SUMMARY

This paper presents a model developed to simulate the exploitation process of a field with liquid and gaseous hydrocarbons, in one or two phases. It combines the classic material balance technique with thermodynamic equations of state.

Its effectiveness as a tool for the reservoir engineer to analyze different exploration alternatives is discussed.

An example is presented on how the model is applied for an oil field having a retrograde condensation gas cap.

Before the model is explained, material balance and equations of state are discussed.

Introduction

Optimizing the development of an oil field is one of the most exciting, gripping tasks for the reservoir engineer. The number of alternatives to be considered is correspondent with the complexity of the field.

In the case of undersaturated, highly homogeneous fields, the variables for analysis generally are distance between wells and the best time to start with water injection, if possible.

In the case of saturated oil reservoirs with an extended gas cap and a significant water drive, there are more alternatives to consider, namely: production rates of each fluid, volume of gas to be reinjected, Feasibility and magnitude of the potential water injection, recovery of condensate and gasolines for different surface installations and operating conditions, etc.

The model is tailored for studying these problems under any thermodynamic situation. It is particularly useful at the early stages of the life of the reservoir, when the data are not enough to make worthwhile the use of a 3D simulator.

The system couples the traditional material balance structure with a PVT simulator that uses equations of state.

MATERIAL BALANCE

Since it first came out in 1936 (1), material balance has been one of the lost powerful tools in reservoir engineering. It is a zero-dimensional model that uses production and pressure data to determine hydrocarbon production and pressure data to determine hydrocarbon volumes originally present in the reservoir. It is also used to infer aquifer and gas cap behavior. Moreover, assuming the original oil and gas and the aquifer and gas cap behavior, the evolution of reservoir pressure can be estimated as a function of the volumes of fluid produced. produced. During the 70s, the increasing use of numerical computers in the oil industry provided an invaluable help to reservoir engineering. Computation tics were greatly reduced and-sensitivity analysis on the balance variables could be run on a routine basis. Although the growth of computer applications allowed widespread use of the multi-dimensional models which, in many circumstances, are better than the conventional material balance, this is still an irreplaceable tool for the initial analysis of a reservoir, since the little information available at this stage would turn the use of more sophisticated techniques into uneconomic and useless.

The method bears substantial economic and financial significance, since those initial calculations are the basis for the most important investment decisions and are also used to design the major installations.

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