Fine description method of the underwater distributary channel in a braided river delta front: A case study of the first Member of the Dongying Formation in the M Oilfield, Nanpu Depression

Abstract

The division accuracy of a single-genesis sand body in a river channel determines the evaluation resolution of residual oil content and limits the efficiency of oil production. The following methods were used to describe the underwater distributary channel of the M oilfield in the Nanpu Depression. First, the seismic attribute was optimized to identify the boundary of a single channel-lobe complex. Then, the channel main stream line was traced with the constraint of the geological knowledge base of the braided river delta front, and the channel boundary was delineated using acoustic inversion technology. Finally, the results of channel characterization were verified with dynamic data. The research shows that the M Oilfield has multiple channel-lobe complexes developed in the same period. Even a single channel-lobe complex contains 2-8 channels. The width of the underwater distributary channel ranges from 80-240 m, with a maximum width of 440 m. The thickness of asingle channel sand body is 2.6-5.8 m, and the width-thickness ratio of the channel ranges from 25∶1 to 78∶1. The dynamic verification data and drilling results show that the prediction accuracy of channel distribution is 90%. The high prediction accuracy of the channel sand body distribution can promote the evaluation resolution of residual oil content, and provide constructive guidance for later development and management. The method has a certain reference value in the underwater distributary channel characterization of the braided river delta front reservoir in the complicated fault block.

Keywords

• braided river delta front
• underwater distributary channel
• comprehensive reservoir prediction
• combination of well and seismic data
• river mainstream
• river boundary description
• dynamic data verification
• nanpu depression