Study on Gas Reservoir Forming Mechanism of DB11 Well in Changling Fault Depression

• 1、School of Management Science & Engineering,Baise University,Baise Guangxi,533000

Abstract：low-yield gas was drilled in well DB11 of the Lower Cretaceous Yingcheng formation in Changling fault depression. The reservoir lithology is Gabbro, mudstone and Tuff. Core and microscopic observations revealed strong thermal metamorphism and many fractures in the dark mudstone around Gabbro. The geochemistry analysis shows that the gas composition of the well is mainly composed of hydrocarbons (96.7%) , but 13C is very heavy (for example, δ13C1 reaches-22.12‰) . Comprehensive Analysis shows that the formation of DB11 well gas pool is closely related to Gabbro. On the one hand, the abnormal high temperature in Gabbro promoted the hydrocarbon generation of organic matter in the surrounding mudstone and produced 13C heavy natural gas. On the other hand, the abnormal high pressure in the Gabbro caused many fractures in the surrounding rock. Moreover, the Gabbro also forms some shrinkage cracks during the condensation process. The resulting gas accumulates close to these fractures. Because the Gabbro is small and the nearby source rocks are not well developed, the reservoir is limited.

Keywords： Changling fault depression gabbro gas reservoir-forming mechanism