Casing pipes in oil well constructions may suddenly buckle inward as their inside and outside hydrostatic pressure difference increases. For the safety of construction workers and the steady development of oil industries, it is critically important to measure the stress state of a casing pipe. This study develops a rugged, real-time monitoring, and warning system that combines the distributed Brillouin Scattering Time Domain Reflectometry (BOTDR) and the discrete fiber Bragg grating (FBG) measurement. The BOTDR optical fiber sensors were embedded with no optical fiber splice joints in a fiber-reinforced polymer (FRP) rebar and the FBG sensors were wrapped in epoxy resins and glass clothes, both installed during the segmental construction of casing pipes. In situ tests indicate that the proposed sensing system and installation technique can survive the downhole driving process of casing pipes, withstand a harsh service environment, and remain intact with the casing pipes for compatible strain measurements. The relative error of the measured strains between the distributed and discrete sensors is less than 12%. The FBG sensors successfully measured the maximum horizontal principal stress with a relative error of 6.7% in comparison with a cross multipole array acoustic instrument. 1. Introduction Many oil and gas wells in China are drilled with high-pressure water injections and shored with casing pipes bolted or welded together from many sections. Casing damage often occurs as a result of pipe corrosion, joint dislocation, and long-term water injection development. It represents the most important factor for unproductive oil and gas wells. By 2003, a total of 5400 casing pipes had been damaged, accounting for nearly 20% of all oil wells in the Shengli Oilfield in China. By 2005, more than 11,188 oil well casings or 18.54% of all oil wells in the Daqing Oilfield had collapsed. This casing damage resulted in the loss of tens of billions of Chinese Yuan [1, 2]. The problems associated with casing damage continue to grow in Chinese Oilfields. Once damaged, most deeply buried casings are difficult to repair in practice. Therefore, the most effective way to maintain the operation of oil wells is to prevent casing pipes from collapsing, requiring a real-time monitoring and warning system for casing pipes. Up to date, no cost-effective and reliable sensing technologies and installation techniques exist for long-term monitoring and evaluation of casing pipes. Traditional casing inspection techniques are not suitable for real-time monitoring of casing damage. Other
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