Seismic events, such as earthquakes, have the potential to induce ground movements that can adversely affect the structural integrity of gas well casings, thereby leading to the occurrence of gas leakage. An experimental investigation conducted in November 2023 aimed to explore the feasibility of employing fiber optic sensing technology for real-time monitoring of gas well conditions during seismic activities, particularly instances of significant fault movements.
In the experiment, a 10-foot-long gas well sample, comprising both outer casing and inner tubing, was affixed to steel plates. The movable portion of the steel plate underwent a maximum displacement of 19 inches. The entire gas well was secured using specially designed clamps with substantial rubber interlayers, simulating the soil conditions surrounding the gas well in a realistic manner without resorting to a large soil split basin for testing. Fiber optic strain sensors were strategically installed on both the outer casing and inner tubing, employing high-strength epoxy.
However, with regard to the outer casing, the experimental setup led to a failure of the clamps to securely restrain the entire sample, resulting in the displacement of rubbers during fault movements. Consequently, the fiber optic cables within the clamps experienced significant stretching, yielding substantial strain readings. The lack of tight attachment of the fiber optic cables to the outer casing resulted in a lack of simultaneous deformation with the outer casing.
Throughout the testing process, no discernible strain was observed for the inner tubing. Nevertheless, as fault displacement increased substantially, and the outer casing came into contact with the inner tubing, strain development was noted. Despite the influence of the experimental setup on test outcomes and the suboptimal performance of fiber optic sensors on the outer casing, the study underscored the utility of fiber optic sensing technology for providing real-time data on gas well conditions in field applications.
Gas well axial loading test
Fiber optic sensing has emerged as a pivotal technology in gas wells, augmenting monitoring capabilities, ensuring safety, and optimizing operational efficiency within the oil and gas industry. Despite the increasing prevalence of its application, there exists a need for more compelling evidence regarding the performance of commonly employed fiber optic cables. To address this, an empirical investigation was conducted at the PEER Lab situated in the Richmond Field Station. The experiment involved the deliberate design of a gas well sample subjected to simultaneous tension and compression loading conditions. The sample, extending to a length of 10 feet, comprised an inner pipe simulating the gas well, an outer pipe representing the surrounding soil, and an interstitial region filled with cement.
Within this experimental framework, meticulous instrumentation was implemented. A fiber optic temperature sensor was embedded in the cement prior to grouting, facilitating a comprehensive capture of the cement curing process. Additionally, two distinct types of fiber optic strain sensors, namely steel-jacketed and polymer-jacketed, were incorporated into the cement matrix. The comprehensive instrumentation strategy included the installation of 16 strain gauges, evenly distributed with 8 positioned on the tension side and 8 on the compression side. The loading conditions imposed on the gas well sample induced a maximum strain level of approximately 800 microstrain. Notably, both fiber optic strain sensors exhibited promising data congruent with that obtained from traditional strain gauges during the loading sequences.
The results of this experiment affirm the viability of employing fiber optic sensing as an efficacious safety monitoring tool, particularly in the context of gas well grouting. This substantiates the role of fiber optic sensing technology in enhancing the integrity and safety protocols associated with critical components of gas wells, thereby contributing to the scholarly discourse on the subject.
