Gas Well Liquid Loading From the Power Perspective

Abstract

Summary This paper introduces a new systematic way to evaluate gas well deliquification options throughout the life of a well by using power as the most general measure of cost. As a gas well depletes, the gas velocity declines to the point that liquid droplets are not removed from the wellbore. Liquids accumulate and impose increased pressure on the sandface. To maintain production, we apply artificial lift. In some cases, such as plungers or foamers, we make better use of the remaining reservoir energy. In other cases, we apply external energy using methods such as gas lift or pumps. Improving gas well recovery by removing wellbore liquids accumulation is of interest to industry in two general ways. First, there is the perennial question of how to select deliquification techniques for the entire life of the well. This paper provides a framework to compare the relative merits of various artificial lift systems through final depletion. Furthermore, stakeholders are demanding more substantial bases for booked reserves, and with more development this method offers a defensible estimation of the economic limit with respect to liquids accumulation that honors the depth, productivity, and completion characteristics of a particular well. To understand the appropriate application of artificial lift power, we proceeded in two stages. First, we modeled a synthetic two-phase gas well including the liquid-loading behavior. The model produced the familiar result of natural flow in early production followed by lower production as the well declines and liquids accumulate. Next, we compared using the well's energy (i.e., siphon or velocity tubing strings) to the addition of external energy (i.e., gas-lift injection and downhole pumps) to optimize production at every stage of the depletion. We used the theoretical external power as a proxy for well operating cost to calculate the economic limit. Ultimate recovery was improved by the addition of external energy. In particular, pumping was found to be favored over gas lift, because it provided lower bottomhole pressures and required less power, thereby yielding higher production at any point in time along with a lower economic limit rate.