Optimization methodology for cycle steam injection with horizontal wells.

摘要

Horizontal wells are becoming a very important component in the thermal recovery of heavy oil reservoirs. The success of a cyclic steam injection project depends strongly on the selection of key parameters, such as cycle length and amount of steam injected. Since analytical models are not available, the design should be supported by numerical simulation. However, the numerical simulation of horizontal wells, especially under non-isothermal conditions, is computationally demanding. When optimization is combined with numerical simulation, the computing time requirement may be prohibitive and it is not guaranteed that the optimum conditions will be found.;In this research, a new methodology has been developed for optimizing the cyclic steam injection process for vertical and horizontal wells. The procedure integrates three stages: oil production characterization, net present value maximization and model validation/tuning. The three-stage procedure provides the optimum number and/or duration of cycles, the optimum amounts of steam to be injected in each cycle and the optimum value of the overall economic indicator.;The characterization stage starts with numerical simulation in a specific range of steam injection conditions. The generated data are used to identify the parameters of a production decline model, describing the effect of injected steam in the particular well. In the optimization stage, the decline model is coupled with a nonlinear, constrained optimization algorithm based on the Quasi-Newton method. Finally, during the last stage the optimal values obtained in the optimization stage are corroborated by numerical simulation and, if necessary, the characterization stage is repeated with a narrower range of the decision variables centered around the currently available best values.;The proposed optimization algorithm was successfully validated with published results obtained from the discrete maximum principle. The three-stage methodology was evaluated on a well documented data set, which had been the subject of a comparative study on the performance of various thermal simulators. The methodology was then applied to determine the optimum conditions of cyclic steam injection for a horizontal well located in Bachaquero field, Venezuela.