Effects of Surfactant-Emulsified Oil-Based Mud on Borehole Resistivity Measurements

SPE Journal ◽  
2011 ◽  
Vol 16 (03) ◽  
pp. 608-624 ◽  
Author(s):  
Jesús M. Salazar ◽  
Carlos Torres-Verdín ◽  
Gong Li Wang
Keyword(s):  
Electrical Resistivity ◽  
Spatial Distribution ◽  
Sensitivity Analyses ◽  
High Resistivity ◽  
Reliable Estimate ◽  
Spatial Distributions ◽  
Oil Viscosity ◽  
Resistivity Measurements ◽  
Fluid Saturation ◽  
Mud Filtrate

Summary We quantify the influence of oil-based mud (OBM)-filtrate invasion and formation-fluid properties on the spatial distribution of fluid saturation and electrical resistivity in the near-wellbore region. The objective is to appraise the sensitivity of borehole resistivity measurements to the spatial distribution of fluid saturation resulting from the compositional mixing of OBM and in-situ hydrocarbons. First, we consider a simple two-component formulation for the oil phase (OBM and reservoir oil) wherein the components are first-contact miscible. A second approach consists of adding water and surfactant to a multicomponent OBM invading a formation saturated with multiple hydrocarbon components. Simulations also include presence of irreducible, capillary-bound, and movable water. The dynamic process of OBM invasion causes component concentrations to vary with space and time. In addition, the relative mobility of the oil phase varies during the process of invasion because oil viscosity and oil density are both dependent on component concentrations. Presence of surfactants in the OBM is simulated with a commercial adaptive implicit compositional formulation that models the flow of three-phase multicomponent fluids in porous media. Simulations of the process of OBM invasion yield 2D spatial distributions of water and oil saturation that are transformed into spatial distributions of electrical resistivity. Subsequently, we simulate the corresponding array-induction measurements assuming axial-symmetric variations of electrical resistivity. We perform sensitivity analyses on field measurements acquired in a well that penetrates a clastic formation and that includes different values of density and viscosity for mud filtrate and formation hydrocarbon. These analyses provide evidence of the presence of a high-resistivity region near the borehole wall followed by a low-resistivity annulus close to the noninvaded resistivity region. Such an abnormal resistivity annulus is predominantly caused by high viscosity contrasts between mud filtrate and formation oil. The combined simulation of invasion and array-induction logs in the presence of OBM invasion provides a more reliable estimate of water saturation, which improves the assessment of in-place hydrocarbon reserves.

Quantitative comparison of processes of oil- and water-based mud-filtrate invasion and corresponding effects on borehole resistivity measurements

Geophysics ◽  
2009 ◽  
Vol 74 (1) ◽  
pp. E57-E73 ◽  
Author(s):  
Jesús M. Salazar ◽  
Carlos Torres-Verdín
Keyword(s):  
Electrical Resistivity ◽  
Flow Rate ◽  
Water Saturation ◽  
Base Case ◽  
Petrophysical Properties ◽  
Resistivity Measurements ◽  
Fluid Saturation ◽  
Mud Cake ◽  
Water Based ◽  
Mud Filtrate

Some laboratory and qualitative studies have documented the influence of water-based mud(WBM)-filtrate invasion on borehole resistivity measurements. Negligible work, however, has been devoted to studying the effects of oil-based mud(OBM)-filtrate invasion on well logs and the corresponding impact on the estimation of petrophysical properties. We quantitatively compare the effects of WBM- and OBM-filtrate invasion on borehole resistivity measurements. We simulate the process of mud-filtrate invasion into a porous and permeable rock formation assuming 1D radial distributions of fluid saturation and fluid properties while other petrophysical properties remain constant. To simulate the process of mud-filtrate invasion, we calculate a time-dependent flow rate of OBM-filtrate invasion by adapting the available formulation of the physics of WBM-filtrate invasion. This approach includes the dynamically coupled effects of mud-cake growth and multiphase filtrate invasion. Simulations are performed with a commercial adaptive-implicit compositional formulation that enables the quantification of effects caused by additional components of mud-filtrate and native fluids. The formation under analysis is 100% water saturated (base case) andis invaded with a single-component OBM. Subsequently, we perform simulations of WBM filtrate invading the same formation assuming that it is hydrocarbon bearing, and compare the results to those obtained in the presence of OBM. At the end of this process, we invoke Archie’s equation to calculate the radial distribution of electrical resistivity from the simulated radial distributions of water saturation and salt concentration and compare the effects of invasion on borehole resistivity measurements acquired in the presence of OBM and WBM. Simulations confirm that the flow rate of OBM-filtrate invasion remains controlled by the initial mud-cake permeability and formation petrophysical properties, specifically capillary pressure and relative permeability. Moreover, WBM causes radial lengths of invasion 15%–40% larger than those associated with OBM as observed on the radial distributions of electrical resistivity. It is found also that, in general, flow rates of WBM-filtrate invasion are higher than those of OBM-filtrate invasion caused by viscosity contrasts between OBM filtrate and native fluids, which slow down the process of invasion. Such a conclusion is validated by the marginal variability of array-induction resistivity measurements observed in simulations of OBM invasion compared with those of WBM invasion.

Pore-Scale Joint Evaluation of Dielectric Permittivity and Electrical Resistivity for Assessment of Hydrocarbon Saturation Using Numerical Simulations

SPE Journal ◽  
2016 ◽  
Vol 21 (06) ◽  
pp. 1930-1942 ◽  
Author(s):  
Huangye Chen ◽  
Zoya Heidari
Keyword(s):  
Electrical Resistivity ◽  
Spatial Distribution ◽  
Dielectric Permittivity ◽  
Pore Structure ◽  
Maximum Error ◽  
New Method ◽  
Pore Scale ◽  
Resistivity Measurements ◽  
Hydrocarbon Saturation ◽  
Permittivity Measurements

Summary Complex pore geometry and composition, as well as anisotropic behavior and heterogeneity, can affect physical properties of rocks such as electrical resistivity and dielectric permittivity. The aforementioned physical properties are used to estimate in-situ petrophysical properties of the formation such as hydrocarbon saturation. In the application of conventional methods for interpretation of electrical-resistivity (e.g., Archie's equation and the dual-water model) and dielectric-permittivity measurements [e.g., complex refractive index model (CRIM)], the impacts of complex pore structure (e.g., kerogen porosity and intergranular pores), pyrite, and conductive mature kerogen have not been taken into account. These limitations cause significant uncertainty in estimates of water saturation. In this paper, we introduce a new method that combines interpretation of dielectric-permittivity and electrical-resistivity measurements to improve assessment of hydrocarbon saturation. The combined interpretation of dielectric-permittivity and electrical-resistivity measurements enables assimilating spatial distribution of rock components (e.g., pore, kerogen, and pyrite networks) in conventional models. We start with pore-scale numerical simulations of electrical resistivity and dielectric permittivity of fluid-bearing porous media to investigate the structure of pore and matrix constituents in these measurements. The inputs to these simulators are 3D pore-scale images. We then introduce an analytical model that combines resistivity and permittivity measurements to assess water-filled porosity and hydrocarbon saturation. We apply the new method to actual digital sandstones and synthetic digital organic-rich mudrock samples. The relative errors (compared with actual values estimated from image processing) in the estimate of water-filled porosity through our new method are all within the 10% range. In the case of digital sandstone samples, CRIM provided reasonable estimates of water-filled porosity, with only four out of twenty-one estimates beyond 10% relative error, with the maximum error of 30%. However, in the case of synthetic digital organic-rich mudrocks, six out of ten estimates for water-filled porosity were beyond 10% with CRIM, with the maximum error of 40%. Therefore, the improvement was more significant in the case of organic-rich mudrocks with complex pore structure. In the case of synthetic digital organic-rich mudrock samples, our simulation results confirm that not only the pore structure but also spatial distribution and tortuosity of water, kerogen, and pyrite networks affect the measurements of dielectric permittivity and electrical resistivity. Taking into account these parameters through the joint interpretation of dielectric-permittivity and electrical-resistivity measurements significantly improves assessment of hydrocarbon saturation.

Rock quality assessment using the effect of mud-filtrate invasion on conflicting borehole resistivity measurements

Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. WA65-WA78 ◽  
Author(s):  
Jesús M. Salazar ◽  
A. Jeff Martin
Keyword(s):  
Wettability Alteration ◽  
Rock Properties ◽  
High Resistivity ◽  
Tight Gas ◽  
Resistivity Measurements ◽  
Rock Quality ◽  
Sandstone Reservoir ◽  
The Difference ◽  
Mud Filtrate ◽  
Tight Gas Sandstone

Unexpected borehole measurements are often inaccurately interpreted due to limited knowledge of the formation, particularly in tight-gas unconventional reservoirs. A novel method was applied to determine reservoir quality and the reliability of borehole array-induction resistivity measurements in a tight gas sandstone reservoir. Four exploration wells drilled with synthetic oil-based mud showed conflicting resistivity profiles. The discovery well showed a conductive invasion profile, but the appraisal wells showed resistive profiles. Simulation of oil-based mud-filtrate invasion was coupled with forward simulation and inversion of array-induction resistivity measurements to determine the difference in such resistivity profiles. Laboratory measurements on rock core and fluid samples were used to calibrate a log-based petrophysical model that was necessary to simulate the physics of fluid-flow mud-filtrate invasion. The dynamic process of invasion was simulated with a multicomponent formulation for the hydrocarbon phase and rock wettability alteration effects due to surfactants present in the mud. Simulated borehole-resistivity measurements were compared to field logs, and the rock properties were modified to secure a close agreement between simulated and field logs. The different invasion profiles corresponded to variable rock quality and mud composition. In the discovery well, good rock quality and thick surfactants in the mud caused a low mobility ratio between filtrate and native fluids, which created a water bank that moved ahead into the formation. This effect created a conductive annulus in the near-wellbore region. In turn, the deep invasion and high resistivity are due to excellent rock quality that is typical of a conventional sandstone reservoir. The shallower invasion and resistive profiles in the delineation wells suggest the tight gas sandstone reservoir we expected to find throughout the formation.

Enhanced Assessment of Fluid Saturation in the Wolfcamp Formation of the Permian Basin

2021 ◽  
Vol 62 (6) ◽  
pp. 737-751
Author(s):  
Sabyasachi Dash ◽  
◽  
Zoya Heidari ◽  
Keyword(s):  
Spatial Distribution ◽  
Water Saturation ◽  
Geometric Model ◽  
New Method ◽  
Model Parameters ◽  
Unique Contribution ◽  
Permian Basin ◽  
Resistivity Measurements ◽  
Fluid Saturation ◽  
Resistivity Model

Conventional resistivity models often overestimate water saturation in organic-rich mudrocks and require extensive calibration efforts. Conventional resistivity-porosity-saturation models assume brine in the formation as the only conductive component contributing to resistivity measurements. They also do not reliably assimilate the spatial distribution of the clay network and pore structure. Moreover, they do not incorporate other conductive minerals and organic matter, impacting the resistivity measurements and leading to uncertainty in water saturation assessment. We recently introduced a resistivity-based model that quantitatively assimilates the type and spatial distribution of all rock constituents to improve reserves evaluation in organic-rich mudrocks using electrical resistivity measurements. This paper aims to expand the application of this model for well-log-based assessment of water/hydrocarbon saturation and to verify the reliability of the introduced method in the Wolfcamp Formation of the Permian Basin. Our recently introduced resistivity model uses pore combination modeling to incorporate conductive (clay, pyrite, kerogen, brine) and nonconductive (grains, hydrocarbon) components in estimating effective resistivity. The inputs to the model are volumetric concentrations of minerals, conductivity of rock components, and porosity obtained from laboratory measurements or interpretation of well logs. Geometric model parameters are also critical inputs to the model. To simultaneously estimate the geometric model parameters and water saturation, we developed an inversion algorithm with two objectives: (a) to estimate the geometric model parameters as inputs to the new resistivity model and (b) to estimate the water saturation. The geometric model parameters are determined for each rock type or formation by minimizing the difference between the measured resistivity and the resistivity estimated from pore combination modeling. We applied the new method to two wells drilled in the Wolfcamp Formation of the Permian Basin. The formation-based inversion showed variation in geometric model parameters, which improved the assessment of water saturation. Results demonstrated that the new method improved water saturation estimates by 24.1% and 32.4% compared to Archie’s and Waxman-Smits models, respectively, in the Wolfcamp Formation. The most considerable improvement was observed in the Middle and the Lower Wolfcamp Formations, where the average clay concentration was relatively higher than the other zones. There was an additional 70,000 bbl/acre of hydrocarbon reserve using the proposed method compared to when water saturation was quantified using Archie’s model in the Permian Basin, which is a 33% relative improvement. It should be highlighted that the new method did not require any calibration effort using core water saturation measurements, which is a unique contribution of this rock-physics-based workflow.

scholarly journals Electrical resisitivity to detect zones of biogas accumulation in a landfill

2015 ◽  
Vol 54 (4) ◽  
Author(s):  
César Augusto Moreira ◽  
Thais Munhoz ◽  
Fernanda Cavallari ◽  
Lívia Portes Innocenti Helene
Keyword(s):  
Electrical Resistivity ◽  
Organic Matter ◽  
Oil And Gas ◽  
Biogas Production ◽  
High Resistivity ◽  
Resistivity Tomography ◽  
Resistivity Measurements ◽  
Sanitary Landfills ◽  
Surface Drains

Biogas produced in sanitary landfills consists in a potential source, formed by degradation of organic matter, this gas is constituted by CH4, CO2 and water vapor. Sanitary landfills represent important depository of organic matter with great energetic potential in Brazil, although presently with inexpressive use. Estimates for production or maintenance of productive rates of CH4 represent one of the main difficulties of technical order to the planning and continuity of collection systems for rational consumption of this resource. Electrical resistivity measurements are routinuously used in profiling oil wells for the determination of levels with accumulations of oil and gas, facing the contrast among fluids and rocks. This paper aims to evaluate eventual relationship among biogas flow quantified in surface drains of a waste cell in landfill, with characteristic patterns of in depth electrical resistivity. The integration of Electrical Resistivity Tomography (ERT) lines allowed for the generation of 3D blocks and a clear distinction among zones of high biogas production, quantified in surface drains, with areas of high resistivity in depth. The results suggest the possibility of use of the method in studies to place drains in areas promising to the collection of biogas for energetic generation in sanitary landfill.

Application of the pole‐dipole resistivity technique to the detection of solution cavities beneath highways

Geophysics ◽  
1986 ◽  
Vol 51 (3) ◽  
pp. 833-837 ◽  
Author(s):  
Douglas L. Smith
Keyword(s):  
Electrical Resistivity ◽  
Water Table ◽  
Strong Correlation ◽  
Country Rock ◽  
Electrode Array ◽  
High Resistivity ◽  
Switching System ◽  
Resistivity Measurements ◽  
Lower Electrical Resistivity

Using a multiconductor electrode cable and a 30‐post switching system, pole‐dipole electrical resistivity measurements with a linear electrode array demonstrated a strong correlation between resistivity anomalies and subsurface voids at four sites in Florida. Solution cavities below the water table are filled with a groundwater‐solute mixture which is characterized by a lower electrical resistivity than the enclosing country rock (Eocene and younger limestone). Air‐filled cavities above the water table exhibit markedly high‐resistivity anomalies. Confirmation drilling of postulated cavities and other anomalies suggests the method can be used with confidence for identification and location of highway‐threatening solution cavities with diameters as small as 3 to 5 m to a depth of 25 to 30 m.

Petrophysical inversion of borehole array-induction logs: Part I — Numerical examples

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. F101-F119 ◽  
Author(s):  
Faruk O. Alpak ◽  
Carlos Torres-Verdín ◽  
Tarek M. Habashy
Keyword(s):  
Salt Concentration ◽  
Sensitivity Study ◽  
Absolute Permeability ◽  
Spatial Distributions ◽  
Layer By Layer ◽  
Fluid Saturation ◽  
Phase Saturation ◽  
Porosity And Permeability ◽  
Mud Filtrate ◽  
Induction Logs

We have developed a new methodology for the quantitative petrophysical evaluation of borehole array-induction measurements. The methodology is based on the time evolution of the spatial distributions of fluid saturation and salt concentration attributed to mud-filtrate invasion. We use a rigorous formulation to account for the physics of fluid displacement in porous media resulting from water-base mud filtrate invading hydrocarbon-bearing rock formations. Borehole array-induction measurements are simulated in a coupled mode with the physics of fluid flow. We use inversion to estimate parametric 1D distributions of permeability and porosity that honor the measured array-induction logs. As a byproduct, the inversion yields 2D (axial-symmetric) spatial distributions of aqueous phase saturation, salt concentration, and electrical resistivity. We conduct numerical inversion experiments using noisy synthetic wireline logs. The inversion requires a priori knowledge of several mud, petrophys-ical, and fluid parameters. We perform a systematic study of the accuracy and reliability of the estimated values of porosity and permeability when knowledge of such parameters is uncertain. For the numerical cases considered in this paper, inversion results indicate that borehole electromagnetic-induction logs with multiple radial lengths of investigation (array-induction logs) enable the accurate and reliable estimation of layer-by-layer absolute permeability and porosity. The accuracy of the estimated values of porosity and permeability is higher than 95% in the presence of 5% measurement noise and 10% uncertainty in rock-fluid and mud parameters. However, for cases of deep invasion beyond the radial length of investigation of array-induction logging tools, the estimation of permeability becomes unreliable. We emphasize the importance of a sensitivity study prior to inversion to rule out potential biases in estimating permeability resulting from uncertain knowledge about rock-fluid and mud properties.

Predicting spatial distribution of heavy metals in agricultural soils using electrical resistivity tomography technique 2D-ERT

2020 ◽  
Author(s):  
Nesrine Chaali ◽  
Daniel Bravo ◽  
Sofiane Ouazaa ◽  
Jose Isidro Beltrán Medina ◽  
Javier Benavides
Keyword(s):  
Heavy Metals ◽  
Electrical Resistivity ◽  
Spatial Distribution ◽  
Pearson Correlation ◽  
Chemical Properties ◽  
Soil Chemical Properties ◽  
Resistivity Tomography ◽  
Resistivity Measurements ◽  
Geophysical Techniques ◽  
Cd Distribution

<p>Increasing consideration is being placed on the environmental impact of soil contamination with heavy metals (HM), especially in productive agricultural areas. So, a key task is to characterize this contamination qualitatively and quantitatively in order to understand the spatial distribution of HM and decide about the adequate management. Traditional sampling to monitor HM distribution is time, cost-consuming and often unrepresentative. Additionally, sparse and punctual data measurements may not allow understanding the real dynamic of HM in the soil profile, and in many cases the collected data fails in providing the needed information. Recently, in-situ geophysical techniques based on electrical resistivity tomography measurements (ERT) were implemented in agriculture as a “proxy” to determine spatial and temporal distribution of HM. The objective of this study was to provide an accurate information for future efficient measures of soil remediation, by understanding the HM distribution, specifically cadmium (Cd) and arsenic (As), using electrical resistivity measurements combined with soil chemical analyses. A UNI-T UT523A devise was used in a “Wenner Alpha” configuration to perform ERT survey at 2 m depth in nine locations of Tolima department-Colombia. 2D-ERT cross sections “Tomograms” were obtained by the Res2Dinv software which allowed characterizing qualitatively the spatial distribution of Cd and As. Chemical concentration values for both Cd (0.36±0.06 mg.kg<sup>-1</sup>) and As (3.00±0.28 mg.kg<sup>-1</sup>) were introduced in the inverse modelling procedure as a solution to provide an easier and reliable alternative to determine the shape, size, and path of the likely electrical resistivity distribution of the studied HM. Tomograms revealed that Cd distribution was mainly observed in deeper soil profile (0.80 m), while As was observed basically in shallower soil layers (0.45 m). Higher electrical resistivity values (330–48000 Ω m) correspond to Cd distribution and lower electrical resistivity values (138-291 Ω m) are related to As distribution. A high positive Pearson correlation (ρ) between electrical resistivity measurements and soil chemical properties (for Cd and As content) was obtained for the nine locations; ρ values of 0.97 and 0.98 were obtained for Cd and As; respectively. A linear regression was performed between ERT measurements and Cd and As contents; (R<sup>2</sup>=0.94, RMSE=0.33) and (R<sup>2</sup>=0.97 RMSE=0.18) for Cd and As; respectively. The results underlie the utility of the combined geophysical techniques, based on electrical resistivity measurements, and soil chemical properties to improve the understanding of HM dynamic.</p><p><strong>Key words</strong>: Geophysical techniques, tomograms, heavy metals, soil chemical properties, spatial distribution, Pearson correlation.</p>

In-situ electrical-resistivity measurements in the high-voltage electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 68-69
Author(s):  
W. E. King
Keyword(s):  
Electrical Resistivity ◽  
Electron Microscope ◽  
High Voltage ◽  
Resistivity Measurements ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
High Voltage Electron ◽  
Wide Range ◽  
Helium Gas

A side-entry type, helium-temperature specimen stage that has the capability of in-situ electrical-resistivity measurements has been designed and developed for use in the AEI-EM7 1200-kV electron microscope at Argonne National Laboratory. The electrical-resistivity measurements complement the high-voltage electron microscope (HVEM) to yield a unique opportunity to investigate defect production in metals by electron irradiation over a wide range of defect concentrations.A flow cryostat that uses helium gas as a coolant is employed to attain and maintain any specified temperature between 10 and 300 K. The helium gas coolant eliminates the vibrations that arise from boiling liquid helium and the temperature instabilities due to alternating heat-transfer mechanisms in the two-phase temperature regime (4.215 K). Figure 1 shows a schematic view of the liquid/gaseous helium transfer system. A liquid-gas mixture can be used for fast cooldown. The cold tip of the transfer tube is inserted coincident with the tilt axis of the specimen stage, and the end of the coolant flow tube is positioned without contact within the heat exchanger of the copper specimen block (Fig. 2).

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