Near-Wellbore Temperature Simulations Assist Design of Water-Shutoff Treatments

Abstract

Abstract Until recently, most water-shutoff treatments were designed for wells needing low-volume treatments. However, many highly productive reservoirs are beginning to produce high volumes of water. The evolution of diagnostic and interpretive techniques such as reservoir description and modeling and production logging have significantly enhanced the degree of accuracy and completeness of production problem diagnoses. Many of these tools can also be used for more effective water-shutoff treatment designs. Near-wellbore temperature simulations allow treatment designs based on realistic treatment temperatures, rather than on bottomhole static temperatures. This paper presents a method of conducting temperature simulations that is applicable to all water-shutoff treatments. This paper describes how engineers used temperature simulation results to design a water-shutoff treatment and its placement for a well in the Norwegian Sector of the North Sea. The results of the simulations allowed optimized treatment placement rates, fluid composition, and shut-in times of the job and constructed temperature histories for different stages of the treatment. These histories clearly showed that different activator compositions and/or concentrations were required for early, intermediate, and final treatment stages. The results of near-wellbore temperature simulations allowed engineers to predict the effects of the following factors:–interval permeability distribution–treatment rate–viscosities of injected fluids Introduction Water production can seriously compromise the profitability of oil- or gas-producing wells. The cost of produced-water disposal is becoming a major burden for many operators. Although prevention is usually more effective than treatment, excessive water production is most often treated rather than prevented. The keys to the success of shutting off or preventing excessive water are–proper identification of the water-production mechanism–appropriate design of the treatment–effective placement of the treatment Steps of Typical Water-Shutoff Treatment Fig. 1 (Page 5) illustrates the process of a typical water-shutoff (or conformance) treatment. Each step of the process will now be discussed. Selecting the Candidate Well. In the first step, a candidate well is identified. A candidate well is usually chosen because it produces enough water to undermine profitability. Next, engineers examine the available well and reservoir data to diagnose the water-production mechanism. Identifying the Water-Production Mechanism. A number of mechanisms such as coning, high-permeability streaks, injector communication with a producer, and natural fractures cause excess water production. A complete profile of the well and its reservoir are necessary for an accurate diagnosis of the mechanism that is causing the excess water production. Factors that help determine water-production mechanisms are–reservoir drive mechanism–production rates (reservoir and well)–connate water and irreducible oil saturations–porosity–permeability heterogeneities–vertical and horizontal permeabilities–relative permeability/mobility to water and oil–location and continuity of impermeable barriers–reservoir dip P. 493^