Study on the depositional system and favorable targets of the Sha-3 Member in the eastern part of the southern slope of Gubei Subsag, Jiyang Depression

The formation of sand bodies in the eastern part of the southern slope of Gubei Subsag (ESS) is complicated and difficult to predict, which seriously restricts the subsequent exploration and development of the reservoir in the ESS. Based on seismic, drilling, well logging, coring, and chemical analytical data, the geological characteristics of the reservoir in the ESS were studied. The main sedimentary systems and characteristics of the Sha3 Member (the Third Member of the Shahejie Formation) were defined, the sand body distribution of different sedimentary genesis was described, and the favorable target area under the coupling of reservoir control factors was clarified. Results show that the origin of sand bodies in different parts of the Sha3 Member in the EES is complex, and the provenance is mainly from the Gudao bulge in the south and the Changdi bulge in the northeast, where the delta and fan delta facies are developed, respectively, and between which coexisting olistostrome deposits were developed simultaneously. In the optimal root mean square, three seismic attributes: amplitude, effective bandwidth, and phase spectrum were selected, and the frequency-division RGB fusion technology was applied to compare and confirm with logging information. The fine characterization of sand bodies of different sedimentary origins was realized, the distribution range of delta sand bodies was found to expand northward, and a new olistostrome-turbidite sand body was discovered. The new favorable target Z242 well area was selected by combining four reservoir-controlling factors, i.e., short distance to the oil source, sand body well-developing, structural high, and fault existence, after which a new favorable target Z242 well area was selected and later, well location drilling confirmed that the new target area has great potential. This research promoted the efficient development of oil reservoirs in the Gubei Subsag and has important guiding significance for the exploration and development in delta facies sandstone oil reservoirs.