Research on Low Shear Rheological Properties of Annulus Drilling Fluid For Cementing in Kuqa Piedmont

Abstract

Aiming at the frequent leakage of cementing casing in the fourth and fifth spuds of ultra deep natural gas wells in Kuqa Piedmont structural belt, Tarim Basin, the actual shear rate of annulus drilling fluid during casing running is analyzed. According to the he Ba rheological model, the test data at full shear rate (1.70–1021.40 s–1) and low shear rate (1.70–340.50 s–1) are used, The total shear and low shear rheological parameters of oil-based drilling fluid are fitted respectively, and the difference of exciting pressure under total shear and low shear rate is analyzed. It is found that the actual drilling fluid shear rate is much lower than the high value of conventional total shear rate of 1021.40 s–1; Under full shear and low shear rate, the rheological parameters vary greatly with temperature and pressure; The casing activation pressure at full shear rate is less than that at low shear rate. With the increase of well depth, the difference between full shear and low shear rate is greater. The results show that for natural gas wells with narrow safety pressure window, the test data should be selected to fit the corresponding rheological parameters according to the actual low shear rate range of drilling fluid, and on this basis, the casing running speed should be reasonably designed according to the allowable casing running exciting pressure, so as to reduce the leakage during casing running.