| 摘要 |
<p>An apparatus and method for measuring differential pressure of mud internal a drill string (20) and mud in a borehole annulus (58) is disclosed. The apparatus typically comprises: a drill collar (126) having a pressure balancing piston (132) in hydraulic contact with the borehole annulus mud; a shaped cylinder (135) in contact with the mud internal the drill string and supported by the drill collar but attached such that axial forces on the drill collar are not transferred to the shaped cylinder, wherein the shaped cylinder (135) has relatively thicker end portions (135a, 135b) in contact with the drill collar, and a relatively thinner portion (135c) such that a gap (139) is formed between the relatively thinner middle portion of the shaped cylinder and the drill collar; a fluid filling the gap and in hydraulic contact with the pressure balancing piston; a plurality of strain gauges (142a-148a), (142b-148b) axially and circumferentially disposed around the relatively thinner middle portion of the shaped cylinder, wherein the axially disposed strain gauges (142a-148a) provide an indication of axial stress and the circumferentially disposed strain gauges (142b-148b) provide an indication of hoop stress; and means for obtaining at least one axial and hoop stress measurement from the plurality of strain gauges, for taking the difference between hoop and aixal measurements, and for providing a pressure determination representing the difference of mud pressure.</p> |
