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Abstract

Effectively engineered flowline bundles are attractive configurations for deepwater field development, because of their thermal performance and cost effectiveness. Bundled-insulated subsea flowlines provide economic alternatives for chemical injection to eliminate or reduce the risk of hydrate, wax or paraffin formation. The purpose of this study is to investigate the thermal interaction among the flowlines and its effects on the overall thermal performance of the bundle, and on the product arrival temperature. Multiphase flow and thermal analysis procedures were conducted for the Garden Banks 216 field pipeline bundle located in the Gulf of Mexico.

The investigated bundle has three flowlines that carry multiphase product fluid and heating fluid. The flowlines are enclosed with insulation and encased in a steel casing pipe. During normal operation, the product can flow in one or two flowlines while the third is for service. When active heating is applied, hot oil will be injected into one of the flowlines at the platform. The heating oil will be circulated through the flowline and the service line, and the third line will be for produced fluid. The pigging loop will be used as the turnover loop.

This study is to determine the steady state performances of each flowline in the bundle, including the multiphase product line and two-single phase heating lines. The temperature profiles are presented for different product flowrates. The effects of product flowrate, injection flowrate and injection temperature on the pipeline temperature profiles and product arrival temperature are discussed.

Introduction

The Garden Banks Block 216 (GB 216) field development is a 3.7-mile subsea tie-in project in the Gulf of Mexico. Flowlines from subsea wells are operating in multiphase flow conditions. The multiphase flow transportation involves transporting an untreated well stream consisting mainly of gas and crude oil, due to a relatively low water cut of the product. Flow assurance is an issue for the GB 216 field development because of the possibility of wax deposition. The designed pipeline system had to be able to maintain the steady state temperatures above the product wax appearance temperature under the operation pressure throughout the subsea system.

Prediction of the multiphase flow behavior of the designed production system was a required part of the design criteria. Compared to a conventional pipe-in-pipe configuration, the multiphase flow and thermal analysis of bundle systems are more complicated, and the information available in the open literature is limited [1-5].

A computer model is needed to simulate the pipeline multiphase flow in a cased, insulated, multiple-flowline bundle. The model should be solved using a multiphase flow simulator, OLGA, combined with a modified conduction heat transfer model. The numerical analytical results are compared with the field data.

The objectives of this paper are:

• Develop a computer model to simulate the multiphase flow in a multiple flowline bundle. The model can be solved by the “Bundle” package of the OLGA simulator.

• Study the thermal performance of the flowline bundle, and the thermal interaction among the product line, service line, and return line.

• Investigate the effects of product flowrate, injection flowrate, and injection temperature on the pipeline temperature profiles and product arrival temperature.