Research On Overflow Law And Control Methods During Closed Underbalanced Drilling

Cracked cave-type carbonate reservoirs are pressure-sensitive,prone to problems with overflow and leakage,and containment of acid gases such as H₂S.Once the overflow leaks into the air and the concentration of hydrogen sulfide reaches 20 ppm,we need to stop the operation,which seriously hinders the exploration and development process of the sulfur-bearing carbonate reservoir.Therefore,to solve the drilling problem of sulfur-bearing carbonate reservoirs,it is necessary to study the overflow law of hydrogen sulfide and treat the hydrogen sulfide into the drilling fluid.This paper compares the characteristics of closed and underbalanced drilling technology and system at home and abroad,establishes the mathematical model to calculate the processing capacity of four-phase separator,and puts forward the possible arrangement and improvement direction of domestic closed underbalanced circulation drilling system.Phase separation system solid phase treatment and degassing desulfurization capacity of the lack of capacity,put forward a reasonable practical program.In order to make better use of the pre-closed balance drilling technology,it provides the theoretical basis for the development of the underbalanced technology.This paper mainly studies the following three aspects:?1?This paper study the law and mechanism of gravity displacement of gas containing H₂S,and determine the pressure window of gravity displacement.In the process of establishing the multiphase flow pressure model in the wellbore with H₂S gas overflow,the control equation of the multiphase flow model we adopt is the continuity equation and the momentum equation.In the process of model establishment,we considerate about factors of the temperature,pressure and PH and other factors on the solubility of H₂S,considering the influence of oil layer thickness and other factors on the amount of air invasion.For the auxiliary equations of multiphase flow,focusing on the flow pattern for strict division,for different flow patterns,given different gas rate,flow rate and so on.Based on the data of the field example,the model is calculated and analyzed,and the changes of wellhead drilling fluid flow,wellhead back pressure and bottom-hole pressure under continuous gas invasion were systematically analyzed,which provide theoretical guidance for engineering design of H₂S gas reservoirs with closed circulation pressure controlled drilling.?2?This paper studies the H₂S identification and monitoring method of underground mine,and realizes the monitoring and control of H₂S along the mine to eliminate the hysteresis and potential hazard of the ground monitoring method.Focus on the research of electrochemical method and overflow monitoring based on information transmission drill pipe means,putting forward the suggestion of rationalization for the development of overflow monitoring technology containing H₂S gas.?3?This paper studies the flow law of multiphase flow and the control method of wellhead backpressure when the invasion gas is drained out of the wellbore by closed-loop pressure control.The equipment and flow chart of the pressure and discharge technology are given,and the control method and the law of invasion.The technical equipment configuration and flow chart of the closed loop control system are given to discharge overflow gas.The control method and the law of the overflow gas invasion are studied,and then the variation of the flow regime of the H₂S natural gas and ordinary natural gas at the time of overflow occurred was compared and analyzed and put forward rationalization suggestions for the development of closed-loop pressure control drilling technology.