Dynamic Simulation Study Of Gas-Liquid Two-Phase Flow For Underbalanced Drilling

Gas-liquid two-phase flow for under-balanced drilling has some advantages, such as protecting low-pressure reservoir, having high-capability of carrying cuttings, preventing and removing leakage, high rate of penetraion, little formation damage etc.Under-balanced drilling is a complex dynamic procedure, because of the existence of negative pressure difference. Formation fluid continuously invades borehole during drilling, leading to pressure change in borehole, and this makes very big impact on the subsequent production and testing.This paper researches gas liquid two-phase flow for under-balanced drilling, on the base of study on gas-liquid two-phase flow pattern, this paper analyzes under-balanced drilling gas liquid two-phase steady-state and dynamic flow model based on the continuity equation, momentum equation and energy equation. According to the steady-state flow regular pattern, to analysis H-K hydrodynamic model, to collate pressure calculation model of under-balanced drilling steady-state design. This also analyzes the dynamics fluid flow of formation fluid, studies the impact on bottom hole pressure while fluid invasion in the under-balanced drilling process. At the same time, combined with operational procedures of under-balanced drilling conditions, to analyze effect law of bottom pressure caused by making a connection, making a trip and throttling valve opening, and establish simulation software of dynamic operational mode on the basis of the affect law and combining design model of steady-state. This can simulate the impact rule of bottom pressure caused by dynamic operational mode, according to the changes of rules we can judge whether it can meet the requirements of under-balanced drilling, and adjust to parameters of steady-state design timely. In order to ensure under-balanced drilling operations, these research results provide a theoretical basis of designing and practicing.