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GoChen, Ganglin (ExxonMobil Upstream Research Co.) | Chu, Dez (ExxonMobil Upstream Research Co.) | Zhang, Jie (ExxonMobil Upstream Research Co.) | Xu, Shiyu (ExxonMobil Upstream Research Co.) | Payne, Michael A. (ExxonMobil Upstream Research Co.) | Adam, Ludmila (Colorado School of Mines) | Soroka, William L. (ADCO)

New measurements of P- and S-wave velocity dispersion in carbonate reservoir rocks from seismic (<100Hz) to sonic (~10kHz) and ultrasonic (~1MHz) frequencies were analyzed to derive the frequency-domain intrinsic attenuation spectrum. Three rock samples were analyzed, all with porosity in the same range: one sample had high permeability and two had low permeability. We used the standard linear solid model to describe the twin relationship between velocity dispersion and attenuation. The analysis led to the following observations:

- P-wave attenuation (1/Qp) and S-wave attenuation (1/Qs) are similar in each of the frequency bands(seismic, sonic, ultrasonic): 1/Qp ~ 1/Qs;
- The attenuation spectrum in each frequency band has an associated characteristic relaxation distance;
- For a given carbonate reservoir rock, attenuation in the ultrasonic frequency band can be ''anomalously'' high (Q~1) but still be “normal” (Q~10-100) in the seismic frequency band.

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Relating seismic wave velocity and maturity in organic-rich shale is still a fundamental issue in the study of organicrich rocks. We found that the inception of the maturity peak -expressed in terms of vitrinite reflectance- (Ro % = 0.65) separates the pressure-dependent anisotropic behavior of organich-rich rocks in two domains: for maturities less than 0.65 (from immature to peak mature rocks), rocks exhibit a low pressure-sensitivity (velocity and anisotropy) but increasing magnitude of anisotropy with increasing Ro%; for maturities greater than 0.65, rocks show an higher sensitivity of velocity to pressure and decreasing magnitude of anisotropy. To start understanding the role of maturation processes and how the spatial arrangement of kerogen could control the elastic properties of these rocks, we complemented traditional rock-physics measurements with the analysis of images obtained using confocal laser scanning microscopy. This latter represents a suitable technique to image organic matter yielding relevant inputs for rock-physics computational analysis.

analysis, anisotropy, Figure, fluorescence, function, image, kerogen, maceral, maturation, maturity, pressure, property, rock, sample, seismic modeling, sensitivity, shale, velocity, vitrinite, vitrinite reflectance

SPE Disciplines:

In present paper we analyze five different thresholding schemes for obtaining the CT scan images of rock to binary images which can be utilized for different property simulation. Riddler''s and Otsu''s methods gave the maximum classification efficiency for the rock samples used. Sensitivity analysis was conducted to assess the impact of change of thresholds on simulated properties like porosity, permeability and formation factor. It showed a consistency in the inter-relation between different properties for different thresholds.

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.51)

Bächle, Gregor (University of Miami) | Eberli, Gregor (University of Miami) | Madadi, Mahyar (Australian National University) | Sok, Rob (Australian National University) | Knackstedt, Mark A. (Australian National University) | Arns, Christoph (Australian National University) | Latham, Shane (Australian National University) | Sheppard, Adrian P. (Australian National University)

Carbonate rocks are extremely diverse and their pore spaces complex and heterogeneous. Large uncertainties in the petrophysical properties of carbonates are due to wide variations in pore type, pore shape and interconnectivity. Petrophysical properties such as acoustic velocity and permeability are directly correlated to the amount and type of porosity, the dominant feature size and the interconnectivity of different porosity types. Accurately measuring these attributes requires the quantitative 3D analysis of the pore structure of carbonates. In this abstract we describe the imaging and analysis of two types of carbonate core; a set of vuggy, recrystallized dolostones and a set of oomoldic limestones. The structure and topology of the pore space is accurately determined via micro-CT analysis and the porosity consistent with experimental data. Acoustic velocity-porosity, pore connectivity and porosity permeability relationships are derived directly on the image data via numerical simulation and compared with measured data on the same rock. Acoustic velocity:porosity trends are good. Pore structural properties (pore size, aspect ratios, pore and throat shape and connectivity) are determined. The correlations between pore geometry and topology and elastic and flow properties can now be directly probed in a systematic manner. Three dimensional imaging and analysis of carbonate core material can provide a basis for more accurate petrophysical modeling and improve carbonate reservoir characterization.

Many studies have demonstrated the importance of the pore structure in carbonates on petrophysical properties (e.g. Anselmetti and Eberli (1993); Kumar and Han (2004); Rossebo et al. (2005)). Traditional pore type classifications describe the pore structures but fail to quantify the pore system for correlations to the rock''s physical properties. In order to quantitatively describe 2-D pore size, pore surface roughness, aspect ratio, and pore network complexity in carbonates a digital image analysis (DIA) methodology was developed that produces repeatable quantitative pore shape parameters. Each of these quantitative parameters describes a certain aspect of the pore shape. When these parameters are compared to acoustic data, the two DIA parameters that capture the pore complexity and the pore size plus the amount of microporosity prove to be the most influential for the acoustic behavior of the samples. Each of these parameters explains about 60% of the variations in velocity at similar porosity ( Bächle et al. (2004); Weger (2006)). These 2D studies have added much to the understanding of the influence of the pore structure on acoustic properties, yet their 2D nature is a limiting factor for a comprehensive mathematical treatment of pore shapes in simulations of acoustic properties.

There is now an opportunity to image and characterise the pore structure of carbonate cores in 3D. This is based on coupling high resolution x-ray micro-tomography and high end computational software methods including visualizing core material at the pore scale in 3D, measuring structural properties and directly predicting physical properties directly from digitised 3D images ( Arns et al. (2005)). In parallel with 3D experimental techniques one can probe higher resolutions using scanning electron microscopy (SEM);

SPE Disciplines:

The sampling requirements for seismic data are determined by the desired resolution, both temporally and spatially. As essentially all seismic data recorded at this time are sampled discretely, a further consideration is the number of bits used to represent each sample. This paper describes methods for sampling and bit allocation to reduce the CPU and disk resources needed in seismic data processing, and at the same time preserving a high level of signal fidelity. The variable bit allocation method is completely general, while the variable bandwidth sampling method is best adapted to the imaging applications.

bandwidth, bit, bit allocation, compression, data, difference, equation, fidelity, Figure, frequency, interpolation, meeting, method, number, reference, sample, seg las vegas, time, window

SPE Disciplines:

In general speaking, the porosity obtained by nuclear magnetic resonance (NMR) measurement is independent of lithology. However, when the matrix has paramagnetic impurity, such as hematite which is one of the paramagnetic mineralogy of the matrix in volcanic rock, the NMR measurement results will be influenced by the internal magnetic field induced by the matrix paramagnetic mineralogy. In the paper NMR transverse relaxation time T2 of the volcanic breiccia samples have been measured with different echo spacing. The experimental results show that T2 measurement is strongly dependent of echo spacing because of internal magnetic field induced by paramagnetic impurity of the matrix, and it also has an obvious impact on NMR porosity.

Breccia, diffusion, effect, field, Figure, formation evaluation, impurity, matrix, measurement, NMR, NMR measurement, pore, porosity, relaxation, relaxation time, resonance, rock, sample, Susceptibility, well logging

Oilfield Places:

- Asia > China > Xinjiang Uyghur Autonomous Region > Junggar basin (0.99)
- Asia > China > South China Sea > China Basin (0.97)

SPE Disciplines: Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)

Elastic moduli of water saturated sedimentary rocks have in some cases been found to be lower than what would be expected from Gassmann-substitution of moduli for rocks in the dry state, Such water weakening of elastic moduli of carbonate sedimentary rocks may be discussed by effective medium modeling. In the present case we use the isoframe model, which is based on upper Hashin- Shtrikman bounds for mixtures of a stiff carbonate frame and a suspension of carbonate particles in fluid. The proportion of carbonate in the frame is given as the iso-frame value ranging from zero to one. We model ultrasonic compressional wave and shear wave data for dry and water saturated samples from a range of geological settings. Our modeling indicates that water weakening is related to permeability. Samples with permeability up to 1 mD have relatively high water weakening possibly as a consequence of fluid interaction with the relatively frequent crystal contacts in the low-permeability samples. For samples with permeability above 100 mD we rather find a stiffening of water saturated samples. This may be a dispersion effect, as high permeability and high frequency may cause the water in the water saturated samples to move out of phase with the solid during propagation of the sonic wave and thus cause a stiffening effect.

Oilfield Places: Europe > Denmark > North Sea > Danish Sector > Block DK 5604/29 > South Arne Oil and Gas Field (0.99)

The Exponentially Weighted Recursive Least Squares (EWRLS) method is adopted to estimate adaptive prediction filters for F-X seismic interpolation. Adaptive prediction filters are able to model signals where the dominant wave-numbers are varying in space. This concept leads to a F-X interpolation method that does not require windowing strategies for optimal results. Synthetic and real data examples are used to illustrate the performance of the proposed adaptive F-X interpolation method.

Spitz (1991) introduced a seismic trace interpolation method that utilizes prediction filters in the frequency-space (F-X) domain. Spitz''s algorithm is based on the fact that linear events in time-space (T-X) domain map to a superposition of complex sinusoids in the F-X domain. Complex sinusoids can be reconstructed via prediction filters (autoregressive operators); this property is used to establish a signal model for F-X interpolation (Spitz, 1991) and F-X random noise attenuation (Canales, 1984; Soubaras, 1994; Sacchi and Kuehl, 2000). Spitz (1991) showed that prediction filters obtained at frequency f can be used to interpolate data at temporal frequency 2 f . Prediction filters estimated from the low-frequency (alias-free) portion of the data are used to interpolate the high-frequency (aliased) data components. Several modifications to Spitz''s prediction filtering interpolation have been proposed. For instance, Porsani (1999) proposed a half-step prediction filter scheme that makes the interpolation process more efficient. Gulunay (2003) introduced an algorithm with similarities to F-X prediction filtering with a very elegant representation in the frequencywavenumber F-K domain. Recently, Naghizadeh and Sacchi (2007) proposed a modification of F-X interpolation that allows to reconstruct data with gaps.

Seismic interpolation algorithms depend on a signal model. F-X interpolation methods are not an exception to the preceding statement; they assume data composed of a finite number of waveforms with constant dip. This assumption can be validated via windowing. Interpolation methods driven by, for instance, local Radon transforms (Sacchi et al., 2004) and Curvelet frames (Herrmann and Hennenfent, 2008) assume a signal model that consists of events with constant local dip. In addition, they implicitly define operators that are local without the necessity of windowing. This is an attractive property, in particular, when compared to non-local interpolation methods (operators defined on a large spatial aperture) where optimal results are only achievable when seismic events match the kinematic signature of the operator. Examples of the latter are interpolation methods based on the hyperbolic/ parabolic Radon transforms (Darche, 1990; Trad et al., 2002) and migration operators (Trad, 2003).

As we have already pointed out, F-X methods require windowing strategies to cope with continuous changes in dominant wave-numbers (or dips in T-X). In this article we propose a method that avoids the necessity of spatial windows. The proposed interpolation automatically updates prediction filters as lateral variations of dip are encountered. This concepts can be implemented in a somehow cumbersome process that requires classical F-X interpolation in a rolling window. In this paper we have preferred to use the framework of recursive least squares (Honig and Messerschmidt, 1984; Marple, 1987) to update prediction filters in a recursive fashion.

algorithm, data, example, Figure, frequency, interpolation, interpolation method, meeting, method, operator, prediction, prediction filter, result, sample, Spitz, time, Trace number

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Lebedev, Maxim (Curtin University of Technology) | Gurevich, Boris (Curtin University of Technology) | Toms, Juliana (Curtin University of Technology) | Clennel, Ben (CSIRO-petroleum) | Pervukhina, Marina (CSIRO-petroleum) | Mueller, Tobias (University of Karlsruhe)

Ultrasonic velocities and fluid saturations are measured simultaneously during water injection into sandstone core samples. The experimental results obtained on lowpermeability samples show that at low saturation values the velocity-saturation dependence can be described by the Gassmann-Wood relationship. However, with increasing saturation a sharp increase of P-wave velocity is observed, eventually approaching the Gassmann-Hill relationship. We relate this transition behavior to the change of the fluid distribution characteristics inferred from CT scans. In particular, we show that for relatively large fluid injection rate this transition occurs at smaller degrees of saturation as compared with high injection rate.

Oilfield Places:

- Oceania > Australia > Victoria > Otway Basin (0.99)
- Oceania > Australia > South Australia > Otway basin (0.99)

Tutuncu, Azra (Shell Exploration and Production Company) | Rojas, Maria Alejandra (University of Houston) | Castagna, John (University of Houston) | Krishnamoorti, Ramanan (University of Houston) | Han, De Hua (University of Houston)

Summary

Visco elastic measurements of four heavy and extra-heavy oil samples were carried out to analyze the dependence of complex viscosity, loss and storage modulus with temperature and frequency. The dynamic rheological tests showed a shear thinning phenomenon typical of non- Newtonian fluids, highly pronounced for seismic and sonic frequencies and for temperatures below 50°C. The Power- Law method that explains the shear thinning behavior was modified to incorporate the liquid crystal theory and the viscosity dependence on temperature based on the concept of activation energy. An expression was derived to predict complex viscosity based on frequency and temperature changes.

Introduction

The need to characterize fluid flow properties of unconventional reservoirs, such as heavy and extra-heavy oils, has increased significantly in the last few years. Heavy oil properties are particularly dependent on frequency and temperature changes. According to its rheological properties, it can be considered a Non-Newtonian viscoelastic fluid, which means shear stress and shear strain rate are not linearly correlated. Since such materials have an elastic component, they are able to support shearing. Previous ultrasonic measurements have shown that shear wave velocity dispersion might be significant for heavy oils at in-situ conditions. Velocity dispersion (for P- and S waves) seems to be negligible for heavy oils in the liquid and glass (elastic) phases (Han et al., 2007).

There have been numerous studies in the past on crude oils concerning the shear-thinning (complex viscosity decrease as shear strain rate increases) behavior obeying the Power- Law model at reservoir temperatures (Wang et al., 2006). Above a certain temperature, sometimes called the liquid point temperature (Han et al., 2006), heavy oil becomes Newtonian and viscosity becomes independent of the shear strain rate (or frequency).

This paper aims to model the shear thinning behavior of heavy oil at a given temperature as frequency increases by using the concept of activation energy of the Arrhenius equation and liquid crystal theory. Laboratory measurements of the viscoelastic properties of four heavy and extra-heavy oil samples are used to improve the model.

Theory and experiment procedure

For non-Newtonian viscoelastic materials, the complex shear modulus (G*) is given by the in-phase elastic component or storage modulus (G'') and the out of phase viscous component or loss modulus (G"). G'' and G" represent the ability for a material to store energy elastically and to dissipate energy respectively.

Results

Viscosity versus Temperature

The complex viscosity trend with temperature for Newtonian and viscoelastic fluids indicates that ?* decreases significantly as temperature increases at low temperatures, while for high temperatures ?* decreases slowly with temperature at high temperatures. This is clearly shown by the DeGuetto empirical model (Figure 1), which predicts similar ?*-T trend but with considerably lower viscosities.

Measured data reflects three stages. In the first stage viscosity decreases rapidly by 2 orders of magnitude for temperatures below 30°C. For temperatures between 40 and 50°C, the viscosities decrease more slowly. At higher temperatures, ?* decreases faster than stage 2 but lower than stage 1 (Figure 1). Results for Sample 1 were repeated using two different rheometers giving similar response.

Thank you!