Technology for Lost Circulation Control during Well Cementing in Piedmont Wells

Complex formation in the Kuche piedmont structure in Tarim Basin had led to frequent lost circulation, which in turn resulted in poor well cementing job. Factors affecting lost circulation are analyzed, including drilling fluid property, clearance between casing string and borehole wall, running speed of drill string and casing string and pump rate, all factors affecting surge pressure. The clearance between drill string/casing string and borehole wall should not be less than 20 mm. Decrease in the yield point of drilling fluid reduces the surge pressure produced when gel structure of the drilling fluid is broken. A better model is presented for better determination of the running speed of drill string/casing string. A concept of increasing the frequency of pump rate is presented together with the control method. By improving the rheology of the drilling fluid, friction in running drill string/casing string can be reduced. The technology presented in this paper provides a guidance to the lost circulation control design for wells drilled in the piedmont structure in Kuche Country, Xinjiang.