Surface deformation measurements have been used for years in oilfields to monitor production, waterflooding, waste injection, steam flooding, and Cyclic Steam Stimulation (CSS). They have been proven to be a very effective way to monitor the field operations and save money for operators wishing to avoid unwanted surface breeches, casing failures and excessive subsidence due to production. This paper demonstrates that more information can be extracted from surface deformation measurements by inverting the surface deformation for the volumetric deformation at the reservoir level, so the aerial distribution of volumetric deformation can be identified. First, a poroelastic model is presented to calculate the deformation due to the volumetric change in the reservoir. Then, a linear geophysical model is formulated to invert for the reservoir volumetric deformation from the measured surface deformation (or tilt). Constraints are added into the procedure as necessary to better resolve the inversion problem. After each inversion, the theoretical surface deformation (displacement, tilt, reservoir compaction and volumetric strain) can be calculated from the inverted volumetric deformation distribution which best fits the measured deformation data (or tilt) at the surface. The technique of mapping fluid flow using surface deformation was applied to real data from a cyclic steam injection project. Introduction Through the decades, many oil companies and individual researchers have studied reservoir compaction and its associated surface subsidence. Two techniques are used: forward modeling for prediction and direct measurements (or monitoring). The forward modeling includes numerical analysis using Finite Element Method and analytical or semi-analytical analysis. The most common monitoring techniques used in oil and gas fields are:Optical instrument leveling surveys or Global Positioning System (GPS) surveys[1]. These are conducted continuously or periodically to determine changes in position of monuments across the field.Interferometric Synthetic Aperture Radar (InSAR) [1]. This enables mapping of surface displacement along the satellite line of sight over large areas.Tiltmeter-based surface deformation monitoring[2,3]. High precision tiltmeters are placed near the earth's surface to measure the displacement gradient (tilt) induced by field operations such as fluid injection and production. Each technique has advantages and disadvantages, and in some cases two or even all three can be used in combination to get the necessary combination of precision, spatial coverage and temporal resolution. In the case history shown here, only tiltmeter data is used and the inversion process calculates and compares measured and theoretical tilt, but only minor changes are needed to perform the same calculations with displacement.

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Surface-deformation measurements have been used for years in oil fields to monitor production, waterflooding, waste injection, steam flooding, and cyclic steam stimulation (CSS). They have been proved to be a very effective way to monitor field operations and save money for operators wishing to avoid unwanted surface breaches, casing failures, and excessive subsidence because of production. This paper demonstrates that more information can be extracted from surface-deformation measurements by inverting the surface deformation for the volumetric deformation at the reservoir level using the inversion techniques from the literature, so that the areal distribution of volumetric deformation can be identified. This leads to a better understanding of reservoir behavior and also provides additional data for integration into coupled reservoir simulation modeling. This paper shows the results of mapped reservoir volume changes from two cyclic steam injection projects using tiltmeter-based surface deformation measurements.

Summary Surface deformation-based reservoir monitoring technologies, such as Tilt, GPS and Interferometric Synthetic Aperture Radar (InSAR), have been successfully applied to monitor fluid flow or pressure changes in the reservoir and fluid migration to shallow depths. Obtaining the subsurface fluid movement from the surface deformation requires performing a geophysical inversion. To get meaningful results from the inversion process requires diligent selection of the inversion method and reservoir block sizes, as well as the application of physically reasonable constraints. The focus of this paper is to provide a workflow and guidelines for field application by studying the inverse problem, the solution methods and associated error estimates for the unknown model parameters, and the resolving power for each parameter. As a field case demonstration, the methodologies are applied to a CO2 monitoring project with InSAR data. Also, the subsurface movement of CO2 will be presented.

Nearly every reservoir-level process generates and propagates outward a pattern of strain that can be detected using sensitive deformation-monitoring technologies. Microdeformation monitoring seeks to precisely detect and characterize strain patterns caused by fluid production and injection, thermal process such as steam flooding, cyclic steam stimulation (CSS), and steam-assisted gravity drainage (SAGD), as well as CO 2 Sequestration (CCS). By solving a geophysical inverse problem, well-characterized strain measurements can be used to identify and illustrate reservoir-level changes on a wide variety of spatial and temporal scales. Bringing surface deformation measurements down to the reservoir level to obtain the fluid migration pathways, volumetric strain, pressure fronts, or thermal fronts allows operators and asset managers to improve their understanding of how different storage and recovery methods work in different types of reservoirs at significant cost savings compared to traditional monitoring technologies.A variety of independent yet complimentary technologies currently exist that allow a complete and accurate characterization of ground deformation patterns required to geomechanically invert for reservoir-level processes. Examples of recent work from California's thermal enhanced oil recovery (EOR) environments using tiltmeters, GPS, and interferometric synthetic aperture radar (InSAR) are highlighted and discussed, showing how the microdeformation process has been employed to improve production surveillance and project operations.