摘要：The acid gas reservoir is common in marine sedimentation,which usually encounters acid gas invasion and overflow.A numerical model considering transient complex wellbore flow and heat exchange was established in the study for acid gas invasion with high CO2 concentration.This can be used to achieve the accurate prediction and therefore facilitate the better control of transient wellbore influx during the acid gas invasion.Using the established model and the collected oilfield parameters,the wellbore transient flow characteristics of acid gas-drilling fluid was further investigated.The results show a higher dissolved concentration of invaded gas containing CO2 than CH4 in drilling fluid,which makes it difficult to detect acid gas invasion with high CO2 concentration at an early stage.When the mixed fluids reach the wellhead,the dissolved quantity and density of acid gas with high CO2 concentration rapidly decrease.This leads to a rapid drop in annular pressure which could readily induce complicated drilling hazards.C02 transforms from supercritical or liquid to gas near the ground within the annulus.In this process,CO2 density slowly decreases before phase transition of CO2 and drops drastically as annular pressure drops to critical point.The fluid flow mixed with CO2 changes from a single-phase flow to a two-phase flow at the phase transition point in the upward flow annulus.Furthermore,this paper shows the characterizations of the variation of annular pressure and temperature,density and dissolution of invaded fluid,void fraction of free gas,kick time in response to acid gas mixed with varying CO2.
关键词：Acid gas with high CO2 concentration;formation liquid influx;transient flow;heat transfer;phase transition of CO2;well control
