Abstract

With the increased use of larger-sized coiled tubing (CT), demand for CT tools is pushing the limits of tool rating and frequently extending the sizes required for jointed tubing operations. This paper describes a high-pressure, high-temperature (HPHT) motorhead designed for larger-sized CT and/or jointed pipe. Motorheads are used for well control, emergency-release disconnects, enabling circulation to the annulus, and establishing circulation to the annulus should the normal circulation path become plugged.

The development and design of the new motorhead will be described, including its special mechanical capabilities that depended on careful alloy and elastomer selection. For example, the flapper valves can withstand 20,000-psi differential pressures in -40 to 400°F temperature cycles (from cold-hot-cold) in a single run. The flappers were designed to close in slam-shut situations without compromising well control, and the hydraulic disconnect can bear higher torque and tensile loads than any similar tool currently available.

The completion fluid in combination with the well fluids presented problems for conventional sealing compounds exposed to pressure and temperature extremes. Results from a two-month testing period are discussed, which included pressure, temperature, tensile strength, torque, and fluid compatibility tests. FEA and CFD analyses were used to simulate flow, pressure, and slam shut conditions, enabling the most effective motorhead design for HPHT environments.

A North Sea case history of a successful well intervention using the new motorhead is also described. Three fully certified traceable HPHT motorhead assemblies were used for six runs over a combined 121 days in wellhead pressures up to 10,800 psi and downhole temperature of 365°F. The tool was tested and serviced between runs. Under these rigorous conditions, it was critical that the valves held backpressure and retained their integrity after continuous pumping under high pressures and temperatures—these objectives were achieved.

Introduction

This paper outlines the request, design, development, and performance history of a high-pressure, high-temperature (HPHT) 3.38-in. OD compact motorhead assembly (MHA) adapted from its coiled tubing roots for application on hydraulic workover (HWO) operations in the North Sea.

The original requests from the operator were for deployment of jointed tubing with a 15,000-psi double-flapper check valve (DFCV); however the requirements and specifications grew significantly over the course of the operation. Eventually, the decision was made to design a new MHA rated to 15,000-psi flapper differential, 400°F temperature, 9-bbl/min flow, H2S compatibility, and sealing ability for 21-day, cyclic hot-cold temperatures.

Final product delivery (two tools and the test prototype) was required within 5 months of the request along with an adapter to run the DFCV solo.

Case history details from this project are included to validate the design.

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