Discussion on the Mud Loss and Borehole Wall Collapse Prevention in Horizontal Drilling in Sulige Gas Field

Borehole stabilization previously in horizontal drilling in Sulige gas field has been realized through increase in mud weight. Presently, the development of the Sulige gas field has entered a new stage of overall development in which formation pressure has been depleted because of gas production. Mud losses caused by high density and difficulties in controlling severe mud losses often led to inability to exert WOB and differential pressure pipe sticking. To prevent mud losses caused by high mud weight, several things have to be done, for example, improve the sealing and plugging performance of the drilling fluid, maintain the inhibitive capacity and activity of the mud filtrates, reduce the ECD to a certain level, and improve the mud rheology and use good engineering practices. The types of the mudstones commonly found in the horizontal section are analyzed, and requirements on drilling fluid studied. Measures for controlling mud losses are discussed. It is presented that to prevent borehole wall collapse, the important thing is to avoid mud losses. If sandstones are drilled in the horizontal section, or, if the mudstones encountered in the horizontal section is stable, mud weigh and flow rate can be reasonably reduced. Mud losses in the horizontal section are generally losses caused by differential pressures, and squeezing LCM slurries may induce new fractures in the formations, hence aggravating mud losses even into adjacent wells. For different formation lithology, such as argillaceous sandstone, sandy mudstone, gray mudstone and carbonaceous mudstone, different mud properties shall be adopted.