Surface and Reservoir Control of Injection Water in the Hewitt Unit Waterflood
Authors: Cox Ennis 
Published: December 2007

The system used to control injection water in the Hewitt Unit, whose source water reservoir is remote from the project, synchronizes the operation of equipment that handles 200,000 barrels of injection water daily. These controlling and monitoring methods, along with an effective remedial approach to problem wells, make it feasible to flood multiple reservoirs simultaneously.

Introduction

The 2,600-acre Hewitt Unit, operated by Humble Oil and Refining Co., is located in south central Oklahoma (Fig. 1). In 1970 a waterflood project was initiated that is designed to simultaneously flood 23 sands ranging in average depth from 1,700 to 2,600 ft subsurface. These Pennsylvanian age sands vary in thickness from 10 to 100 ft and range in permeability from 24 to 230 md. (A composite type log for the field is shown in Fig. 2.) The structure of the sands is a northwest-southeast oriented anticline, faulted on the north and east. To optimize recovery, the Unit is being flooded on a 20-acre, five-spot pattern. All of the producing wells are single-string conventional completions producing wells are single-string conventional completions with all productive zones perforated; production is commingled down hole.

Source water for injection is obtained from five wells, drilled on 640-acre spacing, located 8 to 10 miles from the waterflood area. Produced water is also reinjected in the project area, but it is handled separately. Because the source wells are widely spaced, a control system was needed to synchronize operation of the water-handling equipment and a system was needed to provide pertinent operating data for the remote equipment. These needs were fulfilled by installing one system that measures and transmits data over telephone circuits and converts such data to either electric or pneumatic control.

Simultaneous flooding of numerous zones made it difficult to control and monitor injection into each zone. Installing multiple 2 7/8-in. OD casing strings in injection wells and using surface flowmeters and a subsurface recording wireline flowmeter provided the most economical means of controlling injection.

Surface Control of Injection Water System Requirements and Description

To obtain an operational automated water injection system, there were three main requirements. First, we had to provide controls for synchronized operation of (1) five water-source wells drilled on 640-acre spacing, (2) a booster pump station remote from the waterflood area, and (3) the main injection station. Second, we had to provide auxiliary controls and safety devices to continue operations within prescribed limits, or should the water-handling equipment or the control system fail, to shut down equipment if prescribed limits are exceeded. And third, we had to provide for transmission and display of remote operational data. to the waterflood area.

Fig. 3 shows a schematic layout of the entire system, with provisions for segregating source and produced water. Valves on the injection plant suction produced water. Valves on the injection plant suction header provide flexibility in switching pumps from source to produced operation. Source water from the five wells is produced into a 5,000-bbl surge tank at the booster station located in the source water area. The water is then pumped by three engine-driven, split-case centrifugal pumps into an 8-mile, 16-in. OD cement-lined steel pipe leading to the waterflood area.

JPT

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