Skelly's Approach To Waterflood Physical Plant Design
Authors: Dunlap J.H. 
Published: December 2007

Introduction

The purpose of a waterflood physical plant is to serve an oil producing reservoir in a manner that will return the largest dollar profit to the owner. Many factors influence the actual design of physical plants. These factors can be classified in four broad categories:

Reservoir Requirements Water Supply Rate and Economics Operating Conditions

Design conditions vary widely from one reservoir to another. They may also vary between different operators in the same field using the same water supply. Each waterflood has its own unique set of requirements. The best physical plant for each application is designed for these requirements.

RESERVOIR REQUIREMENTS

The most difficult part of physical plant design is to determine all the various requirements that the producing reservoir will impose on the plant throughout the life of the waterflood. Physical plant design has to be based on a maximum working pressure and a given water injection rate, allowing for the different quantities of supply and produced water to be used. Unfortunately, individual reservoirs perform differently from the calculations and it is often difficult to predict future plant requirements. To compensate for unknown conditions the plant should be flexible so that it can either handle the different requirements or be modified at little cost. The amount of flexibility that is built into a plant is balanced between the cost of the flexibility and the certainty of the calculated reservoir requirements. Much can be learned from similar operations in the area. Pilot waterfloods provide excellent data for physical plant design.

WATER FOR INJECTION

An adequate supply of inexpensive water is essential for waterflood. In many areas it is difficult to obtain water and to determine that the supply will be adequate throughout the life of the flood. Seldom is there a choice between different water supplies of an alternate water source in case the primary water supply fails. Pilot waterfloods or similar operations in an area can furnish valuable information on the quantity and quality of water available from an aquifer. In most cases it is good practice and economics to reuse produced water for injection. The characteristics of the water or waters to be handled will, to a large extent, determine the type of system to be used. It is necessary to obtain a good analysis of the waters and make an evaluation of the different types of systems that could be used. Selection of a system should be based on water quality required, estimated initial investment, operating cost and ease of operation.

It is seldom economical to use large quantities of chemical to change the characteristics of the water. Many treating problems can be reduced or eliminated through mechanical design. For example, incompatible waters can be handled in a split system. Bacteria problems can be reduced by minimizing retention time and eliminating dead areas in the system. Corrosive waters can be handled in non-metallic or internally lined systems. The simplest treating system that can produce the quality of water necessary for injection is usually beat because of the lower investment and ease of operation. The operation of a treating plant is very important. No matter how well a plant is designed, it cannot produce a high quality water unless properly operated. The usual result of either poor design or poor operation is excessive equipment replacement and costly well work.

RATE AND ECONOMICS

The rate at which a waterflood Is conducted depends on the existing physical and economic conditions, which can be broadly classified as follows:

Physical Conditions

1. Reservoir 2. Reserves 3. Water Supply