GB1071416A - Method of and apparatus for logging boreholes - Google Patents

Abstract

1,071,416. Borehole logging. BRITISH PETROLEUM CO. Ltd. Nov. 20, 1963 [Jan. 10, 1963], No. 1167/63. Headings G1A and G1N. A method of logging a borehole comprises running a sonde along a borehole containing conductive fluid and concurrently investigating the formation past which the sonde moves by a guard electrode technique to provide a resistivity log of each of a number of investigation depths of penetration into the formation, by a caliper technique to estimate the mudcake thickness on the borehole wall and the borehole diameter, by a spontaneous potential technique to determine the resistivity of the conducting fluid in the formation and by further means to determine the porosity of the formation surrounding the borehole, the information of all techniques being passed to a position exterior to the sonde in the form of a successive group of multiplexed signals, and a sonde for carrying out the method comprises the necessary logging apparatus together with circuitry for distributing A. C. power from an external source to the investigating means and a time multiplex telemetering system for conveying successive groups of signals related to sampled investigation data to a position exterior of the sonde. The porosity may be determined by a neutron gamma, neutron neutron, gamma gamma or an acoustic velocity device and the sonde may include apparatus responsive to natural gamma radiation and apparatus for measuring continuously mud resistivity and temperature. The concurrently obtained data can be used to give a quantitative analysis of hydrocarbons in the porous formations. Sonde (11), Fig. 1 (not shown) carries electrodes (AA<SP>1</SP>) (BB<SP>1</SP>) (CC<SP>1</SP>) and (X) separated by insulating spacers (13) acoustic transmitters (14) and receivers (16), a radiation source (18), and a lead shield (19) to protect the sonde from radiation effects. The electronic circuitry is housed in a cartridge (20) Fig. 2 (not shown) which fits in the sonde and includes a natural gamma photo-multiplier tube and crystal in portion (21), telemeter circuitry in portion (22), switching circuits in portion (23) a neutron gamma crystal and photo-multiplier in portion (24) and electronic equipment associated with the acoustic equipment in portion (25). The telemetering system is described in Specification 908, 467 and the investigation is controlled by a 12 pulse clock unit which produces output pulses on two additional terminals for each clock pulse through five bi-stable units and 6 gates (G1-G6), Fig. 4b (not shown), transformer (TR2) applying A. C. energy and transformer (TR1) serving as a means to measure the electrode current. The sequential switching of the electrode circuits by the five bi-stable units and the connection of the measuring circuit to the telemeter equipment is described with reference to Fig. 8 (not shown). Resistivity logging is described with reference to Specification 1, 038, 452 and the acoustic logging with reference to Specification 1, 071, 414. The acoustic receiver units (16) are connected to receiver units (30-33) Fig. 6 (not shown) and received first signals serve to stop integrators (I1), (I3), (I5), (I7), which are initiated by an output from the transmitter energizing unit. The first signals from the mud to mud face interface are followed by reflections from mudcake to borehole wall and these two signals start and stop integrators (I2), (I4), (I6), (I8) to measure the distance between the interfaces, the outputs from both sets of integrators being stored in stores (S1-S8) for subsequent sampling by the telemetering system. The spontaneous potential on an electrode located for example 15 feet above the probe is passed through a high impedance amplifier and gated to the telemetering equipment.