Offshore Multiphase Pumping Technology-Identifying the Problems; Implementing the Solutions - Part 1
Authors: Jaggernauth A.J. , Brandt J.-U. , Muller-Link D. 
Published: December 2007

Amoco Trinidad oil Company (ATOC), a subsidiary of Amoco Corporation, is the major single supplier of oil and gas in Trinidad and Tobago. Recently, major gas fields have shown large condensate yields. Consequently, a large offshore gas platform in ATOC's operations necessitated a review of options for production of low pressure oilwells. Flexibility to produce into the existing production system at a higher pressure was mandatory to selection of the optimum option as these oilwells still produce large gas volumes, in addition to liquid and fine sand. The reservoir is characteristic of a strong water drive with a large gas cap. Relative to conventional production facilities (liquid pump, compressor, production separator) the application of multiphase pumping technology proved to be the most cost effective option. The application of multiphase pumping technology in ATOC will he used for pressure boosting and to increase production. ATOC considered the design and installation of a multiphase pump from one of Europe's largest manufacturers of twin screw pumps, located in Germany. ATOC successfully started up and commissioned the first multiphase pump installed on an Amoco offshore platform. Since multiphase pumping technology is relatively new to the offshore industry, challenges in the areas of technology development, operational difficulties, producing behavior of the oilwells had to be overcome for continued multiphase pumping operations. ATOC and the pump manufacturer worked closely to overcome these challenges. The performance of multiphase pumping operations in ATOC's operation is being evaluated and details of this evaluation are presented in this paper.

Introduction

Amoco Trinidad Oil Company (ATOC), a subsidiary of Amoco Corporation, is the largest single major producer of oil and gas in Trinidad and Tobago, operating offshore the East Coast, Trinidad. ATOC, has made worldwide history in the Offshore Industry with the successful application of the first high pressure multiphase pump installed on an offshore platform. The platform is fully equipped with conventional high pressure gas handling facilities. Surface facilities are provided to separate gas from liquid, prior to sales. Gas wells, with its retrograde condensate are produced into a +/- 1000 psig (68 bar) production system. Recent discoveries of strong water drive oil producing reservoirs with large gas caps necessitated a review of methods for handling of additional oilwells with the understanding that these oilwells will eventually decline to pressures below the normal system pressure. Immortelle is an 8-pile, 16-slot drilling platform with production facilities for handling 350 MMCFD gas and 16,000 BLPD, located in 235 feet water in the Atlantic Ocean, Trinidad, West Indies.

Selection of optimum facilities for handling low pressure oilwell production was essential to project's economic success. Some expedient and cost-effective method was desirable for pressure boosting of low pressure oilwells.

Two options were considered for handling low pressure oilwells namely:Installation of conventional surface facilities i.e. low pressure production separator, pump, compressor, flare etc. with attendant structural modifications, andInstallation of a multiphase pump.

Installation of the multiphase pump was selected over the conventional method mainly because of less platform space, much lower installation cost, less surface facilities, easier installation, lower environmental and safety risk with elimination of having flaring facilities on a high pressure gas platform.

A low pressure oilfield application in West Texas was the first Amoco Multiphase pump installed, with a goal of production enhancement.