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GoA feasibility study has been conducted to investigate the effect of type fluid on cleaning efficiency of near wellbore formation damage caused by fines and solids in drilling and drill-in fluids. Dynamic filtration experiments were conducted with fully brine saturated Berea sandstone core samples. Two and four inch OD full size cores with internal holes of 0.9 inch ID were tested to understand the effect of scaling and depth of invasion. The hollow Berea cores were first damaged using the drilling and/or drill-in fluids of different formulations. Then a specially designed ultrasonic tool was used to apply sonification in the hole under various differential pressures. The permeability, differential pressure, sonification amplitude, power and temperature were monitored as a function of sonification time and the energy requirement for near complete permeability recovery was investigated. The compressional wave travel times were recorded during the damage and sonification stages to obtain the correlation between the permeability and P-wave velocities.

The results showed that the permeability increased significantly when moderate power sonification was applied. An increase in differential pressure increased the sonification time necessary to get near complete removal of the solids from the pore space. The results reported here and series of other unpublished data and reports published provide evidence that ultrasonic cleaning is a powerful novel technique to remove formation damage from surfaces and that the sonification time has a significant influence on the efficiency of cleaning.

Berea sandstone, Berea Sandstone Core, compressional, core, drill-in fluid damage, drilling fluid chemistry, drilling fluid formulation, drilling fluid property, drilling fluid selection and formulation, drilling fluids and materials, Efficiency, experiment, flow in porous media, Fluid Dynamics, formation evaluation, hollow berea sandstone sample ultrasonic, particle, permeability, Reservoir Characterization, reservoir description and dynamics, sample, seg las vegas, sonification, Tutuncu, ultrasonic cleaning, Upstream Oil & Gas

SPE Disciplines:

- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (1.00)

Ultrasonic velocities, densities and porosities for a set of coal and surrounding silty coal, silty shale, and shaly coal samples were measured in laboratory. The pressure effect, temperature effect, and saturation effect on velocities and anisotropy were evaluated. The results were compared and correlated with the well log data and discrepancies were analyzed. The potential influences of the coal seams to neighboring gas or oil reservoir seismic response were discussed.

acoustic property, anisotropy, bedding, coal, coal formation, coal sample, coal seam, core, effect, las vegas, porosity, Reservoir Characterization, reservoir description and dynamics, sample, saturation, seismic processing and interpretation, shale, Upstream Oil & Gas, water, water saturation, Wave, well

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

We measured ultrasonic P and S-wave velocities as a function of varying pore pressure (0-6000 psi) and confining hydrostatic pressure (0-7000 psi) for a North Sea overpressured shale sample simulating subsurface pressure conditions. The estimated effective stress coefficient, n as a function of P- and S-wave velocities and bulk and shear modulii is less than 1 and is a function of differential pressure and mode of wave propagation. The value of n for our unloading case is quite low .The simplified assumption of n=1 is not true and depends on the geology and the stress history of the rock. The experimental results indicate that the shale velocities are more sensitive to changes in confining pressure than to changes in pore pressure during unloading.

change, coefficient, differential, effect, equation, experimental study, function, geophysics, North Sea shale, pore, propagation, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock, sample, sandstone, seg las vegas, seismic processing and interpretation, shale, stress, Upstream Oil & Gas

Elastic anisotropy of shale is mainly controlled by the intrinsic anisotropy of individual clay minerals as well as by the textural alignment of grains, pores, and fractures. One of the major challenges in predicting the elastic anisotropy of shales, while using rock physics models, is that the elastic properties of rock-forming clay minerals are poorly known. Since it is impossible to find single and large enough clay crystals for acoustic measurements and ab initio calculations are still incomplete, few data exist on the elastic moduli of clay minerals.

In an attempt to derive the intrinsic anisotropy of pure clay minerals, we present laboratory measurements of compressional and shear wave anisotropy in compacted clay powders at different porosities. In the present work, we focus on the anisotropy of montmorillonitic clays. We used a cold-press method by applying uniaxial compaction in order to obtain compacted mineral aggregates. Different degrees of compaction enable us to obtain samples with variable porosities and crystallite alignments. We measure ultrasonic P- and S- wave velocities along the beddingnormal and the parallel directions. The textural orientation of compacted clay aggregates is found to be controlled by compaction. We obtain the orientation distribution of the clay minerals using synchrotron X-ray diffraction.

Increasing anisotropy of the clay assemblages corresponds to an increase in the preferred orientation of the clay minerals. The combined usage of P- and S- anisotropy measurements with orientation distributions allows us to better constrain the inversion of clay mineral moduli. Our work provides laboratory data on elastic anisotropy of pure clay minerals while linking them to the variation of clay orientation distribution with porosity.

anisotropy, clay, clay mineral, compaction, distribution, elastic anisotropy, elastic property, Epsilon, exponential, formation evaluation, geophysics, intrinsic anisotropy, log analysis, mineral, model, montmorillonite, orientation, porosity, Reservoir Characterization, reservoir description and dynamics, sample, seismic processing and interpretation, shale, stiffness, Thomsen, Upstream Oil & Gas, well logging

Baechle, Gregor T. (ExxonMobil Upstream Research Company) | Eberli, Gregor P. (University of Miami) | Boyd, Austin (Schlumberger Doll Research Center) | DeGrange, Jean Marie (Schlumberger Doll Research Center) | Al-Kharusi, Layaan (University of Miami)

In order to model the effect of oil/gas production or CO2 injection at the seismic scale, we have to understand the effects of pore structure, pressure and fluid changes on velocity at the laboratory scale. To reach this goal, we measured carbonate rocks with a suite of miscible fluids, simulating the entire range of reservoir fluid moduli from light to heavy oils.

In our experiments, compressional velocity (Vp) and shear wave velocity (Vs) are simultaneously measured at a frequency of 1MHz and under increasing effective stress from 3 MPa to 30 MPa. We observe large variations in velocities between 3200 m/s and 6500 m/s and a large scatter in the P-wave velocity-porosity relationship. The P-wave velocity shows up to 2000m/s difference at a given porosity. The velocity increases between 250 and 750m/s as pressure incresases from 3 to 30MPa. The bulk of the samples show increasing Vp/Vs ratios with pressurization, up to values between 1.7 and 1.84. The ratio of normalized bulk versus shear modulus ranges from 0.7 to 0.9.

Twenty-one oomoldic carbonate samples with nearly spherical pores show a weak correlation between velocity and porosity under dry conditions. We attribute the weak correlation between velocity and porosity in rocks with similar pore geometry to variations in inter-crystalline porosity in the rock frame. This finding questions the assumption that spherical pores have a dominant effect on velocity.

Four oomoldic samples were chosen for fluid substitution and saturated "in-situ" with seven different pore fluids. Significant effects of fluid changes on velocity are observed. A linear correlation exists between bulk modulus and fluid modulus (r2 > 0.97). In contrast, shear modulus changes correlated with the viscosity of the fluids: the lower the fluid viscosity, the lower the shear modulus. Our results question common hypotheses for modeling pore-structure effects on acoustic properties in carbonates; (a) P-wave velocity is controlled by the percentage of spherical porosity, and (b) the P-wave velocity in oomoldic rocks is insensitive to fluid and pressure changes because of high stiffness of the rock frame. These findings imply that one has to be cautious in relating rock-physics model parameters to volumetric dominant pore types.

carbonate, effect, ethanol, fluid effect, fluid substitution, glycol, intercrystalline, intercrystalline porosity, moduli, oomoldic rock, pore, pore structure, porosity, Reservoir Characterization, reservoir description and dynamics, rock, sample, seismic processing and interpretation, shear moduli, shear modulus, spherical pore, structure, type, Upstream Oil & Gas

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

**Summary**

Oriented cores of Barnett shale were studied in detail with the help of ultrasonic and X-ray imaging methods. The velocities of compressional wave (*V**P*) and two shear waves (*V**Sh *and *V**Sv*) were measured on 56 samples. As a result, we found a relation between the X-ray images and specific features in behavior of elastic wave velocities. The average splitting of shear waves observed for the Barnett shale cores at room conditions is 30%.

anisotropy, attenuated x-ray beam, Barnett shale, Barnett Shale Core, core, device, direction, elastic wave, formation evaluation, intensity, log analysis, method, mineralogical composition, porosity, Reservoir Characterization, reservoir description and dynamics, sample, seismic processing and interpretation, shear wave, Upstream Oil & Gas, Wave, well logging, x-ray image, x-ray imaging

An analysis of two rock samples, hyaloclastites and basalts, at in-situ reservoir conditions has been done to identify the role of temperature on the seismic velocity and attenuation. The goal is to establish a temperature-dependent fluid substitution analysis of geothermal rocks using Gassmann equation within the framework of Biot''s poroelasticity. The analysis of temperature-dependent wave attenuation is shown for hyaloclastites. The results show that the general decreasing trend of seismic velocity towards temperature may be related to the thermophysical characteristics of fluid. Using Gassmann equation it has been shown that the presence of steam bubbles can reduce the effective elastic property of rocks which indirectly demonstrates the role of temperature to the seismic velocity. The Q factor, i.e., inverse of attenuation, behaves surprisingly almost in the same way as the seismic velocity with temperature, except in the lower temperature range. The Q factor increase with the temperature is supposed to be a quick viscosity decrease. The later decrease of Q factor may indicate the presence of steam bubbles due to the further temperature increase. This finding demonstrates that the application of temperature-dependent fluid substitution modelling using Gassmann equation can be applied for the characterization of geothermal reservoir systems.

In geothermal reservoirs, fluid-steam phase transition, fluid pressure and temperature are some crucial factors that potentially produce and/ or contribute to seismic anomalies. When interpreting such anomalies, realistic assumptions based on validated rock physics models are important (Jones et al., 1980; Boitnott and Bonner, 1994).

A laboratory measurement of temperature dependent seismic velocities of rocks at high temperature reservoir conditions has been referred to, for example in (Kern, 1978; Kern et al., 2001; Punturo et al., 2005; Scheu et al., 2006). However, these laboratory experiments have been mainly employed on dry samples and under deep mantle rock condition, i.e., very high pressures (up to 600 MPa with 50 MPa interval) and very high temperatures (up to 1000°C with about 100°C interval). Meanwhile, many geothermal reservoirs, as the case of Icelandic reservoir being investigated, are characterized by temperature range up to 200-300°C and pore pressure around 10 MPa with the pore water being in the liquid phase (Flóvenz et al., 2005). A controlled petrophysical laboratory experiment simulating those conditions becomes important for the evaluation of such a geothermal resource. An analysis of core scale properties of rock sample at in-situ reservoir conditions is useful to identify the role of temperature on the seismic velocity and attenuation. The goal of this work is to present the result of using Gassmann equation within the framework of Biot''s poroelasticity for a fluid substitution analysis of temperature-dependent geothermal rocks. For that, the measurement of ultrasonic transmission wave has been performed on two samples of volcanic geothermal rocks with different alterations (Bruhn et al., 2007; Jaya et al., 2007). Gassmann equation is then used to relate the effect of temperature on the fluid and on the effective elastic property of saturated rock. In addition, the temperature-dependent wave attenuation is shown for the hyaloclastite sample.

analysis, attenuation, condition, decrease, factor, Gassmann equation, geothermal reservoir, Geothermal Rock, Reservoir Characterization, reservoir description and dynamics, rock, sample, seismic processing and interpretation, steam bubble, temperature-dependent fluid substitution, thermophysical characteristic, Upstream Oil & Gas, Wave

Elastic property changes of bitumen reservoir during steam injection have been poorly understood. We measured and analyzed ultrasonic velocities of bitumen-saturated sediments (oil sands) and then obtained a relation of the velocities with temperature and pressure individually. We also investigated validity of the Gassmann equation for predicting velocity changes. We combined the laboratory measurement results to obtain a sequential rock physics model that can predict the velocity changes induced by the steam injection.

bitumen, bitumen reservoir, change, complex reservoir, decrease, dispersion, elastic property change, enhanced recovery, Gassmann equation, increase, oil sand, pore, psi, Reservoir Characterization, reservoir description and dynamics, SAGD, sample, seismic processing and interpretation, steam injection, steam-assisted gravity drainage, thermal methods, Upstream Oil & Gas

SPE Disciplines:

- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Oil sand, oil shale, bitumen (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Thermal methods (1.00)
- Facilities Design, Construction and Operation > Unconventional Production Facilities > Oil sand/shale/bitumen (1.00)

Chen, 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.

analysis, attenuation, band, carbonate reservoir rock, dispersion, frequency band, relaxation, Reservoir Characterization, reservoir description and dynamics, s-wave attenuation, sample, saturation, seg las vegas, seismic frequency, seismic frequency band, seismic processing and interpretation, spectrum, ultrasonic frequency, Upstream Oil & Gas

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.

anisotropic thomsen, anisotropy, distribution, fluorescence, function, image, kerogen, maceral, Magnitude, maturation, maturity, Microstructure, organic-rich shale, Reservoir Characterization, reservoir description and dynamics, rock, sample, seismic processing and interpretation, spatial arrangement, structural geology, Upstream Oil & Gas, vitrinite, vitrinite reflectance, wavelength

SPE Disciplines:

Thank you!