The Use of Multistage Centrifugal Pumps in Hydraulic-Lift Power Oil Systems
Authors: Boone Douglas M. , Eaton John R. 
Published: December 2007

Introduction

Amoco Production Co., as operator for the Chakachatna Group, erected four platforms in Cook Inlet, AK, during 1965-67. An early decline in producing rates and bottomhole pressures required producing rates and bottomhole pressures required us to use hydraulic lift systems in 1968. These systems have triplex pumps supplying power oil into a common header at 3,400 psig (23 400 kPa) discharge pressure. The pumps are driven by either 200-hp pressure. The pumps are driven by either 200-hp (152-kW) electric motors or 120- and 180-hp (90- and 140-kW) six-cylinder engines fueled by natural gas. Total platform hydraulics varies from 850 to 1,600 hp (635 to 1200 kW).Drilling programs, begun during 1976, required the platform lift systems to expand by about 700 hp (520 kW) on Platform Baker and 1,100 hp (820 kW) on Platform Anna.

Alternatives for Lift Expansion

We studied alternatives for expanding the artificial lift capacity of Platforms Anna and Baker. These included (1) additional triplex pumps similar to units already in service; (2) a turbine-driven, centrifugal pump package to operate in parallel with the existing pump package to operate in parallel with the existing triplex pumps; (3) electrically driven, submersible centrifugal pumps (ESP's) operating as high-pressure, power oil pumps in parallel with existing triplex pumps; and (4) ESP's conventionally installed downhole in new or existing wells. The initial investment and operating costs were lower for the turbine-driven, centrifugal pump package for Platform Anna and the electric submersible pumps Platform Anna and the electric submersible pumps operating as high-pressure, power oil pumps on Platform Baker. Platform Baker. The equipment installed on Platform Anna was an 1,100-hp (840-kW) 12-stage centrifugal pump driven by a gas turbine. This equipment is similar to that in waterflood service on Amoco's Cook Inlet platforms. Centrifugal pumps of this type are usually platforms. Centrifugal pumps of this type are usually available 98% of the time, which is a far better percentage than the positive-displacement pumps. percentage than the positive-displacement pumps. The equipment installed on Platform Baker comprised two 350-hp (270-kW) ESP's to pump power oil in parallel with the existing triplex pumps. power oil in parallel with the existing triplex pumps. Major considerations were the availability of electric power and the lack of adequate floor space for more power and the lack of adequate floor space for more conventional equipment. The ESP's were installed in empty platform well slots and arranged so that they could be serviced by platform cranes.Although economics was a major consideration when choosing to install centrifugal pumps as power oil pumps, other advantages included (1) reduced floor-space requirements, (2) reduced vibrations and noise, (3) reduced pulsation in the hydraulic system, and (4) reduced high-pressure piping requirements, as compared with the triplex pumps.Information obtained from a hydraulic pump manufacturer indicated that the power oil expansion on Platform Baker was the first time that power oil had been generated using ESP'S. However, a power water system does operate on the U.S. West Coast. Likewise, although turbine-driven, multistage centrifugal pumps are used as crude oil shipping pumps, the installation of this equipment on pumps, the installation of this equipment on Platform Anna for power oil service was unique. Platform Anna for power oil service was unique. System Design Details

Design considerations unique to centrifugal pumps exist that must be considered when designing similar installations. Care was taken on Platform Baker to ensure operation of the ESP's at rates to prevent either upthrust or downthrust conditions. The 241-stage pump initially installed on Platform Baker was designed for 4,000 B/D (636 m /d) at 3,400 psi (23 400 kPa). Start-up occurs with the flow valve closed and the relief valve fully open (Fig. 1). The relief valve is sized for a 3,400 psig (23 400 kPa) pressure drop across the valve when opened. After a pressure drop across the valve when opened. After a set time (about 20 seconds) the relief valve closes and the flow valve opens. The pressure relief valve is set to open if the pressure reaches 3,650 psig (25 150 kPa). The flow valve acts as a backpressure valve to keep a minimum discharge pressure of 2,400 psig (16 550 kPa) on the pump.

JPT

P. 1196