With the evolution of casing-drilling technology, connections are subjected
to increasingly stringent well conditions. These conditions include higher
pressures, higher temperatures, and higher mechanical loads for longer drilling
periods. As a result, the performance of the connector under these conditions
is of increasing concern. Most recent casing connection evaluation test
programs are based on International Standards Organization (ISO) 13679 (2002)
requirements. However, API RP7 (1998) is the dominant testing program for drill
stem applications. Because casing-drilling applications combine drilling and
casing concerns, a new test protocol is required to adequately characterize
connection performance (Hegler et al. 2004).
A better understanding of how connection tolerances impact connection
performance under combinations of static and dynamic loading aids in connector
selection and allows the technology to be used in broader casing-drilling
applications. As part of the proposed test program, the static and dynamic
connector performances are evaluated individually to benchmark the design.
Based on these evaluations, additional testing was conducted to determine the
connector static capacity after dynamic loading. This testing demonstrates the
connector performance when used in casing-drilling applications.
This proposed testing protocol can be used to better define connector
performance limits when used in casing-drilling applications leading to
increased operational safety and lower overall risks. This paper includes
results, observations, and conclusions from a subject test conducted in
accordance with the proposed testing protocol on a 9-5/8-inch 53.50 ppf P-110
The objective of this test protocol is to evaluate connection performance
for casing-drilling applications. Tests were conducted in the following four
phases, each with distinctive goals:
Phase I: Design Selection
Phase II: Fatigue to Failure Test
Phase III: Static-Capacity Test
Phase IV: Post-Fatigue ISO Series B Test
Phase I determined the preferred connector design and thread compound
combination. All test specimens were threaded to nominal tolerances, fatigue
tested based on expected field conditions, and subsequently capped-end pressure
tested. Two different connector designs were fatigue tested under identical
loading conditions to determine the preferred connector design. In addition,
two specimens of one-connector design were tested with different thread
compounds to determine the preferred thread compound. After completing the
fatigue testing, the preferred design specimen was tested in accordance with
ISO 13679 CAL II Series B test procedures.
Phase II generated the SN curve for preferred connection design based on ISO
13679 specimen tolerance combinations. Three ISO configurations, with three
specimens of each configuration, were fatigued to failure to determine the SN
curve for each specimen configuration.
Phase III verified the static Service Load Envelope (SLE) of the preferred
connection. The same ISO specimen configurations tested in Phase II were tested
in accordance with the ISO 13679 CAL II Series B test procedure.
Phase IV included post-fatigue ISO 13679 Series B testing. One specimen was
machined for each of the configurations used in Phase II. Each specimen was
fatigue tested to a predetermined number of cycles at a specified stress level.
The fatigue test was followed by an ISO 13679 CAL II Series B test to verify
the connector performance after dynamic loading.
© 2008. Society of Petroleum Engineers
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