SHUTOFF FILTER Russian patent published in 1995 - IPC

FIELD: operation of oil and gas wells. SUBSTANCE: shutoff filter includes body with filtering holes which are plugged with chemically decomposed plugs. Case with radial channels is installed outside the body and forms chamber together with body having upper and lower compartments. Shutoff filter has upper and lower valves. Lower valve is installed for communication of drill string-borehole annulus with body hollow. Communication is effected through case radial channels and filtering holes. Upper valve is installed for communication of body hollow with drill string-borehole annulus. In this case, it is located in the chamber upper compartment. It is spring-loaded in direction of closing on the sode of formation. Spring foce is adjusted for full closing with consideration of possible pressures inside well. It is determined from the expression given in invention description. EFFECT: provision of preservation of filtering and storage capacities of producing formation due to prevention of contaminating liquids from getting into formation during performance of process operations inside the well under pressure exceeding the formation one. 2 dwg