Installation And Operation Of Hydraulic Pumping Systems On Cook Inlet
Authors: Owens Millard E. , Allard Bret R. 
Published: October 2008

Hydraulic pumping systems have been installed on three Cook Inlet self-contained drilling and producing offshore platforms. The design, installation, and operation of these systems, which utilize high pressure crude oil as power oil, have presented some unique problems:

1. Location of pumps and prime movers on the platforms.

2. Routing of high pressure lines.

3. Selection of pipe, valves and fittings, and inspection of fabrication.

4. Instrumentation and control, and fire alarm and extinguishing systems.

5. Control of pulsation and vibration.

6. Design of special downhole equipment.

Introduction

Construction of permanent drilling- producing self-contained platforms in the Cook Inlet began in 1965. Middle Ground Shoal Platform Baker was the second platform to be erected in the Inlet, and was the first of four platforms to be erected by the Chakachatna Group, which consists of Pan American Petroleum Corporation, Skelly Oil Company, Phillips Petroleum Company, and Atlantic Richfield Company, with Pan American as operator for the Group. Following construction of Middle Ground Shoal Platform Baker in mid-1965, two other platforms, Granite Point Platforms Anna and Bruce, were erected. The fourth and final Chakachatna Group platform was South Middle Ground Shoal Platform Dillon, erected in 1967. All of the wells completed on these four platforms were initially flowing wells. Figure 1 shows the relative location of these Cook Inlet platforms.

A rapid decline in producing bottom hole pressures and associated decline in producing rate necessitated the installation of artificial lift facilities early in the life of the wells. Since several of the wells on Middle Ground Shoal Platform Baker were multiple completions and the producing GOR was about 400:1, a gas lift system was installed in mid-1967. The need for artificial lift became apparent on the other three platforms by the fall of 1967.

The operating conditions on Granite Point Platforms Anna and Bruce and South Middle Ground Shoal Platform Dillon were considerably different from the conditions that existed on Middle Ground Shoal Platform Baker, where gas lift had been 'installed. Drilling was still in progress on the Granite Point and South Middle Ground Shoal platforms, which limited the space available for installation of artificial lift equipment. Figure 2, Granite Point Platform Anna, is typical of the South Middle Ground Shoal and Granite 'Point platforms when drilling and production were in progress simultaneously. None of the wells on these three platforms were multiple completions. The GOR at Granite Point was considerably higher than at Middle Groundor South Middle Ground Shoal, averaging about 700:1. All of the wells drilled from each of the platforms had to be deviated, with some deviations quite expensive, in order to reach the desired bottom hole location. These high deviations caused many problems in performing the wireline work connected with the downhole gas lift equipment on Middle Ground Shoal Platform Baker. When all these factors were taken into account, gas lift was not considered to be the proper choice of artificial lift for the remaining three platforms. Rod pumping was not even considered since its use on the platforms would be impractical.