Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (5): 1206-1220.doi: 10.11743/ogg20220516

• Petroleum Geology • Previous Articles     Next Articles

Wettability of the Permian Fengcheng Formation shale in the Mahu Sag, Junggar Basin, and its main control factors

Guowei Zheng1,2(), Zhiye Gao1,2(), Liliang Huang3, Zhenxue Jiang1,2, Wenjun He3, Jiaqi Chang1,2, Longfei Duan1,2, Weihang Wei1,2, Zhiwei Wang1,2   

  1. 1.State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum (Beijing),Beijing 102249,China
    2.Unconventional Petroleum Research Institute,China University of Petroleum (Beijing),Beijing 102249,China
    3.Research Institute of Exploration and Development,Xinjiang Oilfield Company,PetroChina,Karamay,Xinjiang 834000,China
  • Received:2021-09-14 Revised:2022-07-13 Online:2022-10-01 Published:2022-09-02
  • Contact: Zhiye Gao E-mail:zhengguowei7@163.com;gaozhiye@163.com

Abstract:

Shale wettability is of great significance to relative permeability and capillary force of a reservoir, ultimately affecting the hydrocarbon accumulation process in shale as well as the shale oil/gas recovery rate. This study focuses on the wettability characteristics and main control factors of the Permian Fengcheng Formation shale in the Mahu Sag, Junggar Basin, by means of contact angle measurement and spontaneous imbibition plus micro-CT experiment. The results are shown as follows. First, the Fengcheng Formation shale in the Mahu Sag is of generally mixed wettability while prone to oil-wet, and the affinity of different lithofacies to water is listed out from the top, that is, felsic shale, limy felsic shale, dolomitic felsic shale, felsic dolomitic shale, and siltstone. Second, the shale wettability is jointly controlled by multiple factors including organic matter abundance, mineral composition, and pore structure. The shale hydrophobicity is positively correlated with the TOC, dolomite content, negatively with the quartz content, and in staged correlation with the calcite content; the larger the pore volume occupied by macro-pores, the more oil-wet is the shale sample. Third, the connectivity of oil-wet pores tends to grow better along the direction of crack and lamina development. A pore system of clustered type and certain connectivity is prone to form in dolomitic glomerates, which can form an unique shale oil storage space and migration pathway together with the interconnected small pores in the shale matrix. Fourth, the pores less than 1 μm have better connectivity and act as the main migration pathways for shale oil, while those larger than 1 μm with poor connectivity serve as the main storage space for shale oil. Fifth, it is preliminarily concluded that the high-quality shale oil reservoirs are of siltstone and dolomitic felsic shale with well-developed cracks, dolomitic glomerates and laminar structures in the study area according to the wettability characteristics of different lithofacies and sedimentary structure characteristics.

Key words: micro-CT experiment, spontaneous imbibition, contact angle, shale wettability, pore connectivity, shale reservoir, Mahu Sag, Junggar Basin

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