Effective Evaluation Of Fault-bound Traps From Lower Part Of Shayixia Formation On Qinan Slope,Qikou Sag

The Qikou Sag in the Bohai Bay Basin is an important hydrocarbon-rich depression formed in the Cenozoic.It has experienced multiple stages of extensional rifting since the Paleogene.The Qinan slope is located in the southwest of Qikou Sag,many types of fault traps are developed due to fault shielding.With the development of oil and gas exploration on slope areas in recent years,an evaluation of the effective fault-bound traps is necessary.In this paper,taking the lower part of Shayi Formation of the Qinan slope in Qikou Sag as an example,evaluations of the effectiveness of fault traps in the slope area is carried out by comprehensively utilizing 3D seismic data,drilling data,and previous results,the results show that:(1)there are three types of fault-bound traps in the lower part of Shayi Formation of the study area: synthetic fault-bound traps,antithetic faultbound traps,and crossing fault-bound traps;(2)interpretation quality of faults and fault lateral seal quality effect their self-effectiveness.The relay displacement/distance method(D/S)and displacement gradient ratio method(R/G)are comprehensively used to improve the reliability of fault combinations,and using lateral seal evolution method to determine seal capacity for them.53 fault-bound traps has self-effectiveness on Lower Part of Shayixia Formation on Qinan Slope,Qikou Sag.(3)The temporal validity of fault-bound traps determine whether oil and gas can accumulate.Using the maximum throw subtraction method can determine the formation period of fault-bound traps by restoring the growth and connection process of faults.The homogeneous temperature data of the inclusions confirm that the hydrocarbon in the lower part of Shayi Formation in the study area was mainly charged during the deposition period of the Minghuazhen Formation.Therefore,fault-bound traps formed before the deposition period of the Minghuazhen Formation are important for accumlation of oil and gas;(4)Typical fault propagation fold structures and rock mechanics tests show that regional caprock in middle part of Shayi Formation is in the brittle-ductile phase.The shale smear factor method(SSF)is used to evaluate the top sealing ability.When the SSF value is greater than 3.5,oil and gas may escape across the caprock to shallower layers.The comprehensive evaluation results of the fault-bound traps effectiveness in the lower sub-segment of the Qinan slope are in high agreement with the present proven oil and gas distribution.The evaluation results have a certain guiding significance for unexplored fault traps.