Shiyou shiyan dizhi (Jan 2024)
Quantitative evaluation of fault sealing by Weighted Shale Gouge Ratio(WSGR): a case study of Yongan area in Gaoyou Sag, Subei Basin
Abstract
The evaluation of fault sealing is an important part of analyzing hydrocarbon accumulation conditions in fault-block traps. Based on the improved Shale Gouge Ratio (SGR), this paper proposed a new method for evaluating fault sealing, Weighted Shale Gouge Ratio (WSGR). Firstly, the calculation parameters and influencing factors of SGR were analyzed using different geological models, and it is determined that fault distance, mud content, and mud rock distribution are important factors affecting shale smear. It was found that all muddy sediments that slide through the target reservoir have contributions to shale smear within fault distance, but the contributions of different points vary, with higher mud content and closer distances contributing more. Therefore, a new parameter called distance coefficient was introduced to represent the influence of mudstone distribution on shale smear. The distance coefficient is defined as the ratio of the difference between fault distance and the distance from mudstone to the target reservoir to the fault distance. Based on this, a calculation method named Weighted Shale Gouge Ratio (WSGR) was constructed, which is defined as the product of mud content and distance coefficient at each point, summed and divided by the sum of distance coefficients. The sealing performance of known oil and water layers in the upper oil and gas bearing system in the Gaoyou Sag is verified by using Weighted Shale Gouge Ratio (WSGR), and it is considered that when the value of WSGR is greater than 0.6, the fault has good sealing performance, thus determining the sealing discrimination criteria of this method. Finally, good application results have been achieved in the evaluation of fault sealing of Eocene Danan Formation in Yongan and other areas of the Gaoyou Sag.
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