EM gap sub assembly

A gap sub assembly comprising:

• a generally cylindrical housing having an interior connecting surface including right- and left-handed helical grooves;
• a generally cylindrical mandrel having an outer connecting surface inserted into the housing to form a gap between the interior surface of the housing and the outer surface of the mandrel, the outer connecting surface including right- and left-handed helical grooves;
• an electrically isolating medium filling the gap between the housing and the mandrel, the electrically isolating medium mechanically coupling the housing and the mandrel while maintaining electrical isolation between the housing and the mandrel;
• wherein the right-handed and the left-handed grooves on the housing and mandrel surfaces have clearing diameters so that the mandrel can be inserted into the housing without any longitudinal rotation of the mandrel relative to the housing, and
• wherein the interior surface of the connecting portion of the housing includes a region comprising a plurality of axial sections having a staggered internal diameter in which at least one axial section having a first internal diameter is adjacent to axial sections on either side which have larger internal diameters and the outer surface of the connecting portion of the mandrel includes a region comprising a plurality of axial sections having a staggered diameter in which at least one axial section having a first diameter is adjacent to axial sections on either side which have smaller diameters, the plurality of mandrel axial sections matched with corresponding axial sections of the housing so that the space between the housing and mandrel is generally the same across all of the axial sections;
• and wherein the mandrel cannot be removed from the housing by way of an axial force without shearing through at least one layer of the electrically isolating medium.

An electrically insulating gap sub for use with an EM telemetry system, the gap sub comprising:

• a cylindrical housing having an open end and a connecting portion proximal to the open end;
• a cylindrical mandrel having a connecting portion at one end, wherein the cylindrical housing is configured to receive the connecting portion of the cylindrical mandrel, and wherein the mandrel is sized so that the connecting portion of the mandrel can be axially inserted into the interior of a connecting portion of the cylindrical housing to form a generally uniform space between the interior surface of the connecting portion of the housing and the outer surface of the connecting portion of the mandrel;
• and
• a curable electrically isolating medium to be injected within the generally uniform space between the connecting portions of the housing and the mandrel, the cured electrically isolating medium mechanically coupling the housing and the mandrel while maintaining electrical isolation between the housing and the mandrel;
• wherein the gap sub assembly includes at least one of the following:
• a) an axial force resistance assembly in which the interior surface of the connecting portion of the housing includes a region comprising a plurality of axial sections having a staggered internal diameter and at least one axial section having a first internal diameter is adjacent to axial sections on either side that have larger internal diameters, the outer surface of the connecting portion of the mandrel includes a region comprising a plurality of axial sections having a staggered diameter and at least one axial section having a first diameter is adjacent to axial sections on either side which have smaller diameters, the plurality of mandrel axial sections matched with corresponding axial sections of the housing so that the space between the housing and mandrel is generally the same across all of the axial sections;
• and
• b) a torsion resistance assembly in which an interior surface of the connecting portion of the housing includes a first region having right-handed helical grooves formed on the interior surface and a separate second region having left-handed helical grooves formed on the interior surface, an outer surface of the connecting portion of the mandrel includes a first region having right-handed helical grooves formed on the outer surface and a separate second region having left-handed helical grooves formed on the outer surface;
• wherein the interior surface of the housing and the exterior surface of the mandrel do not overlap when the housing and mandrel are connected so that the mandrel can be inserted into the housing without any longitudinal rotation of the mandrel relative to the housing.