Future of Nonmetallic Composite Materials in Downhole Applications
The complete paper highlights examples of nonmetallic materials selection and qualification for upstream water-injection and producer and hydrocarbon wells and presents suggestions for future progress.
Nonmetallic (NM) composite-based materials offer distinct advantages in overcoming the effects of corrosion, scale, and friction on carbon steel to minimize frequent workovers and extend the life cycle of critical downhole products. However, high initial cost and technical-skills limitations pose challenges to more-widespread development and deployment of these materials downhole, particularly in extended-reach drilling and other challenging wells. The complete paper highlights examples of nonmetallic materials selection and qualification for upstream water-injection and producer and hydrocarbon wells and presents suggestions for future progress.
Carbon steel (CS) is the material of choice for downhole applications because of its advantages over other materials in terms of cost, temperature and pressure ratings, and field-construction-support services. The downsides of CS include corrosion, scale, and friction that can result in high repair and workover costs and limitations of equipment life. Corrosive fluids are handled generally by chemically inhibited CS and corrosion-resistant alloys (CRAs). However, CRAs can increase project cost and complexity significantly. NM composite materials have been introduced for drilling and completions in high-risk, corrosive environments to minimize the effect of corrosion, scale, and friction in CS tubulars and extend the well life cycle. The new proposed materials are lightweight, high-strength, and offer superior fatigue and corrosion resistance.
Economic analysis shows that using NM tubulars and internal linings will yield substantial life-cycle cost savings per well, mainly from the elimination of workover operations. However, composite materials pose several challenges. In downhole environments, the materials are subjected to a more-complex set of dynamic stress conditions under variable multiphase fluids and temperatures. Forces such as burst, collapse, tension, and axial compression play a significant role in NM downhole tubular performance. In deep-well operations, service tools are required to perform at high pressures and temperatures. Currently, the industry has explored the opportunity to deploy NM materials in standard applications while pursuing research and development (R&D) to expand the operating envelope to target high-pressure/high-temperature applications.
Composite Material and Design Selections
Composite materials are made by combining two or more materials to create new materials with properties unique from those of the original materials. NM composite materials are divided into two groups—fiber-reinforced plastic and fiber-reinforced epoxy. The matrix materials are classified into three categories: thermoplastic, thermosetting, and elastomeric. A diverse array of reinforcements includes glass, carbon, and aramid of different grades that can be used as tape or braided fibers. The role of the fiber is to carry the overall load, and the role of the matrix is to transfer the stress within the fiber and protect the system from mechanical damage. Proper material selection of fiber and matrix considering functional requirements, temperature, pressure, and chemical and abrasion resistance is key to safe, reliable, fit-for-purpose, cost-effective operation over the design life of the well.
Future NM Applications
Deployments of NM composites for drilling and completions have seldom occurred because of the materials’ cost and the limited number of industrial guidelines and standards supporting downhole applications. Existing applications of NM materials downhole, such as for casing centralizers, drillpipe protectors, and glass fiber-reinforced epoxy (GRE) liners, have been guided and deployed by engineering experience on a case-by-case basis. Fig. 1 identifies several downhole applications that have been replaced, or are expected to be replaced, with NM composites over the next few years.
Though many future deployment opportunities for NM composites upstream exist, some of are at low technology-readiness levels. Others need thorough technical evaluations to become feasible for downhole applications. Currently, a well-developed process exists in the industry to align NM deployment and development among different proponents, technical organizations, and R&D entities to resolve potential challenges. The complete paper presents a detailed discussion of several promising upstream applications.
The full NM composite tubular (tubing/casing) and velocity string provides an alternative solution to conventional CS, providing internal and external corrosion resistance when the tubular is exposed to severe corrosive environments. Use of GRE tubulars in shallow water has increased significantly during the past few years. Currently available composites can operate at downhole temperatures not exceeding 100°C. However, research is ongoing to use composite materials for working temperatures from 150 to 170°C in geothermal wells deeper than 3500 m. A complexity-vs.-time matrix is being developed to support the development plan promoting composite use in upstream oil and gas operations. The main industry focus is on water applications at the time of writing, because these present less associated risk and are more cost-effective than CS.
The development of NM composite tubulars for oil and gas operations is a major challenge because of the high initial costs of raw materials, the necessity of special manufacturing processes, and the complexity of the downhole operating conditions. Therefore, several technical and economic factors need to be evaluated as part of feasibility studies. These are presented in the complete paper.
Most downhole completion systems were developed on the basis of the use of metallics. For instance, metallic sand-screen systems offer a simple and economical method for controlling sand, but are subject to erosion and corrosion issues that limit their life expectancy. Ceramic screens followed. Polymer composite sand screens are being investigated as a cost-effective alternative, but are limited to temperatures below 93°C. Efforts are now under way to expand the operational envelope of composite sand-screen systems by evaluating alternative advanced plastic materials that withstand high downhole temperatures. This would be a breakthrough technology that could resist corrosion and erosion issues faced by conventional sand screens, and could pave the way for other applications in downhole completion systems.
Shape memory polymers, which change their properties in response to external stimuli, also have been investigated as promising materials for downhole applications, specifically in sand management. Shape memory polyurethane foam has several potential applications in downhole zonal isolations, water-shutoff, and fracturing operations.
Dissolvable and drillable composite tools were designed to provide zonal isolation between multistage stimulation treatments. Composite fracturing plugs help mitigate risk during drillout while decreasing time on location and costs to complete unconventional wells. R&D efforts into dissolvable materials that can hold high pressure during completion operations and then can be retrieved look promising.
Elastomer materials have found a niche downhole in the form of seal elements for blowout preventers and packers, O-rings and seals for valves, and power sections for downhole motors. Swellable packer technology has gained momentum steadily. More-demanding applications are pushing the boundaries of elastomers. However, intensive R&D and qualification efforts are ongoing in this area, in which combinations of elastomers such as perfluoroelastomers and engineering plastics such polymides are gaining momentum.
Conventional well-intervention conveyance tools such as steel coiled tubing (CT) and wireline have issues with pitting corrosion and are subjected to high friction, which limits the ability of CT to reach target depth. The first composite CT was not successful. CT based on thermoplastic composites is still under development. Composite wireline to replace conventional metallic lines is also undergoing proof-of-concept studies.
Casing Flex Shoe
A composite flexible shoe reduces side loads at the bottom of the drillstring when running casing with a high build rate and inclination, to minimize the risk of getting stuck off bottom.
A conventional metallic impeller/diffuser for downhole electrical submersible pumps (ESPs) is subject to frequent failure because of the highly corrosive environment. For conventional ESP impellers in such environments, particle erosion and corrosion from sand production is the main cause of component failures. Engineered composite pumps have outlasted metallic parts by many years because the composite pumps resist cavitation better and are not subject to corrosion or electrolysis attack.
NM composites offer many advantages in terms of corrosion resistance and well-life-cycle extension. However, substantial challenges remain. The path forward involves developing roadmaps to accelerate mass deployment, support localization, and encourage investment in research studies. This effort requires joint work with different entities to establish a basis for increasing deployment of cost-effective materials for more-demanding applications. The complete paper includes proposed initiatives for optimizing NM composite expertise and development capabilities.
This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 198572, “The Future of Nonmetallic Composite Materials in Upstream Applications,” by Wael Badeghaish, SPE, Mohamed Noui-Mehidi, SPE, and Oscar Salazar, Saudi Aramco, prepared for the 2019 SPE Gas and Oil Technology Showcase and Conference, Dubai, 21–23 October. The paper has not been peer reviewed.