Premature Yielding Identified in First Comprehensive 2-million-lbm Deepwater Landing String Test Program

Abstract

The purpose of this paper is to present the results of a comprehensive test program conducted with five different sets of deep-water landing string handling equipment consisting of both conventional and unconventional technology. A thorough presentation will be made detailing initial testing at elastic loads approaching yield and final high load testing beyond yield. All stages of the test program will be discussed including original testing protocol, test setup, testing performed, test results, and overall conclusions. This is one of the first standardized test programs used across five different designs of handling equipment. This overall presentation of the test program is made to identify stress levels associated with the extreme loads that occur when landing very heavy casing strings in deep-water wells. Introduction While landing string designs have progressed1, 2, the design of the handling equipment, until recently, has been based upon conventional slip technology. This conventional technology3 and new technology4 has been previously studied. Based upon the increasing loads being placed on landing strings and the associated handling equipment, a group of test participants including BHP Billiton, BP, ChevronTexaco, ExxonMobil, Nexen Petroleum and Oil & Gas Rental Services, Inc. arranged for Mohr Engineering Division, a division of Stress Engineering Services (Mohr) to perform an array of tests intended to increase the level of knowledge in the industry and help better understand the handling equipment currently in use for landing heavy loads. After developing an overall scope of work and understanding of the requisite testing, the field of handling equipment to be tested was determined to include a variety of designs used with landing string loads up to 2,000,000 lbs. Five different sets of handling equipment were tested. These included conventional slips referred to as SLIP A, SLIP B, and SLIP C, conventional power slips referred to as SLIP D and an unconventional slipless5, 6, 7, 8, 9 system referred to as SYSTEM E. Mohr provided the testing services and coordinated the machining and test sample preparation required to complete the tests. After testing was completed, Mohr also reviewed and post-processed the data and prepared a majority of the information contained in this paper. The manufacturers were requested to provide handling equipment for this test. Serial numbers were recorded to verify the handling equipment being tested and each manufacturer performed all inspections and dimensional verifications on equipment provided. After testing, test results for equipment provided were made available to each manufacturer. Each set of handling equipment was tested on instrumented test samples made from a 6.625″ OD × 0.813″ wall S-135 (50.46 ppf) conventional landing string. The test samples were turned on the OD and ID to provide actual dimensions at or very near nominal. Further, the test samples were instrumented with strain gauges, arranged in tri-axial rosettes (hoop, 45° and axial), set on 120° intervals to cover the ID of the entire contact area of the various handling equipment in order to determine the area of greatest strain/stress. The loading plan for the initial elastic test was as follows.