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.

When constructing deepwater wells, incompatibility between synthetic-based mud (SBM) and Portland cements can lead to poor cementation and loss of cement integrity, which in turn may compromise zonal isolation. An alternative cementitious material based on geopolymers has been developed with improved SBM compatibility for primary and remedial cementing purposes as well as lost circulation control. Geopolymer benefits go beyond mere SBM compatibility: it is in fact possible to solidify non-aqueous fluids such as SBM and oil-based mud (OBM) using geopolymer formulations. This also means that non-aqueous fluids (SBM, OBM) can be disposed of in a cost-effective way, which presents a viable option for environmentally acceptable on-site or off-site disposal of drilling muds and cuttings. Geopolymer is a type of alkali activated material that forms when an aluminosilicate precursor powder (such as fly ash) is mixed with an alkaline activating solution (such as sodium hydroxide). A novel SBM solidification method was developed by blending varied amounts of geopolymer and SBM. This solidification method was tested with various sources of precursor powders, SBMs and OBMs. The rheology and strength of the geopolymer/SBM blends were measured under downhole conditions. Strength testing results showed that geopolymer cement lost only 30% of its strength when blended with 10% SBM, while a neat Portland slurry lost 70% strength. Geopolymer/SBM blends containing up to 40% SBM were found to have measurable strength when cured under downhole conditions. By changing the amount of geopolymer and SBM in the slurry, the geopolymer/SBM system can be developed into a lost circulation treatment with low compressive strength, or into a primary cementation material with higher compressive strength. The geopolymer/SBM blends at different mixing ratios have shown great improvement in rheology of the geopolymer cement, allowing for pumpability of the slurry for well cementation. For instance, 30% SBM blends have downhole rheology profiles that approach those of neat Portland slurries.

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The cement annulus between a wellbore and a casing string should provide reliable zonal isolation throughout the life of a well. However, zonal isolation may be negatively affected by several factors which can compromise cement integrity and lead to the development of channels that provide migration paths for hydrocarbons. This paper is dedicated to monitoring the unwanted presence and migration of hydrocarbons in cemented annuli using a sophisticated fiber optic sensing system. The system is comprised of a distributed temperature and strain sensing (DTSS) data acquisition unit and a newly designed fiber optic cable that is capable of detecting hydrocarbons in cemented annuli. The DTSS system is based on Brillouin and Rayleigh backscattering mechanisms, which are sensitive to both strain and temperature changes. The cable consists of a single-mode optical fiber packaged with a hydrocarbon-sensitive polymer. This combination was tested extensively and successfully for its ability to identify cement integrity issues through detection of hydrocarbons in the cement. The presence of hydrocarbons causes the polymer around the fiber to swell, leading to changes in strain distribution on the fiber. These strain variations were detected using the DTSS monitoring system. The observed strain variations were found to be dependent on the type of fluids, which indicates that the proposed system has selective sensitivity to certain hydrocarbons. For example, synthetic-based mud had little effect on strain, while kerosene showed a significant response. In conclusion, the new fiber optic sensing system can be beneficial in verifying zonal isolation by detecting and monitoring any unwanted hydrocarbon migration in cemented annuli, identifying zones from which hydrocarbons are originating, and providing other essential information to identify the need for well intervention such as remedial cementing.

fax 01-972-952-9435. AbstractDuring the last years, significant progress has been made in the use of fiber-optic technology for well and reservoir surveillance purposes. While most effort in this field appears to be concentrated on the development of fiber-optic based temperature-, pressure-and flow meters, comparably few publications have been made to-date about the use of fiberoptic 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-size laboratory tests have demonstrated that the latest generation of this system is sufficiently sensitive to detect casing deformations of less than 10 degrees per hundred feet and covers compressive and tensile axial strain ranges from less than 0.1% to 10%. We will discuss the background technology, the measurement sensitivity and strain-response characterization, as well as the scale-up 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.