Abstract

Water drive reduces gas recovery though the mechanism of water coning that results in liquid loading and killing the wells. Installation at a Downhole Gas Water Separator (DGWS) in the well may prevent the liquid loading. The paper presents another solution to this problem - a dual-completed well with downhole water sink (DWS) drainage and injection installation. DWS wells are different from the DGWS wells by inclusion of a second bottom completion that controls water outside the well and prevents commingled inflow of gas and water to the top completion. The wells have been successfully tested in oil reservoirs.

The study qualifies DWS concept for gas wells by comparing simulated performances of a conventional well, and a DWS well. The simulation runs were made over a broad range of the initial reservoir pressure and permeability values for a gas reservoir with large associated aquifer. Also included is a comparison between DGWS and DWS wells for selected conditions.

The results show considerable advantage of dual completion over conventional wells in low-pressure (subnormal) tight (1 md) reservoirs - a 2.6 - fold recovery increase before killing the well with water. The advantage, however, reduces to 10% for reservoir with normal pore pressure gradient and permeability 10 md. When compared to DGWS wells, the final gas recovery of DWS wells is the same, but DWS produces all the gas 35% sooner than DGWS. The study also identified the best DWS completion design where the top completion is used only for gas production, and the bottom completion for inverse gas coning, gravity separation and water injection.

Introduction

Water production reduces gas recovery by shortening the well's life. Water loads up the gas well killing it when a lot of gas remains in the reservoir.

Various concepts and techniques have been used to solve water-loading problems in gas well. Hutlas and Granberry(1)discussed the techniques used to remove produced water from gas wells in Kansas, Northwestern Oklahoma and the Texas Panhandle. They discussed pumping units, liquid diverters, gas lift, and a concentric dual-tubing string. They concluded that the best devices for removing liquid from gas well are: pumping units -for shallow field having very low permeability, and the combination of liquid-diverter and gas-lift installation for deeper, higher-pressure fields.

Libson and Henry(2) discussed mechanism used to eliminate or minimize liquid loading in the tight low-gas rates reservoirs in the Intermediate Shelf area of Southwest Texas. Pumping units, plunger lift, small-ID tubing, soap injection, and flow controllers were the methods mentioned. They concluded that plunger lift and small tubing strings were the most successful means of eliminating liquid loading in wells with low water rates. Pumping units performed best where liquid rate exceeded 10 BWPD.

Stephenson, Rousen and Rosenzweig(3) presented evaluation of different method for dewatering (unloading) gas wells at the Box Church Field - a high water-cut gas reservoir located in Texas. The evaluation includes rod pump, soap sticks, swabbing, coiled tubing/nitrogen, venting, plunger lift, and gas lift. They concluded that gas lift would be the best option for the field.

This content is only available via PDF.
You can access this article if you purchase or spend a download.