Radioactivity Well Logging (1954)

When science rubbed the magic lamp of nuclear physics, there burst upon the world a terrifying genie. Fantastically destructive, but not without many secrets for man's use in his struggle to master his environment. The lethal powers of radioactivity, deadly byproduct of the super bombs are well known now. But as early as 1940, the oil industry had learned the secrets of these silent rays and harnessed them to the increasingly intensive search for new oil horizons through the process known as radioactivity logging. [Music] [Applause] If in the search for oil we could look deep into the earth, we would find disclosed a geological record of an area's history and its composition. In order to utilize this record in oil exploration, it must be interpreted by two specialized branches of the oil industry. Geology and well logging. Geology as applied in oil exploration helps to identify the formations penetrated by the drill through a study of the appearance, structure and mineral composition of the material found in bore cutings and in cores. [Music] Nuclear physics has proved that every individual straighta of the earth contains measurable radioactivity to a varying degree. Combined with other known geological information about an area, the measurement of this radio activity becomes an additional means of identifying each straight in its plates. Extremely important information when seeking the exact depth and extent of an oil producing zone. [Music] The measurement of natural radioactivity is one of the basic operations of radioactivity logging. Recorded as a gammaray curve. It is a measure of the natural radiation of a formation or expressed in another way a measure of the level of radioactivity of a formation. A complete radioactivity log includes a neutron curve which is an indicator of the fluid content of a formation, an indication to a degree of the relative porocity of subsurface formations and thereby the possible presence of oil, water or gas. This is accomplished by a measurement of radiation which is artificially induced and then detected by the logging tool in its reflected form. Watch this logging tool making a typical gammaray log rising in the well. It measures the level of radioactivity of each formation. Radioactivity in underground formations is of low but measurable intensity. Shale is generally the strongest in natural radiation. Most radioactive material radiates alpha, beta or gamma rays. Alpha and beta rays are so weak that they are ignored for logging purposes. But gamma rays are very energetic. Their strong penetrating power makes them the most effective form of natural radiation available for making a radioactivity log. Now let's discuss the neutron curve. A neutron is one of the essential particles of an atom which is the smallest unit of all elements. The atoms of the different elements are identifiable by the different number of their neutrons and other particles of which they are composed. When a highly radioactive element, radium or palonium is mixed with burillium, neutron emission occurs. These neutrons leave the neutron source to bombard the surrounding area. A neutron source in a logging tool sends these neutrons into the surrounding formations at a terrific rate of speed, setting the stage for other strange natural phenomena. The bombarding neutrons then change form or speed and the results are detected by the logging tool and recorded by the graph above ground. Hydrogen is always present in oil, water and gas bearing formations and therefore it is the most important element encountered in neutron logging. The bombarding neutrons are affected by the hydrogen in the formation. The results are detected and recorded as the neutron curve. In effect, the neutron curve measures the effect of neutrons which have bombarded a formation in a fast stream. The logs are interpreted as proportional to the hydrogen content of the bombarded formation and are therefore an indicator of the degree to which the formation is porous with its accompanying indications as to the existence of oil, water, and gas. Depending on how well the characteristics of a formation are known, the neutron curve helps to eliminate exploration in zones which are probably unproductive. The complete radioactivity log properly interpreted gives much valuable information. The gammaray curve is used principally to measure the level of radioactivity of a formation and is recorded satisfactorily in cased or open hole regardless of bore hole fluid. The neutron curve is also effective under adverse borehole conditions and helps to determine the hydrogen content of a formation. The job of translating gamma rays and neutrons into a radioactivity log is done by a chain of rugged, expertly engineered and specially designed equipment like this logging tool cable and the hoist and recorder truck. The logging tool in the well-trained hands of the logging crew is capable of amazing feats of underground magic. It must operate in bore holes averaging 4 in to 10 in in diameter. To ensure easy unobstructed traverse, maximum outside diameter is limited to 3 and 5/8 in. The smallest tool in use is only 1 and 3/8 in in diameter. So it is obvious that all the working parts have to be stretched out. [Music] The main components from bottom to top include the neutron source, the neutron detector, and a power amplifier, the gammaray detector, a second power amplifier, and a casing collar locator. The uppermost unit is a cable head which is the terminus for the tough electric conductor cable, the link between the logging tool and the hoist and recorder trucks. [Music] The well boore and conditions encountered within it determine every step in the design and manufacture of the logging tool. The sensitive recording power and amplifier instruments are stretched out in chambers which are protected by a smooth heavy alloy steel jacket. Sections are sealed with quick thread connections and special gaskets and they are so precisely machined that the assembled tool gives the appearance of a single unit. This close fit is necessary for defense against the extreme pressures, temperatures, corrosive contamination and other abusive conditions encountered in the bore hole. [Music] Painstaking care and planning in manufacturer is also given the cable in its role as a depth measuring line. It must have minimum stretch under the tension of its own weight and the weight of the logging tool. It must house one or more insulated conductors capable of transmitting the impulses detected many feet underground to the truck. The hoist truck regulates depth control as well as hoist speed which varies from 15 to 100 ft a minute. It is linked to the instrument truck where the impulses from the logging tool are recorded as kicks on graph paper. The gammaray curve, neutron curve, and casing collar locator log are recorded simultaneously as the tool traverses the well. Standard procedure from bottom to top. Here is a logging crew getting ready to take to the field to make a radioactivity log. The logging tool plus the trucks which house the hoist cable and recording instruments are thoroughly checked. Everything is in readiness for the mission. All the necessary instruments are loaded carefully insulated against the shocks and vibrations which may be encountered on the road as the crew travels to the well site. [Music] Upon arrival, the trucks are positioned. The hoist truck is braced against the strain of the weight of the logging tool and cable which will be used in the hole. The derek shiv is secured to the rig to provide ample clearance for the cable as it travels from the hoist cable reel to the well. The crew takes great care in unloading and assembling the logging tool. The tool is made up. The cable head is attached and the electrical connections are established providing the link from the instruments through hoist truck to recording truck. [Music] The Derek crew and the hoist operator use their combined skills and knowhow to move the heavy logging tool to the derek floor where it is placed in a vertical position near the well head. A lastminute check of the detecting apparatus made with a standard of known strength show the instruments to be in perfect working order. The depth measuring devices are set at zero. The hoist operator gets the signal from the recorder truck and the logging tool begins its descent into the well in search of the information which may mean oil. The cable unwinds under the watchful eye of the hoist operator and the measuring shiv sets a steady pace as thousands of feet of cable unwind from the hoist reel. As the tool nears the bottom of the well, the operator slows it down and carefully checks the bottom with the lower end of the tool. The instrument operator records the depth, adjusts the surface instruments, chooses the proper sensitivity on the chart, and all is in readiness. The hoist operator sets the slow, deliberate traverse in motion. The instruments do all the work now while the operators keep a close check on the story that is unfolding deep in the earth. [Music] The gammaray curve shows minimum recordings to the left for dolomite, sandstone, limestone or anhydrite as all are low in natural radioactivity. The pen records to the right for shale clays and volcanic ash which are higher in natural radioactivity. The pen moving to the right indicates greater natural radioactivity in the formation. The neutrons are at work, too. The neutron curve shows a weak minimum recording to the left on the curve, indicating hydrogen present in a porous formation, or a deflection to the right due to the absence of hydrogen in a non-porous formation. Shale's radioactivity kicks the gammaray curve to the right. The neutron curve shows a low reading to the left. Shale is usually impervious, which means that ordinarily there is no way for any fluid to escape, eliminating shale as a possible producer. The appearance of a possible pay zone may be indicated where the gammaray curve on the left side of the chart shows a minimum recording indicating weak natural gamma radiation. The neutron curve being followed by the pencil deflecting to the left indicates large hydrogen concentration with the resultant low neutron deflection. This means the presence of a degree of porocity and a potential pay zone. The casing collar locator is also doing its job revealing the location of the casing collars and their relative positions to possible pay zone. The exact location of these collars is important when perforations are to be made in the casing. And when selecting correct depth for setting bridging plugs, packers, and or cement retainers, knowing where the colors are located, it is easier to determine the correct place to set these tools with the best assurance of obtaining the desired results. Multiply the making of this radioactivity log in an oil producing area many times and the correlated logs will give an accurate profile of an area's geology. Here is a correlated chart of Russell County, Kansas, where if other geological features of the area are known, we can trace this layer of shale and sand or this layer of Madison limestone in the Williston basin. These are similar correlated charts of West Texas and central Kansas. The maximum benefit of radioactivity logs to the oil drilling industry can be seen in the number of vital services that are rendered from the information the logs provide. In open or cased hole, the log properly interpreted can uncover the possible existence of pay zones which have been unknowingly sealed off. The presence of oilbased or extremely salty based muds has no effect on the accuracy of radioactivity logging tools. Nor do extreme pressures or bottom hole temperatures have any influence. The radioactivity log can be interpreted to measure the cement level in a well and is excellent for other workover problems. To find the point to which the cement has risen behind the casing, a radioactive tracer such as carnotite is mixed with a cement slurry. As the cement is pumped into the well, the logging tool can then detect the gamma radiation in the cement, indicating its exact vertical travel. The use of a gamma emmitting isotope has been found useful for providing additional information on the extent to which a formation has responded to fracturing and to trace the exact travel of acidizing fluid in a formation. A radioactivity log provides a record of a new well and complements the electric log. Used in connection with a wildcat well, it takes the guesswork out of a search for poorest potential pay zones. The value of the radioactivity log has also been proved in remedial programs on wells in areas where the once prolific production is depleted. It is a valuable and accurate answer to lost geological information, inaccurate measurements and poor casing records such as are to be found in connection with oil wells which were completed in the early days of rotary drilling. These wells were drilled without the benefit of the standard geological aids we have today like the electric log, sample determination, the time log and mud analysis. An excellent example of the rush to cash in on early flush production is the seminal area of Oklahoma where little attention was given to the possible pays which were unknowingly passed up and cased off. The radioactivity log is in effect a new lease on life for the many depleted and abandoned wells in what once were high oil producing areas of the nation. From its groping experimental beginnings early in the 1940s, radioactivity logging has become a standard operation provided by many service companies whose scope of operations now extend from the United States to the oil producing areas of Canada, South America, and the Middle East. Increased operations have provided jobs for the highly trained men who make and interpret the logs. They are backed by the latest in technical equipment and in many areas are ready to do their job at any time of day over any kind of terrain. Research is kept pace with the operations and provides loggers with new and improved tools of the finest manufacturers. The pioneering gammaray log is given way to an instrument which combines the gammaray detector, neutron detector and casing collar locator plus refinements in the instruments used in recording. Logging tools of 1 and 38 in and 1 and 3/4 in diameter are now ready for work through tubing in permanent type well completion. Modern trucks carriers of the latest scientific equipment are a common sight in the oil producing areas of this country. The Vandagramraph accelerator, an instrument belonging to the family of so-called atom smashers, has made its debut in the research laboratories of the industry to be used as a source of atom particles for research, which will increase the industry's knowledge of the behavior of gamma rays and neutrons. This knowledge will eventually find its way into the creation of improved and more efficient logging tools. The service companies continuing their tradition of qualified technical service to the industry have also expanded their consultant services providing engineers, geologists and other qualified personnel with the knowledge they need to rest the maximum of value and information from the interpretation of radioactivity log as applied to drilling operations. Recognizing the importance of well-trained and well-oriented personnel, the service companies have initiated their own employee training and refresher programs and have provided maximum safety training for their personnel. They have utilized the resources of educational institutions to help the men and women they employ to advance to the pinnacles of leadership in the oil industry. You and I and all our fellow Americans are the beneficiaries of the progressive steps taken by the service and operating companies to master the secrets of nuclear physics to provide greater production and greater reserves from the great underground reservoir of America's energy. [Music]