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We present the Staggered Torsional Electrostatic Combdrive (STEC) fabrication process that creates thick mirrors with hightorque actuators, thereby allowing high-speed optical scanning with large angular deflections.We have demonstrated a 550 pmdiameter mirror capable of scanning an optical angle of 24.9" at its 34 kHz resonant frequency with less than 30 nm static and dynamic deformation.The optical resolution is 350 pixels -very near the diffraction-limited resolution of 355 pixels with 655 nm wavelength light.

Waterflooding of California’s diatomite reservoirs has been 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.

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