Surface Tilt Mapping (STM) has been successfully applied to stimulation treatments, disposal projects and in numerous steam floods to provide information on fluid movements in the reservoir. This proven technology has now been applied to a waterflood in the San Andres formation at a depth of 5600 feet to analyze preferential flow. Since typical water injection rates in the San Andres range from 100 to 300 BWPD, a novel flowback method was developed to maximize the STM response when testing injection wells under normal operating conditions. An analysis technique that allows the removal of earth tides was also applied to further enhance the quality of the data. The STM results showed conclusive preferential flow direction in the seven wells tested. In most wells, multiple tests were performed with good agreement on the flow trend.

This paper is a case history describing fracture optimization of low-permeability highly-stratified stacked turbidite sandstone reservoirs of the B interval of the Elk Hills Field. The occurrence of high-permeability, high-pressured water saturated sands immediately above and/or below the objective oil sands poses a major challenge.

Integration of improved petrophysical understanding, geoscience techniques, hydraulic fracture model calibration and on-site, real-time execution has achieved a two-fold oil production increase in the south east nose area of the field while limiting water production to a 40% increase. Downhole tiltmeter measurements are incorporated to calibrate the fracture model and limit fracture height growth, thus regulating fracture conductivity to the oil saturated reservoirs, and minimizing contact with the adjacent wet zones.

To date, results from surface tiltmeter1 measurements completed during twenty six fracture stages have been used with the downhole tiltmeter2 data and reservoir characterization to optimize the ongoing redevelopment from a peripheral waterflood to a pattern flood.

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. This paper 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 hydraulic fractures, as well as, the dependence of fracture length on the water injection rate. Tiltmeter fracture mapping identified that hydraulic fracturing occurs even 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 independent over the range of rates tested. The HGEU waterflood pattern orientation, pattern spacing and injection rate guidelines were established based on these results.

Waterflooding of California's diatomite reservoirs has heen extensively employed for two reasons: (1) to increase total recovery, and (2) to mitigate the potentially catastrophic effects of reservoir compaction and the resulting surface subsidence. Waterflooding has typically striven to replace each barrel of produced fluid with a barrel of injected water in order to achieve "zero net voidage." The extremely low permeability of the diatomite reservoirs, however, results in the generation of very significant reservoir pressure gradients during waterflooding, even under zero net voidage conditions. These extreme gradients in reservoir pressure, together with the reservoir compaction, result in significant changes in the local reservoir stress field. These local stress perturbations can, in turn, result in reorientation of hydraulic fractures on infill wells and possibly contribute significantly to the potential for wellbore casing failure.

This paper summarizes the (preliminary) findings from extensive field studies of hydraulic fracture orientation in diatomite waterfloods and related efforts to monitor the induced surface subsidence. Included are case studies from the Belridge and Lost Hills diatomite reservoirs. The primary purpose of the paper is to document a large volume of tiltmeter hydraulic fracture orientation data that demonstrates waterflood-induced fracture reorientation-a phenomenon not previously considered in waterflood development planning. Also included is a brief overview of three possible mechanisms for the observed waterflood fracture reorientation. A discussion section details efforts to isolate the operative mechanism(s) from the most extensive case study, as well as suggesting a possible strategy for detecting and possibly mitigating some of the adverse effects of production/injection induced reservoir stress changes - reservoir compaction and surface subsidence as well as fracture reorientation.