Reliable Sub-Sea Umbilical and Down-Hole Injection Systems are an Integral Component of Successful Flow Assurance Programs

Abstract

Sub-sea and down-hole chemical injection systems are necessary components in most successful flow assurance programs. Specially formulated inhibitors and dispersants used in these systems provide solutions to a variety of deepwater and subsurface problems. The prevention or alleviation of wax deposits, asphaltene deposits, hydrate plugs, scale deposits and corrosion depends on an integrated chemical system. This system includes chemical formulation, capillary/umbilical design and proper operation and maintenance. This paper will review these necessary elements of a successful chemical system: chemical formulation, capillary/umbilical design and proper operation and maintenance. Formulation will take account of the requirements for quality, cleanliness and performance, physical properties targets, and compatibilities with well fluids, other treatment fluids, and system components. Design considerations will include compatibilities with the treatment fluids and the external environments as well as mechanical properties. Operation and maintenance will assure continued functionality by providing for cleanliness, redundancy and unexpected problems in every step of the transportation and delivery system. The chemical delivery system must be effective, reliable, forgiving and redundant. Replacement or repair of the system as well as loss of production due to failure can be very costly. In the paper's review of the sub-sea and sub-surface chemical injection systems, laboratory data in conjunction with successful and unsuccessful field results will be used to provide lessons learned and best practices. Introduction Downhole chemical injection systems gained popularity in the oilfield production industry in the early 1980's. This technology has been adapted over the years and more recently become common in deepwater and subsea applications as part of the flow assurance strategy. This chemical deployment method can be very successful with the proper system design, system operation, and chemical products. Flow assurance programs are necessary to produce offshore and in deepwater. Specially formulated inhibitors and dispersants provide solutions to a variety of oilfield problems such as solids deposition and internal corrosion that pose a threat to flow assurance. Blocked or failed production flow paths can result if the flow assurance program is not adequate or fails. The success of the subsea or downhole chemical program is largely dependent on the reliability and functionality of the chemical injection system. Many failed flow assurance programs are attributed to the failure of the chemical injection system. Because these systems are often major capital expenditures and often the cornerstone of a flow assurance program, operators expect the systems to be dependable, robust, and forgiving. The systems are required to serve their function and meet their intended service life. Some current estimates reveal that a failed subsea umbilical can exceed $2MM US per mile to replace and a failed deepwater downhole chemical system can be in excess of $15MM US to recomplete. Mechanisms for failure can include improper design, mechanical failure or capillary restriction. Careful attention to detail during system design, proper chemical product design and selection, and employing industry best practices can increase the chances for success. Design In the design of a capillary or umbilical injection system, there are two primary concerns, the physical system (including materials) and the injected fluids. Appropriate design of both is necessary for a successful system.

Qualification Procedure For Continuous Injection Of Chemicals In The Well -Method Development

“…While continual injection systems are one of the simpler systems in a facility (single fluid, low volume, with a need to maintain a constant rate and a single flow direction) experience in the industry has identified a number of challenges (Shirah 2003, Wylde 2005, Jordon 2005, Olsen 2011). …”

“…If the flowing well bore pressure (plus the crack pressure of the check valve) is less than this, chemical will flow from the injection system until the hydrostatic head is reduced to that of the well bore. This will result in a pocket of vacuum opening within the system (Wylde 2005), probably below the well head check valve (assuming that this has a crack pressure greater that 1 bar). Note that it is more accurate to describe this as a low pressure gas pocket as it will contain a mixture of any gas dissolved in the chemical formulation prior to injection and the most volatile components of the formulation.…”