Controlling Mud Losses into Deep Surface Formations of the Strike-Slip Fault Zone in the Tianhuan Depression in Ordos Basin

In recent years, with the increase of high-yield industrial gas flow wells in the Qingshimao area, this area has The Qingshimao block in recent years has become a high gas production area and will be the next important exploration block in Changqing Oilfield. Geologically the Qingshimao block belongs to the Tianhuan depression in Erdos Basin, with more and more deep exploratory wells drilled in recent years, lost circulation, especially severe mud losses in deep surface section of a well, has been more frequently encountered during drilling. The severe lost circulation is mainly encountered in the Quaternary System in which formation waters are very active, and conventional techniques for controlling the lost circulation are rarely effective. The Luohandong formation, on the other hand, has long section of continuously fractured formation, and the lost circulation is frequently encountered and the treatment is time-consuming. In dealing with mud losses in shallower water-bearing formations, a lost circulation slurry that expands when in contact with water is used to control mud losses. Large particles that can control the rate of mud losses have been developed and used to ensure one trip of drilling through the whole length of fractures. When drilling into stable formations, cementable lost circulation slurries with wide particle size distribution can be used to plug and seal off the long section of fractured formations. These practices have formed a special technology for controlling mud losses encountered in drilling the deep surface hole in the strike-slip fault zone in the Tianhuan depression in Erdos Basin. This technology has been successfully used in the Qingshimao block, and several wells with deep surface holes have been successfully drilled.