Hydrate Control and Remediation Best Practices in Deepwater Oil Developments
Authors: Cochran Steven 
Published: October 2008

Deepwater oil developments, operating and under design, were surveyed regarding their hydrate control and remediation techniques. These techniques were evaluated to establish a best practice for deepwater subsea oil developments based on current technology. Technical issues, level of protection, operability, risks, and cost impacts were all included in the evaluation. As a result of this evaluation, best practices and viable new technologies are recommended.

The results of this study are most applicable to deepwater subsea oil developments; however, they also may also be appropriate for land, shallow water, and/or dry tree developments. It is envisioned that this work will be applicable for concept selection and feasibility evaluation stages (i.e. prior to FEED). The conclusion of the study consists of a best practice using available and proven technology. This best practice can be summarized as follows:Insulate flowlines, risers, trees, manifolds, and jumpers to provide "no-touch" cooldown time tohydrate conditions following shutdown,use wellbore insulation when appropriate,Provide methanol injection points at subsea trees and/or downhole,Provide capability for hot oil circulation in flowlines,Provide capability for depressurization and displacement. Depressurization is the principal method of remediating hydrate blockages. The biggest caveat with the best practice listed above regards remediation, since seafloor topography, system geometry, and produced fluids may not allow sufficient depressurization. New technology that will provide benefits for near-term deepwater oil developments include active heating and low dosage hydrate inhibitors.

Hydrate control and remediation is one of the greatest challenges in developing deepwater oil fields. A significant amount of effort is required in the design phase to develop a production system that achieves hydrate control with an acceptable level of risk. This study provides a design guide for evaluating hydrate control and remediation techniques for concept selection and feasibility work.

Introduction

This paper presents an evaluation of hydrate prevention and remediation techniques to determine a current best practice for deepwater oil developments. Practices currently applied by operators in developments both in operation and under design have been collected and assessed.

Techniques for both preventing the formation of hydrates and remediating hydrate blockages have been considered. Technical issues, level of protection, associated risks, and cost impacts were included in the evaluation of techniques. From the evaluation, recommended techniques are proposed.

Background.

Hydrates are crystalline compounds that form when water and light hydrocarbons or other small compounds (e.g. methane, ethane, propane, nitrogen, carbon dioxide, hydrogen sulfide, etc.) are present together at relatively low temperatures and high pressures. When the temperature and pressure are in the hydrate region, hydrates grow as long as water and light hydrocarbons are available and can eventually develop blockages. Clearing hydrate blockages in subsea equipment or flowlines poses safety concerns and can be time consuming and costly. Hydrate formation is typically prevented by several methods including controlling temperature, controlling pressure, removing water, and shifting thermodynamic equilibrium with chemical inhibitors such as methanol or mono-ethylene glycol.