Gamma-gamma Logs Research Articles

Acoustic televiewer amplitude data for porosity estimation with application to porewater conversion

The ability to detect and quantify rock matrix porosity is explored using acoustic televiewer images and dolostone rock core samples. In particular, an empirical relationship between the acoustic televiewer amplitude response and core-derived total porosity is developed. The performance of the acoustic televiewer amplitude relationship was compared to neutron and gamma-gamma logs, which are traditional nuclear wireline tools commonly used for estimating porosity in dolostones. Acoustic televiewer amplitude results are consistent with the gamma-gamma (density) and neutron (porosity) logs, provide increased vertical resolution, do not require downhole radioactive sources and also provide oriented fracture information. Sample specific porosity and bulk density values from the calibrated acoustic televiewer datasets are then used to improve porewater concentration estimates from rock concentrations.

Acoustic televiewer amplitude data for porosity estimation with application to porewater conversion

Abstract The ability to detect and quantify rock matrix porosity is explored using acoustic televiewer images and dolostone rock core samples. In particular, an empirical relationship between the acoustic televiewer amplitude response and core-derived total porosity is developed. The performance of the acoustic televiewer amplitude relationship was compared to neutron and gamma-gamma logs, which are traditional nuclear wireline tools commonly used for estimating porosity in dolostones. Acoustic televiewer amplitude results are consistent with the gamma-gamma (density) and neutron (porosity) logs, provide increased vertical resolution, do not require downhole radioactive sources and also provide oriented fracture information. Sample specific porosity and bulk density values from the calibrated acoustic televiewer datasets are then used to improve porewater concentration estimates from rock concentrations.

Evaluation and genetic analysis of coal structures in deep Jiaozuo Coalfield, northern China: Investigation by geophysical logging data

Coal structure determines the porosity and permeability in coal reservoirs to a great extent, which not only influences the evaluation of coalbed methane (CBM) reservoirs, but is also closely related to their production efficiency. The traditional methods for identifying coal structure mainly depend on coals in boreholes or underground roadway sections. However, as these methods are expensive and limited to certain conditions, the geophysical logging data have been proven recently to be effective for detecting coal structure in boreholes. The Machang exploration block is situated in the southeastern (deep-seated) part of the Jiaozuo Coalfield, northern China, and the coals in this block have a higher gas content ranging from 25m3/t to 40m3/t but are typified with complex coal structures. Based on the field observation of coal structures for a cumulative length of 447.5m of cores from the 75 boreholes in the Machang block, the cut-off values of the logging data for quantitatively identifying coal structures (including lump coal, lump-powder coal and powder coal) were established using the three well-logging curves of deep lateral resistivity (LLD), gamma-gamma log (GGL) and natural gamma (GR). Subsequently, the relationships of coal structure with the corresponding coal depth, thickness, coal petrology, pore structures were investigated. Finally, the favorable areas for CBM exploration were evaluated according to the distribution of lump, lump-powder and powder coals. The results show that each coal structure has different logging characteristics, with lump coals showing lower GGL, higher GR and LLD, lump-powder coals of medium GGL, GR and LLD, while powder coals showing higher GGL, lower GR and LLD. The coal seam is composed of one to six sub-layers vertically, with a typical combination of powder coals on the top and bottom of the 21 coal seam, with lump coals or lump-powder coals in the middle part. Regional faults play a dominant role in controlling the distribution of coal structures, with the thickness of powder coals decreasing rapidly with increasing distance from faults. Furthermore, thicker or thinner coal seams also can result in a greater degree of damage during coal deformation. From lump coals to powder coals, the vitrinite content, maximum vitrinite reflectance (Ro,max), specific surface area and total pore volume show an upward trend but the average pore size shows a downward trend. The 4 types and 13 sub-types of coal structures were divided based on the established ternary diagram. The central parts in the South and Middle areas, together with the southwestern part of the North area in the Machang exploration block are determined to be the best regions for CBM production.

Transport equation and evaluating formation parameters based on gamma-gamma log data

Computer inversion of measurement data based on the equation of particle transport is a topical component of the modern nuclear-geophysical technologies. In this work we have elaborated an approach and iterative methods for this inversion according to the gamma-gamma method data. In the framework of the “successive approximations according to characteristic interactions” approach, characteristic interactions have been established and iterative methods for the solution of two problems have been developed, namely, the problem of evaluation of the formation density and the problem of evaluation of two parameters—the formation density and the mud cake thickness. The numerical experiments confirm the theoretical concepts on the properties of iterative processes and convergence of methods.

Characterisation of hydraulically-active fractures in a fractured granite aquifer

In this study, the practical usefulness and fundamental applicability of a self-potential (SP) method for identifying the hydraulically-active fractures were evaluated by a comparison of SP methods with other geophysical logging methods and hydraulic tests. Potentially permeable fractures intersecting a shallow, 10-m borehole were first identified using conventional geophysical methods such as acoustic borehole televiewer imaging and temperature, electrical conductivity and gamma-gamma logs. These results were then compared to results of analysis using the SP method. Constant pressure injection and recovery tests were conducted for verification of the hydraulic properties of the fractures identified by various logging methods. The acoustic borehole televiewer and gamma-gamma logs detected the openings or weathering zones associated with fractures intersecting the borehole, but they could not prove that groundwater was flowing through the detected fractures. The temperature and fluid-column electrical conductivity logs were unable to detect the fractured zones where groundwater in the borehole flows out to the surrounding rock aquifers. Comparison of results from the different methods tested showed that the most effective correlation between logs and the distribution of hydraulic conductivity was given by the SP signals, and that SP logging can accurately indicate the location of hydraulically-active permeable fractures. Based on these results, the SP method is recommended for determining the location of hydraulically-active fractures rather than other conventional geophysical logs. This self-potential method can be effectively applied in the initial stage of a site investigation to select the optimal site location or to evaluate the hydrogeological properties of fractures in underground exploration studies, such as those related geothermal reservoir evaluation and radioactive waste disposal.

Borehole Logging in Alpine Periglacial Talus Slopes (Valais, Swiss Alps)

Geophysical measurements were carried out in six boreholes at three periglacial talus slopes in the Swiss Alps in order to determine the talus structure and the geological and permafrost stratigraphy. These are important elements of interpretation of the palaeoclimatic significance of Alpine talus slopes. This study combined three nuclear well logging methods. Natural radioactivity of rocks and ice-rich permafrost were determined by using natural gamma-ray logs through the lack of radioactivity of massive ice. Quantification of the ice content in frozen layers and the air content in unfrozen layers by variations in bulk density was provided by the application of gamma-gamma logs. Neutron-thermal neutron logs were used to calculate the water content, linked with the porosity of the formation. Combination of the three logs allowed three-phase models (rock, ice and air/water) of the subsurface to be obtained. Results show that the air content decreases with depth because of the increasing in-situ stresses that cause compression of the rock debris and the existence of a fine matrix filling the voids. Calculation of the ice content variations shows that talus slopes are frequently partially saturated with ice or, at most, slightly supersaturated with ice. All three logs provide complementary information on the progressive infilling of the voids with depth and the occurrence of ice-rich layers. A similar trend in ice content and the apparent porosity was highlighted by the joint application of gamma-gamma and neutron-neutron logs, which provide a mirror image of these two parameters. Copyright © 2015 John Wiley & Sons, Ltd.

Characteristic interactions and evaluation of the parameters of the transport equation and formation, including porosity, from data of measurements by some nuclear geophysical methods

An important but problematic component of nuclear geophysical technologies is computer inversion of measurement data based on the equation of particle transport. In this paper, we propose an approach and iterative methods for this inversion that are applicable to many problems of evaluation formation characteristics, including elemental composition, from data of corresponding logging methods. This approach is based on defining characteristic elements, interactions, and trajectories and using the superposition principle for transport processes, and linear a priori constraints on unknowns are used. In comparison with the previous publications of the author, this paper deals with a broader type of measurement data, including the reading ratio of detectors and normalized measurements. The iterative methods are specified for problems of determining the porosity and density from data of neutron-neutron and gamma-gamma logs, respectively. For the first of them, the results of numerical experiments are presented.

DETERMINATION OF THE CALORIFIC VALUE OF SYSOLA OIL SHALE FROM GAMMA-GAMMA LOGGING DATA

This historical review addresses one topic in well logging. In 1983- 85 special geophysical work was carried out in the Poinga area of the Vychegda oil shale basin (OSB) in the northeastern part of the East- European Platform, to search for oil shale deposits (1). The results of the study of Sysola oil shale by using the geophysical logging are presented. The density logging data was used to predict the calorific value of oil shale. It is shown that the elementary procedure of elimination of the regional compo- nent from the measured values of the gamma-gamma log provides an excellent correlation between the predicted and true calorific values of oil shale. The regional anomalies of gamma-gamma logging data were determined using the averaging method. The local anomalies of OS layers were calculated. In our calculations not the absolute values of the measured gamma-gamma logging parameter, but relative to average ones were used. So, the accuracy increased significantly and amounted to 87-91%.

여수시 묘도 부근 퇴적암과 안산암에서 물리검층에 대한 자료해석

여수시 묘도 일대에 분포하는 안산암과 퇴적암 지역에서 물리검층 종류인 부유식 P S파 속도검층과 밀도검층을 실시하였다. 연구목적은 이 지역에 분포하는 두 암상에 대해 깊이에 따른 탄성파속도 및 밀도분포를 찾아내어 시추조사를 통해 얻은 지반정보인 암상과 RQD 값을 비교하여 암석 종류에 따른 상호간에 상관관계를 파악하는 것이다. 연구지역에서 두 암석에 대한 탄성파 속도 분포는 깊이에 따라 P파가 약 2,000m/sec 내외이며, S파가 1,500m/sec 내외의 차이를 보였으며, 밀도는 깊이에 따라 약 <TEX>$0.35g/cm^3$</TEX>의 차이로 비교적 넓은 폭으로 나타났다. 이러한 결과는 암석 종류에 대한 차이보다 풍화 정도에 따른 것으로 해석된다. 그러나 RQD, 탄성파속도 및 밀도의 상관성 분석은 비교적 높은 관계를 보이므로 물리 검층자료의 결과를 이용하여 RQD에 관련된 불연속면의 빈도를 유추할 수 있다고 본다. We carried out the Suspension PS log and gamma-gamma log in andesite and sedimentary rocks distributed near the area of Myodo-dong, Yeosu. The main purpose of this study was to find out the distribution of seismic velocities and densities and to analyze the correlation of the two rocks by comparing their geophysical well logs with rock cores. The distributions of P and S-wave velocities for two rocks represented in the study area showed a difference of about 2,000 m/sec and 1,500 m/sec with depth, respectively, while the distributions of densities had a discrepancy of about <TEX>$0.35g/cm^3$</TEX> with depth. However, the results of geophysical well logs analysis were similar to the two rocks. Consequently, it is clear that these results are interpreted as a difference due to weathering rather than rock type. In particular, the RQD values showed a good correlation to geophysical well log data.

Applications of geophysical techniques in permafrost regions

This paper reports the results of some recent geophysical experiments carried out in the Arctic with a variety of methods. In the Beaufort Sea, seismic refraction profiles obtained with both source and receivers on the seabottom indicate the presence of discontinuous near-bottom high-velocity (4200 m/s) material interpreted to be presently aggrading permafrost. Spring-time resistivity soundings taken through the ice in Kugmallit Bay, Beaufort Sea, show the top of permafrost at about 50 m below the bottom. Even for 5-km spreads, the base of permafrost was not observed.Off the southeast coast of Melville Island, refraction seismic profiles shot on the seabottom and resistivity soundings made through summer ice yielded data which correlate with known sub-bottom geology, but which gave no clear indication of either presence or absence of permafrost.Seismic and resistivity measurements made at a number of control sites in the Arctic Islands yielded typical velocities of 3500 m/s and resistivities of 1 × 106 ohm-m for ice-saturated sands. Some correlation was observed between seismic velocity and moisture contents in the range from 10% to 40%.Seismic and resistivity results in IOL Lake at the Involuted Hill test site, Tuktoyaktuk Peninsula, suggest the absence of permafrost under some parts of the lake bottom. On the hill itself, seismic up-hole shooting and VLF resistivity profiling give interpretations of ice distribution which correlate well with drill control. Gamma-gamma logs taken in some of the drill holes correlate well with ice content logged during drilling.

Role of Borehole Geophysics in Underground Waste Storage and Artificial Recharge: ABSTRACT

The optimum utilization of underground space for the emplacement and storage of waste and surface water can be achieved through an understanding of the geohydrologic environment. The emplacement of liquid waste and the artificial recharge of aquifers generally requires the drilling of exploration, injection, and monitoring wells. Some geophysical logs are run on almost all wells drilled for deep disposal. Even more information could be obtained, however, by utilization of all available logging techniques. To date, geophysical well logging has not been applied widely to artificial recharge projects; however, borehole geophysics is being used by the U.S. Geological Survey to study geohydrologic parameters related to recharging the Ogallala Formation on the High Plains of Te as. Geophysical well logs provide preinjection data necessary for the selection of environments for liquid waste or water storage. Logs provide data on the location, thickness, and lateral continuity of storage zones and confining beds, percent and distribution of total or effective porosity, and the relative magnitude of permeability. Intergranular and fracture porosity can be discriminated by crossplotting acoustic velocity and neutron or gamma-gamma logs. The distribution and orientation of preinjection fractures can be determined by acoustic televiewer logs. Logs provide data on the chemical quality of the native fluids and the mineralogy of the aquifer, which are necessary to predict chemical reactions with injected fluids. The temperature and conductivity of the interstitial fluids ay be measured directly and their specific gravity and viscosity may be calculated from log data. Because aquifers overlying injection zones can be polluted by improper well construction or well failure, geophysical well logs should be used to guide the design, construction, and maintenance of injection and monitoring wells. It is important to answer questions such as: are the casing strings and screens properly installed; are they plugged or corroded; does the grout fill the annular space and is it properly bonded to the casing; and, are there leaks through the casing, between pipe strings, or through the annulus? After waste injection or artificial recharge has started, logs provide in-situ measurements of changes in the system. We have found that an increase or decrease in porosity caused by solution or precipitation in pore spaces or cavities may be detected. This type of information not only explains changes in well efficiency End_Page 1597------------------------------ but provides the basis for selecting remedial treatment. Accidental hydraulic fracturing caused by drilling or injection can be the reason for vertical leakage through confining beds, and acoustic televiewer logs can locate these fractures. The distribution and velocity of injected water and the location of chemical or thermal pollution may be determined by means of temperature logs. We have used temperature logs to map the horizontal and vertical distribution of injected fluids. Diurnal thermal changes in injected water provide the basis for measuring the velocity of flow and its change with time. End_of_Article - Last_Page 1598------------

Use of Downhole Gravity Data in Formation Evaluation: ABSTRACT

It has been shown by several workers that the downhole End_Page 1899------------------------------ gravity meter is a high-precision, large-volume, bulk-density tool. It is unique in that bulk densities can be measured directly, i.e., with no calibration and in place. The large rock volume measured ensures that the measurements are relatively unaffected by mud cake, infiltrated zones, washouts, or casing. The use of large-volume density measurements has added a new dimension (depth) to some formation evaluation problems. Bulk densities measured with the borehole gravity log in wells in the Gulf Coast area show considerable deviation from densities measured with the gamma-gamma log. Moreover, they do not show a density change in the over-pressured shale zone. These results suggest that although the physical parameters measured by small volume tools may be quite accurate, they may not be representative of true formation characteristics. With only one exception, densities from a borehole gravity log in a carbonate-shale sequence agree closely with densities measured by the gamma-gamma log. This difference in densities of 0.18 g/cc is attributed to either porosity lateral to the borehole, a lateral change in lithology, or a fault. The high precision and large rock volume measurement capabilities of the borehole gravity meter make it especially useful in measuring low porosities as, for example, that of a fractured quartzite in Libya, and in measuring fluid density behind casing, for example, gas in Texas. End_of_Article - Last_Page 1900------------

Application of Geophysical Logging to Groundwater Studies in Southeastern Saskatchewan

Single-point resistance and spontaneous potential logs in fresh-water filled rotary-drilled test-holes provide data useful in geohydrologic studies in Saskatchewan. These geophysical logs are made by many of the water well drilling contractors in Saskatchewan on a routine basis. The logs provide good resolution of various lithologic units and provide data required to estimate the salinity of water in sand beds prior to constructing a well.Caliper logging offers a potentially useful method for evaluating hole conditions and the effect of drilling techniques on the formation in completion zones. The casing collar locator log run in a previously constructed well near Estevan demonstrates that this device can provide an accurate and objective measurement of the position and length of each joint of casing, the position of the screen assembly, and the location of screened and blanked intervals within the screen assembly. This tool should find general application in water well construction and maintenance practice.The neutron-epithermal neutron log provides a method of measuring the porosity of sand and gravel beds. The response of the gamma log is similar to that of the spontaneous potential log and the neutron-epithermal neutron log deflects in a fashion similar to the resistance and resistivity logs. Nuclear logs offer the advantage that they can be run in cased or uncased boreholes which may be filled with any type of fluid. They require more complicated and expensive instrumentation and slow-speed logging to obtain the required resolution. The normal resistivity logs offer the possibility of determining the concentration of dissolved solids in the formation water. The gamma-gamma log is a poor alternative to the natural gamma and neutron log for stratigraphic correlations.

Application of geocosmic method in solution of certain engineering-geological problems

Radiation intensities of secondary cosmic rays, logged underground, are found to give reliable indications of density of the overlying rocks, of pressures exerted by constructions, efficiency of biological shields (as at atomic power plants), and other situations in engineering, for which gravimetric and gamma-gamma logs are employable, but with less reliability. -- V.P. Sokoloff

Contribution of the sonic log and radiation log (gamma-gamma log) to formation evaluation

[in Japanese]