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Tortuosity tau is defined as the square of the ratio, phi-range of the effective length of pore channels to the length parallel to the overall direction of the pore channels in a porous medium. It has significance in interpreting the hydraulic and electric proper ties of porous media. In this study, experimental results of tortuosity and porosity phi were investigated in relation to different directions of flow in various unconsolidated porous media. When the media (mica, textile fibers, kaolinite, and bituminous soil, with a high phi-range of between 60 - 90 %) are exposed to flow perpendicular to the planes and fibers, tau responds positively to phi. When the media (randomly packed beds of spheres, with a medium phi-range of between 34 - 45 %) are exposed to flow parallel to the planes, tau responds negatively to phi. When the media (glass powders, glass spheres, dry soil, quartz sand, and white sand, with a variety of grain sizes and a medium porosity phi-range of between 37 - 47 %), and other media (g...

Tortuosity tau is physically defined as the ratio (or the square of the ratio) of the effective length of pore channels (through which the hydraulic flow and electric current are conducted) to the length parallel to the overall direction of the pore channels in a porous medium. It has a significant influence on hydraulic flow and electric current because of its response to the variations in lithology, pressure and petrophysical properties. Determination of tortuosity enables one to understand the mechanisms of hydraulic flow and electric current, and the channel-network com plexities in porous media. In this study, physical and mathematical aspects of tortuosity are discussed. Also, tortuosity is mathematically derived as the square root of the dimensionless formation resistivity factor times fractional porosity. Tortuosity can be successfully used for interpretation of the physical behavior of unconsolidated and consolidated porous media, similarly, and for formations characterized by high degrees of com...

Geothermal energy is known today as one of the alternative renewable energy sources which has proven itself technically and economically to be feasible. It is commercially available to the public as a nonpollutant electric power source. Worldwide, 17 countries now operate geothermal power plants. The total usable capacity is 5 gigawatts, with units varying in capacity from a few hundred kilowatts to 135 megawatts (Di Pippo, 1988). The discovered untapped reserves, however, are measured in the tens of gigawatts (Di Pippo, 1988). This article aims at reviewing the potential of the geothermal resources in northwest Iran and looks to the future for possible growth scenarios in Iran.

The historical development of geothermal energy in Nicaragua, together with some geologic and tectonic background information, is presented. Chemistry of thermal waters from different regions of Nicaragua is also discussed. Also included are completion practices in both production and injection wells, production characteristics of both Momotombo units, and flow diagram of one geothermal plant.

During the past quarter of a century, the exploitation of oil and gas reserves, associated with thick sequences of very fine-grained and coarsegrained rocks in the Tertiary Basins, have become increasingly important for fulfilling the world's energy needs. Many exploration and reservoir development problems have arisen which demand an analytical solution. The solution of many scientific and technological problems associated with these geologically young basin sediments requires knowledge of the origin, maintenance, and distribution of abnormally high pore-fluid pressures, chemical changes induced in the interstitial water by compaction, origin and migration of hydrocarbons, temperature gradients, clay minerals phase changes, and subsidence of the surface. Successful drilling to depths greater than 20,000 ft in these sediments and the amounts of hydrocarbons discovered and produced depend to a great extent on our knowledge of the physical and mechanical properties and deformation characteristics o...

Upon determining grain-size distribution and porosity of sandstones from thin-sections, one can estimate permeability. Diagrams showing correlation between porosity and permeability, such as the one presented in this paper (Figure 2), can be used

Dielectric logs can be used to locate and quantitatively evaluate geopressured environments by (a)establishing empirical calibration charts for a given formation or geologic region and/ or (b) using the equivalent depth method.

A circumferential acoustic logging instrument that operates at a radial mode resonance of 120 kHz utilizes opposing pairs of acoustic transmitters and receivers mounted on pad assemblies, which are pressed against the borehole wall. An important feature of the instrument is a baffle system which effectively minimizes the propagation and reception of the direct fluid wave. The incorporation of the baffle allows both types of boundary waves, the Rayleigh and the guided fluid wave, to be more easily recognized. At present, the primary application of the Circumferential Acoustilog® is in locating natural fracture systems. When run with an orientation section, the instrument is also capable of determining fracture direction. Several field examples are presented here which demonstrate the capabilities and effectiveness of circumferential acoustic logs.

New techniques of determining residual oil saturation from logs are proposed. The inherent technical constraints, such as “stripping”, are discusssed.

Interrelationships among various properties of carbonate reservoir rocks are presented here. Properties include porosity (intercommunicating and effective), permeability (effective and absolute), bulk density, specific surface area, median pore size, and residual water saturation. Sonic velocity (and permeability) parallel to the bedding and perpendicular to the bedding are also compared.

Major stages of transformation of dispersed organic matter in sediments and sedimentary rocks during catagenesis are discussed. The paper mainly represents an historical review of views held by Soviet petroleum geologists and geochemists through 1981. The views and theories of N. B. Vas-soevich (whom the authors consider to be a giant of geology) on organic origin of petroleum are presented in detail.

The analysis of the exploitation of the oil and gas fields with abnormally high formation pressures (AHFP) revealed the possibility of the pore water influx from the overlying, undercompacted, overpressured shales into the productive zones, situated at the lower levels. A study of a well with abnormally high formation pressure in South Louisiana showed a change in pulsed neutron logging index of clay caprocks as a result of porosity reduction (compaction), caused by decrease in pore pressure and pore water explusion to the underlying productive zones. The investigation of oil fields in southwestern Turkmenistan and Baku Archipelago in USSR supplied information on an uninvaded resisitivity in clay formations lying above the producing zones. Influx of water from undercompacted, overpressured shales into producing formations was also discussed elsewhere. This paper represents an attempt to evaluate the variation of pore pressure with time in shales overlying the producing formation, and to estimate the volume of the outflowing water from shales in the process of the underlying reservoir exploitation.

The permeability of 16 carbonate reservoir rocks was determined from thin sections, using both Teodorovich's and Lucia's techniques. There appears to be a great need for further research work in this area because of the large discrepancy between the results.

Compressibilities of unconsolidated sands as related to the compaction (upon production of oil and/or water) and subsequent subsidence are discussed. Data required for development of mathematical a...

In this article, the writers briefly cover and emphasize the importance of fractures in reservoir rock studies.

Fundamental principles of the X-ray diffraction of mesomorphic materials are discussed at length, especially for petroleum asphaltenes. Stepwise procedures for handling X-ray diffraction laboratory data are presented.

Mineral assemblages found in argillaceous rocks have been utilized in many phases of oil exploration. Consideration of depositional environment, correlation of formations, analysis of paleotemperature, and interpretation of primary migration of oil in a basin are the main subjects discussed in this article. Many researchers, therefore, have been concentrating on this special subject. Review papers on diagenesis in argillaceous sediments and rocks also have been published in U.S.A., Japn, and elsewhere. In this paper, several studies on the clay mineral assemblages in argillaceos sediments and rocks in the world and Japan are reported. Discussions on the diagenetic transformation of clay minerals in argillaceous sediments and rocks and studies on phase equilibria of mineral transformations are reviewed. Many works on this special subject studied by Japanese scientists are introduced.

Tar sand deposits can be evaluated by realistic and reliable methods using geophysical well-logging data. Digital log analysis gives a continuous in situ determination of the reservoir characteristics. Application of such log-analysis concepts in tar sand deposits is feasible from both the technical and economical viewpoints. Selective coring and specific core analysis, however, are still required on a limited basis in newly discovered tar sand deposits to establish a new set of interpretation parameters that are characteristic for the specific tar sand deposit under evaluation.

Extensive research work has been conducted by the writers on the effects of barite, thinners, and fiocculants (in various concentrations) on freshwater bentonite muds. The PV-----versus-VP----curve...

The presence of organic material in potential source rocks significantly affects geophysical wireline responses. Inasmuch as the latter provide a continuous, complete, and readily available subsurface formation data record versus depth, many investigators have studied the possibility that organic carbon content and the source rock potential of subsurface strata can be identified from wireline logs. The present discussion reviews such log anomalies as observed by means of resistivity, acoustic, nuclear, natural gamma-ray spectral, and pulsed neutron measurements. The application of these well logs in open and/or cased wellbores as an indicator of the amount of organic matter contained in sediments is discussed and illustrated based on empirical correlations established with individual and/or combinations of several logging parameters. Fieldcase examples from several geographical areas are presented.

The Circumferential AcoustilogR (CAL) is an excellent method for determining (1) vertical or near-vertical open fracture systems which intersect a wellbore; (2) the directional, lateral, subsurface, trend of the detected fracture system; and (3) the direction of regional stress patterns A North American field example compares potential fracture identification based on whole core analysis, conventional acoustic (sonic) log responses, and the Circumferential Acoustic log.

The porosity of dolomitized carbonate rocks can sometimes be determined from the matrix grain density of drill chips. This is shown for the Asmari Limestone of Iran. In this case, the grain specific gravity of 2.87 corresponds to a porosity of about 13%.

Swelling of clays in reservoir rocks (formation damage) is of utmost importance to petroleum engineers. Various inorganic and organic chemicals can be used to prevent swelling of clays. Design and operation of a simple apparatus for measuring the swelling of clays (a ‘swellmeter’) using various chemical solutions are presented in this paper.

Several concepts that attempt to determine static (true) formation temperature from log-derived BHT measurements with and without knowledge of drilling fluid circulation time have been reviewed. Whereas several refined models are available, the simple Horner-type technique provides quick and reliable static (true) formation temperature estimates.

A new nomenclature system for the linear saturated hydrocarbons is proposed. It has many advantages including determination of the physical properties of hydrocarbons.

Gamma ray spectral logging can be used for qualitative and quantitative evaluations of argillaceous sediments, in both cased and open boreholes. Well-logging devices record the gamma rays emitted by potassium (K40) at 1.46 MeV, the uranium series nuclide bismuth (Bi214) emanating gamma rays at 1.76 MeV, and the thorium series nuclide thallium (Tl208) emanating gamma rays at 2.61 MeV. The information obtained can be used in strati-graphic correlations, recognition of rock types, determining the amount and type of clay minerals present in clastic formations, establishing rock potential of shales, evaluating diagenetic and catagenetic changes in clay minerals, CEC estimates, and so on.

A systematic study of the effect of different mud additives upon the filtration and wall-building properties of drilling fluids was conducted. Permeability of filter cakes was measured before and after addition of chemicals. A straight-line relationship was generally found to exist between water loss and mud-cake permeability, except in the case of presence of water-loss-reducing agents. Different additives affect values of the slope and the intercept in distinctive ways. Inert materials give rise to low slope values as compared to those obtained with electrolytes, whereas thinners produce intermediate slope values. Similar additives produce comparable slope and intercept values.

Laboratory experiments using a model to simulate a fracture-matrix-type reservoir indicate a relationship between rate of water injection and rate of imbibition. Under conditions of linear countercurrent flow, increased rate of water injection resulted in increased imbibition rates and greater indicated ultimate recovery. The correlation between water-injection rate and imbibition appears to be well denned. The effects of temperature and the condition of the sand face exposed to imbibition were evaluated.