Study Of Wellbore Pressure Fine Control In Managed Pressure Drilling Technology

Western Sichuan region is rich in natural gas resources, but recently a number of deepwells drilled in the area appear more underground complex and engineering accidents, bringserious impact on the region’s oil and gas exploration and development process. The mainreason is the Xujiahe Formation is not only hard, grinding, drilling speed is low, and there areseveral sets of pressure systems, the mud safety density window is narrow, mud loss, stickingand other complex, greatly increasing the non-productive working time. The MPD technologyresearch has been carried out in western Sichuan, in order to solve the above problems, andprovide support for the effective development of gas reservoirs in Sichuan Basin.Single-phase flow hydraulic model. The Newton, Bingham, Power-law, Casson and H-BModels have been evaluated based on theoretical analysis and actual data,and concluded thatH-B model is the most suitable for drilling fluid, which can accurately characterize thedrilling fluid. And pressure drop calculation models were listed. The example shows that thepressure drop formula calculation accuracy can meet the demand for engineering applications.Influencing Factors on the annulus pressure. Modified according to the actual situationon the existing wellbore temperature field calculation model examples show that the averagecalculated temperature value and measuring values on certain points are quite close, theaverage offset is less than1°C, the maximum error does not exceed3°C. Analysis of theinfluence of the temperature and pressure on the drilling fluid parameters, the formula givesthe viscosity and density of the drilling fluid, as with the temperature and pressure changes.Established sudden expansion, sudden contraction flow analytical model and its influencewere analyzed under different Reynolds numbers. The other factors were considered whichaffect the wellbore pressure, including drill string rotation, eccentric annulus, downholeequipment and annular cuttings.Two-phase flow hydraulic model. Based on Wellbore Multiphase Flow decision formulasand and flow pattern identification chart, combined with the wellbore data of Sichuan region,established the Sichuan area multiphase flow diagrams. Combined with the reservoir seepageflow model, considering the gas-liquid two-phase flow characteristics, we made a mathematical model of two-phase flow. According to the Taylor method, discrete derivationwere carried out to the mathematical model of the two-phase flow, using the finite differencemethod. An example were taken to authenticate the calculation model of the multiphase flowin the wellbore after gas invasion, the calculation result is better able to meet the actualdrilling data, generally the error is less than5%. Bottomhole pressure sensitivity underdifferent back pressure, flow rate, mud weight, and the inclination of multiphase flow wereanalysed.Wellbore pressure control technology. Based on the basic principles of the bottomholepressure control, gives the corresponding MPD key parameters design method. In order toimprove control precision, on the basis of the analysis of the conventional control method, thestate-of-the-art model predictive control method was introduced to MPD bottomhole pressurecontrol system in real time, an advanced bottom hole pressure real-time control model wasestablished. The case study shows that when the conventional control method is difficult tomaintain the balance of bottom-hole pressure as gas invades into the wellbore, the predictivemodel control method can quickly and accurately establish the balance by controlling thewellhead pressure.On the basis of theoretical analysis, combined with the geological conditions of thewestern Sichuan region, the MPD equipment was equipped and the computation and controlsoftware system was developed, and field test was carried out in Mapeng23-6HF well. Theresults show that, the drilling pressure monitoring system is accurate, reliable, and thepressure control is quick with high precision. The system can control the casing pressure todesignated value within30s, and the pressure error is less than0.1MPa.Through research and field test, a set of MPD equipment and technology for theformation of western Sichuan region was formed, which can solve many drilling problems,and provided technical support for the effective development of the western Sichuan regiongas reservoirs.