Enrichment Characteristics of Normal-Pressure Marine Shale Gas in the Complex Tectonic Zone: A Case Study of the Lower Cambrian Niutitang Formation in Northern Guizhou

Abstract

The Lower Cambrian Niutitang Formation is a crucial stratum for the exploration of normal-pressure marine shale gas in southern China, with great development potential. To research the normal-pressure shale gas accumulation of the Niutitang Formation in the complex tectonic zone, the shale cores in northern Guizhou were subjected to X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) observation, and tests were conducted to determine total organic content (TOC), bitumen reflectance, and nitrogen isotopes. The results indicate that the equivalent vitrinite reflectance of cores varies from 2.30% to 3.73%, and the TOC content of cores varies from 3.8% to 7.8%. The total gas content of three wells in northern Guizhou is 0.5, 0.3, and 1.4 m³/t, respectively. The TOC content of the shale in the syncline structure is higher than that of the shale in the anticline structure. Nitrogen in shale gas originates primarily from the thermal ammoniation of organic matter, the atmosphere, and the deep crust. Shale gas preservation is favorable in regions with a large range of lifting, and small lifting differences. The syncline is broad and gentle with few faults have better gas accumulation conditions. The Niutitang Formation in the residual syncline of the study area has better gas content than that of other structures. Exploration of shale gas accumulation sweet spots in northern Guizhou should focus on the broad-gentle synclines with minimal changes in stratigraphic lifting, few faults, and no hydrothermal activity at the edges of paleo-uplifts.

Keywords

complex tectonic area / shale gas / hydrocarbon generation / energy resources / Lower Cambrian Niutitang Formation / Northern Guizhou

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