Microcomputer Analysis Of Waterflood Performance In Multilayered Reservoirs
Authors: Finch David F. , Sawyer Walter K. 
Published: December 2007

Utilizing only a microcomputer system, a mathematical method has been devised that will analyze waterflood performance data of multilayered reservoirs with patterns of any size or configuration by matching both oil and water production and then projecting through the life of the project. The projecting through the life of the project. The model will also aid in waterflood operation and early performance analysis under a "what if" mode by a graphical comparison of the calculated oil and water interference radii in each zone for all injection wells in the pattern.

Data requirements of the model are (1) initial oil kick and water breakthrough dates, (2) monthly injection and production (oil and water) volumes and dates, (3) thickness and porosity of each zone and (4) estimates of saturations.

The method developed can be defined as a volumetric analysis employing actual injection data to introduce the time element into the waterflood history. The model is designed to be an operating tool for use by engineers directly involved with the waterflood operation.

Introduction

The art of waterflood prediction has been in a constant state of evolution since its beginning. The black-oil models of today have become so mathematically complex, due to the multitude of real and imaginary factors that have been implimented in attempting perfection, that the outputted results often tend to overwhelm the typical project or field engineer directly involved with the day-today operations of the waterflood.

It is to this end - the needs of the waterflood operating engineers - that this paper is directed. A concept is proposed that requires only real operating data on a pattern by pattern basis supplemented with only intelligent guesses as to reservoir layer thicknesses, porosities, and saturations. Acceptance of the concept as described in the text of this paper will allow operating engineers themselves the opportunity of analyzing their operation. The knowledge gained in the process of acquiring a history match Will change their opinions as to the reservoir parameters and add insight to their operation. The method can locate problem wells and simulate past or future operations in the "what if" mode that will allow intelligent recommendations for real operational changes with all side effects of such changes anticipated.

The required microcomputer system is easily cost justifiable for the field operating office and the appropriate Basic Computer Language can be learned with just a few hours effort.

DESCRIPTION OF THEORY

A restatement of the theory of the three periods in the history of a waterflood, as applied periods in the history of a waterflood, as applied in this paper, is required for clarification. These are:

Radial Encroachment - During this period, the movement of water from the injector into the reservoir is radial until the perimeter of the swept oil bank collides with the swept oil bank of an adjacent injector. If no oil bank is formed, radial encroachment ends with the collision of the radii of the advancing waterfronts.

Interference - the time interval after radial encroachment until the free gas volume has been displaced (by swept oil or injected water) and waterflood production commences.

Constant Rate Displacement - During this period, the adjusted total of the injected volumes of all injectors into the pattern equals the oil or water volume produced from the pattern until the operation is terminated.