Adaptation of a triaxial cell for ultrasonic P-wave attenuation, velocity and acoustic emission measurements

Donald, J. Adam; Butt, Stephen; Яковлев, С. С.

doi:10.1016/j.ijrmms.2004.03.004

Cited by 16 publications

(7 citation statements)

References 23 publications

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“…Such studies can increase basic understanding and help to discriminate between cases where the two methods are either redundant or truly complement each other. Adaptations of existing triaxial cells for ultrasonic P‐and S‐wave measurements are well documented (Birch 1960, 1961; Winkler and Plona 1982; Prasad and Manghnani 1997; Donald, Butt and Iakovler 2004). This paper proposes further modification of such a cell so that also axial resistivity measurements can be carried out simultaneously at reservoir conditions.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell – a feasibility study

Wang

Gelius

Kong

2009

Geophysical Prospecting

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A B S T R A C TAdaptations of existing triaxial cells for ultrasonic P-and S-wave measurements are well documented. This paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions. By employing the top cap and the pedestal of the cell as electrodes, axial resistivity measurements are now feasible. In order to minimize the polarization effect of this two-electrode arrangement, careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band. Radial resistivity measurements are also included in the system by introducing a strap-electrode system.In a reservoir under production changes in both saturations, temperature (if steam injection) and stresses can take place. Therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters. The feasibility of the system to obtain such reliable information is demonstrated, employing a small selection of core samples. In the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion.

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Section: Introductionmentioning

confidence: 99%

Simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell – a feasibility study

Wang

Gelius

Kong

2009

Geophysical Prospecting

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“…The design and validation of this loading and ultrasonic transmission system is described in detail in a related publication (23) . The design and validation of this loading and ultrasonic transmission system is described in detail in a related publication (23) .…”

Section: Methodsmentioning

confidence: 99%

Non-Destructive Techniques to Determine the Effective Stress Coefficient of Sandstone Formations

Frempong

Butt

2006

Journal of Canadian Petroleum Technology

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The concept of effective stress coefficient, "n," is critical for the study of stress and pressure-dependent behaviour of rocks. This parameter is used to scale the pore fluid pressure for the computation of effective stress and impacts on the accuracy of pore pressure and saturation predictions in reservoirs. However, "n" is relatively unknown and difficult to estimate and, in many cases, is often incorrectly assumed to be equal to one. We present a general review of "n" and give a theoretical proof that "n" is less than one for porous rocks. We also introduce a laboratory methodology to measure the value of "n" employing ultrasonic P-wave velocity (Vp) and attenuation quality factor (Qp). We then confirm the value of "n' experimentally by using this laboratory method to estimate "n" of quartz sandstone. We compare our experimental value of "n" to both theoretical and practical results obtained from other literature that used different estimation methodology. We argue from our experimental results that:"n" is not one but varies from zero to one;there is no single value of "n" for a particular reservoir rock;"n" depends on internal factors (porosity and pore geometry) and external factors (pore pressure and confining pressure) of the rock;velocity derived "n" and quality factor derived "n" are slightly different for the same rock; and,for the quartz sandstone used in this experiment, the velocity derived "n" is smaller and also less sensitive to changes in pressure than quality factor derived "n." Introduction Most of the pioneering work on what is now known as effective stress coefficient was done by Terzaghi(1), who showed that most rocks are porous to some degree due to the pore spaces and micro cracks within them. The effect of these pores on the strength of rocks has widely been documented(1–5). A rock with a few or without pores is considerably stronger than porous ones since pore spaces are unsupported within the rock. With the presence of unsupported spaces, the intact rock between the pores has to take larger loads to sustain an overall applied stress. This important phenomenon has a direct bearing on the effective stress of the rock (Figure 1). Thus, the effective stress (Pe) is not directly equal to the differential pressure (Pd). Many writers(4–12) have highlighted the problem caused by this phenomenon and the resulting uncertainties associated with the estimated pressures and saturation in reservoirs. This uncertainty is increasingly significant for reservoir engineering due to the expanding use of seismic techniques for remote estimation of abnormal pore pressures for drill planning and for monitoring reservoir pore pressure changes during production. For example, Carcione and Helle(13) applied a new technique for estimating reservoir pressures from seismic data to an overpressured gas field in the Norwegian North Sea and concluded that once a reliable velocity field was determined for the reservoir formation, the most important part of the prediction process was the determination of the effective stress coefficients and related dry-rock moduli.

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“…The high level of scatter in the Q p values is the result of the digital sampling rate and the number of Pwave samples available after windowing, which averaged approximately 20 samples but was lower for sample PH472-N that showed the most scatter. This problem has been addressed in later research by increasing the digital sampling rate 10-fold, correspondingly increasing the number of P-wave samples and significantly reducing the scatter (Donald et al, 2004). As with the velocity data, samples tested at higher confining pressure have initially higher Q p values.…”

Section: Velocity and Attenuationmentioning

confidence: 99%

Characterization of the permeability and acoustic properties of an outburst-prone sandstone

Butt

Frempong

Mukherjee

et al. 2005

Journal of Applied Geophysics

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Adaptation of a triaxial cell for ultrasonic P-wave attenuation, velocity and acoustic emission measurements

Cited by 16 publications

References 23 publications

Simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell – a feasibility study

Simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell – a feasibility study

Non-Destructive Techniques to Determine the Effective Stress Coefficient of Sandstone Formations

Characterization of the permeability and acoustic properties of an outburst-prone sandstone

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