Study On Predominant Factors And Lost Circulation Control Measurements During Well Killing And Workover Operations Of Carbonate Gas Wells In Changqing

Carbonate gas reservoirs usually have prominent structural features such as natural fractures and karst caves,and the formation leakage channel is complex,resulting in serious leakage in well killing links,which requires temporary plugging.At present,the main control factors of carbonate gas well leakage are unknown,the evaluation method of well killing leakage degree is blank,and the selection of well killing leakage control countermeasures lacks sufficient theoretical basis,resulting in low success rate of well killing and increased production cost.Therefore,Changqing carbonate gas reservoir is selected as the research object,and the multiple regression algorithm is introduced.Taking the increase of pump pressure of wellhead fluid during well killing as the objective function to characterize the leakage,and taking 74 geological and engineering parameters of 59 carbonate gas wells that have been successfully killed as independent variables,the main control factors of well killing leakage are clarified,and the relationship between the increase of pump pressure and each main control factor is clarified;Based on the law of well killing leakage,the requirements of well killing fluid performance and construction technology are formulated by analyzing the engineering main control factors of carbonate gas wells,and the leakage control requirements obtained from the law of well killing leakage are verified by field tests and laboratory experiments;Based on the main control equation of leakage,the classification method of leakage degree of carbonate gas well is established.At the same time,the leakage control effect is evaluated in combination with the increase of pump pressure,and then the control countermeasures of well killing leakage in carbonate gas reservoir are formed and applied in the field.The multiple regression model obtains 10 main control factors of kill loss,of which6 are geological main control factors including permeability,porosity,reservoir thickness,reservoir depth,initial gas saturation and formation pressure before kill,4 are engineering main control factors including viscosity of temporary plugging system,injection capacity of kill fluid pump,consumption of temporary plugging system and solid addition of system,and the correction determination coefficient R~2 of the model is 65.8%.The regression results show that the higher the degree of leakage,the smaller the increase of pump pressure under the condition of consistent kill system performance and process.The indoor experiment verified the correctness of the leakage control demand analyzed by the main control factors.On site,gel particles were selected for temporary plugging of wells S-1X and S-2X.According to the main control factors,the pump pressure increases were calculated to be 4.07Mpa and 3.66Mpa respectively.The actual pump pressure increases in killing operation were 5.0Mpa and 3.0MPa,with an error of more than 30%.After the temporary plugging,the leakage rate of clean water decreased by more than 90%,and the temporary plugging was successfully achieved.The research shows that the multiple regression algorithm studies the factors and laws of well killing and workover leakage in carbonate gas reservoirs,puts forward the evaluation method of leakage degree,provides a theoretical basis for the selection of well killing leakage control countermeasures,improves the matching degree and pertinence of the formulation of single well leakage control scheme,and provides direction guidance for the research of solving similar complex engineering problems.