Wade M. Johnson, Jr., and Jorg Angehrn
Dresser Atlas, Dresser Industries, Inc.
Houston, Texas
ABSTRACT
Increasing use of Dresser Atlas Diplog type surveys for mapping subsurface structure in wildcat areas has resulted in a need for improved instrument accuracy. Measurement of regional dip under five degrees, and often from deviated boreholes, requires improved accuracy of the orientation measurement and Diplog instrument performance.
A new Diplog instrument is described which uses a three-axes vector magnetometer and three-axes accelerometer inclinometer for improved orientation accuracy over that achieved with earlier, mechanical orientation sensors.
The new instrument employs a modern, eight-bit microcomputer downhole to implement a data acquisition and telemetry system. The microprocessor-based system controls the data acquisition and telemetry system which transmits digitally the large amount of data obtained from the Diplog and orientation sensors without signal degradation by the cable. The microcomputer also implements gain ranging by automatic control of the correlation curve measure voltage allowing operation from very low to high resistivities.
The paper provides a system design overview. The objective of the paper is to provide the log analyst increased knowledge of the capabilities and limitations of modern Diplog instruments through familiarity with the measurement technique and basic instrument design. Trends in downhole instrument electronic design are discussed including the rapidly changing field of microprocessor-based instruments.