# US 5,705,812 A · Compaction monitoring instrument system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,705,812 A - Document ID: US5705812A - Status: Granted - Kind: A - Application number: 08/656,503 - Filed: 1996-05-31 - Granted: 1998-01-06 - Earliest claimed: 1996-05-31 - Assignees: Western Atlas International, Inc. - Inventors: James E. Brewer; Richard R. Pemper; Izhar Ahmad; Randy Gold - Web page: https://patentgrep.com/patent/US5705812A ## CPC - E21B 49/006: {Measuring wall stresses in the borehole} - E21B 47/00: Survey of boreholes or wells (monitoring pressure or flow of drilling fluid E21B21/08) - E21B 47/01: Devices for supporting measuring instruments on drill bits, pipes, rods or wirelines; Protecting measuring instruments in boreholes against heat, shock, pressure or the like - E21B 47/092: by detecting magnetic anomalies - E21B 49/00: Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS ## Abstract An apparatus and method for detecting the location of subsurface markers in a formation proximate to a borehole. The apparatus includes marker detectors in a housing having at least two housing sections attached in an initial orientation. The distance between the detectors is measured under controlled conditions with a calibration bar. The initial attached orientation between the housing sections is identified with a calibrator, and deviations from the initial attached orientation are identified by the calibrator after the housing sections are detached and reattached. The calibrator permits well site corrections to be made to the housing sections without recalibration. Gauges permit corrections for temperature and pressure fluctuations, and the corrected distances between the housing detectors is computed. Detectors in the housing generate signals when each detector is proximate to a marker in the formation, and such signals can be processed to identify the elevation of a marker in the borehole, or the distance between markers in the borehole, to determine formation compaction or settlement. In an apparatus having two detectors separated by a spacer, flexible retainers can be positioned between each detector and the spacer to permit thermal expansion or contraction of the detectors relative to the spacer. ## Claims ### Claim 1 An apparatus insertable into a borehole through a geologic formation to detect the location of a subsurface marker, comprising: a first housing section; a first detector engaged with said first housing section for generating a first signal responsive to the marker; a second housing section for attachment to said first housing section; a second detector engaged with said second housing section at a selected distance from said first detector for generating a second signal responsive to the marker; and a calibrator for identifying an initial attached orientation between said first and second housing sections, and for identifying deviation from said initial attached orientation following detachment and reattachment of said first and second housing sections to indicate changes in said distance between said first and second detectors. ### Claim 2 (depends on 1) An apparatus as recited in claim 1, wherein said second housing section is rotatably attachable to said first housing section. ### Claim 3 (depends on 1) An apparatus as recited in claim 1, wherein said second housing section is longitudinally attachable to said first housing section. ### Claim 4 (depends on 1) An apparatus as recited in claim 1, further comprising a connector for attaching said first housing section to said second housing section, wherein said connector cooperates with said calibrator to identify the initial attached orientation between said first and second housing sections and to identify deviations from said initial attached orientation following detachment and reattachment of said first and second housing sections. ### Claim 5 (depends on 1) An apparatus as recited in claim 1, further comprising a controller engaged with said first detector and with said second detector for receiving said first and second signals. ### Claim 6 (depends on 5) An apparatus as recited in claim 5, wherein said first detector is capable of transmitting to said controller a signal responsive to a second subsurface marker, and wherein said controller is capable of calculating the distance between said subsurface markers. ### Claim 7 (depends on 5) An apparatus as recited in claim 5, further comprising a temperature gauge engaged with said first housing for detecting the borehole temperature and for transmitting a temperature signal to said controller, and wherein said controller is capable of correcting the calculated distance between said subsurface markers to account for the difference between the borehole temperature and a selected calibration temperature. ### Claim 8 (depends on 5) An apparatus as recited in claim 5, further comprising a pressure gauge engaged with said first housing for detecting the borehole pressure and for transmitting a pressure signal to said controller, and wherein said controller is capable of correcting the calculated distance between said subsurface markers to account for the difference between the borehole pressure and a selected calibration pressure. ### Claim 9 (depends on 1) An apparatus as recited in claim 1, wherein said controller is capable of correlating said signals with a selected distribution curve to identify each signal segment representative of the marker. ### Claim 10 (depends on 1) An apparatus as recited in claim 1, wherein the subsurface marker comprises a radioactive bullet positioned in the geologic formation proximate to the borehole, and said first and second detectors include scintillation crystals responsive to the radioactive bullet. ### Claim 11 An apparatus insertable into a borehole through a geologic formation for determining the distance between the surface and a subsurface marker, comprising: an elongated member having a lower end for insertion within the borehole; a mechanism for selectively deploying and retrieving a selected length of said elongated member within the borehole; a housing connected to said elongated member lower end, wherein said housing comprises a first housing section and a second housing section attached to said first housing section; a first detector engaged with said first housing section for generating a signal responsive to the marker; a second detector engaged with said second housing section at a selected distance from said first detector for generating a signal responsive to the marker; and a calibrator for identifying an initial attached orientation between said first and second housing sections, and for identifying deviation from said initial attached orientation following detachment and reattachment of said first and second housing sections to indicate changes in said distance between said first and second detectors. ### Claim 12 (depends on 11) An apparatus as recited in claim 11, further comprising a third detector attached to said first housing section and comprising a fourth detector attached to said second housing section, wherein said third and fourth detectors generate signals responsive to said marker. ### Claim 13 (depends on 11) An apparatus as recited in claim 11, further comprising a controller engaged with said mechanism for identifying the length of said elongated member within the borehole and for calculating the distance between said surface and the subsurface marker. ### Claim 14 (depends on 13) An apparatus as recited in claim 13, wherein said first detector is capable of transmitting a signal to said controller responsive to a second subsurface marker, and wherein said controller is capable of calculating the distance between said subsurface markers. ### Claim 15 An apparatus, attachable to the lower end of an elongated member for insertion into a borehole, for determining the distance between first and second subsurface markers, comprising: a housing section attached to the lower end of the elongated member, wherein said housing encloses an interior having a first end and a second end; a first detector within the first end of said housing interior for generating a signal responsive to a marker; a second detector within the second end of said housing interior for generating a signal responsive to a marker; a spacer between said first detector and said second detector; a first flexible retainer engaged with said first detector for permitting thermal expansion of said first detector toward said spacer; and a second flexible retainer engaged with said second detector for permitting thermal expansion of said second detector toward said spacer. ### Claim 16 (depends on 15) An apparatus as recited in claim 15, further comprising a second housing section attached to said housing section, wherein said second housing section is engaged with a third detector for generating a signal responsive to a marker. ### Claim 17 (depends on 16) An apparatus as recited in claim 16, further comprising a fourth detector engaged with said second housing section for generating a signal responsive to a marker, and further comprising a second spacer between said third and fourth detectors, a third flexible retainer for permitting thermal expansion of said third detector toward said second spacer, and a fourth flexible retainer for permitting thermal expansion of said fourth detector toward said second spacer. ### Claim 18 (depends on 15) An apparatus as recited in claim 15, further comprising a controller for receiving said signals from said first and second detectors and for calculating the distance between said first and second subsurface markers. ### Claim 19 (depends on 15) An apparatus as recited in claim 15, wherein said first and second subsurface markers are radioactive, and wherein said first and second detectors include scintillation crystals responsive to said subsurface markers. ### Claim 20 A method of assembling an apparatus for insertion into a borehole through a geologic formation to detect the location of a subsurface marker, comprising the steps of: placing a first housing section engaged with a marker sensing first detector proximate to an attachable second housing section engaged with a marker sensing second detector; attaching said first housing section to said second housing section; and identifying the deviation of a calibrator engaged with said first and second housing sections, wherein said calibrator identifies an initial attached orientation between said first and second housing sections under selected conditions. ### Claim 21 A method of calibrating a subsurface marker detection apparatus having first and second detectors and a calibrator, comprising the steps of: placing a first housing section engaged with a marker sensing first detector proximate to an attachable second housing section engaged with a marker sensing second detector; attaching said first housing section to said second housing section; identifying the calibrator deviation between said first and second housing sections from an initial calibrator orientation between said first and second housing sections under selected conditions; and correcting the distance between said first and second detectors by calculating a correction factor from the deviation identified by said calibrator. ### Claim 22 (depends on 21) A method as recited in claim 21, further comprising the steps of moving at least one of said first and second detectors proximate to the subsurface marker, of generating first and second marker responsive signals correlating to each detector, and of transmitting said detector signals to a controller. ### Claim 23 (depends on 22) A method as recited in claim 22, further comprising the steps of moving at least one of said first and second detectors proximate to a second subsurface marker and of transmitting to said controller a detector signal responsive to the second subsurface marker. ### Claim 24 (depends on 23) A method as recited in claim 23, further comprising the step of operating said controller to correlate said signals with a selected distribution curve to identify each signal segment respresentative of a marker. ### Claim 25 (depends on 24) A method as recited in claim 24, further comprising the step of operating said controller to identify the peak of said selected distribution curve. ### Claim 26 (depends on 22) A method as recited in claim 22, wherein a marker sensing third detector is engaged with said first housing section, and a marker sensing fourth detector is engaged with said second housing section, further comprising the steps of moving at least one of said detectors proximate to a second subsurface marker and of transmitting to said controller at least one detector signal responsive to the second subsurface marker. ### Claim 27 (depends on 26) A method as recited in claim 26, further comprising the steps of moving said first and second housing sections so that each of said detectors generates a signal responsive to a subsurface marker, of transmitting each signal to said controller, and of operating said controller to calculate the distance between adjacent subsurface markers. ### Claim 28 (depends on 27) A method as recited in claim 27, further comprising the steps of detecting the borehole temperature with a temperature gauge, of transmitting a signal to said controller indicating the borehole temperature, and of operating said controller to adjust the calculated distance between adjacent subsurface markers. ### Claim 29 (depends on 27) A method as recited in claim 27, further comprising the steps of detecting the borehole pressure with a pressure gauge, of transmitting a signal to said controller indicating the borehole pressure, and of operating said controller to adjust the calculated distance between adjacent subsurface markers. ### Claim 30 (depends on 22) A method as recited in claim 22, further comprising the steps of detaching said housing first and second sections, of reattaching said first and second housing sections, and of identifying the deviation of a said calibrator from said initial attached orientation.