Abstract: An apparatus for determining fluid-pressure diffusivity in a borehole (12) in a formation (10) includes an electrode (16) and a strain measuring device (18),(20) (or a particle velocity measuring device (18),(20) or a particle acceleration measuring device (18),(20)) disposed a fixed distance from the electrode (16). The electrode (16) injects an electrical current into a point on a wall of the borehole (12). The strain measuring device (18),(20) measures strain (or the particle velocity measuring device (18),(20) measuresd particle velocity or the particle acceleration measuring device (18),(20) measures particle acceleration) at the fixed distance from the point of injection of the electrical current over time. The fluid-pressure diffusivity is determined based on the measured strain (or measured particle velocity or measured particle acceleration) over time.

Abstract: A proportional pressure control valve which includes an electric first stage pilot having a single outlet port configured to provide a variable pressurized hydraulic fluid to the outlet port and at a pressure that is proportional to an electric input signal and which is variable between first and second values and further includes a second stage hydraulic valve which has a spool reciprocally moveable in a bore between first and second positions indicative of a full ON and a full OFF condition. A fluid isolation chamber is oriented in the bore and in a region between a control port and a tank port in the fluid pathway therebetween. The interior wall of the bore and the first and second diameter regions on the spool are configured to always provide a controlled volume fluid flow rate between the control port and the fluid isolation chamber.

Abstract: An apparatus for determining fluid-pressure diffusivity in a borehole (12) in a formation (10) includes an electrode (16) and a strain measuring device (18),(20) (or a particle velocity measuring device (18),(20) or a particle acceleration measuring device (18),(20)) disposed a fixed distance from the electrode (16). The electrode (16) injects an electrical current into a point on a wall of the borehole (12). The strain measuring device (18),(20) measures strain (or the particle velocity measuring device (18),(20) measuresd particle velocity or the particle acceleration measuring device (18),(20) measures particle acceleration) at the fixed distance from the point of injection of the electrical current over time. The fluid-pressure diffusivity is determined based on the measured strain (or measured particle velocity or measured particle acceleration) over time.