In unconventional shale plays, the production profile varies dramatically within an extremely short period of time. Wells often produce at extremely high rates when initially completed and deplete rapidly before reaching production plateaus. This rapidly changing production profile presents a significant challenge to engineers designing artificial lift systems. Because of the method's flexibility and tolerance to a variety of producing conditions, gas lift has become a popular artificial lift choice in these wells. To achieve optimal system performance, engineers often design gas lift installations to produce up the casing early in the well's life. This configuration minimizes pressure losses in the production string, enabling deep injection, improved drawdown, and higher flow rates. As the wells deplete and the production rates decline, the wells must be converted to tubing flow to ensure well stability. As the wells further deplete, they are often converted to intermittent gas lift. Unfortunately, it is not feasible to produce wells with tubing flow gas lift or intermittent gas lift with the typical downhole equipment configuration used in annulus flow wells. Therefore, transitioning to these late-life artificial lift configurations has required a workover rig. A novel downhole equipment configuration was developed to eliminate the need for a workover rig when transitioning from annulus flow to tubing flow gas lift. Side-pocket mandrels with a special pocket porting configuration were selected to enable annulus flow with enhanced gas passage early in the well's life. To transition from annulus flow to tubing flow, the slickline-retrievable valves were pulled and replaced with reverse-flow gas lift valves. A field trial was conducted to demonstrate and test this completion concept. While more investigation is required to justify full field implementation, the initial results have been promising. This project demonstrated that it is feasible to produce wells in annulus flow, tubing flow, and even intermittent gas lift with a single completion using readily available, off-the-shelf artificial lift equipment.
This paper highlights a pilot project in which chamber gas lift was installed in two unconventional horizontal wells. Chamber gas lift, as a combination of deep gas lift and intermittent gas lift, allows for an efficient, closed completion with cyclic injection of high-pressure gas, which expands and rapidly displaces fluid at high velocity from deep in the well. Development of the system was a collaboration internally and in conjunction with the vendor to install what was historically a vertical well assembly through the curve section and into a horizontal wellbore. The chamber assembly was successfully designed, sourced, manufactured, installed, and operated. To modify the design from vertical to horizontal applications, components were custom-designed to maintain a sealed chamber. Components deemed most likely to fail are replaceable by slickline intervention. Results indicate a sustained lower downhole pressure than the previous intermittent gas lift system, an increase in production, and good chamber-sweep efficiency.
Summary In this paper we highlight a pilot project in which chamber gas lift was installed in two unconventional horizontal wells. Chamber gas lift, a combination of deep gas lift and intermittent gas lift, allows for an efficient, closed completion with the cyclic injection of high-pressure gas, which expands and rapidly displaces fluid at high velocity from deep in the well. Development of the system was a collaboration internally and in conjunction with the vendor to install what was historically a vertical-well assembly through the curve section and into a horizontal wellbore. The chamber assembly was successfully designed, sourced, manufactured, installed, and operated. To modify the design from vertical to horizontal applications, components were custom-designed to maintain a sealed chamber. Components deemed most likely to fail are replaceable by slickline intervention. Results indicate a sustained lower downhole pressure than the previous intermittent-gas-lift system, an increase in production, and a good chamber-sweep efficiency.
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