Electric Log Interpretation Research Articles

Selección de pozos candidatos a Fracturamiento Hidráulico en el campo Gustavo Galindo Velasco.

El campo Gustavo Galindo Velasco ubicado en la provincia de Santa Elena, ha comenzado a mostrar signos de envejecimiento o madurez, denominándose campo maduro debido a la reducción de la presión del yacimiento, lo que ocasiona una disminución en la producción de los pozos. Para incrementar la producción de los pozos y prolongar la vida de este campo, se propone la selección de pozos candidatos a fracturamiento hidráulico, para ello, es necesario realizar un análisis preliminar de investigación referente al diseño de completación, historial de producción y reacondicionamiento efectuados en cada pozo, formaciones productoras, estimación de sus reservas, correlación e interpretación de registros eléctricos, calidad y tope del cemento, intervalos a punzar y diseño de fractura. Los resultados obtenidos de la investigación, permiten aproximar el incremento de la producción después de efectuar el fracturamiento hidráulico en los pozos seleccionados y el análisis económico respectivo del proyecto, mediante el uso de los indicadores de rentabilidad.
 ABSTRACT
 The Gustavo Galindo Velasco field located in the province of Santa Elena has begun to show signs of aging or maturity, being called mature field due to the reduction of the reservoir pressure, which causes a decrease in the production of the wells. To increase the production of the wells and prolong the life of this field, the selection of candidate wells to hydraulic fracturing is proposed, for which it is necessary to carry out a preliminary research analysis regarding the completion design, production history and reconditioning carried out in each well, production formations, estimation of their reserves, correlation and interpretation of electric logs, quality and top of cement, intervals to puncture and design of fracture. The results obtained from this research allow to approximate the increase in production after performing the hydraulic fracturing in the selected wells and the respective economic analysis of the project, through the use of profitableness indicators.

Using Least Square for Develop a New Formation Resistivity Factor Correlation and Relationship between the Salinity and the Corrosion

Formation resistivity factor (Fr),introduced by Archie , is an important parameter for electric log interpretation .It is defined as the resistivity of rock fully saturated with brine (Ro) divided by the resistivity of brine (Rw). This factor is function of porosity, resistivity, tortuosity and cementation factor, which are consequently affected also by particle size and degree of compaction .Formation resistivity factor is usually determined experimentally or by using empirical approach. During the present paper, we try to develop a new formation resistivity factor (Fr) correlation based on statistical methods, Least square, by taking into account different parameter such as brine salinity, particle size and degree of compaction. In addition, this study aims to determine the relationship between salinity and corrosion.

Abstract: Biostratigraphy and Paleoecology in High Energy, Bathyal Sedimentary Settings: Studies in the Main Pass area, Louisiana offshore, Gulf of Mexico

ABSTRACT The Main Pass area is an intersection of depositional environments, each of which leaves its own paleontologic imprint in the sedimentary record while mixing with and frequently obscuring others. High energy scouring, reworking, slumping and multiple sedimentary sources often obscure the succession of events that characterize the depositional and biostratigraphic history of the area. Paleontologic methods, such as water mass tracking and multivariate analysis of faunal succession, separate the biostratigraphic imprints of provenance and depositional energy as well as a history of water column changes that alter the depth associations of foraminiferal species. The separation of these factors allows for a minutely detailed understanding of sedimentary regimes and their dominance or recession over time, helping to characterize the types and qualities of potential reservoirs. Beneath regional unconformities in Main Pass representing the major datums are foraminiferal abundance peaks. The foraminiferal faunas of these events are, in part, characterized by cold-water benthics, usually assumed to be of deeper water affinities than those of the surrounding stratigraphic section. Another faunal characteristic of these events is the occurrence of cooler surface water planktonic species often associated with upwellings. The shoaling of deep currents prior or concorrent with lowstand is considered to be the cause for both of these characteristics. Extensive, longer term faunal changes are associated with probable changes in the source of deep and intermediate currents in the Gulf of Mexico. The interpretation of depositional energy regimes as determined by faunal response is tied directly to sedimentary setting, and yields more detailed information than estimates of paleobathymetry do. That the distribution of extant foraminifera was determined primarily by environmental energy was recognized by Uphaw and Stehli (1962) and Leutze (1972). Core data and interpretation of Main Pass seismic and electric logs were used to corroborate the environmental interpretations of the faunal abundances as described below. Figure 1 contains eight foraminifera abundance curves. These are derived from foraminiferal paleontologic data from an eastern Main Pass well spanning the early Pliocene and late Miocene. Curves 1 and 2 are total foraminiferal diversity; these predetermined statistics are provided for reference. Curve 8 is planktonic species abundance. Curves 2 through 7 are abundances for total foraminiferal faunal components separated by Q-mode factor analysis. They are arranged vertically from lowest amount of variance explained (3) to the greatest (7). The position of regional unconformities are indicated by arrows (^) at the base of curve 7. Curve 3 is dominated by species redeposited from the Florida platform. They are common in slumps and slides along the platform edge and in levee sediments along channels traced back to the platform. The contribution of this component to the sedimentary record is local and relatively constant, becoming obvious only when not overshadowed by riverine deposition. Curves 4 and 5 are regarded as representing redeposited species from riverine dominated and high energy neritic sediment sources, respectively. Curve 4 usually corresponds to the abundance of species carried by scouring sands of Mississippi River origin. The species of curve 5 are present in the scour surfaces of major unconformities and at the base of channels. The species represented by curves 6 and 7 are usually regarded as in situ, consisting respectively of moderately energy tolerant neritic species and energy intolerant species usually associated with bathyal water depths and conditions. These faunal components alternately represent, in relative abundance, the lowest energy sedimentation (condensed sections) or the highly productive periods prior to apparent lowstands. These are only a part of the depositional and paleoenvironmental features that can be segregated from high-energy sediments. Information on depositional pathways, freshwater incursion and other surface water environmental changes related to eustacy can be obtained by extension of the same statistical techniques.

CT-Scan-Monitored Electrical-Resistivity Measurements Show Problems Achieving Homogeneous Saturation

Summary X-ray computerized tomography (CT) scans obtained during measurement of the electrical resistivity of core samples revealed some problems in obtaining uniform saturation along the lengths of the samples. The electrical resistivity of core samples is measured as a function of water saturation to determine the saturation exponent used in electric-log interpretation. An assumption in such tests is that the water saturation is uniformly distributed. Failure of this assumption can result in errors in the determination of the saturation exponent. Three problems were identified in obtaining homogeneous water saturation in two samples of a Middle Eastern carbonate grainstone: a stationary front formed in one sample at 1-psi oil/brine capillary pressure, a moving front formed at oil/brine capillary pressure ≤4 psi in samples tested in fresh mixed-wettability and cleaned water-wet states, and the heterogeneous fluid distribution caused by a rapidly moving front did not dissipate when the capillary pressure was eliminated in the samples.

A Depositional Setting for the Mist Gas Field Reservoir Sands

The depositional origin of the upper Eocene Clark and Wilson (C and W) sandstone member (informal) of the Cowlitz Formation near Mist, Oregon, is controversial. Previous workers have suggested a deep-water setting for the C and W sands. However, recent interpretations of integrated surface and downhole data from Oregon's Mist gas field suggest a wave-dominated deltaic to shallow-marine depositional environment for the C and W sandstone. Sedimentary structures, lithofacies associations, mapped sand geometries, and petrographic examinations indicate that strong wave processes reworked a progradational delta-front environment during a transgression, winnowing fines and controlling C and W sandstone deposition. These well-sorted arkosic sands were deposited following an abrupt relative sea level regression; they onlap an underlying basaltic rock suite and were sourced largely from batholithic masses and Idaho and Washington. Outcrop mapping, studies of continuous cores, and electric-log interpretation show that the Clark and Wilson consists of a 400 to 800-ft-thick series of five stacked, massive-to-hummocky bedded, coarsening- and thickening-upward sandstones separated by minor bioturbated siltstones and lignites. Extensive subsurface mapping delineates individual sandstone bodies that exhibit sheet-like geometries and lateral continuity over areas as great as 60 mi{sup 2}. The authors interpret the siltstone and lignite deposits to represent restrictedmore » marine or brackish-water deposition behind a high-energy C and W shoreline.« less

Electric log interpretation for the evaluation of salt water intrusion in the eastern Niger Delta

Abstract The Niger Delta (75 000 km2) comprises a thick (up to 9000 m) sequence of clastic sediments subdivided into the Akata, Agbada and Benin Formations in ascending order. Sands of the Benin Formation constitute aquifers which have been exploited for water supply, although in parts of the delta many of them have been abandoned due to high salinity. Interpretation of 267 oilwell logs for delineating the fresh water-bearing aquifers is reported here. While fresh water sands occur at the upper zone of the Benin Formation in most places, saline water sands were found at the upper zone at depths (ranging from 30 to 947 m) in two well-defined areas, underlain by fresh water sands. The saline water is thought to be connate. The fresh water/saline water interface has been mapped throughout the eastern Niger Delta and is found to be deepest (2237 m) 44 km westsouthwest of Port Harcourt.

Identification of Point-Bar Reservoirs Within Units of Fall River Formation Through Comprehensive Electric-Log Interpretation, Powder River Basin, Wyoming: ABSTRACT

Abstract Quantitative and qualitative electric log interpretation utilizing multiple log responses can be used as a tool to identify Fall River point bar reservoirs. Numerous authors have shown how S.P. curve shapes can be used to identify point bar and fluvial deposits. However, few have attempted to characterize and identify point bar deposits through quantitative and qualitative interpretation using several electric log responses in combination. Multiple log responses are utilized to identify the sharp basal contact, high permeability and larger grain size typical in the lower portion, and the gradation into finer grain size and lower permeabilities typical in upper portions of Fall River point bar deposits. The technique works best in producing wells which are at irreducible water saturation. In these, porosity can be plotted versus water saturation, and relative estimates of vertical grain size changes can be determined. Gamma ray and density logs are utilized to aid in identifying the narrow, channel filling clay plugs associated with point bars. Reservoirs from two fields in the Powder River Basin are used to demonstrate the technique. The Coyote Creek Field includes reservoir rocks interpreted in several ways by previous authors. The second field is a more recent Fall River Third Bench reservoir in the Lonetree Creek Field, where many of the techniques applied in this study were developed. Observation of porosity and resistivity development in vertical sequences, and position on porosity and water saturation crossplots are used to aid in distinguishing between regional depositional environments, point bar deposits, and channel fill.

Upper Cretaceous and Cenozoic Sedimentary Sequence, Baltimore Canyon Trough, United States Atlantic Margin: ABSTRACT

The extent and character of Upper Cretaceous and Cenozoic rock units in the Baltimore Canyon Trough are revealed by geologic data from 29 exploratory wells. These data, released to the public in 1982, have been used previously in the description of regional rock-stratigraphic units in the trough. Now, a more detailed interpretation and correlation of electric logs and mud logs from these wells and a petrographic examination of thin sections have revealed the composition and lateral distribution of these units. Four detailed stratigraphic cross sections were constructed to show rock-unit correlations among 19 exploratory wells based on lithology and electric logs. Thin-section photomicrographs of drill cuttings and conventional cores document the mineralogic composition of these units. The Upper Cretaceous section is composed principally of gray to brown, calcareous mudstone and is 1,555-3,220 ft (475-980 m) thick. One major shaly, glauconitic quartzarenite within the mudstone is present at most of the well sites. An Eocene carbonate unit, 100-1,100 ft (30-335 m) thick, overlies the mudstone. This unit grades from fossiliferous wackestones to calcareous shale. Oligocene to Miocene calcareous mudstone overlies the Eocene carbonate. White to gray, calcareous clay, shale, and siltstone are common constituents, and limestone, dolomite, and sand are minor constituents. Miocene to Pliocene unconsolidated fine to very coarse-grained sand overlies the mudstone. An uppermost unit of predominantly gray clay is present in the eastern part of the basin. End_of_Article - Last_Page 1923------------

Thermodynamics of Salinity Changes Accompanying Compaction of Shaly Rocks

Abstract When a clay or shale with fixed cation exchange capacity is saturated with salt water and the solid matrix is slowly squeezed, so that equilibrium is maintained between the remaining pore water and successive increments of squeezed-out water, these successive increments will contain salt of decreasing normality L N = --- [1 - (n/2L)2], 2 provided the water is conducted away from and out provided the water is conducted away from and out of diffusional contact with the clay as it is produced. Here, n is the cation exchange capacity per unit pore volume and L is a constant determined so that pore volume and L is a constant determined so that this equation correctly relates the initial concentration of solution in equilibrium with the clay, No, and the initial exchange capacity per unit pore volume, no. The pore water remaining in the clay or shale at any point in the squeezing process will contain positive and negative ions of normality: 1 N = -- [L n + n2/4L). 2 In the pores, the positive-ion concentration increases steadily while the negative-ion concentration and N decrease to zero for n 2L. The squeezed-out pore water, if collected and mixed, will contain pore water, if collected and mixed, will contain salt of decreasing normality: 1 N = ---- [L - non/4L]. 2 In deriving these equations, it is assumed that the ratio of activity coefficients of salt inside and outside the porous material is unity, and that there is no association between cations and either anions or exchange sites. Association of cations and exchange sites is treated briefly. Approximations used are thatan increment of salt water passing out of the porous medium does not change volume andthe matrix material does not compress during compaction. The process must be carried out so slowly that the changing porosity and salinity remain uniform throughout the porous material. The given thermodynamic results correspond to a common experiment in which a water-saturated clay cake is compressed and the squeezed-out water is conduced away through a short capillary of minimal volume and dropped into a receiver. The results also approximately describe some geologic situations in which compaction water from shales drains into comparatively thin sands that conduct the water away. Introduction A number of authors have reported progressive changes in the salinity of water squeezed out of clay cakes. The trend of the data is for the salinity of the squeezed-out water to decrease generally as the porosity is reduced. Chilingar et al. reported that the salinity decreases if the compaction is very slow, but can be made to increase if the compaction pressure increases abruptly. Experimental objectives have been to understand salinity changes in shales and sands in geologic settings. Knowledge of expected salinity changes can be applied to quantitative interpretation of electric logs, to interpretation of the direction of hydrodynamic flow over geologic time in compacting sand-shale sequences and to determining whether the more rapid water influx into producing petroleum reservoirs may have come from surrounding shales. Fowler has interpreted detailed data from the Chocolate Bayou field, Brazoria County, Tex., in terms of the last two phenomena. Patchett has shown that logged shale conductivities in wells from a number of sedimentary basins, when converted to a common temperature basis, fall within a narrow range for any given porosity. This is in accord with a finding here that ion concentrations in compacting shales should evolve to values depending on cation exchange capacity but not on the initial salt concentration in the depositional environment. SPEJ P. 377

Electric Well Logging of Hawaiian Basaltic Aquifers

ABSTRACTAn extensive program of electric well logging has been conducted in Hawaii during the past three years to determine the applicability of this tool to the volcanic environment which exists in Hawaii. Electric well logging techniques were found to be useful in Hawaiian basaltic aquifers; however interpretation of both spontaneous potential logs and resistivity logs varies from the conventional interpretation of electric logs in sediments. The interpretation of fluid conductivity logs in Hawaii follows conventional water well techniques.The analysis of spontaneous potential and resistivity well logging in basalts, which constitute most of the Hawaiian aquifers, poses problems because of the relatively uniform composition of the basalts and the complex relation of porosity to resistivity in basaltic aquifers, and because logging usually is performed in water‐filled boreholes. Spontaneous potentials are thought to result primarily from fluid flow rather than from electrochemical potential, and positive SPs generally indicate zones with flow from the aquifers into the well, and negative SPs generally indicate zones with little flow or flow from the well into the aquifer. Resistivity logs indicate the location, number, individual thickness, and total thicknesses of permeable and less permeable formations, and are useful as indicators of water‐yielding zones. High resistivities generally are indicative of dense impermeable basalts and low resistivities are indicative of porous permeable zones most likely to contribute water to the borehole. Both resistivity and spontaneous potential logs provide a direct measurement of depth to water, depth of casing, and depth of hole.

Detection and Estimation of Dead-End Pore Volume in Reservoir ROCK by Conventional Laboratory Tests

Abstract Conventional laboratory core analysis tests on samples of two limestone reservoir rocks indicate that about 20 per cent of PV is in dead-end pores. These tests (electric logging formation factor. mercury injection capillary pressure and miscible displacement) were carried out on 3/4-in. diameter test plugs. Test results show a clear difference between these samples and sandstone or homogeneous limestone reservoir rock. Although the amount of dead-end pore space can be only roughly estimated, the presence of such pore space seems clearly indicated. Pressure transient studies also show presence of dead-end PV. Although they do not give quantitative results, pressure transient data yield a reasonable estimate of the size of the neck connecting dead-end pores to the main flow channels. Introduction Equations conventionally used to describe reservoir flow behavior contain the implicit assumption that all connected pore spaces contributed to both porosity and permeability. Several authors have pointed out the changes in pressure transient behavior and in electric log interpretation that may result if this assumption is incorrect and, instead, dead-end or cul-de-sac pores are present. There is a need for laboratory tests that can detect presence of dead-end pores in core samples. With such information on hand the petroleum engineer can make more rational use of the mathematical tools now available for analysis of reservoir flow behavior. This paper describes laboratory studies designed to detect and, if possible, give a quantitative measure of dead-end PV in laboratory-size core plugs. Three reservoir rocks were used, two of which were limestones suspected of having dead- end pore spaces and a well-known sandstone, used as a comparison standard, in which there is believed to be little or no dead-end pore space. All the studies were designed to measure the natural dead-end PV; i.e., the pore space which is dead-ended because of rock structure. During multiphase flow in a rock without dead-end pores, some parts of one of the phases can become surrounded by the other, thereby giving (for certain flow behavior) an effective dead-end PV 8,9. Such behavior will not be described here. FORMATION FACTOR THEORY One of the simplest laboratory measurements which can be made on core plugs is the electric logging formation factor F. By definition: (1) where Ro is the resistivity of the core plug saturated with a saline solution of resistivity Rw. Difficulties in using this definition of F may arise when the solid framework of the rock is electrically conducting. These difficulties may be largely circumvented by using a highly conducting saline solution so that the conduction contribution of the solid is negligible. There are no useful theoretical relationships between F and the porosity phi. A widely used empirical relation is the one given by Archie: (2) where m, called the cementation factor, is expected to be a constant for a given type of rock. Pirson shows that for reservoir rocks, m varies from about 1.3 for loosely cemented sandstones to 2.2 for highly cemented sandstones or carbonate rocks. SPEJ P. 206ˆ

Reservoir Inhomogeneities Deduced From Outcrop Observations and Production Logging

Abstract Many fields, where the reservoir is coil/posed of sandy layers, show great complexity because of the lack of continuity which results from a particular type of sedimentation. This complexity may be a factor of prime importance in studying reservoir drainage, especially in the displacement of oil by water or gas. This paper describes work done to study this heterogeneity and its influence in the exploitation of the fields of the lower Devonian sandy shale in the Fort Polignac Basin in Algeria. Two lines of research were followed.On the border of the basin, a detailed sedimentological study established rules for the distribution of the sandy zones, which furnished hypotheses necessary for devising a geologic model of the reservoir. A certain number of sandy zones were recognized and characterized by their sedimentation.In the interior of the basin, production logs determined the productivity profile. Study of these point data led to a description of the distribution of oil and gas phases in the reservoir so that the continuity of different zones between the wells could be deduced. These techniques were applied to the study of the lower Devonian sandy shale reservoir of Zarzaitine. The sedimentological study guiding the correlation work, with the aid of the conventional static data (logs and cores), led to the establishment of a useful geologic model of the reservoir. Production logs, thanks to the contribution of dynamic elements, permitted corroboration of the model. In particular, the logs confirmed separation, as proposed by the sedimentological study, of two comparable sandy groups by revealing the continuity of a thin impermeable layer. invisible on conventional logs. INTRODUCTION The heterogeneity of sandstone reservoirs considerably influences the distribution of fluids. as well as their displacement in the reservoir. Rational development of a field and maximum recovery of hydrocarbons are closely tied to an exact and precise knowledge of the internal architecture. We will try to show how it is possible to refine the knowledge of the reservoir by seeking quite different and varied sources of information. Production geology, the group of techniques which leads to ideas concerning reservoir architecture and its geometric description, furnishes the framework of this undertaking. Of these techniques, those used so far are quite varied. Descriptive as well as quantitative, the techniques partake as much of classical geology as of reservoir science. They includegeologic studies of the entire basin, especially a stratigraphic and sedimentological study of the reservoir member at its outcrop, detailed observations of cores taken from wells and, finally. oriented cores;interpretation of geophysical data;interpretation of electric logs, nuclear and sonic logs and dipmeters:petrophysical study of the reservoir on samples taken from wells;reservoir dynamics (study of the production history and, in particular, interpretation of production logs); andanalysis of the fluids and thermodynamic studies. This incomplete list could also includestudy of the migration of the fluids,geochemistry (chemical characterization of the oils),regional hydrodynamics. andinjection and detection of tracers. If most of these techniques are classic, attention will nevertheless be called to applying two of the techniques in conjunction: the study of the reservoir member at its outcrop and the study of dynamic distribution of fluid phases in the reservoir through use of production logs, used in the study of the sandy shale reservoirs of the lower Devonian of the Fort Polignac Basin, Algeria. In particular, their application to the study of the Zarzaitine field where they have led to a new and satisfactory model of the reservoir will be described.

Determining Formation Water Resistivity From Chemical Analysis

Abstract An accurate value of formation water resistivity Rw is essential in calculating formation porosity and fluid saturation from electrical well logs. In the cases where Rw has not been measured directly, it must be obtained from other data, e.g., the SP curve. This paper deals with another approach: how to calculate Rw, from the chemical analysis of the formation water. Introduction It is known that the resistivity of aqueous solutions of pure salts depends on their concentration and on the temperature; the concentrations are given in MPL (mg of solute per liter of solution), or sometimes in ppm (mg of solute per kg of solution): MPL = ppm X specific gravity. Values for different pure salts are available in the literature, but not for solutions of mixtures which are of practical interest. The major component of the dissolved material in almost all formation waters being sodium chloride, it is customary to express the resistivity of formation waters in terms of equivalent sodium chloride concentration, i.e., the concentration of a solution of pure NaCl which has the same resistivity at a given temperature as that of the formation water under consideration. Thus, the problem of calculating Rw from the chemical analysis can also be stated as how to convert the other constituents of the solute into equivalent NaCl concentration. Salts dissolved in water are at least partly dissociated into ions, and do not conserve their identity. If known amounts of several salts are dissolved in water, the solution does not necessarily contain the same salts in the original proportion, but perhaps some other combination of the ions, along with free ions in solution. This is why the chemical analysis of formation waters is often given in terms of ion, as if all dissolved salts were completely dissociated. Our problem then boils down to how to convert the concentrations of the various ions to equivalent concentrations of Na+ and Cl. Dunlap and Hawthorne have proposed to convert the concentration of all other ions to equivalent Na+ and Cl-concentrations by means of constant multipliers; e.g., 0.95 for Ca++: 2.0 for Mg++; 0.27 for HCO-; 0.5 for SO--, etc. Their factors were based on measurements made at 68F on 26 formation water samples from the Texas Gulf Coast, ranging in concentration from 1,500 to 75,000 ppm. Dunlap method is widely used in electric log interpretation, and is often extrapolated beyond its original concentration range. A comparison of Rw, values calculated by this method and values actually measured on formation water samples has shown large discrepancies, especially at higher concentrations. Therefore, two new methods were developed at Sinclair Oil Corp's Tulsa Research Center to calculate equivalent sodium chloride concentration from the chemical analysis of formation water samples. FUNDAMENTAL CONSIDERATIONS The resistivity of a solution, or its reciprocal the conductivity, at a given temperature is determined by the charge, concentration and mobility of the ions actually present. Monovalent ions such as Na+ or Cl- always carry the same charge. Compounds of polyvalent ions, however, may show incomplete dissociation, e.g., NASO4- + Na+ instead of SO4-- + 2Na+. This happens especially in more concentrated solutions. Only very dilute solutions are completely dissociated, as assumed in the chemical analysis report. At higher concentration, the degree of dissociation depends not only on the nature and concentration of the particular salt under consideration but also on the nature and concentrations of the other solutes. Mobility of the ions depends on the viscosity of the solution. It also depends on the degree of hydration of the ions, which in turn is a function of the nature and the charge of the ions and also of the amount of free water available per ion, i.e., the total ionic concentration. The net effect is that the conductivity increases slower than proportional to the concentration, even if a solution contains only one salt such as NaCl, and is different for different salts (Fig. 1). Conductivity can even decline with a further increase in concentration, e.g., if additional salt is little dissociated but ties up some of the free water and/or causes an increase in viscosity. In solutions containing more than one salt, the contribution of one salt to the total conductivity depends not only on the fractional concentration of this same salt, but also on the concentration of all other solutes. A perfect method would give the conductivity or resistivity of a solution as a function of the concentrations of all solutes present. This is so complicated as to be impractical, and a simpler method must be found which is of acceptable accuracy. JPT P. 373ˆ

A Laboratory Study on Rm-Rmf-Rmc Ratios of Drilling Muds

Using the synthetic muds with additives, the mud resistivity, mud filtrate resistivity and the mud cake resistivity were measured, and these relationships were investigated from the standpoint of electric log interpretation.

A Laboratory Study on Drilling Mud Resistivity and Mud Filtrate Resistivity

Drilling mud resistivity and mud filtrate resistivity were measured, using the synthetic muds: those are clay base muds with additives (salt•humic acids•CMC•barite) and oil emulsion muds with additives. From the standpoint of electric log interpretation, dependence of these resistivities on temperature (15°C_??_80°C) and different mud additives is discussed, and the relationship between mud resistivity and mud filtrate resistivity investigated.

Calculation of Formation Temperature Disturbances Caused by Mud Circulation

Abstract Quantitative interpretation of electric logs requires knowledge of formation temperature. In this paper, methods are developed for computing changes in formation temperature caused by circulation of mud during drilling operations. The basis of the method is the mathematical solution of the differential equation of heat conduction. The solution of this equation is presented in a series of graphs. These graphs are used to determine formation temperature disturbance at various radii for arbitrary mud circulation histories. Example comparisons with field results show reasonable agreement. It is concluded that, in general, the temperature disturbances caused by circulating mud are small beyond 10 ft from the wellbore but are quite significant near the wellbore. Introduction Quantitative interpretation of electric logs requires knowledge of the formation temperature in order to establish the resistivity of the formation water with accuracy. To determine the formation temperature, the temperature disturbances produced by circulating drilling mud must be evaluated. The objective of this investigation was to develop a method for the numerical determination of these temperature disturbances at any distance from the wellbore as a function of time. The first step was to solve the differential equation describing the temperature behavior in the formation during and after mud circulation. This solution was used to calculate a series of curves relating temperature disturbance to shut-in time for various circulating periods. An "exact" method for computing formation temperatures with the use of these temperature-disturbance plots is described, and the results of an application of this method to a well in Montana are presented. Procedures for approximating formation temperatures are also discussed. BASIC EQUATIONS AND ASSUMPTIONS With the assumptions thatcylindrical symmetry exists, with the borehole as the axis,heat flow is due only to conductivity andvertical heat flow in the formation is zero, the temperature distribution around a wellbore is defined by the following differential equation. ...........................(1) where T = temperature, r = radius, Cp = specific heat capacity of formation rock, p = density of formation rock, K = thermal conductivity of formation rock, and t = time. In terms of dimensionless time, and dimensionless radius, the constants in Eq. 1 disappear, and it becomes ...........................(2) Other simplifying assumptions made in the treatment of the temperature problem are as follows.The formation can be treated as though it is radially infinite and homogeneous in extent, as regards heat flow.The presence of mud cake can be disregarded.The effect of heat generated by bit action is negligible.After mud circulation ceases, the rate of radial heat flow at the wellbore is negligible and is assumed zero for purposes of calculating temperature change with time. These assumptions are believed to be reasonable because of the agreement achieved between calculated and measured borehole temperature in a well, to be discussed later. Further, the agreement at the wellbore indicates that temperatures in the formation were also approximately correct, since it is the formation temperatures that determine wellbore temperature after ceasing circulations. JPT P. 416^

The Significance of Particle Shape in Formation Resistivity Factor-Porosity Relationships

Abstract Results of laboratory tests are presented to show that the value of "m", in the Archie expression is determined by the shapes of the particles in the system. The value of m, "the shape factor", is constant for a system of particles of a given shape for a range of values. Applying this concept, one can predict relationships for mixtures of particles with different shapes, and these predicted relationships are useful in electric log interpretation. It is suggested that an equation of the form can be used to describe the properties of natural formations containing varying amounts of sand and clay. From this work and values of "a" and "m" reported in the literature, it appears that in many cases rocks in the same geological horizon have a common primary porosity but contain varying amounts of a particular clay. It is concluded that the equation can be applied to a rock-water system only when values of "a" and "m" have been established for the particular system. Introduction The petroleum literature contains many reports of the results obtained by determining formation resistivity factor and porosity of rock samples from oil fields all over the world.

Techniques of Electric Log Interpretation

Abstract The generally used techniques of electric log interpretation are reviewed and discussed, including the determination offormation water resistivity from the SP curve,true resistivity values from log data,water saturation from electric logs, andformation porosity from resistivity data. Particular emphasis is placed on the assumptions made in log interpretation. It is hoped that efforts will be stimulated which, in the future, will make it possible to reduce the number of assumptions necessary for log interpretation. Introduction Petroleum engineering and geology can be said to be based upon both facts and assumptions. So too, are the various techniques of electric log interpretation. For the last few years, some assumptions which have been made in developing log interpretation methods have been repeated so often that they are now accepted by many persons as facts. In reviewing the principles of resistivity and potential curve interpretations, many of the assumptions (and how they affect the results of interpretation) will be considered. Because this is a review, the purpose of this paper is not to present new methods of interpretation. However, the reader of this review should be stimulated to consider whether he should accept these assumptions as they are made now or whether he would prefer to explore possible ways to reduce the number of assumptions required for log interpretation. Assumptions To emphasize the assumptions used in most interpretations of electric logs, they will be tabulated here and then referred to as each technique of interpretation is discussed. No particular emphasis is inferred by the order of tabulation.

Techniques of Electric Log Interpretation

Techniques of Electric Log Interpretation

Electric Log Interpretation in Exploring for Stratigraphic Traps in Shaly Sands: DISCUSSION

Electric Log Interpretation in Exploring for Stratigraphic Traps in Shaly Sands: DISCUSSION