| 摘要 |
Oil and other fluids are pumped from a well drilled into chalk or other difficult-to-produce formations by applying a back pressure to the formation concurrently with pumping fluid from the formation. One embodiment a pump suitable for performing the method includes a reciprocating piston with a check valve to permit the passage of fluid through the piston during downstrokes and to prevent its passage during upstrokes. The pump also includes a second check valve having a telescoping link that permits the downward passage of fluid for a first portion of the downstroke of the pump piston but prevents the passage of the fluid during a second portion of the piston downstroke. The combined action of the two valves is to lift fluid on the pump piston upstroke and force a portion of the previously lifted fluid back into the well, and thus into the formation, during the first portion of the downstroke. The movement of a portion of the fluid back into the formation acts to clear material bridges that block fluid access to the well and also to continuously fracture the formation to enhance fluid entry into the well. In a second embodiment the telescoping link and associated valve are replaced by an elongated, tapered rod which passes through the central opening of annular collar on its downstroke and forces the collar against a valve seat to block the downward passage of fluids. On its upstroke the rod permits the collar to rise from the valve seat to permit the upward passage of fluids.
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