Research On Wellbore Pressure Simulation And Control Technology In Deep High Pressure Gas Well Gas Intrusion

The characteristic on deep marine gas fields mainly is complex fracture type carbonate reservoir that with high pressure in China. Because most of the deep gas reservoirs are narrow safety pressure window, this is a challenge to the well control. Now the well-control technology needs shut-in immediately after overflow.That leads to the bottomhole pressure dramatic increase which will cause blowout. The conventional well-control technology needs shut the well to compute bottom-hole pressure. The precise wellbore flow model is not only the premise to control the wellbore pressure, but also the key for safe and efficient drilling. The theory of multi-phase flow in wellbore is an important part of the well-control technology. Based on the theory of multi-phase flow in annulus, a method for the HTHP (High temperature high pressure) well when a gas kick happened has been put forward. In the thesis,the research mainly focuses on the following aspects:A model of gas rising in the drilling mud was established. By dimensional analysis, considering the comprehensive properties of fluid and bubble characteristic, a correlation for CD in non-Newtonian fluid was proposed based on the Buckingham Pi theorem. The new correlation is at better agreement with the experimental results thean conventional approaches.A physical model and unsteady model during circulation, circulation-stop and gas kick were established for predicting the temperature distributions of drilling fluids inside the drilling string and in annulus.Based on dynamic wellbore temperature profile, drilling fluid density change with temperature and pressure were analyzed, equivalent static drilling fluid density model which can accurately describe equivalent static density along the wellbore was built. Hydrostatic column pressure calculation model was corrected, which enhanced wellbore pressure prediction accuracy.Based on the theory of multi-phase flow in annulus, building a well control method which needn’t shut the well to simulate the gas kicking and compute the bottombole pressure. Using this method to kill, the invased gas and wellhead back pressure were lower than those of conventional well killing methods.Writing software program with VB language to create back pressure calculation, which is used to analyze the two-phase flowing law and pattern in annular and to simulate the gas-kicking course calculating the back pressure during the course of reservoir exposure area increasing. The wellbore temperature distribution, annular two-phase flow distribution and pressure can be calculated.