Simulation of the Influence of Fracture Gas State on Gas-Liquid Replacement Based on Fluent Two-Phase Flow

Abstract

Aiming at the hazards caused by drilling into fractured formations during oil drilling, linear prediction of physical properties of CO₂/H₂S under different well depths are carried out, based on Fluent to simulate gas-liquid placement in near-critical, critical and supercritical states of gas. The results show that when the well depth is small, the CO₂/H₂S near-critical state and the initial bottom hole pressure of the critical state invading the annulus are lower than the formation pressure, and the gas invading the annulus is suspended in the annulus until the hydrostatic pressure of the missing drilling fluid is supplemented for about 1s and 1.2 s respectively, the formation pressure can be balanced before the upward return can be continued; the bottom hole pressure of the supercritical state invades the annulus rapidly drops within 2 s; the gas-liquid replacement rate in the supercritical state is slower than that in the non-supercritical state, with a difference of 60-80 s. During the drilling process, it can be judged according to the bottom hole pressure change whether it has encountered a fractured formation and the state of the gas contained, and well control measures should be taken in time.