Natural fracture prediction in Keshen 2 ultra-deep tight gas reservoir based on R/S analysis, Kuqa Depression, Tarim Bas
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Geosciences Journal
GJ
Natural fracture prediction in Keshen 2 ultra-deep tight gas reservoir based on R/S analysis, Kuqa Depression, Tarim Basin Hui Zhang1, Wei Ju2,3*, Guoqing Yin1, Xinyu Liu1, Zhimin Wang1, Sijia Liu4, Ke Wang5, Hui Yang2, Ke Xu1, and Wenbo Luan2 1
Institute of Exploration and Development, PetroChina Tarim Oilfield Company, Korla 841000, China School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China 3 Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Mineral, Shandong University of Science and Technology, Qingdao 266590, China 4 School of Computer Science and Technology, China University of Mining and Technology, Xuzhou 221116, China 5 PetroChina Hangzhou Research Institute of Geology, Hangzhou 310023, China 2
ABSTRACT: Within ultra-deep tight sandstone gas reservoirs, natural fractures indicate significant effects on reservoir performance because they can serve as storage spaces for hydrocarbons and improve the permeability. Accurate prediction of natural fractures in ultra-deep reservoirs is critical to the exploration and development of tight gas in Keshen 2 Block of Kuqa Depression. In this study, several conventional logs are selected and the R/S analysis method is introduced to predict the development and distribution of natural fractures in ultra-deep tight sandstone reservoirs. Fracture development coefficient Q is calculated based on the second derivatives of lg(R/S) function and corresponding weight of each log parameter, which matches well with linear fracture density measured from image logs. There is a positive correlation between parameter Q and fracture density, higher Q values usually indicate larger fracture density. Factors causing mismatches between calculated parameter Q and fracture density are also analyzed. Fracture dip angle, fracture filling condition, vertical resolution of logs, multiple interpretations of conventional logs, and lateral detection difference between image and conventional logs may contribute to generate those false appearances. The results in this study are expected to provide new geological references for the exploration and development of ultra-deep tight gas in Keshen 2 Block of Kuqa Depression. Key words: natural fracture, ultra-deep tight gas, R/S analysis, Keshen 2 Block, Bashijiqike Formation, Kuqa Depression Manuscript received April 29, 2020; Manuscript accepted September 23, 2020
1. INTRODUCTION Recently, with further exploration and development of unconventional resources, ultra-deep tight sandstone reservoirs have become an important research direction and a hot topic in Kuqa Depression of Tarim Basin (Li et al., 2017; Shen et al., 2017). Tight sandstone reservoir is commonly defined as sandstone layers with overlying matrix permeabilities of less than or equal to 0.1 × 10–3 μm2 (Zou et al., 2017). As the target layers and geothermal *Corresponding author: Wei Ju School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China T
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