Abstract

The definition of incremental developments, such as additional perforations, work-overs or in-fill wells, for mature fields is sometimes a difficultexercise. The use of reservoir flow simulators is often required to forecastthe incremental oil, which can be associated with any new operation. However, in fields with a large number of wells available, the number of possiblealternative arrangements can be very large and very difficult to handle for theperson in charge of the simulations. The situation becomes even morecomplicated when interactions appear between the different operations underconsideration. In such cases, new tools are needed.

In this paper, we present a methodology for the optimisation of a pressuremaintenance project for an offshore reservoir in West Africa. The startingpoint is a "history matched" dynamic model. The method is based on the use ofexperimental design. Experimental design can be defined as the strategy forchoosing simulations in such a manner that the information required is obtainedas efficiently and precisely as possible. In a first part, the theoreticalbackground of the technique will be described briefly. Then application of themethod to the field case will be presented. The field has been developed bywater flooding for approximately 7 years, with a total of about 30 wells. Priorto our intervention, 11 production wells had been identified as potentialcandidates for conversion into water injectors.

The work was performed in two phases with two different experimentaldesigns:

  1. Rankingof the 11 candidate wells leading to the identification of themost promising operations. This phase requires a strong reservoir expertise tointerpret the simulations results

  2. Detailed determination of the best work-oversto be performed

The final results consist of reservoir simulation runs with the bestconfigurations. The optimal result was obtained by converting 6 of the 11wells. Use of our methodology enabled a better result to be found more rapidlythan by a conventional "trial and error" approach, while keeping to a minimumthe number of simulation runs required.

Conclusion:

In this study, we provided the reservoir engineer with an efficient methodto manage a problem where a large number of possible combinations could beconsidered. The methodology used is systematic.

Technical Contributions

  1. Identification of the key simulations to be performed to identify thehighest potential returns.

  2. Optimisation of the incremental development policy for a mature field

Introduction

Mature fields may represent substantial potential reserves to be recovered.Maximising their recovery is one of the aspects of the reservoir engineer'swork. The task is sometimes a complex one due to the vast amount of data andinformation to be managed. Flow simulators are used to obtain a synthesis ofall this data in order to achieve a better understanding of the reservoirsunder study, but are also used above all to establish production forecasts thatwill serve to determine the economics of any new project. Once the reservoirmodel has been built and matched to the production history, the impact, interms of reserves, of various possible operations can be tested. An operationmay be, for example, additionnal perforations, new in-fill wells, aredefinition of the pressure maintenance policy, etc.

Quantifying the impact of different operations is often complex because ofthe possible interactions between these actions. One example is the drilling ofadditional wells.

Conclusion:

In this study, we provided the reservoir engineer with an efficient methodto manage a problem where a large number of possible combinations could beconsidered. The methodology used is systematic.

Technical Contributions

  1. Identification of the key simulations to be performed to identify thehighest potential returns.

  2. Optimisation of the incremental development policy for a mature field

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