Using Dynamic Simulation to Assess Effectiveness of Downhole Pump for Gas Well Deliquification

摘要

Reservoir pressure depletion in gas reservoirs causes gas flow reduction with time and eventually leads to liquid loading as the gas flow up the well can no longer efficiently lift the associated liquids to surface. Liquid loading has a detrimental impact on production and a suitable deliquification method is required to continue production and maximize recovery. A downhole pump is one such deliquification measure where the pump sits at the bottom of the producing interval and evacuates the accumulated liquids up an insert (coiled tubing) string. It is important to assess beforehand whether the pump will effectively remove the liquids and hence deliver sufficient business value. A transient multiphase simulator has been used to simulate the gas well liquid loading process in a candidate well completed with 5.5” tubing, followed by the deliquification process triggered by a downhole pump installed 20 m above the bottom of the producing interval on a 1.5” coiled tubing. Simulations have been conducted for seven different liquid pump rates, three reservoir pressures and two water-to-gas ratios to assess the effectiveness of the pump under different operating conditions and to arrive at the optimum pump size and operation methodology. Simulations indicate that the downhole pump is capable of deliquifying the well and restoring production. However, for a given pump capacity and reservoir pressure, the surface gas production may either oscillate or settle at a steady state value. Oscillations occur when the pump capacity is too high and causes gas ingress into the pump, which introduces partial albeit temporary liquid loading of the wellbore. Continuous steady state gas production occurs when the pump capacity is not too high and an equilibrium situation is reached between the liquid being pumped out and the liquid being produced. The optimum pump rate is controlled by the effectiveness of the downhole separation between the gas and liquid phases and will minimize oscillating ingress of gas into the pump. This study emphasizes the role of transient simulations in predicting the effectiveness of a deliquification measure before embarking on field deployment. The simulations provide valuable insight into flow and pressure transients inside the wellbore during a gas well deliquification using a downhole pump. The information retrieved from the transient simulations is used to decide the optimum pump capacity and operation guidelines. To the best of authors’ knowledge, this is the first time that a transient simulation of a downhole pump for gas well deliquification is presented in open literature.