Study on borehole stability in Miquan Area at Piedmont Tectonic Zone of Junggar Basin Southern Margin

The stratum of piedmont tectonic zone of Junggar Basin southern margin is rather fragmentized and not stable because of tectonic movement, and it includes large section of highly water sensitive mudstone and coal bed, so the wellbore is easily washed out and collapsed during the process of drilling operation. Based on the drilling data and rock debris collected at Miquan Well 1, the geological characteristics of easily collapsed and hydrated stratum are analyzed, and the software to calculate three pressure profiles is coded. the formate and zwitterion drilling fluid are studied comparatively. The results of indoor test and filed application show that the formate drilling fluid can resist mud-making, stabilize wellbore, prevent sticking by lubricating wellbore, and prevent the pollution of clay, and has a good rheological property, so it meets the requirements of drilling operation at the piedmont tectonic zone of Junggar Basin southern margin.