Systems, methods and apparatus for downhole monitoring of production conditions using EM telemetry
A gap sub for wellbore fluids comprises an electrical isolation structure to electrically isolate two metallic ends of the gap sub and a housing mounted outside of the gap sub. The housing accommodates an “external gap” and a toolstring for acquiring in-situ measurements of wellbore and near-wellbore conditions and transmitting the measurements to surface using EM telemetry. The gap sub comprises an antenna rod connected to the “external gap”, the antenna rod straddling the electrical isolation structure in the gap sub to be electrically isolated from one metallic end of the gap sub and electrically coupled to the other metallic end of the gap sub.
1 . A gap sub for wellbore fluids, the gap sub comprising:
an electrical isolation structure to electrically isolate two metallic ends of the gap sub;
a housing mounted outside of the gap sub, the housing accommodating an “external gap”, and a toolstring for acquiring in-situ measurements of wellbore and near-wellbore conditions and transmitting the in-situ measurements to surface using electromagnetic (EM) telemetry; and
an antenna rod connected to the “external gap” in the housing, and the antenna rod straddling the electrical isolation structure in the gap sub to be electrically isolated from one metallic end of the two metallic ends of the gap sub and electrically coupled to another metallic end of the two metallic ends of the gap sub.
2 . The gap sub of claim 1 , wherein the toolstring comprises:
one or more electronic sensors able to measure the wellbore and near-wellbore conditions;
an EM transceiver for encoding measurements from the one or more electronic sensors, modulating an EM waveform and transmitting the EM waveform to the surface; and
a power source, such as a battery pack, to provide electrical power to the one or more electronic sensors and the EM transceiver.
3 . The gap sub of claim 2 , wherein the one or more electronic sensors are integrated with the EM transceiver in a single module or provided in separate modules that can be coupled together.
4 . The gap sub of claim 3 , wherein the single module comprising the one or more electronic sensors comprises a shoulder that presses against an internal lip of the housing under wellbore fluid pressure to rigidly secure the toolstring inside the housing.
5 . The gap sub of claim 1 , wherein the housing is in a form of a pressure housing comprising a pressure transducer at an upper end of the pressure housing.
6 . The gap sub of claim 1 , wherein, the “external gap” is in a form of an adjustable antenna isolator assembly adjustably accommodated at least partly within a lower end of a pressure housing.
7 . The gap sub of claim 6 , wherein the adjustable antenna isolator assembly is attached to a first end of the antenna rod at the one metallic end of the gap sub and electrically isolated from the housing.
8 . The gap sub of claim 7 , wherein a second end of the antenna rod is coupled to the other metallic end of the gap sub via a conductive element.
9 . The gap sub of claim 6 , wherein the adjustable antenna isolator assembly is accommodated at least partly within the pressure housing to enable fine adjustment of an axial position of the adjustable antenna isolator assembly in the pressure housing.
10 . The gap sub of claim 9 , wherein the fine adjustment is achieved with external threads on an outer collar of the adjustable antenna isolator assembly engaging with internal threads in the pressure housing.
11 . The gap sub of claim 1 , wherein the housing comprises one or more ports to bleed-off trapped pressure inside the housing when the gap sub is retrieved to the surface.
12 . The gap sub of claim 11 , wherein an adjustable antenna isolator assembly comprises one or more seals, wherein fine adjustment of an axial position of the adjustable antenna isolator assembly in a pressure housing until the one or more seals clear the one or more ports provides a vent mechanism to bleed-off the trapped pressure inside the pressure housing.
13 . The gap sub of claim 1 , wherein the gap sub provides full-wellbore access, with a pressure housing mounted on an exterior surface of the gap sub.
14 . The gap sub of claim 1 , wherein the gap sub comprises upper and lower metal tubes and the electrical isolation structure is in a form of a hollow composite electrical isolation collar in between the upper and lower metal tubes.
15 . The gap sub claim 1 , wherein the gap sub comprises an assembly for creating an electrical connection between a transmit/receive line on an EM transceiver with the one metallic end of the gap sub.
16 . The gap sub of claim 1 , wherein the gap sub comprises an assembly for establishing an electrical connection between a ground plane on an EM transceiver with the other metallic end of the gap sub.
17 . The gap sub of claim 1 , wherein the gap sub comprises threaded pin and/or box connections at either the one metallic end or the other metallic end of the gap sub, configured to be inserted at a desired position within a tubing string.
18 . The gap sub of claim 17 , wherein the gap sub comprises a thread locking compound applied to threads of the threaded pin and/or box connections to ensure torque rating of the gap sub equals or exceeds the torque rating of the tubing string above and below the gap sub.
19 . A method of acquiring in-situ measurements of wellbore and near-wellbore conditions and transmitting the in-situ measurements to surface using an electromagnetic (EM) telemetry, the method comprising:
providing a gap sub between tubing joints in a tubing string for wellbore fluids, the gap sub comprising an electrical isolation structure to electrically isolate two metallic end members of the gap sub;
mounting a housing outside of the gap sub, the housing accommodating an “external gap” and a toolstring for the EM telemetry; and
connecting an antenna rod to the “external gap” to electrically isolate the antenna rod from one metallic end member of the two metallic end members, and the antenna rod straddling the electrical isolation structure in the gap sub, with another metallic end member of the two metallic end members of the antenna rod mechanically and electrically connected to the other metallic end member.
20 . A system to acquire in-situ measurements of wellbore and near-wellbore conditions and transmitting the in-situ measurements to surface using an electromagnetic (EM) telemetry, the system comprising:
a gap sub between tubing joints in a tubing string for wellbore fluids, the gap sub comprising an electrical isolation structure to electrically isolate two metallic ends of the gap sub;
a housing mounted outside of the gap sub, the housing accommodating an “external gap” and a toolstring providing the EM telemetry; and
an antenna rod connected to the “external gap”, and the antenna rod straddling the electrical isolation structure in the gap sub to be electrically isolated from one metallic end of the two metallic ends of the gap sub and electrically coupled to another metallic end of the two metallic ends of the gap sub.
21 . The system of claim 20 , wherein the system comprises one or more of following:
the toolstring comprises one or more electronic sensors able to measure the wellbore and near-wellbore conditions, an EM transceiver for encoding measurements from the one or more electronic sensors, modulating an EM waveform and transmitting the EM waveform to the surface, and a power source, such as a battery pack, to provide electrical power to the one or more electronic sensors and the EM transceiver;
the one or more electronic sensors are integrated with the EM transceiver in a single module or provided in separate modules that can be coupled together;
the single module comprising the one or more electronic sensors comprises a shoulder that presses against an internal lip of the housing under wellbore fluid pressure to rigidly secure the toolstring inside the housing;
the housing is in a form of a pressure housing comprising a pressure transducer at an upper end of the pressure housing;
the “external gap” is in a form of an adjustable antenna isolator assembly adjustably accommodated at least partly within a lower end of the pressure housing, wherein, optionally:
the adjustable antenna isolator assembly is attached to a first end of the antenna rod at the one metallic end of the gap sub and electrically isolated from the housing;
a second end of the antenna rod is coupled to the other metallic end of the gap sub via a conductive element;
the adjustable antenna isolator assembly is accommodated at least partly within the pressure housing to enable fine adjustment of an axial position of the adjustable antenna isolator assembly in the pressure housing, the fine adjustment is optionally achieved with external threads on an outer collar of the adjustable antenna isolator assembly engaging with internal threads in the pressure housing;
the housing comprises one or more ports to bleed-off trapped pressure inside the housing when the gap sub is retrieved to the surface;
the adjustable antenna isolator assembly comprises one or more seals, wherein the fine adjustment of the axial position of the adjustable antenna isolator assembly in the pressure housing until the one or more seals clear the one or more ports provides a vent mechanism to bleed-off the trapped pressure inside the pressure housing;
the gap sub provides full-wellbore access, with the pressure housing mounted on an exterior surface of the gap sub;
the gap sub comprises upper and lower metal tubes and the electrical isolation structure is in a form of a hollow composite electrical isolation collar in between the upper and lower metal tubes;
the gap sub comprises a first assembly for creating an electrical connection between a transmit/receive line on the EM transceiver with the one metallic end of the gap sub;
the gap sub comprises a second assembly for establishing an electrical connection between a ground plane on the EM transceiver with the other metallic end of the gap sub;
the gap sub comprises threaded pin and/or box connections at either the one metallic end or the other metallic end of the gap sub, configured to be inserted at a desired position within a tubing string; and
the gap sub comprises a thread locking compound applied to threads of the threaded pin and/or box connections to ensure torque rating of the gap sub equals or exceeds the torque rating of the tubing string above and below the gap sub.