Improved method for quantitative fault sealing evaluation in sand-clay sequences: A case study from the west subsag of Bozhong Sag in the Bohai Bay basin, China

• Published in: Marine and petroleum geology 2024-11, Vol.169, p.107062, Article 107062
• Main Authors: Song, Xianqiang, Fu, Xiaofei, Li, Huiyong, Wang, Haixue, Liu, Zhida, Xu, Peng, Jiang, Fei, Xie, Zhaohan
• Format: Article
• Language: English
• Subjects: Effective fault normal stress; Fault seal; Fault-bounded trap; Quantitative evaluation; Sand-clay sequences
• ISSN: 0264-8172
• DOI: 10.1016/j.marpetgeo.2024.107062

This research aims to enhance the assessment of fault sealing capacity and predicting sealing hydrocarbon column height prior to drilling, which is instrumental in enhancing drilling success rates. Traditional methods for fault seal evaluation, which primarily consider the fault rock's clay content, often overlook the influence of effective fault normal stress (σNeff). This research analyzed numerous drilled fault-bounded reservoirs in the west subsag of Bozhong Sag to determine the fault sealing's buoyancy pressure (Pb). The shale gouge ratio (SGR) and σNeff for these faults were computed, and a calibration of the relationship between SGR and Pb across varying σNeff ranges was conducted to define the sealing failure envelope. This calibration reveals distinct fault sealing failure envelopes at different σNeff intervals, underscoring the significant impact of σNeff on fault sealing capacity. Consequently, an improved SGR parameter (ISGR) was proposed to incorporate both the fault rock's clay content and the influence of σNeff on fault sealing. By plotting ISGR against Pb, fault sealing failure envelopes were established, and a relationship between fault sealing capacity and ISGR was formulated. This relationship provides a novel means to evaluate the Pb sealable at specific ISGR values. Comparisons of the ISGR algorithm with other algorithms demonstrate a superior correlation with seal capacity in our samples. The fault sealing capacity of drilled fault-bounded traps was evaluated using this relationship, and the predicted hydrocarbon column heights are in close alignment with actual measurements, validating the reliability and accuracy of the ISGR algorithm in fault sealing evaluation. The consideration of both clay content and σNeff in the ISGR parameter and the associated calibration method makes it particularly suitable for assessing the fault's sealing capacity in diverse sand-clay sequences with varying strike and burial depths. •A new parameter considering clay content and effective fault normal stress is raised.•ISGR-Pb relationship, calibrated via reservoirs, outlines sealing failure envelopes.•Calibrated ISGR-Pb relationship effectively evaluates fault sealing capacity.•ISGR parameter and calibration apt for faults with varied strike and burial depths.