Performance of Horizontal Wells Subject to Bottomwater Drive

Abstract

Summary This paper discusses the performance of a horizontal well subject to bottomwater drive and delineates conditions under which this completion mode is more appropriate. Information presented will enable the engineer to decide what productivity presented will enable the engineer to decide what productivity improvements may be expected from horizontal-well completions. The productivities of horizontal wells operating under bottomwater drive productivities of horizontal wells operating under bottomwater drive are discussed in terms of displacement efficiencies. Results and the discussions are also applicable to oil production by gas-cap drive. Introduction Developments in horizontal-well technology and performance during the past few years have placed horizontal wells among the commercially viable well-completion techniques - I As noted in Refs. 2 through 5, when no fluid intrusion into the reservoir across the reservoir boundaries exists, pseudoskin factors can be used to determine the productivity improvement that can be expected from horizontal-well completions. The behavior of waterdrive reservoirs poses a more complicated problem, and investigation of the poses a more complicated problem, and investigation of the productivities of wells operating under such conditions requires a different productivities of wells operating under such conditions requires a different treatment. In such systems, bottomwater will tend to encroach into the oil zone and to reach the well after some time. This work presents information that enables the engineer to decide on the productivity improvements that may be expected from horizontal-well completions under bottomwater drive. Refs. 6 through 8 investigate water encroachment into the oil zone caused by production from a horizontal well. Ref. 6 extends the classic treatment of the water-coning phenomenon presented by Muskat and Wyckoff to horizontal wells. Refs. 7 and 8 use hodographs to account for the deformed shape of the oil/water boundary caused by production from a horizontal well. Refs. 7 and 8 state that the pattern of flowlines for the bottomwater-drive mechanism is the same as that for the lateral edgewater-drive mechanism in the vicinity of the well, and hence the shape of the oil/water boundary obtained for the latter can be used for the former near the well. This observation appears to be in conflict with Musket's, comparison of the two waterdrive mechanisms. In this work, we recognize the distinct flow characteristics of bottomwater-drive reservoirs. Although our analysis involves the assumptions used by Refs. 11 and 12, the model we use accounts for the basic phenomena underlying the behavior of wans producing under bottomwater-drive conditions. The necessary solutions in the Laplace domain were obtained by the Green's function product method 13 (see Refs. 14 and 15 for details). An alternative and more powerful approach to derive the solutions given in Ref. 14 is given in Refs. 16 and 17. Ref. 14 also presents a summary of the derivations for vertical and point-source wells. The effect of a constant-pressure gas cap on well performances would be similar to that of an active aquifer at the bottom of the formation. Analytically, both cases can be investigated with the same model. Therefore, although we discuss the bottomwater-drive case, all results and discussion also are applicable to the constant-pressure-gas-cap case. Kuchuk et al. recently discussed some aspects considered in the first part of this work and presented solutions that consider only a laterally infinite reservoir. This study also investigates the influence of no-flow boundaries. This aspect is particularly important for deliverability predictions. Although Ref. 18 obtains some solutions by the Green's function product method, as in this study, it uses primarily the solution procedure suggested in Ref. 19. Ref. 18 principally attempts to derive the solution in the Laplace domain so that solutions to the wellbore storage and skin problem in horizontal wells can be developed. As shown in Refs. 14 and 15, the Laplace domain form of the solutions can be obtained in a straightforward manner with the Green's function product method. The analytical solutions presented in Refs. 14 through 17 are new and to the best of our knowledge are not available elsewhere in the literature.