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The relations among the resistivity, elastic-wave velocity, porosity, and permeability in Fontainebleau sandstone samples from the Ile de France region, around Paris, France were experimentally revisited. These samples followed a permeability-porosity relation given by Kozeny-Carman’s equation. For the resistivity measurements, the samples were partially saturated with brine. Archie’s equation was used to estimate resistivity at 100% water saturation, assuming a saturation exponent, . Using self-consistent (SC) approximations modeling with grain aspect ratio 1, and pore aspect ratio between 0.02 and 0.10, the experimental data fall into this theoretical range. The SC curve with the pore aspect ratio 0.05 appears to be close to the values measured in the entire porosity range. The elastic-wave velocity was mea-sured on these dry samples for confining pressure between 0 and . A loading and unloading cycle was used and did not produce any significant hysteresis in the velocity-pressure behavior. For the velocity data, using the SC model with a grain aspect ratio 1 and pore aspect ratios 0.2, 0.1, and 0.05 fit the data at ; pore aspect ratios ranging between 0.1, 0.05, and 0.02 were a better fit for the data at . Both velocity and resistivity in clean sandstones can be modeled using the SC approximation. In addition, a linear fit was found between the P-wave velocity and the decimal logarithm of the normalized resistivity, with deviations that correlate with differences in permeability. Combining the stiff sand model and Archie for cementation exponents between 1.6 and 2.1, resistivity was modeled as a function of P-wave velocity for these clean sandstones.
- North America > United States (1.00)
- Europe > France > Île-de-France > Paris > Paris (0.24)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.48)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Laboratory Measurements of Resistivity And Velocity For Fontainebleau Sandstones.
Gomez, Carmen T. (Stanford University, Currently Shell Exploration and Production Company) | Dvorkin, Jack (Stanford University, Currently Shell Exploration and Production Company) | Vanorio, Tiziana (Stanford University, Currently Shell Exploration and Production Company)
Summary The objective of this study was to experimentally revisit the relations among the resistivity, elastic-wave velocity, porosity, and permeability in Fontainebleau sandstone samples from the Ile de France region, around Paris, France. In our resistivity measurements, we partially saturated the samples with brine. We used Archie’s equation to estimate resistivity at 100% water saturation, assuming a saturation exponent of 2. Using self-consistent approximations (SC) modeling with grain aspect ratio 1, and pore aspect ratio between 0.02 and 0.10, the experimental data fall into this theoretical range. The SC curve with the pore aspect ratio 0.05 appears to be close to the values measured in the entire porosity range. We also measured elastic-wave velocity on these dry samples for confining pressure between 0 and 40 MPa. We used a loading and unloading cycle and did not find any significant hysteresis in the velocity-pressure behavior. For the velocity data, using the self-consistent model with a grain aspect ratio 1 and pore aspect ratios 0.2, 0.1, and 0.05 fit our data at 40 MPa, while pores aspect ratios ranging between 0.1, 0.05, and 0.02 are a better fit for the data at 0 MPa. Both velocity and resistivity in clean sandstones can be modeled using SC approximation. In addition, we found a linear fit between the P-wave velocity and the decimal logarithm of the normalized resistivity, with deviations that correlate with differences in permeability. Introduction Velocity and resistivity of rocks depend on porosity, texture, mineralogy, and pore fluid. Studies by Wyllie et al. (1956, 1958) showed that porosity is the primary factor affecting P- and S- wave velocities. Later studies (Nur and Simmons, 1969; Domenico, 1976; Mavko, 1980; Murphy, 1984) have refined our understanding of rock properties showing how pore type and pore fluid distribution (i.e., saturation heterogeneity) may contribute to variations in the P- and S- wave velocities. Pore geometry, in particular, affects pore stiffness which, in turn, influences the velocity sensitivity to pressure (Mavko, 1980; Mavko and Nur, 1978; O’Connell and Budiansky, 1974) as well as to saturation (Mavko and Mukerji, 1995). In this study, we measure porosity, resistivity and velocity in Fontainebleau sandstones. We examine the porosity and resistivity relation using effective medium models, such as differential effective medium (DEM) (Bruggeman, 1935; Berryman, 1995) and self consistent (SC) (Landauer, 1952; Berryman, 1995), and a semi-empirical model by Archie (1942). We follow a similar procedure for P- and S-wave velocities as a function of porosity, using effective medium models, including also DEM and SC, and semi-empirical models, including the stiff sand model (Gal et al., 1998), the Raymer-Hunt-Gardner relation (Raymer et al., 1980), and Wyllie’s time-average equation (Wyllie et al., 1958). Elastic and electrical methods can contribute in different ways to characterizing rock. We examine the relation between resistivity and velocity. Both properties in this study were not measured in the same pressure, temperature, and saturation conditions due to limitations in the laboratory setups; therefore, the derived cross-property relations must be used with caution.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geophysics > Seismic Surveying > Seismic Processing (0.76)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.48)
Carbonate rocks have major economic significance; 60% of the world's oil reserves lie in carbonate reservoirs and the potential for additional gas reserves is huge. However, the relationship in carbonates between measured geophysical data and rock properties is complex, due to the large variety of textures that arise during postdepositional diagenesis and to the chemical processes (i.e., dissolution and replacement by newly formed phases) that characterize carbonate-forming minerals. Most experimental and theoretical rock physics research has focused on siliciclastic and shaly rocks. However, applying insights gained from clastics to carbonates is rarely straightforward, and thus is questioned in the literature.
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline (1.00)
Abstract We worked to establish relationships among porosity, permeability, resistivity, and elastic wave velocity of diagenetically altered sandstone. Many such relationships are documented in the literature; however, they do not consider diagenetic effects. Combining theoretical models with laboratory measured data, we derived mathematical relationships for porosity permeability, porosity velocity, porosity resistivity, permeability velocity, velocity resistivity, and resistivity permeability in diagenetically altered sandstone. The effects of clay and cementation were evaluated using introduced coefficients in these relationships. We found that clean sandstone could be modeled with Kozeny’s relation; however, this relationship broke down for clay-bearing and diagenetically altered sandstone. Porosity is the first-order parameter that affects permeability, electrical, and elastic properties; clay and cement cause secondary effects on these properties. Rock physics modeling results revealed that cementation had a greater effect on elastic properties than electrical properties and clay had a larger effect on electrical properties than elastic properties. The relationships we provided can greatly help to determine permeability, resistivity, and velocity from porosity and to estimate permeability from resistivity and velocity as well as to determine resistivity from velocity measurements.
- North America > United States (0.68)
- Europe > Norway (0.48)
- Europe > United Kingdom (0.47)
- Europe > Denmark > North Sea (0.29)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate > Phyllosilicate (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Europe > United Kingdom > North Sea > North Sea > Northern North Sea > South Viking Graben > Block 16/28 > Andrew Field (0.99)
- Europe > United Kingdom > North Sea > North Sea > Northern North Sea > South Viking Graben > Block 16/27a > Andrew Field (0.99)
- Europe > United Kingdom > North Sea > Central North Sea > Northern North Sea > South Viking Graben > Block 16/28 > Andrew Field (0.99)
- (5 more...)
Summary Carbonate rocks are important hydrocarbon reservoir rocks, characterized by a wide range of facies, porosity, and rock fabric. Such a complexity challenges a proper prediction of reservoir properties from remote seismic surveys. We started a comprehensive laboratory study on carbonate rocks to understand how physical properties such as mineralogy, pore shape, porosity, pore connectivity, fluid type, and pressure control seismic wave propagation. Such an understanding helps to delineate failures of seismic property predictions in these rocks. We built a database of hydraulic, transport, and acoustic properties of carbonate samples capturing a broad variability of lithofacies and depositional environments. This paper focuses on how mineralogical composition and microstructure affect porosity-velocity trends as well as pressure-velocity sensitivity. Results show that carbonates may not be as homogeneous as often reported in the literature: such heterogeneity controls the elastic behavior of carbonate rocks affecting both the velocity-porosity trend and the elastic input parameters to be used while modeling the seismic response. Furthermore, acoustic measurements under variable pressure show that carbonates experience anelastic deformation which, together with pore shape, controls velocity sensitivity to pressure. Introduction Understanding the controls on petrophysical properties of carbonates is a key issue for interpreting and predicting changes in seismic images and acoustic log. Studying the effect of porosity, fluid and pore type on velocity as well as its sensitivity to pressure is fundamental to assessing the magnitude of velocity changes in 4D seismic, calculating impedance models for synthetic seismic, and evaluating velocity sensitivity in fluid-substitution problems. Past experimental and theoretical rock physics research has focused mostly on siliciclastic and shaly rocks (see Nur and Wang, 1989; Wang and Nur, 1992; Wang and Nur, 2000, for a comprehensive review). The applicability of these findings to carbonates is often questioned. Unlike siliciclastic rocks, carbonates generally show 1) a heterogeneous pore system which affect pore compressibility and in turn, rock sensitivity to saturation (Wang, 1997; Mavko and Mukerji, 1995), 2) rock-fluid chemical interactions which affect diagenesis and modify pore space and permeability. Yet, carbonates are considered to show a smaller compositional variation predominantly calcite and dolomite (Adam et al., 2006; Assefa et al., 2003; Vissapragada et al., 2001; Anselmetti and Eberli, 1997). Results from laboratory studies (Baechle et al., 2005; Eberli et al., 2003; Anselmetti and Eberli, 1997; Wang, 1997; Rafavich et al, 1984) have shown that porosity and pore type are the two factors mainly controlling the seismic response in carbonate reservoirs. In agreement with both Wang et al. (1997) and Rafavich et al. (1984), Eberli et al. (2003) emphasize that the acoustic properties of carbonates strongly depend on porosity. Nevertheless, their measured values show a large scatter around the mean velocityporosity trend. Such scatter, introduces significant uncertainty when inverting seismic data for porosity or composition. Eberli et al. (2003) and Anselmetti and Eberli (1997) relate this scatter to pore type. Pore type and thus, pore compressibility which affect high-frequency effects, is also believed to be determinant for the poor applicability of Gassmann’s relation.
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.48)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling (0.49)
- Geophysics > Seismic Surveying > Seismic Processing (0.35)