Investigation of gas carryover with a downward liquid flow

An investigation into gas carryover resulting from the downward flow of water was conducted. Water accumulation in a gas well is responsible for well-productivity decline and left untreated will eventually result in the well loading up and ceasing to produce. Submersible pumps offer a viable means of removing water from the well; however, gas interference can significantly degrade pump performance and even result in pump failure. An effective means of mitigating this problem is to place the pump below the producing interval, effectively allowing gravity to separate the gas and water. The rule of thumb (in this instance) is to limit the downward liquid velocity to values less than 0.5 ft/sec to ensure gas/water separation. High steel prices dictate smaller casing strings be used where possible to enhance project economics in operations such as coalbed methane. However, smaller pipe sizes result in higher flow velocities for a corresponding surface flow rate. These higher flow velocities reduce separation efficiency, which could jeopardize project success. To quantify the relationship between gas-carryover and liquid velocity, a full-scale model was built and actual gas carryover rates were measured. Two sizes of annular flow geometries representative of those used in the field were used in the test. The results were also confirmed with separate measurements taken from a test-well facility. These studies show the traditional rule-of-thumb value of 0.5 ft/sec to be conservative. Multiphase-flow pattern maps also were integrated into the study as a supplemental aid to the development of operation guidelines and to add insight into operational practices of submersible pumps As a result of this work, smaller casing sizes were successfully used resulting in substantial project cost savings.