effect on shale oil mobility. Under low viscosity conditions, the crude oil in the replacement areas is highly mobile, with a smaller cutoff than the primary zones according to the nuclear magnetic resonance (NMR) mobility interpretation. The movable oil quantity, oil saturation, pore pressure, and brittleness are the key factors affecting the productivity of the replacement areas. Based on these research insights, a sweet spot evaluation technique combining the weights of these four factors was reconstructed, revealing an accuracy of sweet spot identification in the replacement areas exceeding 80%. The research results provide theoretical support for the stable production of shale oil in the Lucaogou formation.

Key words: Jimsar sag, Lucaogou formation, shale oil, non-producing reserves, development potential, sweet spot evaluation

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