Method and well logging apparatus having acoustic and neutron pads

Abstract

Abstract A WELL LOGGING INSTRUMENT ADAPTED FOR TRANSVERSING AN EARTH BOREHOLE HAS A NEUTRON PAD MEMBER ON ONE SIDE OF THE INSTRUMENT WHICH IS NORMALLY SPRING-FORCED INTO CONTACT WITH THE BOREHOLE WALL DURING SUCH A TRANSVERSAL. THE INSTRUMENT HAS ON ITS OPPOSITE SIDE AN ACOUSTIC PAD WHICH IS ALSO NORMALLY SPRING-FORCED INTO CONTACT WITH THE BOREHOLE WALL DURING SUCH A TRANSVERSAL. THE ACOUSTIC PAD HAS AN ACOUSTIC TRANSMITTING TRANSDUCER AND A PAIR OF ACOUSTIC RECEIVING TRANSDUCERS FOR PRODUCING AN ACOUSTIC TIME INTERVAL MEASUREMENT. EACH TRANSDUCER IS MOUNTED ON AN ACUTE ANGLE FROM THE LONGITUDINAL AXIS OF THE ELONGATED INSTRUMENT HOUSING AND IS MOUNTED IN A FLUID MEDIUM CHOSEN TO MATCH THE ACUTE ANGLE SO THAT A STEEP RISING WAVE FRONT PASSES THROUGH THE FORMATION SURROUNDING THE BOREHOLE AND PRODUCES A STEEP RISING SIGNAL AT THE RESPECTIVE RECEIVERS, THEREBY PERMITTING AN ACCURATE MEASUREMENT OF ACOUSTIC WAVE TRAVEL TIME FROM TRANSMITTER TO FIRST RECEIVER AND FROM FIRST TO SECOND RECEIVER. THE NEUTRON PAD, HAVING A CAPSULED NEUTRON SOURCE AND AN EPITHERMAL NEUTRON DETECTOR, RESPONDS TO VARIATIONS IN FORMATION POROSITY AND TO THE THICKNESS AND CONSTITUENCY OF MUD AND MUD CAKE INTERVENING BETWEEN THE PAD AND THE FORMATION. THE ACOUSTIC PAD SERVES TO INDICATE THE EXTENT OF THE EFFECT ON THE NEUTRON-DERIVED POROSITY MEASUREMENT DUE TO THE MUD AND MUD CAKE AND PERMITS A CORRECTED POROSITY TO BE DERIVED AND RECORDED.

Inventors

• 👤 Arthur H Youmans

Bibliographic Details