Post-Yield Design of Thermal Service Tubulars and Connections - Case Studies
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Cited by 6 publications
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The first thermal pilot project in the Huyaparí field (formerly Hamaca) in the Orinoco Belt in eastern Venezuela was designed to use ‘non-thermal’ wells in an existing cold producing field to explore steam stimulation injection and production response while maintaining wellbore integrity and safe operations. The pilot project consisted of performing cyclic steam stimulations in active horizontal producers. The selected candidates were active wells producing extra heavy crude oil (8–9 °API) from prolific unconsolidated sands with 30% porosity and >5 Darcy permeability. A selection process was implemented to identify wells based on favorable sand quality and dynamic reservoir conditions to address potential issues of relatively high-pressure high-temperature saturated steam injection conditions. A risk analysis was implemented to design the injection completion and workover program to maintain well integrity during high-temperature steam injection (550 °F). Well injection completion consisted of concentric vacuum-insulated-tubing (VIT), thermal hydraulic-set packer, thermal wellhead conversion, and high temperature downhole sensors; all designed to protect Class B cement and 9.625-in. J-55 BTC production casing. In addition, open-ended injection tubing was installed inside standalone 7-in. slotted liner (0.020-in.) approximately 1500 feet past production casing shoe depth to mitigate potential steam backflow. The steam injection phase consisted of delivering 80% quality steam at wellhead using a portable steam generator (25MMBTU). Upon injection completion, the well was left shut-in for five days to undergo a soak period to dissipate heat to reservoir. Finally, the wells were converted back to production by safely removing the injection completion and installing a 5.5-in. production tubing, sucker rods, insert rod pump, and downhole intake temperature-and-pressure sensors for monitoring reservoir behavior. This paper will discuss well selection criteria to achieve reservoir injection and production results, injection completion design based on wellbore risk analysis, and well integrity performance based on strain-based design using the Modified Holliday Stress Ratio (HSR) approach for thermal service tubulars of the first cyclic steam stimulation project in ‘non-thermal’ wells.
The first thermal pilot project in the Huyaparí field (formerly Hamaca) in the Orinoco Belt in eastern Venezuela was designed to use ‘non-thermal’ wells in an existing cold producing field to explore steam stimulation injection and production response while maintaining wellbore integrity and safe operations. The pilot project consisted of performing cyclic steam stimulations in active horizontal producers. The selected candidates were active wells producing extra heavy crude oil (8–9 °API) from prolific unconsolidated sands with 30% porosity and >5 Darcy permeability. A selection process was implemented to identify wells based on favorable sand quality and dynamic reservoir conditions to address potential issues of relatively high-pressure high-temperature saturated steam injection conditions. A risk analysis was implemented to design the injection completion and workover program to maintain well integrity during high-temperature steam injection (550 °F). Well injection completion consisted of concentric vacuum-insulated-tubing (VIT), thermal hydraulic-set packer, thermal wellhead conversion, and high temperature downhole sensors; all designed to protect Class B cement and 9.625-in. J-55 BTC production casing. In addition, open-ended injection tubing was installed inside standalone 7-in. slotted liner (0.020-in.) approximately 1500 feet past production casing shoe depth to mitigate potential steam backflow. The steam injection phase consisted of delivering 80% quality steam at wellhead using a portable steam generator (25MMBTU). Upon injection completion, the well was left shut-in for five days to undergo a soak period to dissipate heat to reservoir. Finally, the wells were converted back to production by safely removing the injection completion and installing a 5.5-in. production tubing, sucker rods, insert rod pump, and downhole intake temperature-and-pressure sensors for monitoring reservoir behavior. This paper will discuss well selection criteria to achieve reservoir injection and production results, injection completion design based on wellbore risk analysis, and well integrity performance based on strain-based design using the Modified Holliday Stress Ratio (HSR) approach for thermal service tubulars of the first cyclic steam stimulation project in ‘non-thermal’ wells.
Post Yield Strain Fatigue Experiments to Validate Low Cycle Methodology for Tubular and Connections
Post yield design methodology using Ductile Failure Damage Indicator (DFDI) for well tubulars was proposed and has been used for tubulars and connections life assessment. The tubular design assessment model incorporates a connection strain localization factor (SLF) to assess the fatigue life of the tubulars. Critical strain, a material-dependent parameter essential for DFDI, is obtained using the uniaxial stress-strain tests (i.e., strained to failure uniaxial tests). Understanding the impact of accumulated cyclic damage on critical strain is essential to the post-yield design approach. This paper aims to validate and evolve the low cycle methodology by 1) quantifying the effect of accumulating cyclic plastic strain on the critical strain through a series of post-yield axial and thermal strain fatigue experiments, and 2) applying the post-yield design approach to assess tubulars and connections. Low cycle fatigue experiments demonstrating the critical strain measurement and its dependency on the thermal and axial-strain cycles will be discussed in the paper. Critical strain (K55 and L80) from monotonic tests is compared to critical strain obtained from cyclically preconditioned samples. Effect of cyclic plasticity on critical strain is established quantitatively. Coupons are also subjected to the post-yield axial and thermal cycles to failure and compared to critical strain-based DFDI design predictions. Since connections are known to be the weakest link in the casing system, the impact of connection thread-forms on the strain localization factor is demonstrated using a series of finite element models and the experimental material responses. Axial strain-controlled loading would be applied on the tubulars and connections to estimate the damage using the DFDI approach. A systematic approach to delineate the dependency of critical strain on cyclic straining validates the effectiveness of DFDI in thermal well design. Further, the quantification of SLF for integrating connection into thermal well design provides a complete solution.
Although thermal heavy oil recovery methods are extensively used, no unified and standardized basis exists for selecting materials and configuring intermediate (production) casing/connection systems for these extreme-service applications. Thermal intermediate casing systems must accommodate a wide variety of mechanical and environmental loads sustained during well construction, thermal service at temperatures exceeding 200°C, and well abandonment. Numerous operator- and field-specific designs have been used with good success and only a few isolated challenges, but industry's use of its operating experience to calibrate tubular design bases for future wells has been limited. This paper identifies the benefits and components of a unified casing system design basis for thermal wells, aimed to be technically comprehensive, inclusive of the available elements of industry's collective knowledge and experience, and adaptable to technological advancements. The technical element of the unified basis broadly relates to the engineering foundation used to make three primary design selections: material, pipe body, and connections. For each design selection, the paper provides an overview of the associated technological challenges and the current state of the industry in addressing those challenges, including the commonly-adopted design approaches. Key performance considerations include integrity during well construction, connection thermal service structural integrity, pipe thermal service integrity and deformation tolerance, connection sealability, and casing system environmental cracking resistance. Where applicable, the paper identifies interdependencies that exist between design selections (for instance, the impact of pipe material selection on the thermally-induced axial load that must be borne by the tubular and connection), and discusses mechanisms for accounting for those added complexities in the design. Ultimately, the intent of this paper is to provide a framework for referencing existing technical knowledge and for considering further development and field benchmarking work that will reduce the technological uncertainty and increase simplicity in thermal casing system designs. Industry will benefit from a unified engineering approach that offers operators sufficient flexibility to accommodate application requirements and prior experience.
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