The Fundamentals Can Still Solve Engineering Problems
Authors: Freeman D.C. 
Published: December 2007

Significant technical advances have been made over the past half century with regard to the kinds of tools available for solving petroleum engineering problems. In particular, reservoir simulators are now widely used and provide a means of solving problems that previously could not be handled.

The credibility of reservoir simulation is well documented. The usefulness of a particular simulation is governed by the completeness and quality of the input data; in cases where either factor is inadequate resulting performance predictions are suspect. However, because of the high degree of credibility generally afforded simulation, it is at times employed when simply the application of basic petroleum engineering principles is the better choice. Practicing engineers, as well as students of Petroleum Engineering, are encouraged to maintain a focus on these fundamentals.

Introduction

The primary objective of Petroleum Engineers is to economically maximize the recovery of oil and gas from each reservoir discovered. To accomplish this, the behavior of the reservoir under a variety of production schemes must be examined. Basic reservoir engineering fundamentals, analytical models, and reservoir simulators, the latter two based on the former, are available for use.

Although its potential was first recognized some fifty years ago, at present the use of reservoir simulation is increasing, largely due to the proliferation of high speed computers. Simulation is the only means available to quantitatively describe multiple phase fluid flow in heterogeneous reservoirs having a production scheduled determined by reservoir properties as well as external forces, e.g., market demand. To take full advantage of a reservoir simulator, detailed reservoir description is required, which in turn necessitates complex mathematical expressions that may be difficult to understand. This causes some engineers to avoid the use of simulators and others to misuse them.

The most frequent misuse of reservoir simulation is a kind of "overkill". Some twenty-five years ago it was observed that decisions concerning reservoir behavior previously made using only basic reservoir engineering fundamentals or analytical models suddenly required the use of models in several thousand grid blocks. Too often, twenty-five years ago, the most sophisticated tool available was routinely applied to engineering problems that could be solved by the use of the fundamentals, and the same is true today.

The credibility of reservoir simulation also enhances its misuse. Because simulation carries such a high degree of credibility and at times even awe, engineers may be further compelled to apply it to support decisions made regarding reservoir performance even if available data, due to a lack of completeness and/or quality, do not warrant its use.

Practicing engineers are encouraged to maintain a focus on the fundamentals, and this message must be communicated to students of Petroleum Engineering. With numerous small-scale simulators available for classroom use, students become quite comfortable with their use. The perceived accuracy of simulation and accompanying desire to generate computer output to solve a problem begins to take shape.

Following are two case histories that illustrate the use of the fundamentals to solve engineering problems. In both cases, acceptable solutions were obtained at a fraction of the cost of the use of more complex tools.

Case History I

A reservoir study on a California waterflood was performed to address the following specific objectives:Confirm original reservoir oil-in-place,Evaluate primary and waterflood production,Assess the degree to which numerical simulation would increase the understanding of historical reservoir performance and assist in planning for future operations.

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