Optimization of Gas Field Operations
Authors: O&apos;Dell P.M. , Steubing N.W. , Gray J.W. 
Published: December 2007

The optimization model described here provides the following, which affect operating decisions:a long-term plan for recompletions in multiple-pay fields;a short-term plan that specifies which wells to produce, and at what rate, for various demand requirements; anda measure of the effect that future demand and changes in environment might have on operating policies and profit. policies and profit.

Introduction

Our purpose here is to describe some techniques for determining optimum field development and production scheduling from multireservoir gas fields. In the past, the operator developing such a field has often past, the operator developing such a field has often produced one zone at a time in a given well, not produced one zone at a time in a given well, not recompleting in the next zone until the first has reached its limit of economic production. Recompleting at optimum time, which normally occurs during the period of declining production, speeds up the predicted period of declining production, speeds up the predicted cash flow for the well. A higher cash flow rate for the field can be obtained without sacrificing reserves by insuring that the updip well in each reservoir is not recompleted until it has reached the limit of economic production. In addition, when field deliverability exceeds sales demand, the wells to produce must be selected through logical procedures. produce must be selected through logical procedures. Intuition would tell us to produce the wells with highest current income. However, greater profits can be obtained by producing the wells that contribute most to present value profit. A simple numerical example is described that indicates that careful recompletion and production planning is worthwhile. To accomplish this optimization, a computer program has been developed. This approach was program has been developed. This approach was necessary because of the complexity of the options available under a large gas sales contract. A typical example in Offshore Louisiana is a contract involving four fields, more than 50 wells, and more than 100 reservoirs with both solution-gas and gas-well-gas production. Optimization of recompletions and production production. Optimization of recompletions and production scheduling, which is subject to many physical and contractual constraints, enables the producer to meet increasing delivery requirements and to maximize present value profit. present value profit.

Optimization Procedures

To optimize gas field operations, the well performance and the gas sales contract must be modeled. In multireservoir fields, recompletions must be considered. What we are looking for is a model that is realistic, yet easy to use. We begin by describing the well performance model. performance model.

Well Performance Model

It is assumed that interaction between wells within a reservoir is sufficiently accounted for when the pro-production. The slope of these curves is permitted pro-production. The slope of these curves is permitted lied as a function of the reservoir cumulative production. In steeply dipping reservoirs with strong production. In steeply dipping reservoirs with strong water drive, the production rate is constant until the well first produces water. At this time, the reservoir cumulative production is simply the volume of gas contained between the original gas-water contact and the level of the bottom perforations in the subject well. After the well first produces water, production rate is assumed to decline linearly with reservoir cumulative. The well performance model is illustrated in Fig. 1.

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