The shale gas field in Sichuan Basin is located in a complex mountains and hilly areas, and the predrilling and drilling operation are difficult and costly due to well site logistical limitations. Therefore, based on many successful case histories of factory drilling and completion work in the North Amercia, and considering the terrain and the geologic and development characteristics of shale gas reservoirs in the Sichuan Basin, an applicable "factory drilling" model was established. In this case, "factory drilling" involved standardizing predrilling engineering, optimizing design of exploration and drilling operations, streamlining engineering, launching an assembly-line drilling operation, establishing a comprehensive utilization of resources and uniform and integrated crew management as its foundation. The standardization of predrilling engineering contained well patterns arrangement and well site deployment, well patterns adopted cluster well with single or double row, 8 wells at the most in a single well pad and the maximum distance between wells is 600m. The drilling engineering optimization design included well trajectory design and interwell anti-collision calculation, the extending direction of the horizontal section was orientation of the maximal horizontal principal stress. The engineering module included the PDC bit selection, drilling methods and matched technical modules. Assembly-line drilling operation involves batch drilling in the same section and reclaiming the waste drilling fluid according to the situation. The field test results indicated that factory drilling could help increase rig operation efficiency, shorten well construction cycle, improve the comprehensive utilization rate of resources, and reduce the waste fluid discharge in the working areas. In WeiYuan shale gas district, there was a sharp decrease in the average well construction period, from original 149d (well W201H3) to the present 72d (well W204H1-3), the corresponding ROP improved from 2.67m/h to 8.35 m/h, and recycling rate of drilling fluid are reached 70%. This study provided a new idea and a reliable technological means to achieve the high-efficiency and low-cost exploitation of unconventional natural gas resources.

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