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.
Subsurface geomechanical stresses can cause formation faults, slippage, and compaction. These movements result in well failures, impacting production and resulting in significant expense and lost revenue. Traditional means for detecting such failures are limited and usually require interrupting production to re-enter the well, resulting in late detection of the problem and limited counteractive options. A fiber optic support device has been developed to permanently monitor strain and temperature on sand screen products for gravel-pack and frac-pack applications. This technology, especially when paired with an optical wet connect, provides for long-term reservoir monitoring at the sand face, resulting in early detection of subsurface movements at a high resolution. With this information, operators can plan early mitigative actions, and monitor the results of these actions in real time. This fiber support device provides a means of holding a helically wrapped optic fiber rigidly in place at the sand face, with no negative impact on the sand control functionality of the sand screens. New techniques were developed to manufacture this technology, as well as a new method to install the fiber. Dry connects have also been developed to allow connections between individual sand screens and enable longer monitored intervals. The paper will describe this new technology, review test results to date, and discuss potential applications.
Subsurface stresses can cause formation faults, slippage, and reservoir compaction, which can damage or permanently shut in a well. Traditional means of detecting these failures are limited and usually require moving a costly rig onto locations, and then interrupting production to re-enter the well. This results in late detection of issues and allows limited counteractive options. A new Real Time Monitoring Compaction (RTCM) system has been developed to actively monitor strain and temperature of wells. The system consists of three key enabling technologies: A fiber optic support device deployed at the sand face, a cost effective high-flow liner system that protects the instrumentation in openhole applications, and two optical wet connects for up to 12 channels. The fiber optic support device provides a means of holding a helically-wrapped optic fiber rigidly in place at the sand face. This new technology can be installed over traditional sand screens in gravel pack or frac pack applications, with no negative impact on the sand control functionality of the screens, or the quality of the pack. The installed fiber optic provides the equivalent of a strain gauge positioned every centimeter along the length of the producing zone. For openhole applications, a high-flow liner system was developed to protect the fiber optic support device, and the control lines. This system includes a special quick connect that simplifies the on-rig assembly and allows torque transmission in an openhole deployment. Two 6-channel optical wet connects are the final key to this system, allowing a total of 12 connected channels. This game changing technology provides an information conduit between the fiber optic at the sand face and operators at the surface. The same wet connect can also be used to connect more traditional means of measurements such as pressure-temperature gauges, or distributive temperature sensing (DTS). The information relayed through this system allows the operator to infer flow and detect subsidence or compaction of the sand face before the well is compromised, allowing time to plan and execute mitigative actions. This paper will discuss the design, testing, and potential applications of this new system. Introduction The production of hydrocarbons can often cause a decrease in porosity of the rock formation containing them. This phenomenon is known as compaction. Wells can sustain significant damage as the formation layers shift or move along formation boundaries as a result compaction. Fig. 1 illustrates this type of shift caused by compaction. The wellbore on the left of Fig. 1 illustrates the original location of the well, and the wellbore on the right illustrates the same well after compaction (Earles 2010).
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