Summary During the last several years, significant progress has been made in the use of fiber-optic technology for well and reservoir surveillance. While most effort in this field appears to be concentrated on the development of fiber-optic-based meters for temperature, pressure, and flow, comparably few publications have been made to date about the use of fiber-optic technology for monitoring deformations of well tubulars and casings. In this article, we report on recent advances in our development of a real-time fiber-optic-based casing imager. This device is designed for continuous, high-resolution monitoring of the shape of casings or well tubulars and, therefore, enables the determination of strain imposed on the well. Small-scale and full-casing-sized laboratory tests have demonstrated that the latest generation of this system is sufficiently sensitive to detect casing deformations of less than 10°/100 ft and covers compressive and tensile axial-strain ranges from less than 0.1 to 10%. We will discuss the background technology, measurement sensitivity and strain-response characterization, as well as the scaleup work that has been performed to date. Our article also includes an overview of field-test results and illustrates how real-time deformation monitoring could form a significant component of reservoir-surveillance strategies.

Casing deformation can be used as a direct indicator or measurement of reservoir geomechanical strain, such as may occur withVertical compaction accompanying pressure depletion of high-compressibility hydrocarbon reservoirs;Vertical strain dilation due to stress arching;Shear events associated with fault movement and reservoir bed boundary movement during subsidence;Localized strain events such as pipe ovalization due to highly anisotropic loading or formation strain anisotropy; andPressure changes due to depletion of or injection into reservoirs. Identifying and quantifying these events early can help an operator remedy a potentially damaging production scenario, apply the correct seismic transit time correction during time-lapse reservoir seismic monitoring, or monitor production, injection, and pass-through zones for pressure depletion effects. We have installed, in an industry first, a high-resolution fiber-optic strain imaging system in a producing well. The theoretical, experimental and early deployment test trial details of this technology were reported in SPE 109941, presented at the 2007 SPE ATCE. In this paper, we will report high-resolution strain monitoring results obtained on a set of casing joints which were instrumented with several thousand fiber-optic strain sensors, deployed as a single fiber cable in an onshore production well, installed using normal rig equipment. Of particular interest at this early stage in the well's life is the demonstration of the strain measurement resolution and sensitivity, as evidenced by our ability to monitor the differential pressure between the inside and outside of the casing while circulating prior to cementing, during the cementing operation and while the cement was curing. This monitoring yielded excellent results while cementing the instrumented intermediate casing string, as well as while cementing the production casing string. Cemented at a measured depth of 8000 feet in an unconventional gas well, the strain-instrumented casing joints in conjunction with a distributed temperature sensor and external pressure gauge have continued to provide strain, temperature and behind-casing pressure readings through the remainder of the well construction, completion, hydraulic fracturing and the current, early production operations some six months after initial installation. Introduction The subsurface is host to a number of substantial geomechanical stresses that threaten well integrity. In several instances, this has lead to a complete loss of the well (Cernocky 1995; Morris 1998). For example, reservoir compaction can exert large stresses on a well, which can be initiated by producing from highly compressible layers in the reservoir. As the reservoir fluids are produced, load stresses from the overburden will cause the sediments to consolidate and ultimately compact. Compaction results in both a compression of the reservoir and an extension in the overburden (Morris 1995; Bruno 2002; Bruno 1992). The wells in these zones will undergo significant axial strains and tend to bend and buckle. In addition to compaction, active faults or slip surfaces can also cause intersecting wells to shear and stop producing. Such events threaten not only the life and production of the well, but also the ultimate recovery of a reservoir if they are not effectively addressed as part of a reservoir surveillance program.

A novel fiber Bragg grating based palladium tube sensor was designed for hydrogen leakage detection in aerospace vehicles. The sensor fabrication method was developed and the sensor response was characterized in terms of total wavelength change, response time and degassing ability. Several factors that influence the sensor performance, including the tube thickness, purging temperature, purging gas, hydrogen concentration, and operation temperature, were studied. The sensor response was improved by reducing the thickness of the palladium tube to around 33 .tm, optimizing the operation temperature to 95°C, and thoroughly degassing the sensor in nitrogen at 95°C for 4 hours. At these conditions, the total wavelength change was about 0.6 nm, the response time (the time to reach a 0.05 nm wavelength change) was about 2 minutes for the four-hour 4% hydrogen tests.

We report the use of a fiber-optic distributed sensing system to monitor structural fatigue on an aircraft undergoing a full scale fatigue test. This technique involves using optical frequency domain reflectometry to demodulate the reflected signals from multiplexed Bragg gratings that have been photoetched in the core of an optical fiber. The optical fibers, containing a high density of Bragg gratings, were applied along the surface of a Lockheed Martin P-3C Orion fatigue test article to assess the suitability of this technique for long-term structural damage detection and monitoring.Preliminary results indicate good agreement with quasi-collocated foil strain gauges and demonstrate great potential for supplementing or replacing conventional non-destructive evaluation techniques.