Optimization of Smart Well Production through Nonlinear Model Predictive Control

Abstract

Abstract In this paper, we present an algorithm for optimizing reservoir production using smart well technology. The term smart well is used to indicate an unconventional well equipped with down hole inflow control valves (ICVs) and instrumentation. This additional instrumentation extends the degree of freedom in the field production planning, since production can be efficiently distributed on the different well segments available. By proper utilization of the ICVs through optimal production planning, an increased oil recovery for the reservoir can be expected. We propose a method for optimal closed-loop production known from control theory as model predictive control (MPC). A commercial reservoir simulator, ECLIPSE, is used for modeling and predictions. MPC is chosen for its ability to provide an optimal solution for the constrained multivariable control problem. To compute the optimal ICV settings, we propose using a nonlinear MPC (NMPC) application, which can handle the severe nonlinearities found in reservoir models. The NMPC uses a single shooting multi-step quasi-Newton (SSMQN) method to solve the optimization problem. As the term multistep suggests, this is an iterative method which solves a sequence of quadratic problems (QPs) in each time step. We apply our method to a benchmark reservoir model with multiple geostatistical realizations. This model has already proven potential for increased oil recovery by using optimization techniques. We show an even additional increase over the former approach in production totals, using the SSMQN method, with as much as 68% increase in one case, and 30% on average compared to a reference case. Introduction Reservoir management has traditionally been performed on the basis of long and short term plans made by production engineers in a manual, ad hoc fashion. The overall goal is obviously to maximize the total hydrocarbon production and recovery factor while minimizing total cost and staying within operational constraints. But reservoir models have generally been viewed as too large and computer resources too scarce to apply full scale production optimization. Meanwhile, on the downstream end of the production line and in process industry in general, advanced control techniques have been gradually developing and implemented with prosperous results. Recent technological advances have opened for new possibilities within reservoir production. New reservoir mapping techniques offer more accurate reservoir models and the computational cost of simulating the models has decreased significantly. Well completions are more sophisticated than ever and supply new dimensions of flexibility to the day to day field operation. This new well generation is better known as smart wells. A smart well is a unconventional well equipped down hole with ICVs. Smart wells offer control of the total flow through individual segments and branches, as well as temperature and pressure measurements. The potential benefits from proper use of ICVs in a real-time control application are substantial. This is because continuous redistribution of the production from the available branches can delay or avoid break through of gas and/or water for as long as possible.