Controls on the productivity of shale gas wells in complex structure areas and optimizing well locations:An example from southern Yongchuan gasfield,Sichuan Basin
The productivity in southern Yongchuan gasfield was evaluated in an effort to sustain the efficient development in complex structure areas.Based on this evaluation,some controls of geological,drilling and fracturing parameters on this productivity were assessed quantitatively by means of single factor analysis and gray correlation.In addition,the optimized well locations in such areas were pointed out.Results show that(ⅰ)the study area is characterized by huge variations in burial depth,well-developed faults and fractures,and complicated in-situ stress,bringing about great challenges in its de-velopment.Because of strong heterogeneity,this productivity varies intensely in different wells and is controlled by a vari-ety of factors;and(ⅱ)as for the development of shale gas in the complex structure areas,it is unavailable to keep parallel to faults or give up an included angle with in-situ stress.The closer one gas well is to major faults,the poorer the produc-tivity is.Better productivity can be gained while penetrating through minor faults.In conclusion,the productivity of shale gas wells in the complex structure areas is mainly influenced by drilling length in high-quality reservoirs,faults,sand-frac-turing intensity,cluster spacing,and wellbore trajectory and azimuth.What's more,it is suggested to adopt the horizontal-well optimization deployment of"long horizontal interval,shallow burial depth,large included angle,and staying away ma-jor faults but penetrating through minor ones",namely selecting shallow reservoirs above 3,800 m in depth,ensuring the drilling length over 1,500 m in quality reservoirs,holding the included angle between horizontal-well azimuth and maxi-mum principal stress more than 60o,keeping away from level-A major faults while the penetrated minor faults below level C.
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