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Resistivity and spontaneous (SP) logging
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Journal Articles
Journal:
Journal of Petroleum Technology
Publisher: Society of Petroleum Engineers (SPE)
Journal of Petroleum Technology 22 (11): 1437–1446.
Paper Number: SPE-2551-PA
Published: 01 November 1970
...E.A. Koerperich Koerperich, E.A., SPE-AIME, Shell Oil Co. In this method of logging, a recording of the potential difference between two SP electrodes yields a curve that may facilitate and improve sand counts, and that might be amenable to automatic computerized interpretation. Spurious SP...
Abstract
Koerperich, E.A., SPE-AIME, Shell Oil Co. In this method of logging, a recording of the potential difference between two SP electrodes yields a curve that may facilitate and improve sand counts, and that might be amenable to automatic computerized interpretation. Spurious SP electrode noise signals can be substantially reduced or eliminated from the potential-difference curve. Introduction Wellbore SP currents and their applicability in the location of subsurface sand bodies were discovered in 1931 and the usefulness of this measurement has persisted to the present day. Through the steadfast persisted to the present day. Through the steadfast endeavors of many researchers, knowledge and understanding of the SP has slowly evolved from the original mere recognition of its existence to its present-day quantitative use. Some common applications present-day quantitative use. Some common applications of the SP curve include bed correlation, sand counting and formation-water resistivity determination. This report relates to the determination of net sand counts from SP data. Many influences combine to complicate SP interpretation and to restrain its use as a unique, infallible indicator of permeable bed boundaries. The distribution and intensity of SP, currents are largely influenced by properties of the drilling and formation fluids. wellbore diameter and invasion depth, and by various characteristics of the subsurface strata. Quantitative use of the SP curve is severely restricted in salt, carbonate, and fresh water provinces, Shaly sand formations create difficulties with SP interpretation, and this topic has been the subject of many publications. An even greater problem is SP noise, which has long been a source of low-quality and erroneous SP curves, particularly since the advent of offshore drilling operations. A principal source of noise is associated with the surface "ground" potential to which the wellbore spontaneous potentials are referenced. Being located at the surface, the reference potential is vulnerable to voltage disturbances created by surface objects. Thus, all these factors that mold SP character should be accounted for, as adequately outlined in the literature, when the curve is being analyzed quantitatively. Many times the exact influence of some or all of these factors affecting SP response cannot be predicted. For this reason, auxiliary tools, whenever predicted. For this reason, auxiliary tools, whenever available, are used in conjunction with the SP to determine net sand. Short spaced, highly focused resistivity devices or pad-type resistivity devices are commonly used for this purpose. Despite the limitations of the SP curve, there are a number of occasions and areas where it satisfactorily reflects permeable bed boundaries. Many times auxiliary logs are not available to refine the SP sand count, leaving the SP as the primary indicator of bed boundaries. In these cases, the method of recording and presenting SP data as outlined in this report can presenting SP data as outlined in this report can usefully supplement the SP curve. This method of presentation is directly derived from a single conventional presentation is directly derived from a single conventional SP curve or from two conventional SP curves recorded simultaneously at different depths in the wellbore. When the data presentation is derived from a single down-hole electrode the resultant curve (Delta V curve) is subject to all the limitations and required corrections associated with the SP recording, including the presence of noise signals when they exist on the SP. When the, Delta V curve is derived from two downhole electrodes, it is subject to the same limitations except the SP noise. JPT p. 1437
Proceedings Papers
Paper presented at the SPWLA 48th Annual Logging Symposium, June 3–6, 2007
Paper Number: SPWLA-2007-H
... (m), from the combined use of borehole raw array-induction resistivity measurements and spontaneous potential (SP) in water-bearing intervals. Combined inversion of resistivity and SP measurements is performed assuming a piston-like invasion profile. In so doing, the reservoir is divided into...
Abstract
Abstract Knowledge of initial water saturation is vital to estimate original oil in place. In addition, accurate estimation of permeability is necessary to select perforation intervals, layers for fluid injection, and to forecast production. Reliable assessment of these two petrophysical properties is possible when rock-core measurements are available. However, such measurements are not always available, and if they are, their reliability is sometimes questionable. This paper describes a new inversion methodology to estimate connate water resistivity (R w ) and Archie?s cementation exponent (m), from the combined use of borehole raw array-induction resistivity measurements and spontaneous potential (SP) in water-bearing intervals. Combined inversion of resistivity and SP measurements is performed assuming a piston-like invasion profile. In so doing, the reservoir is divided into petrophysical layers to account for vertical heterogeneities. Inversion products are values of invaded and virgin formation resistivity, radius of invasion, and static spontaneous potential (SSP). Connate water resistivity is calculated by assuming membrane and diffusion potentials as the main contributors to the SSP. Archie?s or dual-water equations enable the estimation of m. We successfully applied this combined estimation method to two data sets acquired in clastic formations. One data set corresponds to a high-permeability, lowsalt concentration reservoir and the second set is associated with a high-permeability, high-salt concentration formation. Values of R w and m yielded by the inversion are consistent with those obtained from Pickett?s plots, thereby confirming the reliability of the estimation. Results are used as input to estimate water saturation in hydrocarbon-bearing intervals. Accurate estimation of initial water saturation allows us to apply the physics of mud-filtrate invasion to estimate permeability. By progressively modifying permeability and performing multiple mud-filtrate invasion simulations we are able to match borehole resistivity measurements, thereby obtaining the estimate of absolute permeability. In a vertically heterogeneous formation, the estimated permeability increases between 25% and 85% with respect to the initial-guess in the most prospective intervals. The method described in this paper is an efficient alternative to perform petrophysical analysis of exploratory and appraisal wells wherein rock-core measurements may not be available. Introduction Initial water saturation in a hydrocarbon reservoir has an enormous impact on the calculation and production of original oil in place. In addition, permeability is regarded as the most important variable in selecting perforation intervals, layers for injection, and to forecast production. When laboratory measurements (core, water analysis, etc.) are available, these two variables are properly constrained. However, such measurements are not always available, and if they are, their reliability may be questionable. Therefore, there is a strong need for alternative methods to estimate initial water saturation and permeability. Two of the main parameters needed to calculate water saturation are R w and m, which can be obtained from connate water analysis and special core analysis, respectively. Core measurements are often expensive because they involve the cost of extracting the core sample and laboratory work. Moreover, measurements of water resistivity are difficult due to the need to acquire connate water samples when wells are already in production and water-injection/steam-flood have been applied to enhance production. Fluid samples taken by fluid acquisition tools are often contaminated with mud-filtrate
Proceedings Papers
Publisher: Society of Petroleum Engineers (SPE)
Paper presented at the SPE Rocky Mountain Regional Meeting, May 11–13, 1988
Paper Number: SPE-17516-MS
... conventional sp analysis SPE Society of Petroleum Engineers SPE 17516 Water Resistivity From Spontaneous Potential Logs in the Minnelusa Formation, Powder River Basin, Wyoming by B.A. Policky, Marathon Oil Co., and W.P. Iverson, U. of Wyoming SPE Members Copyright 1988 Society of Petroleum Engineers This...
Abstract
Abstract Water resistivity (Rw) values computed from the spontaneous potential (SP) log frequently yield low values for the Minnelusa formation of the Powder River Basin, Wyoming when compared with Rw values determined directly from water samples. These anomalies arise when conventional SP analysis techniques for obtaining for determining the SSP deflection and a new equation which solves for RW have been developed. To construct and validate the new technique and equation, a complete appraisal of the current methods of obtaining estimates for water resistivity has been provided. A substantial number of wells, which produced 100% water upon testing and span a large cross-sectional area of the basin, were analyzed. In addition, oil producing wells have been included to verify Rw estimates for intervals bearing hydrocarbons. Using this new procedure has resulted in significant improvements in the accurate evaluation of the hydrocarbon potential of a prospective interval within this formation. Introduction Rw is generally obtained from three different techniques, directly from formation water samples, the SP log, and/or from resistivity-porosity log. For the Minnelusa, Rw values reported in catalogs vary by three orders of magnitude within the project area shown in Figure 1. Since Rw samples from adjacent wells may not be applicable, other means of determining Rw must be pursued. Utilizing the SP log, Rw has been previously derived from the conventional SSP equation, (1) SSP = − ( 61 + 0.13 Tf ) log ( Rafe Rwe ) and using equivalent resistivity charts to determine true Rw. Such Rw values from conventional SP analysis are consistently low when compared with RW from actual water samples or Rwa analysis from sonic and resistivity logs. Consequently, a saturation estimate with that erroneously low Rw produces a misleading low water saturation. Rectifying these anomalous Rw values and restoring confidence in the SP log, 112 wells that recovered 100 % water upon testing were analyzed to develop the new procedure for determining Rw. All selected water wells within the study area were taken from a catalog listing, allowing for only pure water recovery and discarding any wells that reported contamination with mud, gas, or oil. T hat restriction allowed for appraising and comparing all the well known techniques for determining Rw. A detail map is provided within Figure showing specific well locations. As shown in that figure, a good distribution of wells exists. Therefore, a procedure for determining Rw could be developed that was applicable to the majority of the basin. For each well, Rw values derived from conventional SP analysis (ie. Schlumberger SP-1 Chart and equation (1) were compared against catalog Rw values. That comparison is displayed in Figure 3. A Rw range of 0 to 6 ohm-m (converted to 68 degrees F (20 degrees C), spans the axes of that figure which dramatically shows that conventional SP analysis for estimating Rw yields values that are consistently low, when compared against catalog Rw values. P. 353^
Proceedings Papers
Paper presented at the SPWLA 56th Annual Logging Symposium, July 18–22, 2015
Paper Number: SPWLA-2015-B
... Abstract Spontaneous Potential (SP) and Gamma Ray (GR) logs are often the only measurements available in many old hydrocarbon fields. Reliable coupled petrophysical interpretation of GR and SP logs requires previous accurate quantitative calibration for the effects of shale laminations, water...
Abstract
Abstract Spontaneous Potential (SP) and Gamma Ray (GR) logs are often the only measurements available in many old hydrocarbon fields. Reliable coupled petrophysical interpretation of GR and SP logs requires previous accurate quantitative calibration for the effects of shale laminations, water electrolyte concentration, temperature, bed thickness, borehole diameter, hydrocarbon saturation, and invasion, among others. Although the latter effects on SP logs are well known, there is no published numerical algorithm that quantifies the relative contributions of all geometrical, petrophysical, and fluid effects on SP logs. This paper develops a new mechanistic description of SP logs for their numerical modeling and petrophysical interpretation in vertical wells penetrating horizontal layers. The main objective of the new SP modeling method is to estimate water saturation reliably in wells where only SP and GR logs are available but where resistivity and porosity calibrations can be performed in a key well within the same field or can be inferred from core data. The mechanistic SP modeling algorithm is based on the fundamental concept of anion and cation migration in aqueous solutions with unequal electrolyte concentration via diffusion and membrane potentials. It explicitly accounts for specific borehole conditions, temperature, variable shale properties, finite bed thickness, shale laminations, hydrocarbon saturation, and invasion (including salt concentration profiles) in the numerical modeling of SP logs. Further, hydrocarbon saturation effects on SP logs account for the rock's effective throat radius. Sensitivity studies are carried out to quantify selectively the effect of each environmental and geometrical variable on measured SP logs. The modeling algorithm is also successfully used to reproduce SP logs acquired in the presence of salt and water saturation fronts in invaded hydrocarbon-saturated rocks. Examples of application include sandstone sequences that have internal shale laminations.
Proceedings Papers
Md. Iftekhar Alam, Andrew Katumwehe, Khumo Leseane, Fathiya Al-Hadhrami, Brooke Briand, Daniel Morse, Sam Wei, Estella Atekwana
Publisher: Society of Exploration Geophysicists
Paper presented at the 2018 SEG International Exposition and Annual Meeting, October 14–19, 2018
Paper Number: SEG-2018-2998496
... including electrical resistivity, spontaneous potential (SP), and EM 34. In addition, Total Dissolved Salt (TDS) data were provided from groundwater samples collected from wells. Our results from EM 34, Resistivity and TDS, suggest a highly conductive zone in the study area. Presence of conductive medium in...
Abstract
ABSTRACT Landfill leachate plumes have been one of the major environmental concerns because of their ability in contaminating shallow ground water aquifers. Leachate plumes transport toxic materials, which are hazardous to groundwater resources. The Norman landfill research site is a closed municipal solid waste landfill, formerly operated by the city of Norman, OK. Current study was conducted to map the edges of the Norman landfill leachate plume. Both geophysical and geochemical approaches had been adopted to locate the boundary of the plume. Several geophysical techniques were applied including electrical resistivity, spontaneous potential (SP), and EM 34. In addition, Total Dissolved Salt (TDS) data were provided from groundwater samples collected from wells. Our results from EM 34, Resistivity and TDS, suggest a highly conductive zone in the study area. Presence of conductive medium in the subsurface may have been caused by higher concentration of contaminants from the leachate. All the results obtained from different geophysical techniques represent significant correlation. This anomalous area of conductive zone relates to an area of higher chloride concentration, identified from TDS data. Therefore, by integrating all the results from geophysical and geochemical methods used for this study, the edge of the leachate plume was located along the central part of our survey lines. Present study suggests that an integrated geophysical approach using various tools can be successfully applied to locate conductive zones associated with contaminant leachate plume, which is farther validated by chloride concentrations from TDS data. Presentation Date: Wednesday, October 17, 2018 Start Time: 9:20:00 AM Location: Poster Station 3 Presentation Type: Poster
Journal Articles
Petrophysics - The SPWLA Journal of Formation Evaluation and Reservoir Description 25 (04).
Paper Number: SPWLA-1984-vXXVn4a2
Published: 01 July 1984
... salinity within the interval analyzed. CONCEPT OF THE RESISTIVITY - SPONTANEOUS POTENTIAL CROSSPLOT The development of the R, - SP crossplot utilizes two basic relations, equation (4) and the simplified form of the SP formula: SP = -K log R,f R, (5) where R, is the mud filtrate resistivity and K is a coefl...
Abstract
The apparent formation water resistivity (Rwa), the Ro overlay, and the Resistivity (Rt) Porosity (0) crossplot are among several methods used in picking out hydrocarbon-bearing zones. One condition essential to the use of these techniques is that the formation water resistivity (Rw) remains constant or varies in a narrow range over the interval analyzed. If this condition is not met, a zone with water resistivity abnormally higher than that of other zones within the interval of interest can be mistaken for a hydrocarbon-bearing zone. Also, a hydrocarbon-bearing zone with abnormally low water resistivity can be over looked. The use of Resistivity (Rt) Spontaneous Potential (SP) crossplot together with the Rt 0 crossplot can prevent such gross misinterpretations. This paper reviews the concepts of the Rt SP crossplot, its advantages and limitations. Field examples illustrating the proposed interpretation techniques are discussed.
Proceedings Papers
Paper presented at the SPWLA 48th Annual Logging Symposium, June 3–6, 2007
Paper Number: SPWLA-2007-ZZ
... the determination of permeable layers, they influence the calculation of formation water resistivity which requires the Static Spontaneous Potential (SSP) computed from the SP. In order to correct these effects, many correction charts have been created. However, in very complicated logging...
Abstract
Abstract After permeable layers are drilled using water based mud and if mud salinity is different from formation water salinity, dipole layers form along borehole wall, layer boundaries and invasion zone boundaries. The dipole layers produce Spontaneous Potential (SP) in the borehole. So, for long time, well logging analysts have used the SP curve to determine permeable reservoirs and to compute formation water resistivity. Like other logs, the SP is also affected by logging environment conditions, such as invasion, shoulder beds, borehole, etc. Even though these effects do not influence the determination of permeable layers, they influence the calculation of formation water resistivity which requires the Static Spontaneous Potential (SSP) computed from the SP. In order to correct these effects, many correction charts have been created. However, in very complicated logging environments, the charts cannot completely correct the mentioned effects. So, more useful correction methods need to be developed. In this paper, we present a joint inversion method to compute SSP from the SP and dual laterolog/dual induction logs. At first, formation boundaries and permeable layers are determined using SP, Gr and resistivity curves. Then formation resistivities are inverted from dual laterolog/dual induction logs. In the permeable layers, three parameters (invasion zone resistivity, virgin formation resistivity and invasion radius) are inverted, and in the non-permeable layers, only formation resistivity is inverted. Finally, using the inverted formation resistivities, the SSP is inverted from SP data. The SSP inversion is performed by inverting the SSP point sources instead of inverting the potentials across the dipole layers. The point sources are located at the junction points between layer boundaries and invasion zone boundaries and the junction points between layer boundaries and borehole wall. Because in this method, the shape of the boundaries does not need to be considered, inversion becomes easier. An inversion code has been developed based on the proposed method and the code has been used to invert SSP and calculate formation water resistivity in oilfields in Africa and China. As an example, in a clean sand reservoir with thickness 7 (m) and maximum SP 70 (mV), the inverted SSP is 83.2 (mV) and the computed salinity from the SSP is 2,416 (ppm) which is very close to the formation water salinity 2,330 (ppm) obtained by formation water analysis. Introduction The SP is induced when there is different salinity between mud filtrate and formation water. In water based mud cases, the SP log is useful to indicate permeable reservoirs as well as to compute formation water salinity/resistivity. The formation water resistivity is one of the key parameters used to compute formation water saturation. There are several methods to obtain the formation water resistivity like performing a formation water test to take a direct measurement or inferring the value from the SP log. The later method is a service offered free of charge making it the most economic currently available. As in the case of other logs like resistivity logs, the SP log is affected by well logging environment conditions, such as borehole, invasion and shoulder beds. In order to understand these effects, scientists have made numerical simulation and laboratory study(Taherian, R. etc, 1992, Zhang, G.J., etc 1999).
Proceedings Papers
Publisher: Society of Petroleum Engineers (SPE)
Paper presented at the Fall Meeting of the Society of Petroleum Engineers of AIME, October 7–8, 1962
Paper Number: SPE-437-MS
... formation temperature SP coefficient spontaneous potential curve well logging correlation investigation Upstream Oil & Gas mud filtrate brine solution core plug determination log analysis water resistivity coefficient apparatus Formation Resistivity Factor Formation Water...
Abstract
Publication Rights Reserved Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and considered for publication in one of the two SPE magazines with the paper. Abstract A study has been made to try to improve the determination of water saturation of a given zone by use of the SP log. A method has been derived which appears to be an improvement in previous methods. Previous studies have shown that the formation water resistivity, a needed factor in the Archie equation for determining water saturation, is related to the magnitude of the SP deflection and to the mad filtrate resistivity by a coefficient which is a function of formation temperature. Evidence has indicated that this coefficient also varies with geographical location. An attempt was made to find a variable which would express this apparent variation in geographical location. The formation resistivity factor was selected and found to be satisfactory. The resulting empirical correlation relates the SP coefficient, formation temperature, and the formation resistivity factor. For the data used, this method produced results which were better than those of previous methods. An experimental study has been made which tends to confirm the trends and influences discovered in the empirical work. Introduction In order to calculate the formation water saturation using the familiar Archie equation, ................(1) the formation resistivity factor, F, the formation water resistivity, Rw, the true formation resistivity, Rt, and the saturation exponent, n, must all be determined or estimated. Values for Rw and Rt may be estimated by use of logs and correction and correlation charts. Values for F and n are usually determined from core analyses, or they may be estimated from logs and/or correlation charts. The accuracy of the estimated values of Rt, F, and n is usually 30%, but the approximated value of Rw is often in error by more than 100 percent. An incorrect assumption of Rw may lead to a very large error in Sw. Many times water resistivities can be measured from DST samples from the well in question or from the same zone in nearby wells.
Journal Articles
Journal:
Journal of Petroleum Technology
Publisher: Society of Petroleum Engineers (SPE)
Journal of Petroleum Technology 63 (05): 83–85.
Paper Number: SPE-0511-0083-JPT
Published: 01 May 2011
... Upstream Oil & Gas chemical composition log analysis breakthrough real-time measurement real time system waterflooding Brine te potential intelligent well inflow mineral surface SP signal gradient spontaneous potential water front reservoir electrode ek potential salinity saturation...
Abstract
This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 135146, ’Real-Time Measurements of Spontaneous Potential for Inflow Monitoring in Intelligent Wells,’ by M.D. Jackson, SPE, M.Y. Gulamali, E. Leinov, J.H. Saunders, and J. Vinogradov, Imperial College London, prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed. Spontaneous-potential (SP) signals are generated during hydrocarbon production because of gradients in the water-phase pressure (relative to hydrostatic), chemical composition, and temperature. Measurements of SP during production, taken with permanently installed downhole electrodes, could be used to detect water that is encroaching on a well while the water is several tens to hundreds of meters away. Introduction SP measurements, logged before production or injection using wireline tools, are primarily electrochemical (EC) in origin. Contrasts in chemical composition between formation and drilling fluids give rise to “junction” or “diffusion” potentials in permeable beds, while the exclusion of (typically) negative ions from the pore space of fine-grained rocks (e.g., mudstones and shales) results in “membrane” potentials. Together, these EC potentials typically dominate the SP log, although in some cases, electrokinetic (EK), or streaming, potentials, which arise from gradients in fluid pressure (relative to hydrostatic), also may contribute. However, gradients in fluid pressure, chemical composition, and temperature also will be present during hydrocarbon production, particularly during waterflooding or steamflooding where colder or hotter water of a chemical composition different from that of the formation brine is injected into the reservoir. Consequently, if the casing is either nonmetallic or is insulated electrically from the formation, SP signals will be observed during production. This study characterized the magnitude of these SP signals to determine if their measurement, using permanently installed downhole electrodes, might be useful in monitoring fluid flow. SP Components The SP acts to maintain overall electro-neutrality when a separation of electrical charge occurs in response to gradients in pressure, chemical composition, or temperature. In a water-wet reservoir rock, charge separation occurs at the mineral/water interface because the water reacts with the mineral surfaces to leave an excess of (typically) negative charge on the mineral surface and an excess of positive charge in the water adjacent to the mineral surface. This arrangement of charges at the mineral/water interface is known as the electrical double layer. The negative charge on the mineral surface is immobile, but some of the excess positive charge in the adjacent water is mobile and will move with the fluid. If the water is subjected to a pressure gradient, which causes it to flow relative to the mineral surfaces, then some of this positive charge is transported with the flow. The net excess of positive charge moving with the flow gives rise to a so-called streaming current. To balance this streaming current, a conduction current is established and the electrical potential required to maintain this conduction current is the EK, or (more specifically) streaming, potential. The term EK is used here for consistency with the terminology used to describe the EC and thermoelectric (TE) potentials.
Proceedings Papers
Paper presented at the SPWLA 50th Annual Logging Symposium, June 21–24, 2009
Paper Number: SPWLA-2009-65257
... Conventional Spontaneous Potential (SP) measurements are usually affected by many factors such as formation thickness, formation resistivity, mud resistivity, and borehole diameter. Because of these factors, the measured SP values could be much less than the Static SP (SSP) values and thus...
Abstract
Conventional Spontaneous Potential (SP) measurements are usually affected by many factors such as formation thickness, formation resistivity, mud resistivity, and borehole diameter. Because of these factors, the measured SP values could be much less than the Static SP (SSP) values and thus rendering the formation water resistivity determined from the SP inaccurate. This paper presents a new tool called Static SP Tool (SSPT) that can directly measure the SSP. SSP is the electrochemical potential consisting of the diffusion potential and membrane potential. Conventional SP measures the potential difference of the SSP on the mud column in the well. When the formation is very thick, the measured SP is close to the SSP because the mud column resistance is high enough to represent all the resistances in the SSP electric current loop. To directly measure the SSP, the conditions of large mud column resistances should be created in the real well situations. In order to simulate the condition of a large mud column resistance, a new sonde with an electrode array was designed. The electrodes consist of M0, M1, M2, A1, and A2, in which M0 is in the center and all others are symmetric pairs above and below the M0 electrode. The SSP current flowing through the mud inside the borehole creates a potential difference called Vm1m2 between M1 and M2. Based on the value of Vm1m2, the electronics inside the SSP tool supplies a current to the A1 and A2 electrode array. This current creates a potential between M1 and M2 having the same value and opposite polarity as Vm1m2 reducing the potential difference at M1 and M2 to zero. There is now no current flow between M1 and M2. In the other words, the virtually infinite large mud column resistance is simulated and the SP measured on M0 is very close to the SSP. The SSPT was tested in several oilfields in China. In one of the test wells that has complete coring data, the formation water salinities computed from the SSP curves are very close to the lab analysis data from the cores. The vertical resolution of the SSP curves is as thin as 30 cm. With the help of the Rw computed from the SSP curves, several bypassed thin oil-bearing zones were found from log interpretations. INTRODUCTION The SP measurements are affected by some other factors like true resistivity of the permeable formation, resistivity and invasion diameter of the mud filtration invaded zone, resistivity of the adjacent shale formation, resistivity of the mud; and borehole diameter (Schlumberger, Log Principles/Applications). When computing formation water resistivity (Rw) from conventional SP logging curves, we need to do some environmental corrections like borehole, formation thickness, and invasion (Schlumberger, Log Charts, Bissiouni, Zaki and Mathews, Diane M.). Therefore, the desired SP logging tool is to measure the equivalent SSP curves directly without the effects by these factors. Based on the SP measurement method (Schlumberger, Log Principles/Applications), the SP value is the electrical voltage drop on the mud column due to the SP current flow inside the borehole.
Journal Articles
Journal:
SPE Journal
Publisher: Society of Petroleum Engineers (SPE)
SPE Journal 17 (01): 53–69.
Paper Number: SPE-135146-PA
Published: 16 January 2012
... long been used to characterize reservoir properties such as permeable-bed boundaries and formation-brine resistivity ( Schlumberger et al. 1934 ; Mounce and Rust 1944 ; Doll 1948 ; Hallenburg 1971 ). The SP signal recorded during logging is primarily electrochemical (EC) in origin; contrasts in...
Abstract
Summary Spontaneous potential (SP) is routinely measured using wireline tools during reservoir characterization. However, SP signals are also generated during hydrocarbon production, in response to gradients in the water-phase pressure (relative to hydrostatic), chemical composition, and temperature. We use numerical modeling to investigate the likely magnitude of the SP in an oil reservoir during production, and suggest that measurements of SP, using electrodes permanently installed downhole, could be used to detect and monitor water encroaching on a well while it is several tens to hundreds of meters away. We simulate the SP generated during production from a single vertical well, with pressure support provided by water injection. We vary the production rate, and the temperature and salinity of the injected water, to vary the contribution of the different components of the SP signal. We also vary the values of the so-called "coupling coefficients," which relate gradients in fluid potential, salinity, and temperature to gradients in electrical potential. The values of these coupling coefficients at reservoir conditions are poorly constrained. We find that the magnitude of the SP can be large (up to hundreds of mV) and peaks at the location of the moving water front, where there are steep gradients in water saturation and salinity. The signal decays with distance from the front, typically over several tens to hundreds of meters; consequently, the encroaching water can be detected and monitored before it arrives at the production well. Before water breakthrough, the SP at the well is dominated by the electrokinetic and electrochemical components arising from gradients in fluid potential and salinity; thermoelectric potentials only become significant after water breakthrough, because the temperature change associated with the injected water lags behind the water front. The shape of the SP signal measured along the well reflects the geometry of the encroaching waterfront. Our results suggest that SP monitoring during production, using permanently installed downhole electrodes, is a promising method to image moving water fronts. Larger signals will be obtained in low-permeability reservoirs produced at high rate, saturated with formation brine of low salinity, or with brine of a very different salinity from that injected.
Journal Articles
Petrophysics - The SPWLA Journal of Formation Evaluation and Reservoir Description 36 (05).
Paper Number: SPWLA-1995-v36n5a3
Published: 01 September 1995
...). In addition, Figure 5 shows the SP excursion is much smaller in the more conductive solution than that measured in the resistive solution. In logging environments, this corresponds to the case of a freshwater 40 The Log Analyst September-October 1995 Spontaneous Potential: Laboratory Experiments and...
Abstract
The complex distribution of electrochemical sources in the borehole environment has historically limited the quantitative interpretation of spontaneous potential (SP) logs. In addition, SP models based on characterizations of these sources have been poorly validated because of the difficulty of generating realistic SP signals in controlled environments. In this article, we report on our SP experiments and models to address these problems. We describe a novel experimental technique for simulating SP signals in the laboratory. By placing synthetic, ion-selective membranes between aqueous saline solutions of different concentrations, we created source distributions that approximated those encountered by borehole logging tools in oilfield formations. Configurations of cation-selective and anion-selective membranes simulated cases of piston4ike invasion, sawtooth-shaped invasion, and no invasion of a sand zone flanked by two shale layers. We used these data to validate a forward model that represents SP sources as electrical double layers. Also, we devised an inversion scheme to estimate the transference numbers of the membranes (and hence their strengths as SP sources), assuming that their geometric distribution is known. Results from both the forward and inverse models agree with the experimental data. This suggests that these simple models could be successfully adapted to the analysis of SP field logs.
Journal Articles
Journal:
Neftyanoe khozyaystvo - Oil Industry
Publisher: Oil Industry Journal
Neftyanoe khozyaystvo - Oil Industry 2019 (10): 38–41.
Paper Number: OIJ-2019-10-038-041-RU
Published: 01 October 2019
...O. B. Kuzmichev; A. V. Zhonin; Yu. V. Martynova; S. A. Kolomasova The PDF file of this paper is in Russian. In layers of limited thickness and high resistance, the amplitude of the spontaneous potential (SP) logs differs significantly from the amplitude corresponding to the layer of unlimited...
Abstract
The PDF file of this paper is in Russian. In layers of limited thickness and high resistance, the amplitude of the spontaneous potential (SP) logs differs significantly from the amplitude corresponding to the layer of unlimited thickness. For a more accurate determination of reservoir properties by the SP method it is necessary to move from the apparent values of the curve to the static potential of the reservoir, that is, to solve the inverse problem. The article presents an analytical solution for a direct problem of the SP method in case of rocks in a well crossing an electrically inhomogeneous layer of limited thickness with a zone of drilling mud penetration. The analytical solution of a similar problem proposed by Schlumberger-Doll Research (M.R. Taherian, at al.) for an impenetrable formation in the absence of penetration zone is discussed. It is shown Schlumberger's solution is a subcase of the analytical solution regarded in present article. On the basis of the analytical solution of the direct problem the inverse problem of the SP method was solved taking into account the potentials of rock matrix. Solving the inverse problem in conjunction with the electric logging data is shown on the example of middle Cretaceous reservoirs (Achimov deposits) in Western Siberia. For this purpose we used algorithms of numerical solution of the direct problem in case of well crossing an electrically inhomogeneous layer of limited thickness with a zone of drilling mud penetration by the integro-interpolation method, and the analytical solution of the direct problem for a layer of limited thickness with regard to the potential of rock matrix. The results of numerical and analytical solutions of the inverse problem are almost identical. Proposed algorithms are intended to use in the Rosneft corporate software for petrophysical modeling.
Proceedings Papers
Publisher: Society of Petroleum Engineers (SPE)
Paper presented at the SPE Annual Technical Conference and Exhibition, September 19–22, 2010
Paper Number: SPE-135146-MS
... upstream oil & gas waterfront magnitude production well brine jackson sp signal Measurements of spontaneous potential (SP), logged prior to production or injection using wireline tools, have long been used to characterize reservoir properties such as permeable bed boundaries and formation...
Abstract
Spontaneous potential (SP) is routinely measured using wireline tools during reservoir characterization. However, SP signals are also generated during hydrocarbon production, because of gradients in the water phase pressure (relative to hydrostatic), chemical composition and temperature. We suggest that measurements of SP during production, using electrodes permanently installed downhole, could be used to detect water encroaching on a well while it is several tens to hundreds of meters away. We simulate numerically the SP generated during production from a single vertical well, with pressure support provided by water injection. We vary the production rate, and the temperature and salinity of the injected water, to vary the contribution of the different components of the SP signal. We also vary the values of the so-called ‘coupling coefficients’ which relate gradients in fluid potential, salinity and temperature, to gradients in electrical potential. The values of these coupling coefficients at reservoir conditions are poorly constrained. We demonstrate that the SP signal peaks at the location of the moving waterfront, where there are steep gradients in water saturation and salinity. The signal decays with distance from the front, typically over several tens to hundreds of meters; hence the encroaching water can be detected before it arrives at the well. The SP signal at the well is dominated by the electrokinetic and electrochemical components arising from gradients in fluid potential and salinity. Larger signals will be obtained in low permeability reservoirs produced at high rate, saturated with formation brine of low salinity, or with brine of a very different salinity from that injected.
Journal Articles
Petrophysics - The SPWLA Journal of Formation Evaluation and Reservoir Description 42 (03).
Paper Number: SPWLA-2001-v42n3a2
Published: 01 May 2001
... resistivity of a sample of water, calculation using a water saturation equa- tion (e.g., the Archie equation) in a nearby wet zone, or using the value of R, from a nearby well or field (assuming the water has the same properties), and calculation of R, from the spontaneous potential (SP) log. The conventional...
Abstract
Most engineers and geoscientists participating in petrophysics training programs dislike the chart book technique for deriving R, from the spontaneous potential log. This process can be done on a computer or calculator quite easily if the chart for converting R, to R,, (and the inverse conversion R,, to R,) is represented mathematically. Equations are presented in this paper that describe R, as function of R,, and temperature (and the inverse transformation R,, as a function of R, and temperature) which very closely match the curves in the Schlumberger chart SP-2. These equations can easily be utilized in a computer to calculate R, from the static spontaneous potential, temperature, and R,/ values for a formation. Sample functions written in Visual Basic are provided and can be used in an Excel spreadsheet or as an independent program on a Windows PC.
Journal Articles
Petrophysics - The SPWLA Journal of Formation Evaluation and Reservoir Description 39 (03).
Paper Number: SPWLA-1998-v39n3a4
Published: 01 May 1998
... Log Analysts Upstream Oil & Gas NMR log conductivity log analysis water saturation porosity log analyst shale Reconstruct SP Houston coates chemical activity saturation resistivity log well logging cec model filtrate clay mineral water-filled porosity interpretation...
Abstract
New nuclear magnetic resonance (NMR) measurements-such as inincralogy-free porosity, direct hydrocarbon volume and type, and clay-bound water and its tic to cation Exchange capacity (CEC)-have brought a new level of quality to log-derived water saturation, both in the flushed zone and in Virgin formation. However, the inversion of resistively logs Into water-filled porosity remains heavily dependent on formation water resistively on many occasions, the log analyst has no direct measure of and the R,,, estimate that the analyst must make can introduce a high degree of uncertainty in Subsequent calculations. Suchasituation led to a search for a method that could be used to help ensure high-quality R, selections. A method was found that integrated NMR and spontaneous potential (SP) measurements.
Journal Articles
Journal:
Journal of Petroleum Technology
Publisher: Society of Petroleum Engineers (SPE)
Journal of Petroleum Technology 24 (02): 151–153.
Paper Number: SPE-3570-PA
Published: 01 February 1972
... Spontaneous Potential (SP) Log. As implied by Gillingham, zonal differences between SP logs run in wells while they are shut in and during injection are related to flow rate. This technique has the sensitivity to profile most open-hole or fiber-glass-lined fresh water injection wells, but lacks the...
Abstract
SP logs recorded in a West Texas waterflood exhibited enough sensitivity to indicate zones taking fluids in open-hole wells and in wells lined with fiber glass. These surveys are logged both when the wells are shut in and during injection, and the difference in values is the electrokinetic component of the measurable spontaneous potential, which is proportional to the rate of flow into each zone. Introduction In waterfloods such as the Wasson flood in West Texas, uniform injection of water into all productive zones is essential to efficient oil recovery. Wells in the Wasson San Andres field penetrate more than 200 ft of stratified dolomite section. Premature flood breakthrough in a small part of this section can cause producing wells to water out after recovering only producing wells to water out after recovering only a fraction of the total oil reserves. Therefore, profile logs such as flowmeter logs, temperature logs and radioactive-tracer surveys are periodically, run in injection wells so that zones of high intake can be isolated and those of low intake can be selectively pumped into at higher rates, pumped into at higher rates, Conventional profile surveys, however, are generally not reliable in those old wells completed open hole, shot with nitroglycerin, and later cased with an uncemented fiber glass liner. Uncemented liner and hole-size effects confuse the profile interpretations. These problem wells are best surveyed using an unconventional profile tool, the Spontaneous Potential (SP) Log. As implied by Gillingham, zonal differences between SP logs run in wells while they are shut in and during injection are related to flow rate. This technique has the sensitivity to profile most open-hole or fiber-glass-lined fresh water injection wells, but lacks the quantitative accuracy of radioactive-tracer and flowmeter surveys. Field Operation The SP device is the simplest logging tool available. It is basically a recording voltmeter with one electrode lowered inside the wellbore and the other electrode grounded at the surface. In profile logging, the downhole electrode is usually lead, weighted with 10 to 20 ft of insulated sinker bars and machined to pass through 2-in. tubing. The surface equipment includes a standard SP logging panel. The surface electrode consists of a simple electrical connection to the iron wellhead. This round connection is stable and common to most injection wells. Detectable galvanic potentials associated with unlike electrodes (lead and potentials associated with unlike electrodes (lead and iron) are constant on all logging runs in a particular well and are unimportant. The first step in SP profile logging is to survey the well while injecting at a normal stable injection rate. Use of a lubricator allows entering the well without interrupting the flow. The well is surveyed while logging both up and down until the curves repeat within about 3 mv. Runs in one direction occasionally have less noise and drift than in the other direction. In addition, fast logging speeds - greater than 100 ft/ min reduce drift caused by the relative water motion past the down-hole electrode and also reduce the past the down-hole electrode and also reduce the probability of recording, spurious noise. In practice, probability of recording, spurious noise. In practice, the bottom few feet of hole are not logged. Sometimes electrically charged sediment on bottom attaches to the sonde, causing drift as it later washes off. The next step requires surveying the well while it is shut in and stablized. The well is sufficiently stable when the SP signal from a stationary sonde, positioned opposite a zone that was taking fluid, positioned opposite a zone that was taking fluid, stablizes. This zone is chosen from known data or picked by trial and error. picked by trial and error. JPT P. 151
Journal Articles
Journal:
Neftyanoe khozyaystvo - Oil Industry
Publisher: Oil Industry Journal
Neftyanoe khozyaystvo - Oil Industry 2016 (08): 20–24.
Paper Number: OIJ-2016-08-020-024-RU
Published: 01 August 2016
... podschetnykh parametrov na osnove sovmestnoy interpretatsii dannykh karotazha PS i elektrometodov GIS dlya starogo fonda skvazhin (In- tREst) (Determination of calculation parameters on the basis of the joint inter- pretation of SP logging and electrical methods data for old wells (IntREst Authors: Kuz'michev...
Abstract
The pdf file of this paper is in Russian. The problem of estimation of low-resistivity reservoirs volumetric data is considered. Low-resistivity reservoirs are oil and gas saturated ones, which true resistivity is below its critical value at the oil-water interface. During tests it is possible to obtain substantial oil or oil with water inflow from low-resistivity reservoirs, which by the results of well logging materials interpretation are defined as water-saturated. Bigradient (divergent) method of the spontaneous polarization logging is developed in KogalymNIPIneft Branch of LUKOIL-Engineering LLC in Tyumen. The method differs from the existing method of measuring the spontaneous potential by higher sensitivity to the resistance of part of layer, not changed by penetration of drilling fluid, and by higher resolving capacity along the axis of the well (interlayer stratification). Hardware-methodical complex allows to measure spontaneous potential with new scheme, the first and the second differences of the spontaneous potential - with divergent logging method of L.M. Alpin. The original method of an oil and gas saturation index estimating of structurally complicated, including low-resistivity, reservoirs is developed. Also the variant of oil and gas saturation index estimating according to the standard spontaneous polarization logging in the complex with the electric methods of borehole survey according to proposed method is provided for. The example of interpretation of low-resistivity oil-saturated reservoirs of Jurassic deposits of Maloklyuchevoye field of LUKOIL-West Siberia LLC is given.
Journal Articles
Journal:
Journal of Petroleum Technology
Publisher: Society of Petroleum Engineers (SPE)
Journal of Petroleum Technology 2 (07): 205–214.
Paper Number: SPE-950205-G
Published: 01 July 1950
... clean sand Computation drilling fluid management & disposal drilling fluid formulation salinity electromotive force boundary sand streak expression shaly sand pseudo-static sp resistivity variation mud filtrate potential drop connate water sp current T.P. 2912 THE SP LOG IN SHALY...
Abstract
As a continuation of the earlier paper on the general subject of the SP log, amore complete analysis of certain features of the SP log in shaly sands isgiven. The pseudo-static SP in front of shaly sands is compared, on atheoretical basis, to the static SP in front of clean sands, as a function ofthe respective amount of shale and sand in the formation, and of the relativeresistivities of the shale, of the uncontaminated part of the sand, and of theinvaded zone of the sand. As a conclusion, the advantage of using reasonably conductive mud in this caseis shown. The discussion is illustrated by field examples. Introduction The discussion reported in the present paper is based on a theoreticalanalysis, and not on experiment. The field examples, joined to the text, areshown only as qualitative illustrations of the essential results of thisanalysis. Although the hypotheses made in the theoretical developments mayperhaps be somewhat improved, it seems, nevertheless, that the results obtainedaccount reasonably well for the actual phenomena, and give a fair approximationof their order of magnitude. The paper contains a mathematical analysis of a tri-dimensional distribution ofpotentials and current lines, due to spontaneous electromotive forces arisingat the contact of shales and free electrolytes, as a function of the geometryand of the respective resistivities of the different media involved. It isassumed, although this hypothesis is not proven, that the emf's remain the sameeven if the shale occurs in very thin layers or in dispersed particles. It has already been pointed out that, all other conditions being the same, thedeflection of the SP log in front of a shaly sand is smaller than opposite aclean sand. When the thickness and the conductivity of a clean sand are largeenough, the deflection of the SP log reaches a limiting value which is equal tothe "static SP" of the clean sand. It is generally convenient to takethe static SP of shale as the reference value or "base line." As aconsequence, and for the sake of abbreviation, the expression, "static SPof a clean sand," is often used to designate the difference between thestatic SP of that sand and that of the shales, which difference is a measure ofthe total electromotive forces involved in the chain mud sand-shale. T.P. 2912
Proceedings Papers
Paper presented at the SPWLA 28th Annual Logging Symposium, June 29–July 2, 1987
Paper Number: SPWLA-1987-SS
... ABSTRACT In the early days of well logging the Spontaneous Potential (SP) log was used extensively by Interpreters to detect the presence of clean permeable zones and to estimate the potential of hydrocarbon prospects. Unfortunately, in today's modern formation evaluation programs, except for...
Abstract
ABSTRACT In the early days of well logging the Spontaneous Potential (SP) log was used extensively by Interpreters to detect the presence of clean permeable zones and to estimate the potential of hydrocarbon prospects. Unfortunately, in today's modern formation evaluation programs, except for well-to-well correlation and qualitative shaliness estimation, little use is made of the SP log. Some of the usual reasons for not taking full advantage of the SP measurement are:SP amplitude is reduced in thin beds. SP character at bed boundaries is affected by the resistivity and degree of invasion of permeable formations, as well as by the resistivity of adjacent impervious beds. SP amplitude is affected in shaly sands by the presence of laminated or dispersed clays. Despite progress made in our understanding of the electrochemistry of shaly sands, one major roadblock in a more quantitative use of the SP is still our inability to properly correct for thin-bed effects. A finite element method for the solution of Poisson's equation has been used to simulate the axisymmetric spatial distribution of the SP under various borehole and formation condition. The SP vertical profile calculated in this manner on the hole axis are compared with previous results obtained on a Resistor Network analog computer and extended to more complicated geometry. A deconvolution technique based on the solution to the forward problem has been optimized for the SP log in synergy with the resistivity profile derived from the new Phasor reduction tool and a precise delineation of the reservoir boundaries from microdevices. Examples of improvements in interpreting Gulf Coast shaly sand reservoirs are presented.
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