The Optimization of Casing Programs for Horizontal Wells in the Fuling Shale Gas Field

Due to the large size of conductors and boreholes in the first drilling section in the Fuling Shale Gas Field,the horizontal wells had issues such as low ROP,severe sidewall collapse during the first drilling section,and borehole instability during the second drilling section.Accordingly,the sealing points of casing were determined based on analyzing drilling engineering and geologic features of Fuling Area,based on the William drilling-speed equation,sizes of conductors and borehole of the first drilling section were reduced,the set depth of surface casing was withdrawn upward from the Changxing Formation to the top of Feixianguan Formation,and in the second drilling section,set the depth of intermediate casing was changed from 3.00-5.00 m into the turbidite sandstone to 50.00-100.00 m into the Longmaxi Formation.The optimized casing program has been applied to horizontal wells in the Fuling shale gas since late 2014,as a result,the ROP of the horizontal wells got higher,and drilling cycle was shorted.Compared with the 30 horizontal wells drilled in 2013,the average ROP of 105 horizontal wells drilled in 2015 was improved by 65.74%,and the average drilling cycle was shorted by 20.95% while the average well depth increased,which showed the optimization of the casing program effectively enhanced ROP,reduced the downhole complication and a shortened drilling cycle.