Abstract
Gas shales from the Wufeng-Longmaxi Formation in Anchang syncline in northern Guizhou area of Sichuan Basin are stable in distribution and can be classified as type I shale gas reservoir with great resource potential. The exploration and development of shale gas in Anchang syncline have achieved great progress. However, the enrichment rule and accumulation pattern of shale gas in Anchang syncline are still not clear at the present. Gas pressure in the Wufeng-Longmaxi Formations shales in Anchang syncline is normal. The maximum tested gas production in the field ranges from 18,000 to 58,000 m3/d. However, gas production of shale wells varies greatly even in the same platform. In order to understand the shale gas enrichment and accumulation and improve the effective development of shale gas in this area, comparative analyses on the geological characteristics and preservation conditions of gas reservoirs in several typical wells were carried out from the perspective of geology, petrophysics, geophysics, and well logging. Results show that shale gas in Anchang syncline has the characteristics of accumulating in both deep central position and gently wings. Tectonic preservation condition is the key factor to high gas production in Anchang area. The hydrological conditions, syncline structure, fault distribution, and cap rock quality comprehensively control the gas pressure and gas bearing capacity of shale reservoir. According to these factors, an accumulation model of shales with normal gas pressure is established: syncline controls the distribution of gas reservoir; fault controls the boundary of the reservoir; preservation conditions controls gas capacity. The results are benefit for the rolling exploration and development of shale gas in Anchang area, and are important for the development of normal pressure shale gas in northern Guizhou area.
Highlights
With the growing demand for energy, unconventional oil and gas have gradually become the hotspots of fossil energy development (Jarvie et al, 2007; Hao et al, 2013; Rezaee, 2015; Xu et al, 2019)
The results show that the fault distance in Anchang syncline is negatively correlated with gas content, maximum tested gas production rate, and average daily gas production
There are mainly three aspects related to the enrichment pattern of shale gas in Anchang area (Figure 9): 1) The enrichment of shale gas in Anchang syncline is controlled by sedimentary facies and preservation conditions
Summary
With the growing demand for energy, unconventional oil and gas have gradually become the hotspots of fossil energy development (Jarvie et al, 2007; Hao et al, 2013; Rezaee, 2015; Xu et al, 2019). Based on the exploration practice of shale gas in the Wufeng-Longmaxi Formation in Sichuan Basin and its surrounding areas, many researchers argued that the distribution and enrichment of shale gas reservoirs with normal pressure were obviously controlled by the tectonic movements These observations effectively support the rapid development of marine shale gas in China.
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