Application of double-loop three-control method in the intelligentproduction of CBM wells

At present, the production of CBM wells is mainly controlled manually. Once gas wells cannot be controlled in time at the initial stage of water and gas production, stress closing, slack coal plugging, formation gas locking and other damages may occur, and consequently, the production of gas wells will be influenced. In this paper, a production control strategy of double-loop three-control was worked out to address the challenges, such as long water drainage and gas recovery cycle of CBM wells, difficult control of critical desorption pressure, and great impact of liquid level fluctuation on gas production. This control strategy, with dynamic liquid level control as the core, realized intelligent control on the production of CBM wells at different stages (liquid reduction, desorption and gas production) by way of closed loop controls on both casing pressure and flowing pressure (double-loop) and controls on liquid reduction, flowing pressure and casing pressure (three-control). Based on the theory of double-loop three-control (dominated by the frequency conversion control technology), an intelligent production control device was developed for CBM wells by using modern ARM control technologies. With the device, double closed loop control could be realized on bottom hole flowing pressure and wellhead casing pressure of CBM wells. This method was applied to the 2×108 m3 CBM productivity construction project of PetroChina Huabei Oilfield Company. With this control system, production equipments can realize intelligent adjustment of parameters and safe operation at each production stage, with lower labor cost and production cost. Moreover, this system makes CBM exploration and development more intelligent, more accurate and safer. Therefore, it presents a better prospect of application and dissemination. © 2015, Natural Gas Industry Journal Agency. All right reserved.