A study is made of the effectiveness of some wellsite applications of wireline formation testing tools, with emphasis on "quick-look" permeability indicators in sandstone reservoirs. Approximate values of the "in situ" formation permeability can be calculated from wireline formation tester information. The methods proposed are (a) analysis of the pressure build-up curve (as the primary method) and (b) averaging the two permeability values obtained from the pressure draw-down analyses of the two pre-tests (as the secondary method). The objective is to sample a representative cross-section of the sands in the reservoir unit, and to project the permeability data derived to cover the entire reservoir. It may be more important to obtain an estimate of permeability deeper into the reservoir, away from the formation which has probably been altered by the drilling process. For this purpose, it can be better to use the pressure build-up data from the wireline formation tester. Whereas this technique makes more of an attempt to indicate the virgin formation permeability, it is the harder of the two techniques to rigorously apply. It is often difficult to locate the relevant section of the build-up curve to analyse. A case study shows examples of the effectiveness, as well as the limitations, of techniques for "quick-look" evaluation of wireline formation tester data to determine effective formation permeability. In spite of the evident limitations on permeability determinations described, this application is seen as a useful supplement to some of the other roles of the tool, such as: establishing formation pressures, pressure gradients and fluid contacts; formation sampling; reservoir depletion monitoring. A useful application of the technique is envisaged as a wellsite or "quick-look" "net pay" indicator. It is often essential to try to estimate semi-quantitatively the effective permeability throughout the reservoir towards the end of the drilling process.

In 1935, when I became a Schlumberger logging engineer in the Gulf Coast, only a few wells drilled in the United States were logged with the primitive hand recorded resistivity and self-potential logs. By 1950, with an array of new and improved resistivity and nuclear logs, well logging was considered an indispensable aid to exploration for, and exploitation of, oil and gas.

Borehole logging probes designed for measuring rock densities in low-grade copper deposits were tested at the Bougainville open-cut mine in both blast holes and diamond-core drilled holes that were shallow, roughwalled, and drained of fluids. The method, based on both the density and the diameter-sensitive S-factor responses, gave measurements that were insensitive to borehole diameter variations. Although radiation safety indicated the use of an only moderately strong source of primary radiation (50 MBq*60Co) for these operations, good precision was achieved for 2 m strata, namely 0.035 g cm -3. in blast holes and 0.016 g cm -3 in diamond-core drilled holes where the mean density of the rocks was about 2.6 g cm-3. The corresponding accuracy of about 0.05 g cm-3, obtained in both types of boreholes, was apparently limited by the geostatistical variability of the rock density.

A technique for automatic dip determination is described which uses novel methods frequently employed in solving artificial intelligence problems. Formation dip computations can be separated into three stages: Separate pre-processing and analysis of each of the Curve-to-curve correlation Determination of formation dip through the combi-. With the new technique, pre-processing involves the use of frequency and statistical analysis of each individual microresistivity measurement through the application of techniques paralleling those used in image processing. Curve-to-curve matching is performed by dynamic programming optimization, providing the large number of curve-to-curve correlations required for detailed stratigraphic interpretation. A number of ordered pad combinations are used to produce a picture of all possible dips. The resulting sum of all possible dips may, however, be contradictory due to noise included in the original data acquisition. To alleviate this problem, mathematical optimization is applied to select the proper geologically-meaningful dip computations. The resulting computation provides a very detailed and precise series of dip computations presented in a format which lends itself to meaningful stratigraphic interpretation. four microresistivity measurements nation of the above correlations.

Acoustic, mechanical and electrical properties were measured on suites of low-porosity rocks. Three rock types were represented in these suites; gneiss and schist, granite, and metarhyolite. All are similar in chemical makeup, but differ substantially in texture. The three rock types exhibit a wide range in unconfined compressive strengths, from 3500 to 60,000 tons per square meter. Many of the measured properties, such as density, acoustic wavespeeds, and dielectric constant, show a pronounced correlation with strength. However, in each case, a significant number of data contradict these correlations, so that the correlations would have to be used cautiously in inferring rock conditions from geophysical measurements. Measurements of electrical properties indicate that conductivity and dielectric constant in water-bearing samples are nearly independent of frequency to frequencies of 1 gigahertz. Attenuation rates for electromagnetic waves at frequencies ranging from 100 megahertz to 1 gigahertz are 0.6 to 6 db per meter, for rock resistivities ranging from 100 to 1000 ohm-meters.

Scientists in the People's Republic of China are pursuing an aggressive minerals exploration program that is dependent upon borehole-geophysical techniques for locating and evaluating mineral deposits. In addition to conventional slimhole well-logging probes that are used in the United States, the Chinese have developed multiple detector magnetometer probes that are primarily used for iron-ore exploration and evaluation. They also commonly use hole-to-hole electrical techniques for pinpointing mineral deposits. A radar system, which operates with both the source and receiver antennas in the same hole, or with the source and receiver antennas in different holes, has been developed for use in high-resistivity environments. Most of the borehole-geophysical equipment that is used in China is portable, with logging units consisting of individual probes rather than large integrated logging systems.

PROLOG is a computerized wellsite log analysis program package. The programs in PROLOG are designed to enhance the information obtained from Dresser Atlas Computerized Logging Service (CLS) Units. PROLOG is based upon two basic analysis packages, Wellsite CRA for complex reservoir analysis and Wellsite SAND for clastic sediment sequences. Both CRA and SAND present detailed formation evaluation in a 4-track format supported by depth shift routines, a true vertical depth option, data edit routines including borehole (washout) and environmental (invasion) log response corrections, and crossplot routines (frequency, Pickett (1966), Hingle (1959), histograms, etc.) The present paper provides a detailed discussion of the PROLOG programs along with several field examples.

Electrical investigations carried out in regions containing sedimentary rocks showed that sediments generally are good electrical conductors, a fact which at the present time is used for structural investigations by electrical methods. It is of fundamental importance, not only for these investigations but also for electrical prospecting in general, to know the electrical properties of various soils and rocks. It will be useful, therefore, to discuss this question with the hope that the general points of view discussed in this paper will perhaps be completed by further observations and determinations of material from various localities.

Well logging is the basic source of continuous information, along the borehole axis, in evaluating oil and gas-bearing formations. Thus, the accuracy of well logging equipment is of utmost importance. In this paper an electric network is suggested for the calibration of electric well logging equipment and the examination of their accuracy and reliability. The electric connection between the downhole sondes of n different electrodes and the 3-dimensional subsurface environment can be described by means of a resistance matrix of order n. An equivalent resistance network, simulating the subsurface formation, is then deduced from the resistance matrix. For the more general cases of induction and dielectric logging equipment, the matrix is of a complex nature and is comprised of complex impedances. The equivalent network simulating electric logging equipment working with electrodes consists of resistances, whereas that simulating induction and dielectric logging equipment consists of complex impedances. The magnitudes of the components of the equivalent resistance (or impedance) network are determined by an inversion of the resistance (or the impedance) matrix. By applying the equivalent simulating networks, the accuracy and reliability of electric well logs can be substantially improved. This is especially important in ultradeep holes where high bottom hole temperatures and mud pressures are encountered.

A convenient and relatively accurate method for determining the connate water resistivity, Rw, values for wells in the Powder River Basin, Wyoming is described. This method is based on the change in the spontaneous potential (SP) response with different mud filtrate resistivities (Rm f) on repeat logging runs. The values of Rw obtained agree closely with those derived from conventional crossplot techniques of resistivity, Rt, and core porosity values.

Many well-log-derived mapping parameters may be used in exploration for oil and gas in order to map the petroliferous regions in wildcat areas. Past articles listed over 75 such parameters, and many others are discussed elsewhere. However, three such parameters are of special significance as they have proved to be practical reconnaissance exploration tools and, in addition, they establish a solid basis for new surface exploration methods that measure the areal distribution and the flux density of electrotelluric currents generated by oil and gas accumulations. The first such tool is the SPgradient, particularly in shale sections, but also in gypsum and anhydrite beds. This parameter was originally named the Vertical Migration Parameter (VMP), but it is now known to represent the intensity and polarity of vertical electrotelluric currents. Such currents are generated by oil and gas accumulations and also by mineral deposits such as copper, sulfur, uranium, and, when their polarity is reversed, by geothermal reservoirs. SP gradient mapping has been successful in predicting petroliferous trends in Florida, Colorado, Texas and Alabama, in which states a number of oil and gas fields were subsequently discovered. The second log derived-mapping parameter is the true radioactivity of certain well defined shale sections and also of siltstones. The method has been verified over more than 30 known oil and gas fields, both structural and stratigraphic accumulations. It predicted four oil fields in Texas. The third parameter is differential compaction within normally compacted geologic sections. It does not work in the geopressured or abnormally pressured zones. This parameter has been used mostly as confirmation of the existence of hydrocarbon accumulations under pressure.

Companies that utilize wire logging services require efficient service for the expenditure of logging costs and rig time. As computer programs were developed to allow rapid and dependable normalization of well logs, it became apparent that additional quality control was needed at the well site. An example of a Quality Control Form to be completed by the service company representative at the time of logging is presented. A statistical comparison of the data by geographic area and service company is discussed.

A pulsed neutron source technique for measuring the macroscopic thermal neutron absorption cross section, Zma, of common rock materials is described. The method requires only one thermal neutron lifetime determination for a mixture of crushed rock saturated with pure water. The error in determining is less than or equal to 1 C.U. (capture unit = l(r3cm-*). However, to reduce the effect of thermal neutron diffusion relative to absorption it is necessary to use crushed rock samples weigh mg approximately 15 to 20 kg. Although this limitation precludes application of the technique to small core samples, the method can be used to determine Z,, for any laboratory model whose material of construction is available. Results are given for both igneous and sedimentary rocks which outcrop sections exceed the cross sections one would calculate for a given rock on the basis of its primary minerals. It is concluded that most of the rocks probably contain strongly absorbing trace elements such as boron or gadolinium.

For many years log analysts have used the gamma-ray log to make simple shale-volume calculations. I became interested in the accuracy of these methods while writing a series of computer log interpretation programs. Often the gamma-ray is the only shale indicator we have and many felt it was of little value. While examining gamma-ray cross-plots for shaly-sand analysis I noticed trends in the log responses which were predictable. I will first review the classical method and attempt to show its shortcomings. Then I will show a reliable method of shale volume calculations using the gamma-ray.

A Dual-Spacing Thermal Neutron Decay Time logging tool has been developed which embodies several new features to improve the recording of C and 7 and to provide additional information. Lower statistics and faster logging speeds are achieved by use of the Complete Scale Factor ** system and an increase in the yield of the pulsed neutron source. The tool has a 1-11/16-inch diameter, and has two detectors. It is combinable with a Gamma Ray logging tool. Some of the data it provides are: C, the neutron capture cross section 7, the thermal neutron decay time a Ratio curve, derived from the count rates of the two detectors a Count-Rate Display for comparison of the count rates from the two detectors a Quality Control Curve, which is used to validate the Z and Ratio recordings The ration and E data can be used to calculate an Apparebt porosity for the formation and an apparent Water salinity for the formation water. The count rate Display is designed to facilitate gas identification Response data are shown for C and Ratio measurements in laboratory sandstone formations of 18 percent and 34 percent porosity with cased boreholes. Borehole sizes were %in., 10-in., and 12-in., and casing sizes were 5 1/2-in., 7-in., discussed. Methods for using and analyzing the logs provided by this tool, run either in casing or in casing and tubing, are described. Log examples are shown. and 9 5/8-in. Results of an extensive field-test program are

This paper presents the results of a comprehensive literature survey and an evaluation on the effects of pressure on the electrical resistivities of aqueous sodium chloride solutions for varying temperatures and concentrations. It is concluded that pressure does affect the electrical resistivities of aqueous NaCl solutions; however, these effects are small. No suitable theoretical methods exist for predicting these pressure effects. The theoretical methods proposed in the literature require data on the pressure effect on parameters such as viscosity, compressibility, and dielectric constant of the solutions, which are not available for all the temperatures and concentrations ranges, and are thus limited. The range of experimental data available to predict the effect of pressure on resistivity of NaCl solutions is graphically shown. At constant low temperatures, the effect of pressure can be predicted using graphs prepared from the experimental data of Korber'O and Adams and Ha1l.l For salinities under 6000 PPM (parts per million), graphs have been prepared from the experimental data of Quist and Marshal l1 to predict the effect of pressure. No reliable data exists in the literature for making quantitative predictions of the effect of pressure on the resistivities of NaCl solutions of higher concentrations at high temperatures. Need for further experimental work in this area is obvious.

During the past several years a number of papers have been published which point out that the most well-known commercial logging devices for the measurement of the thermal neutron capture cross section do not always agree in the absolute values measured. There are a number of reasons for these discrepancies, including different philosophies in tool design, gating systems and types of detectors. This paper reviews the results of a series of tests in a variety of controlled environments and also actual logged results for one of these devices, the Dresser Atlas Neutron Lifetime Log.* The controlled environments include the API test pits and several test tanks in which measurements were made with boric acid in concentrations such that the capture cross section of the solutions varied up to a maximum of almost 100 sigma units (0.lcm-1); The field results include multiple runs in the same borehole under a wide spectrum of different possible borehole conditions, including holes that are air or gas and fluid filled, cased and uncased, and high to low salinity fluid filled. The results of instruments of varying diameter are also compared. The inescapable conclusion of this collage of test measurements and field results is the fact that the Neutron Lifetime Log measures the value of thermal neutron capture cross section with an exceptional accuracy.

Resistivity measurements produced by the various types of Laterologs attempt to minimize the influence of the borehole and the adjacent formations. This is accomplished by forcing a thin sheet of electrical current to flow radially into the surrounding formation of interest. This type of logging system provides an excellent means for determining the true formation resistivity (Rt) in the presence of a large resistivity contrast between the adjacent formations and the zone of interest (Rt/Rs) and/or when the borehole contains a very high salinity fluid, such as a saturated salt mud. A new Laterlog system has recently been introduced to the industry and features an unique electrode arrangement. This new log is referred to as a Dual Laterolog and records two resistivity curves on one log run. One of the curves represents resistivity measurements made by a shallow investigating device and the other records measurements from a deeper investigating electrode arrangement. Claims for this new Dual Laterolog system are that reliable resistivity measurements can be obtained when a hydrocarbon bearing formation is deeply invaded with a high salinity salt mud, moderate to low resistivity formations exist immediately below highly resistive beds, such as an evaporite section, and formations of extremely high resistivities.

A resistivity log and ionic potential curve can be constructed from measurements made on clay and shale taken from the shale shaker. This can be done simultaneous with drilling, allowing for the lag necessary to get the cuttings to the surface. Using the following measurements, a complete electric log can be obtained: Resistivity of a slurry of shale fines and distilled water; Resistivity of slurry filtrate; and Sodium ion potential of the slurry filtrate. All of these measurements may be made fast enough by one technician so that at least one log data point can be obtained for each 20 foot depth interval. Theory and case histories show that the following equations apply in determining overpressures in the earth using the the slurry data: where R is for shale slurries.

Accurate estimation of oil yields in Green River Formation oil shale requires knowledge of the presence or absence of cavities (vugs) left after the natural ternoval of the mineral nahcolite (NaHCO,). Conventional well logs have not provided a means for detecting the vugular porous zone. This paper describes a three-arm caliper logging system, logging technique, and mathematical correction method used by the U. S. Bureau of Mines to locate and compensate for the vugular porosity. the caliper defines the zone by sensing a high frequency of minor diameter variations as small as 1/10 inch. Estimations of oil yields and oil shale reserves from density logs can be significantly improved when the vugular zone's thickness is known. A porosity-density correction method is presented.