Evaluation of Sealing Performance of Multi - Stage Abutting Faults in The Bohai Bay Basin, China

Abstract

The network composed of NWW- and NNE-trending abutting faults in the Bohai Bay Basin, China, has been demonstrated to significantly contribute to the hydrocarbon accumulation in the fault block traps. However, strong hydrocarbon productivity heterogeneity has been reported in drilling practices, and hydrocarbon leakage has been suggested to be the main reason for some drilling failure. Therefore, it is critical to analyze and evaluate the sealing performance of abutting faults. Massive drilling and 3D seismic data were combined, and three influential factors were identified. (1) Leakage at the intersection of abutting faults. Specifically, there are four stages in the intersection of abutting faults, namely isolation, early abutment, intermediate abutment, and full abutment, all of which could be recognized by strike-projected throw distribution diagrams in structural physical experiments. The sealing performance at the intersection was found to first rise and then fall from Stages 1 to 4. (2) The time interval between the hydrocarbon charging and leakage. The arrival of the fault at the free surface during the growth, as could be identified in the T-Z profile, was usually associated with rapid underground pressure release, causing violent hydrocarbon leakage. Meanwhile, the intersection timing, as could be obtained by the backstripping technique, determined the effective preservation of charged hydrocarbons. Therefore, the time interval between these two processes could well characterize the effective charging timing and corresponding seal performance. (3) Transpressional stress. The early-formed abutting faults could experience rejuvenation and oblique extension in the later abutting stage, during which the angle between the early-stage fault strike and the later-stage extension was negatively correlated with the transpressional stress, and thus positively correlated with the sealing performance. Using above three factors, the sealing performance of 10 drilled structures with abutting faults in the Bohai Oilfield was comprehensively evaluated, during which the factors were rated, followed by weighted summation. The sealing performance was found to be well positively correlated with the height of the trapped oil column, which significantly verified the effectiveness of this method in evaluating the sealing performance of abutting faults.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019