Barreto, Rodrigo (Weatherford) | Badrak, Robert (Weatherford) | Howie, William (Weatherford) | Spadinger, Rodrigo (Vallourec) | Santos, João (Vallourec) | Rodrigues, Ricardo (Vallourec) | Zeemann, Annelise (Tecmetal) | Emygdio, Guilherme (Tecmetal) | Fontes, Carlos Henrique (Tecmetal)
Drillpipe risers (DPR) constructed with high sulfide stress cracking (SSC) resistance are designed and fabricated to suit subsea completion and early production operations in sour environments (H2S). Early production operations typically include extended well testing (EWT), which is required to evaluate production characteristics. The riser string, among other components, is composed of drillpipe riser joints. The DPR joint manufacturing process includes welding a tool joint with a pipe body via rotary friction. The tool joint is a forged, quenched and tempered high strength low alloy steel piece with threaded connectors. The pipe body is a high strength low alloy seamless tube with upset ends, which are also fully quenched and tempered. After the friction weld process, the heat affected zone (HAZ) of the weld is heat treated to meet material properties and performance requirements.
Performance requirements in sour service wells include material low hardness which is difficult to obtain on high strength quenched and tempered steel, especially on a weld zone. With this challenge in mind, a DPR manufacturer engineered a superior combination of chemistry, friction welding conditions, and heat treatment parameters that are designed to meet both mechanical and SSC resistance requirements for sour service.
This paper presents the results of the testing qualification process, which was co-developed together by the involved companies, using joints with extremely accurate thermal cycles control and chemistry balance, to meet mechanical properties in the weld line region and microstructures that make the DPR suitable for operations in H2S enriched environments. The post welding heat treatment (PWHT) variables were critical, since tiny variations resulted in major differences among samples. Each sample was evaluated through optical microscopy (OM) and scanning electron microscopy (SEM), mechanical testing and SSC resistance test according NACE TM0177. The temperatures and time limits for the PWHT cycles associated with the tempering effects on the microstructure were determinant to maintain optimal performance in the H2S test.
Additive manufacturing (AM) processes have been shifting from primarily prototyping products to the production of fully functional end parts and components. An understanding of the material characteristics necessitates an evaluation of the mechanical and corrosion behavior in order to determine and quantify the limitations of AM processes.
This paper focuses on characterizing Alloy 718 produced via the Direct Metal Laser Sintering (DMLS) process in the as-fabricated and heat treated condition. The printed Alloy 718 material was produced on a single plate comprised of rectangular, cylindrical and round shapes of varying section thickness that were subjected to evaluation that included chemistry, microstructural, mechanical, fatigue and corrosion testing. Heat treated sections were solution annealed and precipitation hardened in accordance with API 6ACRA.
The precipitation hardened nickel based alloys are widely utilized for downhole applications such as drilling and completion equipment. Additive manufacturing, or three-dimensional (3-D) printing, has received a great deal of attention in recent years. Additive manufacturing is a suite of emerging technologies that fabricates three-dimensional objects directly from digital models through an additive process, typically by depositing and ”curing or solidifying in place” successive layers of polymers, ceramics, or metallics. Unlike traditional manufacturing processes involving subtraction (e.g., cutting and shearing) and forming (e.g., stamping, bending, and molding), additive manufacturing joins materials together to build products. Additive manufacturing technology is shaping the future of product development and manufacturing in small complex geometry components and specialized applications.
Additive manufacturing was originally conceived as a way to make prototypes but has slowly transformed itself to the extent that it is increasingly being used to deliver final products. Recent improvements include enhancements of the speed and performance of additive manufacturing machinery, an expanding range of input materials, and falling prices for both machinery and materials. The development of AM technology and the state-of-the-art has recently been accelerating because of improvements in laser and electron beam AM equipment using powder injection, powder bed or wire feed systems that has also benefited by advances in the build for additive manufacture software programs. The new design for manufacturing software programs in developments such as predictive modeling of residual stresses during the laser powder bed builds helps identify issues with a given design or build orientation to reduce/eliminate build failures.
As the severity of sour drilling applications has increased, the requirement for drill stem materials resistant to sulfide stress cracking (SSC) has accelerated. Sour service drillpipe, traditionally manufactured with SSC resistant upset tubulars and tool joints, has been available for some time. Sour Service drillpipe metallurgy is not specifically controlled by NACE MR 0175/ISO 15156,1 however these tubulars and tool joints are often evaluated in accordance with the standard. The friction welds joining the upset tubulars and tool joints were not resistant to SSC and were not evaluated. This has been acceptable for many sour drilling applications since the weld is not the mostly highly stressed region of the drillpipe joint and because the operator has a certain degree of control over the environment through the drilling fluid properties and additives. As more severe environments with higher Hydrogen Sulfide (H2S) concentrations were identified for exploration and development, it became apparent that a fully SSC resistant drillpipe system including the friction welds was necessary.
This paper presents the successful development and qualification of SSC resistant friction welds for critical sour applications. It describes the engineering and manufacturing philosophy employed, laboratory testing procedures with results presented and applications for the SSC resistant drillpipe. Since NACE MR 0175/ISO 15156 does not address friction welds the engineering team developed unique and innovative criteria together with testing procedures for the new weld technology. A new patent pending four-point bending test procedure and fixture were developed that employed unpolished samples that represent the surface finish of the product in service, in contrast to the polished samples used in NACE TM-0177 testing. This paper provides background information on the evolution of sour service drillpipe and reviews case histories where sour service drillpipe has been successfully used including the new pipe with SSC resistant friction welds. The paper can benefit drilling engineers involved in critical sour drilling operations.
Sour Service Drillpipe
The drillpipe assembly incorporates a tool joint that is typically manufactured from a forging and a friction weld that attaches the tool joint to the upset of the pipe body. This is the same manufacturing configuration that has been employed on drillpipe for decades and has been adapted to incorporate materials that resist SSC for dritical sour applications. The manufacturing technology for critical service drillpipe has evolved significantly in the last several years. Major advances relating to pipe specifically developed for use in areas with significant H2S content have been realized.
Sulfide Stress Cracking (SSC) due to the presence of H2S gas in the downhole drilling environments has led to the development of sour service drillpipe, which is engineered to have resistance to SSC. Previously available sour service drillpipe was comprised of an SSC resistant upset to grade tube and tool joint. The friction weld areas that are used to join the tool joints to the upset ends of the tubes were not manufactured for resistance to SSC.
The weld area of sour service drillpipe has not been SSC tested in the past, and there have been no documented SSC failures in the weld zone of sour service drillpipe. There are several factors that make an SSC failure in the weld zone of sour service drillpipe unlikely. The region on both sides of the weld has a much larger cross-section (1.5 to 2.0 times) than that of the tube. This larger weld area cross-section means the stress experienced in that area is less by the same proportion. This reduced stress makes the likelihood of failure due to SSC significantly less likely. It is generally possible during drilling operations to control the well environment and help prevent SSC failure of the drillpipe and weld zone.2 Implementing the following practices can help control the drilling environment and prevent SSC:
- Maintain the drilling fluid density to minimize formation fluid influx.
- Neutralize H2S in the formation fluids by maintaining a mud pH of 10 or higher.
- Utilize sulfide chemical scavengers and/or corrosion inhibitors.
- Use oil-base drilling fluids.
The application requirements including various combinations of corrosion resistance, high strength, high impact/fracture toughness, and environmental cracking resistance are presented in relation to the challenges that they represent for welding. Achieving these requirements is discussed in relation to welding process limitations, material limitations and availability of suitable consumables. Several examples are presented that illustrate the problems associated with meeting design requirements.
A review of technology and applications for the in-situ expansion of solid tubulars is presented. The techniques used to accomplish expansion are compared and contrasted with respect to post-expansion performance and suitability for different construction and remediation applications. The evolution of tool designs for both cone and rotary systems and the influence of expansion simulation techniques are discussed. A review of mechanical and environmental performance of steels and corrosion resistant alloys (CRAs) is summarized and the results of recent testing work introduced.
Industry utilization of solid expandable technology has become established in recent years. As of November 2004, the principal expandable service companies have made more than 320 installations. The range of applications has been fairly diverse but can be broadly categorized into well construction or completion/remediation functions.
The impetus for solid expandable tubular development can be traced to early work by operators in the late eighties1,2. The original drive, and still a major aspect in current products and new developments, was to reduce or eliminate the tendency for telescoping in the casing program. The potential primary and secondary cost benefits generated are significant and have been sufficient to initiate long-term research and development programs within operator and service companies. Subsequent opportunities for expandables in different functions, e.g. hanger, isolation, casing repair and sand control devices, were identified and developed concurrently with well construction technologies. In addition to testing and development work on functional and operational aspects of expandable technologies, operators and service companies have been working to determine the effects of expansion on material performance; including both mechanical and corrosion-related aspects. This paper aims to provide an overview of solid expandable technology, applications and testing and to cover some new areas of development.