Numerical Simulation of Effect of Eccentricity on Annulus Pressure of Aerated Drilling

Abstract

Aerated drilling can effectively solve the mud leakage, reservoir pollution and the critical question of the effect of productivity. It also can protect, find and correctly evaluate oil and gas resources. The technology of aerated drilling is applied to detailed exploration and step-out well of oil and gas field of low pressure, this technology has wide applications. Based on the previous researches, the effect of drill string under the condition of eccentricity on annulus pressure is considered in this paper. After in-depth investigations, annulus pressure of concentric and eccentric conditions are analyzed through the CFD numerical simulation, the distribution law of pressure of eccentric annulus along well depth is expounded. The following conclusions can be showed through the CFD numerical simulation: the annulus pressure of aerated drilling follows curve, the pressure decreases gradually from the bottom to wellhead. The pressure does not vary abruptly in the position of changing area of annulus cross-section, the reason is that the gravitational pressure drop plays the leading position in the annulus pressure drop. Liquid is incompressible fluid, although the gas volume is changed, the density of gas is small relative to the density of liquid, so the density of drilling fluid changes little in the variable cross-section. Under the same conditions, the flow pressure drop of eccentric annulus is less than concentric annulus. Key words: Aerated drilling; Concentric annulus; Eccentric annulus; Annulus pressure; CFD numerical simulation