Abstract

Examples illustrating the effectiveness of coiled tubing conveyed jet pump completions as a remedial repair method instead of traditional workovers are discussed. This completion technique was applied to previously shut in wells in a declining oil field with high workover costs, providing an effective and economic repair method.

Two hydraulically pumped oil wells were shut in due to mechanical problems with damaged downhole hydraulic pump assemblies. This paper describes a method whereby a 3-1/2" tubing packer was used to land 1-3/4" coiled tubing inside the existing 3-1/2" tubing. A 1-1/4" jet pump seated in a pump cavity at the bottom of the 1- 3/4" coiled tubing used high pressure hydraulic fluid to pump reservoir fluids and exhausted hydraulic fluid up the 3-1/2" × 1-3/4" annulus.

Jet pump performance was simulated using a computer model to determine the optimal combination of coiled tubing and jet pump sizes that minimized friction and maximized production. Pump performance curves were compared to the well's inflow performance relationship (IPR) curves to predict well performance and power oil pressure and rate requirements. Several remedial options were compared and analyzed to determine the most economically feasible repair method. Field installation procedures were optimized in the second well, resulting in lower costs.

Introduction

Alaska's Cook Inlet Oil Fields are located approximately 60 miles southwest of Anchorage. Cook Inlet platform locations are shown in Fig. 1. A total of 15 platforms have been set in the Inlet, of which 10 are operated by Unocal Four platforms, Anna, Bruce, Baker, and Dillon rely entirely on downhole hydraulic pumps for artificial lift.

Rig and workover operations are often uneconomic due to high mobilization costs. In 1993, one well on the Baker Platform and in 1994, one well on the Anna Platform were shut in indefinitely due to problems with downhole hydraulic power oil equipment. This paper details the new workover technique that economically returned these wells to oil production.

Description of Hydraulic Power Oil Lift System. Produced oil is the hydraulic fluid used on the platforms. Produced oil from the stock tanks is pressurized to 4000 psi at the surface and is referred to as power oil. A controller on each well controls the rate of power oil pumped down the well's power oil tubing string.

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