Sedimentary characteristics and favourable area selection of tight sandstone gas reservoirs in the Sanjianfang Formation of the Shengbei Depression, Tuha Basin

Abstract

Objective The Shengbei Depression is the largest petroliferous depression of the Tuha Basin. With the strong demand for the exploration and development of tight sandstone gas in the Middle Jurassic Sanjianfang Formation, it is urgent to study the sedimentary characteristics and predict favourable exploration zones of the Sanjianfang Formation. Methods Using core, well logging, and seismic data, the high-resolution sequences and sedimentary characteristics of the tight sandstone gas reservoir in the Sanjianfang Formation of the Shengbei Depression were studied. A lacustrine delta system was identified, and favourable exploration zones of tight gas reservoirs were predicted. Results Three long-term sequences (L1, L2, L3) and five medium-term sequences (M1, M2, M3, M4, M5) were developed in the Sanjianfang Formation in the Shengbei Depression; particularly, these medium-term sequences can be regionally identified. The deposition of the M1 to M3 sequences involved a braided river delta in the lake, but the deposition of the M4-M5 sequences involved a meandering river delta in the lake. The favourable tight gas reservoirs of the Sanjianfang Formation in the Shengbei Depression were mainly developed in subfacies of the delta front. On the plane, the Shengbei 5 and Shengshen 3 well areas of the M2 sequence, the Shengbei 5 and Shengbei 6 well areas of the M3 sequence, and the Shengbei 5, Shengbei 6, and Shengtan 1 well areas of the M5 sequence are favorable exploration areas. The favorable reservoir rarely appears in the M4 sequence. Conclusion This research can promote the exploration of tight gas reservoirs in the Sanjianfang Formation of the Shengbei Depression in the Tuha Basin.

Keywords

• stratigraphic sequence
• sedimentary facies
• middle jurassic
• sanjianfang formation
• shengbei depression
• tuha basin
• tight sandstone
• gas reservoir