Wireline Formation Test Enables Shale-Oil Quality Evaluation

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 23404, “Shale-Oil Quality Evaluation of Sand/Shale Laminated Reservoir Based on Wireline Formation Test,” by Ming Chen, Yongde Gao, and Jinbo Wu, CNOOC, et al. The paper has not been peer reviewed. Copyright 2024 International Petroleum Technology Conference. _ Shale oil and gas are among the more strategic oil and gas replacement resources in China. The second and third members of the Paleogene Liushagang Formation in the western South China Sea are primary source rocks featuring multiple mature laminated shale and sand oil reservoirs. The authors applied a shale-oil-evaluation method based on sandstone wireline-formation-testing (WFT) data. Introduction Weizhou shale oil in the Beibu Gulf of the South China Sea regionally occurs in a large fault block formed by the northeast- and northwest-trending faults, including the east, middle, and west blocks. From bottom to top, it is developed with the Liu 3 member early-stage and late-stage laminated shale-oil reservoir of the upper-sequence lake intrusion, and the Liu 2 member early-stage sandwich-type shale oil, the middle-stage laminated shale oil, and the late-stage matrix shale oil of the lower-sequence lake intrusion. The early- and late-stage laminated shale oil of the Liu 3 member of the upper-sequence lake intrusion is developed mainly from a thin sheet sand in the fan delta front. The early-stage sandwich-type shale oil of the Liu 2 member of the upper-sequence lake intrusion is developed mainly from a turbidite sheet sand, while the middle-stage laminated shale oil is developed mainly from turbiditic laminated sand. In 2022, the first pilot well of offshore shale oil in this block was drilled and commercial oil flow was obtained, indicating that this area contained good shale-oil resources and the material foundation for developing large- and medium-sized shale-oil fields. WFT Data All WFTs described in this paper were performed with a modular formation dynamics tester. Representing a new generation of WFT, the modular tester can be used for pressure measurement, mobility assessment, fluid identification, downhole fluid sampling, productivity prediction, and other logging operations. The WFT in shale-oil reservoirs always will show the formation as tight or dry, so the fluid composition, water production, and formation pressure cannot be obtained directly. In shale and sand laminated reservoirs, the sandstone and shale are in equilibrium; thus, their formation pressure and fluid properties are consistent.