Reassessing Operational Strategies for Wax Management Reduces Expenses
Authors: Wilson Adam 
Published: October 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27532, “The Importance of Periodic Reassessment of Operational Strategies for Wax Management,” by David M. Lavenson, SPE, Rama Venkatesan, SPE, Michelle K. Young, and Neal Kebert, Chevron, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission.

This paper presents a case study that is an example of how reassessing a flow-assurance risk-management strategy for operating assets can identify opportunities for optimization. Too often, flow-assurance risks are examined only after problems occur. In the absence of these events, many may assume the flow-assurance risks are managed optimally. Periodic reassessment of the risk-management strategies is a key concept for full life-cycle flow-assurance engineering.

Introduction

Flow-assurance risks for offshore fields can be managed in a variety of ways that can be defined generally into risk-management or risk-avoidance strategies. As offshore developments progress into deeper waters with more-challenging technical issues, more-costly risk-avoidance strategies can jeopardize overall project economics. In contrast, risk-management strategies are considered through means of mechanical, thermal, operational, or chemical adjustments to manage the flow-assurance risk rather than attempting to remove it entirely.

Waxy crude oils are fairly common in offshore operations. As system temperatures drop below the wax appearance temperature (WAT), wax crystals will precipitate and cause deposition issues because of the thermal gradient between the bulk fluid and the pipe wall. A variety of mitigation techniques can reduce the effects of wax deposition on flowlines and pipelines offshore, including insulation, addition of heat, pigging, and the addition of paraffin inhibitors. In the development stages of a project, these risks are quantified by use of fluid properties and additional laboratory testing in order to estimate the required risk level and economic options for risk mitigation. The selected methods for managing the risk are used for first oil and adjusted and optimized while minimizing risk of compromising safe and reliable operations. Given the dependence of flow-assurance risks on various fluid and system properties, these risk-management strategies require periodic reassessment to ensure an optimized approach. This paper will present a case study where reassessment of a flow-assurance risk-management strategy resulted in an optimized approach that generated significant operational-expenditure savings.

An offshore, brownfield development in West Africa has two subsea export pipelines that transport a medium-gravity waxy crude oil to an intermediate platform and eventually onshore. The crude in the export lines is from multiple wells and commingled, with each crude featuring varying amounts of wax, resulting in a combined oil that has a WAT ranging from 70 to 85°F. Ambient water conditions are less than 50°F, resulting in a temperature gradient across the fluid and pipe wall to the seawater. Because of the length of the export pipelines and lack of insulation, the oil cools to temperatures below the WAT well before the export line terminates at the intermediate platform.