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.