Reservoir Performance History Matching Using Rate/Cumulative Type-Curves

Abstract

Abstract This paper presents an analysis technique for characterizing reservoirs from production performance. Unique to this technique is the incorporation of the instantaneous bottomhole flowing pressure (BHFP) to both the production rate and to the cumulative production for a well depleting a reservoir. This allows a single rate/cumulative analysis for wells producing with constant BHFP, constant rate, and wells with variable rate or variable BHFP (including wells with shutins). This solution provides a powerful diagnostic type- curve which can be generated with almost any wellbore/reservoir situation encountered. Extension of the method to gas reservoirs through use of pseudopressure and viscosity- compressibility normalization allows these wells to be analyzed using the slightly-compressible fluid solution. Well performance during transient flow and depletion flow are examined. Simulation results are compared with the analytic solution. The use of spreadsheets to perform well test analysis is also demonstrated. Introduction Recently, decline-curve analysis has expanded to permit engineers to analyze a petroleum reservoir directly in regard to its fluid-flow characteristics and its volumetric extent using rate-time type-curves of the constant terminal pressure solution of the diffusivity equation. This analysis is of enormous value to reservoir managers whose goal is to maximize oil and gas production from a petroleum reservoir. Reservoir extent, continuity, and flow capacity are paramount characteristics that are considered when developing models. that predict reservoir performance while using alternative depletion strategies, such as during fluid-injection projects or enhanced recovery. Reservoir producing conditions to which this technique can be readily applied are those whose actual bottom-hole flowing pressure (BHFP) closely approximates a constant value. Most wells, however, produce with variable BHFP. The work presented here focuses on an alternative rate-cumulative type-curve format whereby variable BHFP is incorporated into dimensionless variables containing both the production rate and the cumulative production providing. a unified approach that can be applied to any reasonable variability in the producing rate or flowing pressure history. The proposed method, with application to single phase and multiphase flow, provides the practicing engineer a better method for decline curve analysis and therefore propagates better reservoir characterization from production data. Pressure Normalization One advancement in decline-curve analysis presented here includes pressure normalization of cumulative production. Like pressure normalization of production rate, variations in bottom-hole flowing pressure (BHFP) are accounted for by dividing cumulative production by the pressure difference between initial and bottom-hole flowing pressures. The technique of combining pressure-normalized production rate (PNR) and pressure-normalized cumulative production (PNO) is an improvement over rate normalization alone in the analysis of reservoirs based on production data. To apply this technique, determination of BHFP from surface-measured flowing-tubing pressure (FTP) is required along with determination of the original static reservoir pressure. Data can then be presented by plotting PNR versus PNO. This technique is then extended for use with gas reservoirs by further incorporating changes in viscosity and compressibility during reservoir depletion. This technique relies heavily on either measured BHFP or FTP. P. 947