Mapping Reservoir Volume Changes During Cyclic Steam Stimulation Using Tiltmeter-Based Surface-Deformation Measurements

Abstract

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.

Estimating permeability from quasi-static deformation: Temporal variations and arrival-time inversion

“…Such deformation has been observed in both geodetic data (Castle et al 1969, Evans et al 1982, Dussealt et al 1993, Bruno and Bilak 1994, Chilingarian et al 1994, Castillo et al 1997, Fielding et al 1998, Wright 1998, Mossop and Segall 1999, Du and Olson 2001, Stancliffe and van der Kooij 2001, Vasco et al 2002, Du et al 2005, Vasco and Ferretti 2005 and time-lapse seismic surveys (Guilbot and Smith 2002, Hatchell and Burne 2005, Hawkins et al 2007, Staples et al 2007). Furthermore, current and planned instrumentation, such as permanent sea floor sensors and high precision pressure gauges (Sasagawa et al 2003) can generate useful displacement measurements.…”

“…Furthermore, current and planned instrumentation, such as permanent sea floor sensors and high precision pressure gauges (Sasagawa et al 2003) can generate useful displacement measurements. The resulting deformation can be used to infer volume and pressure changes within the reservoir (Vasco et al 1998, Mossop and Segall 1999, Vasco et al 2000a, Du and Olson 2001, Du et al 2005, Vasco and Ferretti 2005.…”

“…First, there have been several developments in the past few years advancing the state-of-the-art in geodetic monitoring. For example, downhole tilt meters can provide dense time sampling of deformation at a wide range of depths, from the surface to several thousand meters (Wright 1998, Du et al 2005. Space-based techniques, such as Interferometric Synthetic Aperture Radar (InSAR), can sample surface deformation with a spatial resolution (pixel size) of meters to tens of meters and an accuracy of the order of a centimeter to a few millimeters (Massonnet and Feigl 1998, Burgmann et al 2000, Ferretti et al 2000, 2001).…”

“…Such estimates offer high resolution, three-dimensional sampling of deformation over a producing reservoir. Based upon a geomechanical model the deformation can be mapped into pressure changes within the reservoir (Vasco et al 2000a, Du et al 2005, Vasco and Ferretti 2005.…”

Reservoir monitoring and characterization using satellite geodetic data: Interferometric synthetic aperture radar observations from the Krechba field, Algeria

“…Currently, time-lapse seismic surveys are providing additional deformation measurements, distributed throughout the overburden (Guilbot and Smith 2002, Landro and Stammeijer 2004, Tura et al 2005, Hatchell and Bourne 2005, Barkved and Kristiansen 2005, Hall 2006, Roste et al 2006, Rickett et al 2007, Staples et al 2007). Recently, the observed deformation has been used to better understand fluid flow and the heterogeneity of flow properties within the reservoir (Vasco et al 2000a, Vasco et al 2001, Du et al 2005, Vasco and Ferretti 2005, Hodgson et al 2007, Vasco et al 2008.…”