Overview and prospect of fracture propagation and conductivity characteristics in deep shale gas wells

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There are tremendous shale gas resources in China, however, many of them can’t achieve economical production due to a lower effective stimulated reservoir volume (ESRV). Up to now, very few researches have been conducting on the mechanisms of fracture propagation and conductivity, which are the two main controlling factors of the effective development of shale gas play. As we all know that with the increasing depth of shale gas wells, many parameters such as in-situ stress, stress difference between minimal horizontal stress and maximal one, rock mechanics, etc. are all changed a simultaneously, which results in different fracture propagation and conductivity mechanisms. Therefore, firstly, a comprehensive analysis on fracture propagation and its conductivity characteristics in shallow wells were conducted. The mechanism of single fracture propagation and multiple fractures’ propagation simultaneously in open hole wells were summarized in detail. Besides, the effect of casing completion and fracturing treatment parameters on single fracture initiation and propagation was analyzed, and the corresponding results for multiple fractures may take references to that in open hole wells. Based on above studies, the mechanism of conductivity of single fracture and complex one in the condition of multiple affecting factors were analyzed too. After that, the proppant transport pattern within the complex fracture and its transportation law in divergent fracture were simulated, which may be used to optimize treatment parameters of hydraulically fracturing and achieve the object of expected conductivity and maximal ESRV. Finally, according to the formation geologic characteristics of deep shale gas play, the future research tendency was indicated, such as the mechanism of fracture propagation in the mode of well pad with multiple horizontal wells and multiple clusters, and in the condition of mixed natural fractures pattern with both horizontal interface and high angle fractures, the mechanism of high conductivity of network fracture formed by rock self-supported, which has great significance for developing deep shale gas play economically and effectively.