Study of Borehole Instability Rule and the Application in Sulige Gas Field

Shale borehole instability problem is the global and universal problem. There are lots of causes of Bore Hole Lost Stability; it included two aspects--------natural aspect and artificial aspect. To solve the borehole instability problem, mud chemic and sandstone mechanics was worked on. Sugeli gas field is one of the main area of Changqing Oil Field, its density limit of drilling fluid is narrow, so we should choose the high precision density limit of drilling fluid to prevent the reservoir damage and drilling accident in the drilling process. Simultaneously, hydration of this area is bad, the wall side is stability when using the water free under balance drilling fluid, once it occur the water it is heavy caving. This paper base on the study of borehole instability rules, use the rules in Sulige Gas Field mud density prediction. The result shows the practice of M-C criterion is the biggest, and then is D-P criterion, the last is the Lade criterion, the lade criterion is first used by this software in our country to predict the borehole stability, and the result of it is reliable.