Experimental Study On Downhole Throttling Of Foam Drainage And Gas Production

Downhole choking technology is a key technology to exploiting low-permeability gas field economically and effectively. Development mode of combining downhole choking technology and low pressure gas gathering can reduce ground engineering investment greatly and improve the development efficiency of low-yielding and low permeability gas field effectively. However downhole choking technology in foam drainage wells can result poorly designed gas nozzle size because of unclear understanding of foam choke flow's pressure drop. Gas wells can not drain properly and foam drainage's success rate reduces, so it is an urgent need to establish a relationship of predicting foam choke pressure drop accurately. A correct understanding of the foam choke flow's characteristics is essential to establish foam choke flow model and design nozzle size exactly. Therefore, this article uses theoretical and experimental method, studies foam choke flow behavior deeply, and establishes different concentrations pressure drop model of foam choke flow.Specific work is completed as follows:According to the actual production, physics simulation experimental device of downhole choking vertical gas well is designed and built. This device total height is 6m, flow diameter is 30mm, and nozzle height is 2.5m. At the same time, it is equipped with the appropriate supply equipment and detection system. It can simulate flow state of any point in pipe and provide conditions for air-water two-phase choke flow and foam choke flow experiments.139 groups air-water two-phase choke flow with foam choke flow comparative experiments and 192 groups different concentrations of foam choke flow experiments are carried out by the built experimental devices. The range of experimental test parameters is as follows:nozzle diameters are 2,4,6 and 8 mm, gas flow rates are 10 to 120 m3/h, liquid flow rates are 0.5 to 6 m3/d, foam concentration are 0,0.1,0.3 and 0.5%. Using a digital camera captures the wellbore flow rule change, comparatively analyzing variation rule of the air-water two-phase choke flow and foam choke flow's pattern and critical pressure ratio, studying different concentrations of foam nozzle flow's pressure drop characteristics.In order to design foam flow nozzle diameter accurately, predicte gas well production performance and analyz gas effusion, the predictive ability of choke flow pattern, mass flow rate and pressure before the nozzle of Perkins model, Sachdeva model, Ashford model and Slip numerical model are evaluated using 113 groups critical flow and 79 groups sub-critical flow experimental datas of different concentrations foam choke flow. Result shows that Slip numerical model is better.Model evaluation showes that adding foaming agent changes the gas-liquid slip regulation and increases the choke pressure drop. Slippage factor calculation formula is calculated using experimental datas by considering foam agent concentration and the mass fraction. This calculation formula combining with Slip numerical model improves the accuracy of predicting pressure drop when foam fluid flows through nozzle. At last, it is given a pressure drop model of foam choke flow.A coupled model of predicting pressure and temperature of foam drainage well with a downhole choking technology is established using nodal system analysis and setting choke as nodal point. It gives parameters design method of foam downhole choking technology and analyzes the influence of downhole choking technology to the carrying capacity of wellbore fluid. The nozzle's depth and diameter design of on-site choke gas well-J11P11H are carried out in this article.It is found that experimentally established pressure drop model of foam choke flow considering foam concentration provides a method to design parameters of foam downhole choking technology, improves the downhole choking technology level and gives certain reference value of foam flow study.