Horizontal Well Gas/Water Shutoff-Field Results

Abstract

Abstract Many horizontal wells have been drilled to control gas or water coning. However, after breakthrough, attempts to control inflow location along these wells have been expensive and frequently unsuccessful in reducing GOR and WOR. Cemented casing, casing with ECPs, open hole packers, selective stimulation and formation plugging agents have all been tried. Husky's experience with slightly inclined wells, over the past several years, suggested a "new" technique, which has recently been proven successful. Simply lowering tubing in a well, slightly inclined from horizontal, resulted in doubling of oil production rate and reducing gas production by 50%. Details of well configuration, field production results and a simple analytical model, explaining why it works, are presented in this paper. Special reservoir conditions which must exist for this technique are also discussed. Introduction One of the most successful applications of horizontal wells has been the reduction of gas or water coning(1–6), while at the same time improving areal drainage(7. 8). However, because of reservoir heterogeneity and pressure gradients across a reservoir, caused by production and injection operations, breakthrough of gas or water often occurs in one small part of a horizontal well. The resulting production of large amounts of gas or water with the oil increases processing cost and depletes reservoir energy. Therefore many attempts have been made to control inflow from along horizontal wells. Cemented casing, casing with ECPS(9), open hole packers(7), selective stimulation(5) and formation plugging agents(4) have all been tried, often without success. While experimenting with slightly inclined wells, a possible "new" way to control excess gas and water production was discovered. Husky has drilled slightly inclined wells in the Black, Rainbow, and Rainbow South Fields to eliminate uncertainty of oil/water contact location(9), and to drain oil from a moving oil bank in waterflooded pools with a gas cap, but no gas injection. There are several other possible reasons to drill a slightly inclined well, including to drain multiple porosity stringers and to allow the end of the well to be plugged off when excess gas or water production occurs. Production logs have shown that horizontal wells can act as good horizontal separators(3. 11). Also, drawdowns in many horizontal wells have been shown to be very low, in the range detectable only by quartz or sensitive strain gauges(7). These factors suggest that it might be possible to control the type of fluid being produced from some wells by simply changing the tubing inflow points. Although many authors have explored the effects of pressure drops in horizontal wells(12. 13), the specific use of variable tubing inflow points to control producing GOR or WOR has not been clearly stated. Analytical Model A simplified spreadsheet model was built to evaluate wellbore pressure changes and fluid inflow along a slightly inclined wellbore. The model incorporates the effects of productivity, gravity, momentum and single phase friction pressure drop. The tubing inflow location to achieve maximum flow of oil without gas or water production was evaluated.