A modern approach to the selection of sucker rod pumping systems in CBM wells

摘要

A modern methodology is presented for the selection of sucker rod pumping systems in CBM wells. Based on the IPR techniques and fluid flow characteristics in CBM reservoirs, CBM well performance is analyzed to couple the pumping unit performance and CBM production capacity. Then production rates can be reasonably estimated for a given set of conditions. Size of pumping unit, plunger size, polished rod stroke length, pumping speed and rod string taper are chosen as the basic design variables that characterize the pumping system. Each of these variables will influence the efficiency of the system. Water production rate and pump setting depth are the most important factors while developing the optimization criterion. And the pump setting depth for a desired size of pumping unit is determined for any production rate by an iteration algorithm which systematically incorporates the kinematic analysis, CBM well inflow performance and vertical flow effects into the selection process. The loads of polished rod and rod string tapers are also determined by the iteration calculation. An optimization objective function is set up to rate the available pumping modes and it is programmed as a function of the design variables and operational parameters. Then the optimization criterion is proposed to select the appropriate pumping mode from a large number of combinations of pumping system parameters. The criterion is given by its capacity to allow the maximum water production rate, maximum and minimum polished-rod load and gear peak torque under maximum pump setting depth not out of the ratings. And this makes the selection of an appropriate sucker rod pumping system within the limitations of available equipment by a mathematical programming method possible.