Connection Performance Evaluation for Casing-Drilling Application
Authors: Buchner Bas , Bunnik Tim , Langford Steve 
Published: October 2008

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 ISO 136791 requirements. However, API RP72 is the dominant testing program for drill stem applications. Drilling with casing applications combine drilling and casing concerns. As a result, a new test program is required to adequately characterize connection performance when used in casing drilling applications3.

As part of the test program, the static and dynamic connector capacities are individually evaluated to benchmark the design. Based on these results, additional testing is conducted todetermine the connector static capacity after dynamic loading for an expected drilling period at an expected maximum build rate. This testing demonstrates the connector performance under drilling with casing application conditions.

This testing program may be utilized to better define connector performance limits when used in drilling with casing applications leading to increased operational safety and lower overall risks. A better understanding of how connection tolerances impact connection performance under combinations of static and dynamic loading conditions will aid in connector selection for drilling with casing applications and may allow the technology to be used in broader applications.

The paper includes results, observations, and conclusions from a subject test per the testing program. The subject test is currently being conducted on a 9-5/8" 53.50ppf P-110 drilling with casing connector.

Introduction

The objective of this project is to evaluate the connection performance for casing drilling application. Tests were conducted in four phases, each with distinctive goals.Phase I: Design SelectionPhase II: Fatigue to Failure TestPhase III: Static Capacity TestPhase IV: Post-fatigue ISO Series B Test

The objective of Phase I test was to find the best connection and thread compound combination. Three samples with different thread compounds were tested. DWC/C and DWC/C-SR connections were fatigue tested with the same loading condition. All samples were threaded to nominal tolerances and subsequent capped-end pressure test determined the best design for Phase II test.

Phase II was to generate the SN curve for DWC/C-SR connection. Three ISO configurations, with three samples in each group, were tested at different stress levels. Connections were fatigued to failure with different stress range. Fatigue performance with respect to sample configuration was investigated. ISO 2 configuration is the worst-case for fatigue.

Phase III was the static capacity verification test. Three ISO configurations, identical as tested in Phase II, were tested with ISO Series B service load envelope (SLE). The configuration with the best pressure containability was chosen for Phase IV test.

Phase IV included the post-fatigue ISO Series B test. The specimens were fatigued to pre-determined cycles at a certain stress level, followed by an ISO Series B testing. The testing format was modified based on ISO 13679 requirement.