Chapter 36 HPHT In-Situ Strain Measurement of Polymer Composites for Oilfield Applications Daniel Sequera, Yusheng Yuan, and John Wakefield Abstract In recent years composite materials have been used extensively for drillable and other tools in oilfield operations because of their light weight, longer fatigue life, corrosion resistance and cost effectiveness. This requires determining their mechanical properties in such downhole conditions. Downhole tools are typically exposed to hot-wet environments above 93 C(200 F) and 34 MPa (5000 psi). Conventional environmental test methods conduct post-conditioning mechanical tests in dry conditions under ambient pressure, where the test condition is untrue and often giving misleading results. A previous publication presented an in-situ strain-gage measurement method using conventional resistive strain gages to determine the tensile strain and modulus of the composites in immersed hot-wet environment. However, satisfactory results were obtained only up to 93 C(200 F). This paper presents a new in-situ strain measurement technique, where an AC excited Wheatstone bridge with inductors is used. Thus, the sensor can operate as long as the inductors can resist the environment. Materials for the inductors were carefully selected to withstand how-wet conditions. The objective is to obtain the high-pressure-hightemperature (HPHT) in-situ tensile strain and tensile moduli of selected composite materials without discontinuing the hot-wet exposure cycle. Effect of the hydrostatic pressure on the tensile properties of the composites in hot-wet condition is presented. Keywords Polymers • Composites • Hot-wet condition • In-situ extensometer • In-situ stress-strain • In-situ strain measurement • Hydrostatic pressure-dependent elastic modulus 36.1 Introduction Composite materials have been used extensively for downhole application in the oil field, such as drillpipes and drillable tools, because of their lightweight, corrosion resistance, fatigue life and cost effectiveness. In these applications, tools are exposed to hot-wet conditions, typically above 93 C (200 F) and 34 MPa (5000 psi). Depending on the application, composite material tools are exposed to hot-wet conditions for a period of time where moisture absorption and elevated temperatures induce hygrothermal effects and deterioration on the tools, leading to performance degradation and premature failure. Under the conventional test procedure for environmental effects, material performance is evaluated by first exposing test specimens to an application fluid (i.e., brine, oil, etc.) at the desired temperature and pressure, which can be easily accomplished in pressurized autoclaves, then removing the specimen from such environment to conduct post-aging mechanical tests on a material testing system at either room temperature or elevated temperature and under ambient pressure in dry condition. This technique enables the specimens to reach exposure temperatures above the boiling temperature of the fluid. However, the moisture and pressure conditions of the test specimens under mechanical load in the conventional test procedure are not the same of those of a real application. Furthermore, the conventional test method may generate additional hygrothermal damage by thermal and pressure cycles during specimen transfer between sample conditioning and mechanical testing, by sample dry-out, and additional cracking or delamination may occur when the exposed wet specimens are tested at an elevated temperature due to dry heating. Thus, the conventional environmental-mechanical test method often provides misleading results. Previous publications by Yuan and Goodson [1, 2] presented a high-pressure-high-temperature (HPHT) in-situ mechanical test method that has been successfully used for various mechanical tests conducted in a simulated HPHT fluid and gas environment. This in-situ test method is capable of conducting mechanical tests directly in a given fluid and gas condition under required temperature and pressure after a period of environmental exposure, which combines the specimen D. Sequera (*) • Y. Yuan • J. Wakefield Baker Hughes Inc., 14990 Yorktown Plaza Dr., Houston, TX 77040, USA e-mail: daniel.sequera@bakerhughes.com #The Society for Experimental Mechanics, Inc. 2017 W.C. Ralph et al. (eds.), Mechanics of Composite and Multi-functional Materials, Volume 7, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-41766-0_36 295
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