The Study On The Operation Condition Diagnosis And Troubleshooting Of Gas-Lift Wells

The gas lift production technology as one of the main artificial lift methods is used for resume production when the nature flowing stop. It is an energy supplement way for nature flowing. The gas lift technology is adaptable which is widely used in high gas oil ration reservoir production. The production efficiency of gas lift well is significance for efficient oilfield development. The gas lift well production efficiency depends on the analysis and troubleshooting of gas-lift well. As the consequence, studying on the operation condition diagnosis and troubleshooting of gas-Lift Well is significance.In the process of gas lift well production, the condition of design injection point transforms、the possible hole or the casing-tubing communication、the gas lift valve opening and closing abnormal or the wellhead choke limiting productivity will occur when the water cut arises、the fluid supply capacity variation、the gas injection pressure fluctuation and the multiphase flow pattern transformation. It is better to determine the gas injection point location when the gas lift well is production. It helps to guide and adjust the working system of oil wells that is critical for gas lift oilfield efficient development. The key parameters which are the production pressure data are analyzed for the gas lift operation condition. It includes the tubing head pressure、casing head pressure、the production tubing pressure line along the wellbore、the injection pressure line、the test rack opening and closing pressure for gas lift valve and the well bottom hole flowing pressure. Combining with the production pressure data and the theory of gas lift knowledge can be analyzed and diagnosed to the gas lift wells. The domestic and foreign literature that is regarding to the qualitative and quantitative diagnosis analysis and troubleshooting method is summarized in this paper. After mastering the qualitative method of gas lift operation condition diagnosis, the quantitative technique of gas lift operation condition diagnosis was focused on studying. The quantitative basic technique for the gas lift operation condition diagnosis is the mathematical simulation model that is to build the production pressure model for tubing、 injection pressure model for casing and the temperature distribution model for down hole. All gas lift valves status are judged and the gas flow rate through the gas lift valve are calculated depending on combining the down hole gas lift valve parameters such as the size of all valve、the test rack closing pressure and opening pressure with the above three models. The complexity of the diagnostic process stems from the fact that a considerable number of possibilities can take place in a normal operation of a well on gas lift and ever-present uncertainties of the quality of the data needed for the calculation. Besides, based on the research thought of foreign scholars this paper introduces the concept of fuzzy logic. The fuzzy control system can be obtained satisfactory results for a rough mathematical model. This paper describes the most important principles underlying a gas lift trouble shoot analysis and how it can be integrated using fuzzy logic to hand the complexity of the lifting process and the uncertainties of the data. The model of fuzzy logic trouble analysis for gas lift well is established to determine which one is the operation gas lift valve. This article main research contents include:1) The key section for mathematical simulation diagnosis model and fuzzy logic trouble analysis model is the calculation of multiphase pressure and temperature. Hence, collecting the current epidemic multiphase pipe flow pressure and temperature calculation methods from domestic and foreign survey literature. These calculation methods include the vertical well and inclined well pressure model、empirical and semi-empirical temperature model. The adaptive to these different multiphase pipe models is also studied.2)The mathematical simulation basic model for gas lift troubleshooting is improved then the mathematical simulation models for two cases of the multi-point gas injection and the unknown production is put forward. The two improved models are verified feasible by actual wells in a domestic oilfield.3) The fuzzy logic for gas lift trouble shoot analysis is established creatively by combining the knowledge and experience of gas lift with the fuzzy logic theory. The fuzzy logic system completes the trouble shoot process including three steps which are fuzzificationn、fuzzy processing and defuzzification for the key object parameters. The objective of fuzzy logic system in this paper is to determine which one, of all possible points of injection,is the one that most closely fits current production conditions. The fuzzy logic model is verified feasible by an actual well in a domestic oilfield.4)The number of possible operation conditions that can take place in a gas lift oil well are analyzed as well as the reason and troubleshooting methods for common failure is summarized.