Artificial Lift Techbook 2019

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54 | April 2019 | ARTIFICIAL LIFT: CASE STUDIES A s gas wells mature, production tends to fall off, caused by declining natural drive energy from reservoirs. When the natural drive is too low to generate enough gas production at the surface, the well will normally be abandoned due to economic factors. Sometimes even before a gas well reaches its predetermined economic limit, the lower gas production reduces the gas velocity, which in turn decreases the liquid-carrying capability of the gas stream. The low liquid-carrying capacity makes liquids drop out of the gas stream and accumu- late in the well to form a hydraulic column. This is called liquid loading. The hydrostatic pressure of the liquids causes the reservoir pressure to slow down or even stop gas production completely, even- tually resulting in premature abandonment of the gas well. Industry estimates reveal that only about 60% of natural gas from reservoirs is recovered from conventional wells and only about 15% to 20% is recovered from unconventional wells. Existing artificial lift methods for gas wells remove liquids in the vertical sections of the well or reduce the hydrostatic pressure of the liquid column. Current artificial lift technologies, however, cannot remove the liquids completely in both the vertical and horizontal sections of the well or increase reservoir drawdown. Reliable downhole artificial lift To address these challenges, Upwing Energy has developed a practical, robust and cost-effective downhole artificial lift system. The company's new Subsurface Compressor System (SCS) changes the pressure profile along the depth of a gas well (Fig- ure 1). It provides both a suction effect to lower the intake pressure near the producing zones and a boosting effect to increase the discharge pressure downstream of the compressor. The lower downhole flowing pressure increases drawdown, facilitating the flow of gas from the formation into the wellbore to increase production (Figure 2). The higher dis- charge pressure from the compressor will overcome the pressure losses along the pipe and increase the wellhead pressure to flow the gas into the surface gathering system. With both the suction effects and the boosting effects of the subsurface compressor at work, the well can produce gas from the formation under the lowest possible downhole pressures or even close to vacuum, while forcing the produced fluids uphole with enough push. This in effect increases production and delays well abandonment (Figure 3). With the delayed abandonment, the accumulated gas produc- tion from the well, and thus the recovery factor, will be highly improved. The subsurface compressor also reduces liquid loading (Figure 4). With the increased gas produc- tion due to higher drawdown as well as the suction effects of the subsurface compressor, the gas velocities in the wellbore at the intake side of the subsurface compressor will increase tremendously. The higher gas velocities in turn will improve the liquid sweeping capabilities of the well in both the vertical and hori- zontal wellbore. At the intake side of the subsurface compressor, the lower pressure will promote the mass diffusion of the liquid molecules into the high-veloc- ity gas stream. This further increases the liquid sweep- ing capabilities. Thus, both the higher gas velocities and lower pressures in the well will enhance the liquid Downhole artificial lift technologies improve gas production and recovery in liquid-rich gas wells. Adding Value with Downhole Compression By Kuo-Chiang Chen Upwing Energy

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