Drilling technology of ultra-deep ultra-long shale gas horizontal wells in Dazu, West Chongqing

To deal with the technical challenges faced by the ultra-deep ultra-long shale gas horizontal drilling in the Dazu block of West Chongqing, such as high difficulty in well trajectory control, intensive drill vibration, and high downhole temperature, the reservoir selection for the horizontal well platinum target was optimized, the box range of the horizontal well was set as 5-8 m above the base of the Wufeng Formation, and the profile was designed in accordance with the fault dip angle. The casing program was improved to isolate layers prone to lost circulation or collapse. Moreover, the ATC rotary steerable system with high build-up rates, together with formation-adapted bits, was adopted to reduce difficulties in trajectory control and improve the penetration rate. The bottomhole assembly and drilling parameters were optimized in an interval-wise manner and the oil-based drilling fluid system was selected, in an attempt to ensure well stability and reduce drilling risks. At last, the slow-slacking approach was used to reduce the drill string vibration and extra cooling was deployed for drilling fluid circulation to deal with high formation temperature. Field applications of these techniques help to complete well construction of multiple ultra-deep ultra-long horizontal wells in this block and accumulate operation experience for ultra-deep ultra-long shale gas horizontal drilling. The key technology for ultra-deep ultra-long shale gas horizontal drilling in the Dazu block of West Chongqing has been formed.