Evaluation of a downhole tiltmeter array for monitoring hydraulic fractures

Abstract

A series of hydraulic-fracture experiments using a downhole tiltmeter array, called an inclinometer array, was conducted at the Department of Energy (DOE)/Gas Research Institute (GRI) Multi-Site facility in Colorado. The inclinometer array was used to measure the deformation of the reservoir rock in response to hydraulic fracture opening and confirm microseismically measured results. In addition, the inclinometer array was found to be a useful tool for accurately measuring closure stress, measuring residual widths of both propped and unpropped fractures, estimating proppant distribution, and evaluating values of in situ moduli. KEYWORDS INTRODUCTIONHydraulic fracturing is now understood to be a complicated process (Gidley et al, 1989) governed by the injection parameters (fluid viscosity and density, injection rate), rock-mechanics properties (moduli, strength), in situ stress, and discontinuities (faults, fractures, bedding) within the reservoir medium. Because of the complexities introduced by common reservoir discontinuities, the fracturing process is poorly represented by standard models, and discrepancies between model results and production are often resolved by the introduction of any number of ad-hoc mechanisms that can be artificially adjusted to obtain the desired result (Warpinski et al, 1994).As instrumentation technology and computer processing capabilities improve, however, it is slowly becoming possible to image hydraulic fractures using microseismic techniques introduced in the 1970's (Albright and Pearson, 1982;Hart et al, 1984). This advanced technology should provide sufficient data to better understand the fracturing mechanisms, validate models, and truly optimize fracture design, One final issue yet to be resolved, though, is the correlation between the "seismic" image of the fracture and the actual rock deformation (Warpinski, 1994). This paper describes the use of a downhole tiltmeter array, dubbed an inclinometer array to distinguish it from surface tiltmeters, to measure the actual rock deformation and provide a comparison with the microseismic results (Branagan et al, 1996). In addition, the inclinometer array has also provided other useful information on fracture behavior and reservoir properties, some of which is described here. € # l m f m m O F M B~# r n r n

Unconventional Well Test Analysis for Assessing Individual Fracture Stages through Post-Treatment Pressure Falloffs: Case Study

“…Investigating compelling field evidence using a downhole measurement that indicates what exactly occurs in the subsurface is paramount. Figure 4 illustrates the tiltmeter measurements of well #2B from the Gas Research Institute/Department of Energy M-site, which is defined as an indication of fracture displacement or fracture width [29]. Wang and Sharma [20] used recorded data to explain the relationship between normalized tilt and formation pressure (Figure 4).…”