A new fracture diagnostic technology for mapping hydraulic fracture dimensions is introduced: downhole tiltmeter fracture mapping. Downhole tilt fracture mapping involves deploying wireline-conveyed tiltmeter arrays in offset wellbores to measure hydraulic fracture growth versus time. This technology has been employed to map over 100 fracture treatments in the last eighteen months. Allowing, for the first time, the gathering of statistically significant data-sets on how hydraulic fractures actually do grow - albeit, within only a few fields so far. In addition to providing fracture diagnostic data (fracture length, height, width and asymmetry), this new capability allows enhanced utilization of hydraulic fracture models because model predictions can be "calibrated" with insitu observations of fracture growth. The mapping concept is quite simple: creating a hydraulic fracture involves parting the rock and deforming the reservoir. Downhole tiltmeter mapping involves measuring the fracture-induced deformation in a nearby offset well(s) versus time and depth and inverting the data to obtain the created fracture dimensions. The principles are the same as for surface tiltmeter mapping, but the different array geometry make it very sensitive to fracture dimensions and less sensitive to fracture orientation - just the reverse of surface tiltmeter mapping. This paper will explain the fundamental concepts, the implementation strategy (wireline arrays, processing and modeling), present three field case studies, and briefly discuss the implications on fracture modeling. P. 585

This paper introduces a new fracture diagnostic technology that allows economic mapping of hydraulic fracture dimensions. The downhole tiltmeter fracture mapping technology requires the use of an offset wellbore(s) for running wireline-conveyed downhole tiltmeter arrays. For the first time, hydraulic fracture dimensions including growth during pumping can be measured at a relatively modest cost. In addition to providing fracture diagnostic data (fracture height, width and length), this new capability allows enhanced utilization of hydraulic fracture models because model predictions can be "calibrated" with in-situ observations of fracture growth. The concept is quite simple: creating a hydraulic fracture involves parting the rock and deforming the reservoir. Downhole tiltmeter mapping involves measuring the fracture-induced deformation in a nearby offset well(s) and solving the geophysical inverse problem to obtain the created fracture dimensions. The technology follows the same principles as surface tiltmeter mapping, but the different array geometry and placement make it very sensitive to fracture dimensions and less sensitive to fracture orientation - just the reverse of surface tiltmeter mapping. This paper will explain the fundamental concepts, the implementation strategy (wireline conveyed tiltmeter arrays, data acquisition, processing, and modeling), and three field case studies of measured hydraulic fracture growth.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSubsidence monitoring is most commonly conducted using either level surveys or GPS surveys of elevation monuments to determine changes in elevation across a field as a result of injection and production activities. Several operators near Bakersfield, CA are using tiltmeter-based subsidence monitoring to obtain highly detailed maps of subsidence with continuous data acquisition.The tiltmeter measured subsidence is then correlated to production and injection on a day-by-day basis so the impact of individual injection and production events can be quantified. The data is presented in a video format that allows visual assessment of the field motion. In some fields, the monitoring array is also equipped with monuments for periodic level survey and GPS measurements of the ground motion. This paper discusses the design and installation of tiltmeter subsidence monitoring arrays and the format of the results. In addition, the subsidence data is correlated to field activities to show how the monitoring can be used to correlate ground movement with reservoir events.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractRefracturing can be used to increase production in poorly fractured wells. A different application of this technology is to refracture wells with strong initial fractures. In this paper, we provide evidence of increased production due to refracturing two tight gas wells having deeply penetrating initial fractures. Surface tiltmeter measurements show refracture orientations at oblique angles to the azimuth of the initial fractures.

In secondary and enhanced oil recovery projects, it is critical to determine if hydraulic fracturing occurs during water injection and, if fracturing occurs, to understand its associated impacts on oil recovery. If hydraulic fracturing occurs under normal injection operating conditions or, if the production and/or injection wells are fracture stimulated, knowing the orientation and dimensions of the created fractures are critical for determining the proper pattern alignment to optimize sweep efficiency. Thispaper presents the application and results of tiltmeter mapping techniques used at the Howard Glasscock East Unit (HGEU). Tiltmeter mapping was used to determine the existence, orientation, and geometry of created hydraulicfractures, as well as, the dependence of fracture length on the water injectionrate. Tiltmeter fracture mapping identified that hydraulic fracturing occur seven at very low water injection rates (less than 250 BWPD) at the HGEU creating significant fractures (exceeding 400 feet of half-length). The mapping also showed that the length of the fractures was relatively rate in dependent over the range of rates tested. The HGEU waterflood pattern orientation, pattern spacing and injection rate guidelines were established based on these results. Introduction The Howard Glasscock East Unit produces from multiple formations in the Howard Glasscock Field of West Texas. Prior to this work, a portion of the Unitwas under pilot waterflood operations in the Seven Rivers, Queen and San Andresformations using 40-acre inverted 9-spot patterns. The Seven Rivers and Queenare sandstone formations and the San Andres is a carbonate formation. It was determined that the initial water injection scheme was insufficient to effectively waterflood these formations and would need to be altered as the waterflood was expanded to the entire Unit. It is has been documented that hydraulic fractures can improve areal sweep efficiency if the waterflood patterns are properly aligned. In many cases, directional permeability in reservoirs has been directly attributed to fracturing (both natural and induced). If the waterflood patterns are not aligned properly, the waterflood will be adversely affected, especially if the fractures are long relative to the well spacing. These adverse effects areshown to increase as the mobility ratio increases, as typically seen in EOR projects. Evaluations were undertaken at the HGEU to insure that the waterflood wouldnot be adversely effected by possible fracturing in the water injection wells and to determine if the water injection rates could be increased. As part ofthis evaluation, the following critical questions were put forth:*Are hydraulic fractures being created at the current water injection ratesand pressures?*If present, what are the azimuths of the created fractures (both for thewaterflood-induced fractures in the injection wells and for the proppedfracture treatments in the producing wells)?*What are the hydraulic fracture lengths and are they different for differentwater injection rates?*What is the fracture geometry for the propped fracture treatments in theproducing wells?*Are these fracturing issues different for the sandstone (Seven Rivers andQueen) and the carbonate (San Andres) formations?Tiltmeter mapping techniques, incorporating both surface and downhole tiltmeter arrays were effectively employed in both the active waterflood andun-waterflooded areas to answer these questions.