A Local Control Element to Reduce Automation Costs of Injection Wells
Authors: Crowley D.W. 
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers, Inc.

The cost-saving potential of a local control element, the automatic flow controller, is established by examining typical automated injection systems. This local control element accurately and automatically regulates the set injection rate. A new rate may be "dialed" easily without systems downtime or extra parts. The reliability of this kind of device reduces the need for constant remote supervisory control and many metering functions. The local control element promotes design simplicity and reduces the need for instrument level training for operating personnel.

Introduction

The reservoir engineer's recommendation for the most efficient flooding of the zone determines the choice of the systems design for automatically controlling a waterflood injection. The primary method of varying the progress of a flood front is to adjust the injection progress of a flood front is to adjust the injection rate and control this rate accurately. A reliable method providing this capability then becomes the primary concern in automating the injection well.

Equipment costs must be evaluated in designing any automation system. In today's market, the engineer may literally "buy as much automation as he hits money to spend." The equipment is evaluated by the amount of automation necessary and its required degrees of sophistication.

Basic Systems

Generally, there are three basic systems designs used in automating an injection well. Actual systems may incorporate specific features of all three designs, but the basic distinctions still remain. Fig. 1 represents diagrams of the three basic systems. In these systems, point X is a centralized location, often geographically established, containing data processing functions. Point Y represents field operations at the injection pattern location.

In general, the systems have certain unique characteristics. System A has maximum operational flexibility from the data processing center, utilizes relatively complex instrumentation, and requires maximum capital investment. System B has direct telemetered data input to the data processing center, has centralized monitoring functions, and has a local control element that automatically regulates injection rate. System C incorporates maximum design simplicity and economy, has the lowest basic equipment cost, and has manual input to the data processing center.

Systems B and C are becoming more and more attractive because of their estimated lower cost. This cost difference depends on the substitution of a local control element for the supervisory automatic control capability. The local control element of System B replaces 50 percent of the basic diagram of System A. percent of the basic diagram of System A. In actuality, the local control device is substituted for an electro-mechanical or electro-pneumatic control valve. A savings is established by a direct reduction in valve costs and a reduction in the requirement for telemetering equipment, receiver controllers, and other accessories; thus, investment and operational costs decrease.

The investment dollar savings of Systems B and C revert to a rather simple evaluation. The operations justification of Systems B or C over System A calls for considerable thought and examination.