This paper focuses on tubing material selection study conducted for a high CO2 oil field located offshore of Peninsular Malaysia. The field's CO2 concentration varied laterally and with depth. The highest CO2 concentration of 66 mol% in gas had been recorded from well test and fluid data. This resulted in severe corrosive environment in the wells. Based on the well surveys, many existing wells which were completed with API-5CT L80-13Cr had suffered from localised corrosion within a span of two (2) years of production. Existing material selection was revisited in order to prevent corrosion in future development wells. An important change made was to conduct material qualification test specific for the field conditions on several corrosion resistant alloy (CRA) materials. The details of the test and findings are presented. To better understand the corrosion severity in existing well completion, well survey results are also discussed.
This paper intends to share the approach adopted by Petronas Carigali Sdn Bhd (PCSB) to evaluate the fatigue performance envelope for a selected casing connection to support the ever expanding Casing while Drilling (CwD) technology. This paper elaborates the original testing procedure which included both fatigue testing followed by sealability test after repeated fatigue cycles to best simulate downhole drilling environment as experienced by the casing connections during CwD operation. Fatigue performance and gas sealability reliability after undergoing fatigue cycles is one of the key selection criteria for casing connection for CwD application. This is of paramount importance to prevent unforeseen downhole fatigue failure which could lead to the loss of pressure containment and/or the severance of casing string if sufficient tensile load is applied. Currently, there is no established industry recommended practice on the testing procedure to validate the connection's reliability to cater for CwD application. The closest available is API RP 5C5 or ISO 13679 which only focuses on OCTG premium connections' sealability performance. PCSB, being one of the pioneer operators who have adopted CwD aggressively is determined to ensure that all casing connections used in CwD applications are physically tested and validated to establish a reliable fatigue envelope. In this project which took about 1 year to complete, a semi-premium connection without metal-to-metal seal threaded on 13-3/8 in. 68 ppf L80 pipe was tested in a 2-phase testing program. Phase 1 saw the connection being subjected to cyclic bending to failure while Phase 2 focused on connection gas sealability after going through a pre-set fatigue cycle. The novelty of this fatigue evaluation test procedure is that it attempted to delve deeply into the effect of test specimen preparation on the resulting fatigue data such as thread interference, thread taper, running compound, make up torque, surface treatment and etc. The ultimate objective of this test procedure with further refinement implemented is to ensure that the SAF (Stress Amplification Factor) obtained would be sufficiently reliable for future CwD applications in PCSB which will eliminate the risk of unexpected downhole failure in the form of fatigue and/or loss of containment.
A new Oil Country Tubular Goods (OCTG) Corrosion Resistant Material (CRA) 17-Chrome (17CR) was introduced in late 2011. The corrosion resistance performance of such material was claimed to be comparable to a higher grade material of duplex stainless steel 22-Chrome (22CR) under a given aggressive corrosion environment. In addition to that, 17CR was expected to be significantly competitive and commands shorter delivery lead time compared to 22CR as it does not require cold-drawing process to achieve the required high yield strength. PCSB had evaluated this new material for one of its massive LNG development projects through a series of qualification testing. These LNG carbonate fields were highly corrosive with CO2 and H2S content up to 22 mol% and 140ppm respectively. Maximum bottom hole temperature anticipated was more than 180 degrees Celsius. Material selection for production tubing was therefore of paramount importance in such severe well condition to ensure that long term well integrity was not compromised with this newly developed material. Through the establishment of a multidisciplinary team, PCSB had established a set of rigorous qualification test procedure, fully aligned with industry standards to ensure that the identified risks were mitigated from both material and connection perspectives. This paper will describe the systematic approach that was used to evaluate the reliability of the new material with a premium connection under the defined worst case conditions; discuss the corresponding results which led to significant cost savings for the mentioned project.
The ongoing low oil price environment underscores the need to be constantly prudent. Long term sustainable changes implementation are necessary in all areas to preserve profitability including that of effective drilling materials and surplus management with OCTG (Oil Country Tubular Goods) being the prime issue from both quantity and price perspectives. Drilling operators especially those with large scale and diversely complex well programs have to manage excessive surplus mess uncontrollably amassed when oil prices were high. Some opted to dispose while others chose surplus reutilization. Disposal seems to be an easier way out as it frees up yard space and reduces preservation cost but it incurs value leakages as it often fetches unreasonably low scrap prices. PETRONAS took on a bold strategy to overcome the issue by channeling efforts on producing a robust OCTG standardization program as well as enhancing reutilization through reverse engineering which involves meticulously designing wells casing programs based on available surplus. These initiatives aim to take materials management to a higher level of efficiency and avoid future excessive surplus accumulations. This paper will walk through the various hurdles and solutions in the course of delineating Fit-For-Purpose (FFP) configurations and minimum technical criteria for OCTG material and connections specifications to satisfy PETRONAS’ application requirements for all well types ranging from conventional to High Pressure High Temperature (HPHT) and Deepwater. It also describes various operational challenges from onshore machine shop support to offshore tubular running equipment and services which were critical pieces in putting together the standardization puzzle. It will further provide a lowdown on the misperception of having the lowermost specifications and lowest prices as the primary drivers in realizing the greatest value for money for OCTG applications especially for operators with wide ranging application needs.
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