# US 8,739,897 B2 · Pressure compensation and rotary seal system for measurement while drilling instrumentation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,739,897 B2 - Document ID: US8739897B2 - Status: Granted - Kind: B2 - Application number: 11/945,542 - Filed: 2007-11-27 - Published: 2009-05-28 - Granted: 2014-06-03 - Earliest claimed: 2007-11-27 - Assignees: Schlumberger Technology Corporation - Applicants: Richard E. Thorp; Raju M. Eason; Charles Borsos - Inventors: Richard E. Thorp; Raju M. Eason; Charles Borsos - Web page: https://patentgrep.com/patent/US8739897B2 ## CPC - E21B 47/017: Protecting measuring instruments - E21B 47/20: by modulation of mud waves, e.g. by continuous modulation - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS ## Abstract A pressure compensation system for a wellbore instrument coupled to a drill string includes a shaft rotatably mounted with respect to an instrument housing. A lubrication chamber included in the instrument has at least one bearing for rotatably supporting the shaft. The lubrication chamber includes a face seal coupled on one face to the shaft and on another face to the housing. A pressure compensator establishes hydraulic communication between the lubrication chamber and the interior of the drill string. The compensator includes a barrier to fluid movement between the lubrication chamber and the interior of the drill string. The barrier enables pressure communication therebetween. The compensator includes a pressure communication port extending between the barrier and a portion of the shaft exposed to the interior of the drill string. ## Claims ### Claim 1 A pressure compensation system for a wellbore instrument coupled to a drill string, the instrument including a shaft rotatably mounted with respect to an instrument housing, the system comprising: a lubrication chamber disposed in an annular space between the housing and the shaft, the lubrication chamber including therein at least one bearing for rotatably supporting the shaft, the lubrication chamber including a face seal coupled on one face to the shaft and on another face to the housing; a pressure compensator in hydraulic communication between the lubrication chamber and the interior of the drill string, the compensator including a barrier to fluid movement between the lubrication chamber and the interior of the drill string, the barrier enabling pressure communication therebetween, the compensator including a pressure communication port extending between the barrier and a portion of the shaft exposed to the interior of the drill string, wherein the pressure compensator comprises a removable enclosure configured around the shaft and configured to be removed from around the shaft when the shaft is disassembled from the housing such that access to the removable enclosure is obtained without removing the shaft from the housing, the removable enclosure having a bladder; and a valve disposed in an interior passage of the shaft, wherein the valve closes upon removal of an upper portion of the shaft. ### Claim 2 (depends on 1) The system of claim 1 wherein the barrier comprises a piston slidably mounted in a chamber, the chamber disposed in at least one of the housing and the drill string. ### Claim 3 (depends on 1) The system of claim 1 wherein one end of the pressure communication port is open to the interior of the drill string in an uppermost portion of the shaft. ### Claim 4 (depends on 1) The system of claim 1 wherein one end of the pressure communication port is open to the interior of the drill string proximate the face seal. ### Claim 5 (depends on 1) The system of claim 1 wherein one end of the pressure compensation port is open to a mud chamber disposed inside the instrument housing. ### Claim 6 (depends on 5) The system of claim 5 further comprising a first bellows at least partially filled with liquid and disposed in the mud chamber, the first bellows configured to have a crush pressure at least as high as a maximum expected mud pressure inside the drill string. ### Claim 7 (depends on 1) The system of claim 1 wherein an uppermost end of the shaft includes a feature configured to engage with a mating feature on a recovery instrument for retrieving the wellbore instrument from the interior of the drill string. ### Claim 8 (depends on 1) The system of claim 1 wherein the bladder has hydraulic fluid therein and is in fluid communication with the lubrication chamber, wherein the pressure compensation port is in pressure communication with an exterior of the bladder. ### Claim 9 (depends on 8) The system of claim 8 further comprising an hydraulic recharge reservoir disposed in the instrument housing, the hydraulic recharge reservoir in fluid communication with the lubrication chamber and maintained at a selected pressure above a hydrostatic pressure in the wellbore, wherein momentary reduction in fluid pressure in the wellbore enables transfer of fluid in the recharge reservoir to the lubrication chamber to compensate for lubrication chamber fluid loss across the face seal during operation thereof. ### Claim 10 (depends on 9) The system of claim 9 further comprising a valve disposed in an outlet of the recharge reservoir, the valve actuatable to close the outlet when a portion of the shaft is removed from the wellbore instrument. ### Claim 11 (depends on 1) The system of claim 1 wherein a rotor of a mud flow modulation telemetry device is coupled to the shaft and a stator thereof is coupled to the housing. ### Claim 12 (depends on 1) The system of claim 1 further comprising one or more bellows comprised of metal disposed between the housing face of the face seal and the housing. ### Claim 13 A wellbore instrument, comprising: a housing configured to be coupled to a drill string; a shaft rotatably mounted with respect to the housing; a lubrication chamber disposed in an annular space between the shaft and the housing; a pressure compensator in hydraulic communication with an interior of the drill string and the lubrication chamber, the pressure compensator configured to maintain a fluid pressure in the lubrication chamber at a fluid pressure inside the drill string proximate the instrument; a face seal configured to seal a space between the shaft and the housing, one face of the face seal coupled to the shaft, another face of the face seal functionally coupled to the housing, at least one of the housing face and the shaft face including a metal bellows coupled between the respective one of the housing face and the housing and the shaft face and the shaft, wherein the pressure compensator includes a pressure communication port, and wherein the pressure compensator comprises a removable enclosure configured to be removed from around the shaft when the shaft is disassembled from the housing such that access to the removable enclosure is obtained without removing the shaft from the housing, the removable enclosure having a bladder; and a valve disposed in an interior passage of the shaft, wherein the valve closes upon removal of an upper portion of the shaft. ### Claim 14 (depends on 13) The instrument of claim 13 wherein pressure compensator includes a piston slidably mounted in a chamber, the chamber disposed in at least one of the housing and the drill string. ### Claim 15 (depends on 13) The instrument of claim 13 wherein one end of the pressure communication port is open to the interior of the drill string in an uppermost portion of the shaft. ### Claim 16 (depends on 13) The instrument of claim 13 wherein one end of the pressure compensation port is open to a mud chamber disposed inside the instrument housing. ### Claim 17 (depends on 16) The system of claim 16 further comprising a bellows at least partially filled with liquid and disposed in the mud chamber, the bellows configured to have a crush pressure at least as high as a maximum expected mud pressure inside the drill string. ### Claim 18 (depends on 13) The system of claim 13 wherein one end of the pressure compensation port is open to the interior of the drill string proximate the face seal. ### Claim 19 (depends on 13) The instrument of claim 13 wherein an uppermost end of the shaft includes a feature configured to engage with a mating feature on a recovery instrument for retrieving the wellbore instrument from the interior of the drill string. ### Claim 20 (depends on 13) The instrument of claim 13 wherein the bladder has hydraulic fluid therein and is in fluid communication with the lubrication chamber, wherein the pressure compensation port is in pressure communication with an exterior of the bladder. ### Claim 21 (depends on 20) The instrument of claim 20 further comprising an hydraulic recharge reservoir disposed in the instrument housing, the hydraulic recharge reservoir in fluid communication with the lubrication chamber and maintained at a selected pressure above a hydrostatic pressure in the wellbore, wherein momentary reduction in fluid pressure in the wellbore enables transfer of fluid in the recharge reservoir to the lubrication chamber to compensate for lubrication chamber fluid loss across the face seal during operation thereof. ### Claim 22 (depends on 21) The instrument of claim 21 further comprising a valve disposed in an outlet of the recharge reservoir, the valve actuatable to close the outlet when a portion of the shaft is removed from the wellbore instrument. ### Claim 23 (depends on 13) The instrument of claim 13 wherein a rotor of a mud flow modulation telemetry device is coupled to the shaft and a stator thereof is coupled to the housing.