New understandings of the factors controlling of deep shale gas enrichment in the Wufeng Formation-Longmaxi Formation of the southern Sichuan Basin
In recent years,great breakthroughs in deep shale gas have been achieved continuously in Luzhou,Changning and Yuxi Blocks of southern Sichuan Basin as the exploration and development of the Wufeng Formation-Longmaxi Formation shale gas steps to deep layers(burial depth:3 500-4 500 m)in the Sichuan Basin,which demonstrates the promising development prospect of deep shale gas.In order to accurately understand the low resistivity,high water saturation and low gas production which emerge locally in the deep shale of southern Sichuan Basin,this paper systematically analyzes the factors controlling shale gas enrichment from three aspects:the evolution of shale organic matter maturity,the migration characteristics within shale gas source,and the influence of regional multistage fault activity.And the following research results are obtained.First,the graphitization of high and over mature organic matter leads to a significant reduction in shale resistivity and gas content.After the organic matter maturity(Ro)is greater than 3.6％,the gas generating capacity of organic matter gets depleted,the granular porosity decreases significantly,and the water saturation increases greatly.Second,shale gas shows the characteristics of"lateral migration within the source",and the gas bearing property of shale is related to the relative height to the current structural zone,which is specifically reflected as high gas saturation at high altitude areas and low gas saturation at low altitude areas.Third,Class Ⅰ faults have an obvious controlling effect on the dissipation of natural gas,so it is suggested not to deploy wells within 1.5 km from Class Ⅰ faults.Class Ⅱ faults have a limited effect on gas bearing property,and the volumetric fracturing of shale gas 700 m away from Class Ⅱ faults is less influenced.In conclusion,giving full consideration to the influence of thermal evolution degree of shale organic matter,relative height relationship of structures and fracture development characteristics on shale gas enrichment is conducive to improving the evaluation criteria of deep shale gas,is of great practical significance for recognizing resource potential and selecting favorable areas of deep shale gas,and provides a theoretical support for promoting the large-scale reserve increase and benefit development of deep shale gas.
万方数据
维普
