Abstract: Hydraulic fracture extension in earth formation zones of interest may be monitored by placing one or more monitor wells in predetermined positions on opposite sides of an azimuth aligned with the expected fracture plane extending from a fluid waste injection well. The monitor wells are provided with arrays of vertically spaced triaxial geophone units and the signals from the geophones are transmitted to a central processing unit for treatment and analysis to determine the location of micro-earthquake events which occur as the fracture propagates radially and, usually, vertically away from the injection well. Geophone signals are converted to digital format and selectively stored on magnetic tapes or in a shared memory of a central processing unit which is operable to display selected channels for geophone signals in a way so that minimum arrival time of a signal at a particular geophone will indicate the growth of the fracture in real time to control fluid waste disposal, for example.

Abstract: A system and computer program for determining the location of a seismic event in an earth formation zone using seismic traces corresponding to the event collected from one or more sensors in the zone. A graphical data window is displayed of the seismic traces corresponding to the event, the traces representing observed arrival time signals from the sensors plotted with respect to time. A window of a base map of the positions of the sensors within the zone is also displayed. Displayed in the data window is a curve plotting calculated arrival time signals for the traces, the curve being developed from a user-selected one of the observed arrival time signals displayed in the data window and from a user-selected trial location of the event selected in the base map window. The program enables user-repositioning of the trial location in the base map window such that the displayed curve moves in correspondence with the repositioning of the trial location.

Abstract: A method and apparatus for installing an array of sensors in a wellbore wherein the sensors are incorporated into the lower end of a transmission cable which, in turn, is used to lower the array into the wellbore. A load-bearing cable is simultaneously run into the wellbore side-by-side with the transmission cable and the two cables are clamped together at spaced intervals whereby a substantial portion of the tensile forces in the transmission cable is transferred to the load-bearing cable.

Abstract: A method for determining the approximately length and the azimuth of a hydraulic fracture after it has been formed in a subterranean formation without requiring the use of dedicated monitor wells or the need for positioning sensors at subsurface locations. Basically, the present method involves the comparison of routine, seismic surveys carried out at the surface before and after the fracture is formed to thereby determine the approximate length and azimuth of the fracture.

Abstract: A method for releasably, acoustically-coupling an acoustical-energy sensor in a wellbore wherein the sensor is lowered in the wellbore and a soluble cement is flowed into the wellbore to completely encompass the sensor. The soluble cement is allowed to harden to physically bond and thereby acoustically couple the sensor to said wellbore. When it is desired to remove the sensors, a solvent is flowed down the wellbore and into contact with the hardened soluble cement to dissolve the soluble cement. The dissolved cement is then circulated out of the well and the sensors removed so that the well is again available for other operations.

Abstract: A system and method for the real-time monitoring of the location (e.g. vertical extent) of a fracture within a waste disposal formation as that fracture is being formed. Acoustical-energy sensors (e.g. geophones) are isolated within the annulus of the well through which the waste material is injected into the formation. This eliminates the need for expensive, dedicated monitor wells while protecting the sensors from the abrasive effects of the injected waste material.

Abstract: A method for installing an instrument at or near the bottom of a cased well. A cavity is formed within the body of a float shoe or float collar positioned at the bottom or near the bottom of a casing string as it is assembled for installation in a well. An instrument is positioned within the cavity and an appropriate electrical cable is run from the instrument along the outer side of the casing string to the earth surface. The float shoe or float collar provides mechanical protection for the instrument during the installation of the casing string in the wellbore and during the cementing operation and ensures good acoustic coupling of the geophones to the earth in the downhole applications.