Oil well service tool

In an earth borehole survey instrument package movable through a pipe bore from the earth surface to a restraining device at a downhole location, apparatus to reduce the deceleration rate of instruments in the package comprising:

• an elongated generally cylindrical housing with a sealed enclosure, a lower and an upper end, and longitudinal central axis;
• a piston and cylinder pair attached to said housing lower end situated for relative motion of said piston in said cylinder in response to downward force applied by said housing and resisted by the downhole locating device;
• a fluid body subject to fluid discharge in sympathy with said piston and cylinder relative motion;
• an orifice in communication with said fluid body comprising a plurality of holes through the wall of said cylinder, distributed along a dimension traversed by said piston relative motion to change the number of holes subject to said fluid discharge in sympathy with said piston position relative to said cylinder;
• an instrument within said sealed enclosure situated for axial motion relative to said housing;
• a piston and cylinder pair situated in said enclosure for axial relative motion in sympathy with movement of said instrument with force communication means to said instrument and one of said pair, and force communications means to said housing and the other of said pair;
• a fluid filled body situated within said cylinder and piston pair arranged to discharge fluid from said body in response to piston and cylinder relative motion;
• an orifice in communication with said fluid body through which said fluid may flow;
• and
• a tapered rod situated to extend into said orifice in sympathy with relative motion of said piston and cylinder;
• whereby the deceleration forces imposed upon the housing by the dashpot effect of the cylinder and piston on the lower end of the housing may be regulated over the travel distance of the housing relative to the pipe bore location device during deceleration after travel through the pipe bore, the internal piston and cylinder arrangement serving a similar function to further protect the instrument from deceleration forces acceptable to the housing.

In a well bore survey package to be lowered into a borehole with shock of deceleration upon reaching the selected survey position downhole, apparatus to reduce peak deceleration loads imposed upon delicate instruments within the descending package comprising:

• an elongated housing having a sealed enclosure and a generally central axis;
• a well survey instrument situated in said enclosure mounted for movement along said axis from a first position to a second position;
• a collapsible cylinder with a fluid filled enclosure made smaller by collapsing said cylinder from a first extended position to a second collapsed position, said collapse in sympathy with movement of said instrument from said first to said second position;
• a variable resistance fluid escape means for fluid to move out of said fluid filled enclosure upon collapse of said cylinder;
• control means to regulate said resistance to fluid escape responsive to the position of said instrument relative to said first and second positions;
• bias means to urge said instrument from said second position to said first position;
• means to convey deceleration loads from said instrument to said cylinder;
• and
• means to convey deceleration loads from said cylinder to said housing;
• whereby the shock of suddenly stopping the housing from movement through a pipe bore will be transmitted to the instrument at a reduced deceleration rate by allowing the velocity energy of the instrument to be distributed with reasonable uniformity over the travel of the instrument and collapsable cylinder as they move axially within the sealed enclosure.

In an instrument package used to measure physical factors in earth boreholes by being moved from the earth surface down the bore of the pipe string in the earth borehole to a preselected position in the pipe bore for measurement activity apparatus to reduce the acceleration loads imposed upon instruments contained within the package comprising:

• an elongated generally cylindrical housing having an upper end and a lower end, a sealed enclosure, and a longitudinal centerline;
• shock absorber means at the lower end of the housing to reduce the acceleration rate of the remainder of the package when the package is accelerated by velocity change in moving through the pipe bore;
• acceleration control means in said shock absorber to apply a reasonably uniform acceleration force to the package as velocity is changed over the acceleration travel distance;
• means inside the package enclosure to allow movement of the instrument a distance along said central axis to provide an acceleration travel distance to said housing;
• shock absorber means associated with said movement means to apply retarding forces to the instrument as it moves along said central axis;
• shock absorber control means responsive to the amount of movement of the instrument along said axis to regulate the acceleration forces to a reasonably constant value;
• bias means to return the instrument to a preselected position within the enclosure after the acceleration movement;
• and
• bias means to return the package to a preselected axial position after the acceleration movement;
• whereby the package and instrument are protected from sudden acceleration when the package velocity through the pipe bore is changed.