Abstract: A method for determining the height and length of a fracture (3) in a borehole (1) involves generating pressure waves in the fluid in the wellbore using a valve (4) and measuring the response at the well-head by means of a transducer (5). A theoretical model of the wellbore-fracture system is generated and compared with the measured response to determine the height and length of the fracture.

Abstract: A method for determining the height and length of a fracture (2) in a borehole (1) involves generating pressure waves at closely spaced frequencies by means of a transmitter (3) at the wellhead. The response at the wellhead of the wellbore-fracture system to the resultant standing waves is measured by means of a transducer (6). A theoretical model of the wellbore-fracture system is generated and compared with the measured response to determine the height and length of the fracture.

Abstract: A cryogenic cell comprises a sealed external annular chamber, adapted to be maintained under vacuum which chamber surrounds a heat shield. A section of the shield is exposed and is adapted to make contact with a closed cycle cooler. The shield encloses a sealed inner chamber adapted for the storage of a solid/liquid refrigerant. The shield has a relatively thin base and sidewall and the section which is exposed is a relatively thick upper collar which has a well leading to the top of the inner chamber immediately above and in contact with the top of the inner chamber. The inner chamber is connected at its lower end to a section containing an absorbent and the latter section is connected at its lower end to a further chamber suitable for the reception of a gamma radiation detector. The cryogenic cell is suitable for keeping the semi-conductor detector of a neutron borehole logging tool at the required low temperature.

Abstract: The bulk rock strength of strata is determined by logging a borehole with an instrument to obtain a Neutron-Neutron log or a Hydrogen Index log of the hole and determining from the log in conjunction with the lithology of the strata the strength of the strata rocks by applying an inverse relation formula.