Typical setup for radioactivity well logging.(Images courtesy of Baker Atlas)

In 1939, the management at the Houston office of the Lane-Wells Company recognized that it had a problem. Drilling was down 12% for the first six months of that year, and well services competitors were taking greater shares of the oilfield service business. The Lane-Wells cased-hole perforation service was still in great demand, but locating the exact perforation zone through casing proved increasingly difficult — especially as the wells went deeper. The company did not have a logging instrument which could locate the perforation zone with a high degree of accuracy.

Lane-Wells knew the kind of device it needed — a radioactivity logging instrument which detected gamma rays. Virtually all formations emitted radioactive gamma rays capable of penetrating steel, cement, and rock. The gamma rays could be interpreted to reveal important data about the formations including their types, depths, thicknesses and sequences. Developing such an instrument, though, would require a large expenditure of funds. The crucial need for the tool in the field also prohibited a lengthy development program.

Concurrently, the management of Well Surveys, Inc. (WSI) in Tulsa, Okla., was also aware of their pressing business need: customers to purchase or lease their new Gamma Ray Log instrument. The tool functioned properly in the lab and in test wells, and WSI was convinced the tool would operate efficiently in the oil field. Several WSI patent applications had been submitted for the advanced technology within this instrument, but the device had not yet generated any revenue. Further developments and improvements to the instrument were beyond the financial capability of this small firm. WSI needed revenue from the instrument, but many companies in the oilfield industry were unsure of the reliability and accuracy of radioactive logging instruments.

Cooperation yields success

When Lane-Wells discovered WSI might have a functioning Gamma Ray Log, meetings were held and field tests occurred at the Tulsa location under the eyes of Norm Dorn, the chief engineer from Lane-Wells. It took several months to convince Dorn that the WSI Gamma Ray Log was a practical and reliable tool for determining borehole formation characteristics. By May 1940, though, he was certain this instrument was exactly what Lane-Wells needed. Lane-Wells then signed an exclusive license with WSI to buy and operate all of their radioactivity well-logging instruments for use in the United States. Later negotiations extended the license to Canada and Venezuela.

It was a mutually beneficial arrangement. WSI had a guaranteed buyer for its products as well as revenue and field experience to enhance the devices. The Gamma Ray Log (and subsequent radioactivity logging instruments) increased the suite of services that Lane-Wells offered clients, improving their ability to obtain work.

A proven value

The Gamma Ray Log proved to be a very useful and versatile survey instrument. Lane-Wells quickly discovered how to use the instrument for a variety of purposes.

Variations in radiation amounts emanating from formations made the tool useful in determining lithology. Correlating openhole and cased-hole logs, usually in conjunction with a casing collar locator, was also an early application. If the well had radioactive depth markers from tracers, the gamma ray log located these and obtained accurate depth measurements. In older fields lacking any logging, the instrument was exceptional at detecting bed definitions.

The gamma ray log was very advanced by the standards of 1940. The instrument was housed in a steel cylinder about 9.75 ft (3 m) long with an outside diameter of 35?8-in.
The upper part of the tool contained a 3-ft (1-m) ionization chamber filled with a mixture of inert gases under pressure and fitted with insulated electrodes connected externally to a battery within the tool housing. Under normal conditions, the gas in the ionization chamber was non-conductive and no current flowed between the electrodes. When the chamber was lowered into an oil well and brought into the vicinity of radioactivity, the gamma rays partially ionized the gas, making it conductive. A small current then flowed between the electrodes. The current was proportional to the intensity of gamma rays entering the chamber.

The extreme sensitivity of the device was remarkable. According to Lane-Wells literature, the current changes in the ionization chamber amounted to one ten-trillionth of an ampere. Yet the instrument produced a visible log deflection for quantities of radioactive substances as small as one-hundredth of a microgram when placed outside the ionization chamber.

An amplifier inside the gamma ray log boosted the current sufficiently to be transmitted up the wireline cable to the instrument truck. This truck contained additional amplifiers, controls and a high-speed automatic pen-type recorder. The recorder was run in synchronism with a depth-measuring sheave and provided a continuous graph that was visible to the operator.

In the field

A standard logging job involved two specially built trucks. One carried the wireline cable and hoist, a generator, and controls to conduct the hoisting operations. The second, lighter-weight truck carried the high-speed recorder and other electronic equipment used in the recording of the logs. Rigging up at a well involved unloading the rig equipment and instruments, spotting the truck, suspending and centering the weight indicator and measuring sheave assembly over the well, threading the cable over the sheave, connecting the cables and making up the instrument on the cable. When everything was connected and checked, the measuring devices were zeroed to the proper surface reference, the instrument response to standard was noted, and the instrument was lowered into the hole.

Inside the instrument truck, the operator activated the recorder when the tool reached the planned depth. Logging continued as the instrument was hoisted to the surface. Several hundred feet of the log being recorded was in plain view of the customer and operator. Based on this information, plans for the next operation on the well could be made immediately.

If the customer wanted to gun perforate before the log was formally prepared, the original record could be used to select perforation zones. As the Lane-Wells gun perforator could be run on the same hoist equipment that was used in the logging, the customer was offered a fast and convenient service combination.

Through a mutually beneficial business arrangement almost 70 years ago, a historic oilfield logging tool was brought into commercial use. Successive generations of the Gamma Ray Log have continued to verify the usefulness and value of this tool.

The Lane-Wells Company purchased Well Surveys in 1954 and the firm eventually became Baker Atlas.

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