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Well Integrity in the Times of ISO 13679 and Premium Connections: Experiences and Way Forward
Abstract
Developments in OCTG connections defining well integrity and mechanical performance of oilfield tubulars are not something newas a continuous feedback between field challenges and theinnovative nature of the Industry is something derivated into newer, more intensive Full Scale Testing procedures and novel analytic tools for connection performance evaluation in the last decades. The relationship between all those factors has been condensed in the present paper which gives shape to a comprehensive "technical history" for Premium Connections, hidden and scattered so far in issued patents, manufacturer manuals, brochures and selected field cases generated between 1935 and 2017.
Design schools can be well defined by manufacturer and region;apart from this, theadvancements in testing and manufacturing made possible to adjust the connection to the technical constraints put fromthe field, namely a high need for gas tightness and enhanced torque capabilities. Last but not least, it was discovered that, among all oilfield equipment used during upstream operations, it was (next to advancements inSSSV's)the constant evolution of tubular connectiontechnologieswhat contributed to "crystallize" the modern concept of Well Integrity, especially after the big offshoredevelopments seen from 1971 on. As a corollary, the impact of current standardization protocols ISO 13679 / API 5C5 on well integrity in terms of metallic seal integrity will be assessed in the light of the tribological and mechanical evolution of the MTM seal during testing and validation.
The seal failure of tubing and casing connections compromises underground gas storage well safety. This work proposes a systematic uncertainty analysis framework for connection sealability assessment. The framework covers reliability analysis and reliability sensitivity analysis and attempts to provide more effective support for the reliability design of connection seals. The reliability analysis introduces an adaptive Kriging with stopping criterion P-Monte Carlo simulation (AKP-MCS) method, which can provide a satisfactory estimate of failure probability with a small number of performance function evaluations. This metamodeling technology can effectively reduce the numerical efforts required for the reliability assessment of connection sealability. In the reliability sensitivity analysis, the refined metamodel obtained from the reliability analysis is coupled into a single-loop Monte Carlo simulation (MCS) method. The classifier attribute of this metamodel can meet the requirement of the single-loop MCS method to classify the signs of sampling points. This attribute enables sample matrices to be evaluated on this metamodel instead of the performance function, making the reliability sensitivity assessment more feasible. The proposed method is first demonstrated with four academic examples with promising results. Next, an illustrative tubular connection case is provided. The proposed scheme gives estimates of the failure probability and reliability sensitivity close to the classical model but requires less computational cost. The results of the analysis can provide useful information for the scheme decision-making and reliability optimization of connection seal design.
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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