Ага Видел две статьи в SPE и еще в Petrophysics
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Society of Petroleum Engineers Language English
Document ID 19618-PA DOI 10.2118/19618-PA
Content Type Journal Paper
Title
Pore-Space Statistics and Capillary Pressure Curves From Volume-Controlled Porosimetry
Authors
Toledo, Pedro G., Scriven, L.E., Davis, H. Ted, University of Minnesota
Journal SPE Formation Evaluation
Volume Volume 9, Number 1 Pages 46-54
Date March 1994
Copyright
1994. Society of Petroleum Engineers
Discipline
Categories none
Preview
Summary
Far more information about pore space of reservoir rock samples can be obtained from volume-controlled mercury porosimetry than from conventional pressure controlled mercury porosimetry, as Yuan and Swanson (1986) demonstrated in landmark experiments with their new Apparatus for Pore Examination - APEX. Earlier researches (e.g. Mohanty et al. 1987, Heiba et al. 1982) established capabilities of simulating processes like mercury injection with mechanism-based, processes like mercury injection with mechanism-based, computer-facilitated models of pore level displacements in the pore network. We bring these capabilities and some new features to bear on APEX to discover how much useful information about a porous medium can be extracted from volume-controlled mercury displacement. The disordered nature of porous media we reduce to decorated network approximations onto which any pore size distribution, pore structure, and topological feature can be mapped. Such networks can represent sandstones and carbonates closely, including pore systems that display bimodal size distributions, diagenetically altered shapes, random or correlated heterogeneities, and stratification. APEX mercury injection is quasi-static; so is our simulation. Displacement under these circumstances consist of smooth, reversible changes linked by jumps in capillary pressure, the sequence of which follows from the structure of the porous medium and the saturation history. Thus, careful examination of fluctuations in the capillary pressure provides detailed information about pore structure, notably distributions of pore size and pore structure, notably distributions of pore size and pore volume. pore volume. The results account quantitatively for the APEX mercury capillary pressure curves so precisely measured by Yuan and Swanson. In our work, sample size - an aspect not reported previously - is found to be a major factor in APEX response. By Monte Carlo simulation of APEX mercury injection we find the optimum size of specimen for examining pore space of given properties. By the same means we investigate added kinds of experiments that extend the capabilities of APEX mercury injection, namely withdrawal experiments, withdrawal after partial reinjection and full scanning loops. We also investigate the potential use of high pressure mercury porosimetry to characterize microporosity pressure mercury porosimetry to characterize microporosity and surface roughness in reservoir rocks.
Introduction
Mercury porosimetry, the forced intrusion of mercury into a porous material, has been used to characterize the microstructure of the pore space since Washburn (1921) suggested how to obtain a `pore size distribution' from measurements of volume injected versus pressure applied. Ritter and Drake (1945) authored the first work fully devoted to mercury porosimetry, describing the construction and operation of the equipment, reporting many experimental data and forming the basis of subsequent developments. In 1949 Purcell introduced the technique to the petroleum industry. Since then, mercury capillary pressure curves measured on reservoir rock samples (cores, chips, etc.) have been used routinely in connection with petroleum exploration and production. The goal is to get information on relationships between petrophysical properties and the microstructure of the pore space, particularly information useful for predictions of porosity, permeability, relative predictions of porosity, permeability, relative permeabilities, and residual oil saturation of reservoir permeabilities, and residual oil saturation of reservoir rocks.
http://www.onepetro.org/mslib/servlet/onepetropreview?id=00019618&soc=SPE Society of Petroleum Engineers Language English
Document ID 14892-PA DOI 10.2118/14892-PA
Content Type Journal Paper
Title Resolving Pore-Space Characteristics by Rate-Controlled Porosimetry
Authors Yuan, H.H., Swanson, B.F., Shell Development Co.
Journal SPE Formation Evaluation
Volume Volume 4, Number 1 Pages 17-24
Date March 1989
Copyright 1989. Society of Petroleum Engineers
Discipline
Categories none
Preview
Summary.
By monitoring the mercury capillary pressure in rate-controlled porosimetry (intrusion) experiments, new information regarding the pore space of a rock sample has been obtained. With this technique, called an apparatus for pore examination (APEX), it is now possible to resolve the pore space of a rock sample into two interconnected parts. One part identifies the individual pore systems (pore bodies), which are low-energy sumps or regions of low capillarity. The other part corresponds to the pore throats that interconnect with pore systems.
New capillary-pressure curves have been obtained by partitioning the total capillary-pressure curve (normal capillary-pressure curve) into two subcurves: the subison capillary-pressure curve, which details the distribution of pore bodies, and the rison capillary-pressure curve, which details the distribution of pore throats. We present APEX data on Berea sandstone and San Andres dolomite that show the volume distribution of low-capillarity regions within the pore space of these rocks. These regions of low capillarity are the principal pore-space regions that trap the residual nonwetting phase upon imbibition of a strongly wetting fluid, as measured by toluene/air systems. The residual nonwetting-phase saturations as determined by the APEX method and by the toluene/air method are in excellent agreement. Thus, the detailed volume distribution of pore systems responsible for trapped nonwetting-phase saturation is determined from APEX measurements, which can have important implications for EOR.
Introduction
Mercury porosimetry has long been used to characterize the void space of porous materials and has been the subject of a review. The measurement of pore-size distributions from mercury capillary-pressure curves has been of great benefit to formation evaluation in the oil industry. Mercury capillary-pressure curves measured on reservoir-rock samples have been used in petroleum exploration and production since Purcell introduced the technique to the industry. Besides being used to indicate the distribution of PV, capillary-pressure curves have also been used for the calculation of permeability and estimation of residual oil saturation.
Capillary-pressure curves normally give information only on poreneck sizes rather than on the exact volume of the pore space behind pore necks. Because of the nature of the conventional (pressure-controlled) method of measuring capillary-pressure curves, it is possible to have different distributions of pore systems that would yield the same capillary-pressure curve. In the usual experiment, mercury pressure is raised in increments and the injected mercury volume is measured. This is a pressure-controlled measurement of a mercury capillary-pressure curve. Because of the inherent ambiguity in capillary-pressure curves, attempts to derive relationships between various petrophysical properties through capillary pressures are not always successful.
An alternative method of measuring capillary-pressure curves is by rate-controlled injection of mercury into the sample, where the injection rate is kept constant and the mercury capillary pressure is monitored instead. Fluctuations in the mercury meniscus may occur because of various degrees of constriction along the pore path. Because capillary pressure is inversely related to the radius of curvature of the mercury meniscus, fluctuations in the curvature of the mercury meniscus respond as fluctuations in capillary pressure. The Young-Laplace equation relates the capillary pressure, Pc, to the radii of curvature of the mercury interface:
..........................................(1)
where a is the interfacial tension (IFT) and r, and r, are principal radii of curvature.
If one thinks in terms of cylindrical pore throats that constrain the position of the mercury, then Eq. 1 can be replaced by
..........................................(2)
where r is the radius of the corresponding cylinder and 0 is the contact angle. Some have referred to this as the Washburn equation. We presume that on the drainage cycle of the capillary pressure the IFT and the contact angle are constant and fluctuations in the mercury pressure are caused by fluctuations in the radius of the constraining pore throat. We assume that the contact angle and the IFT are unchanged throughout the experiment. Thus, detailed examination of fluctuations in the mercury pressure can provide detailed information on the structure of the pore space within a porous medium.
An advantage of this measurement technique is that ambiguity in capillary-pressure curves disappears because different pore types behind the same size pore neck will have different pressure responses. In this paper, we discuss rate-controlled measurement of capillary-pressure curves and show how detailed volume distributions can be obtained from this experiment. We call this technique APEX. This report is limited to the discussion of the application of pore-system distributions. The application of APEX capillary-pressure curves to other items mentioned above, such as the determination of permeability and relative permeability, is not included, although some description of the pore-throat capillary-pressure curve is given.
The observation of fluctuations in mercury pressure during mercury injection is not new. In 1959, in an unpublished Shell report, Gates observed pressure fluctuations with mercury porosimetry of vuggy carbonates. In 1966, Crawford and Hoovers were able to record capillary-pressure fluctuations on a chart recorder during the injection of water into synthetic porous media. The infinitesimally slow displacement of a wetting fluid by a nonwetting fluid was discussed in detail by Morrows in 1970. He introduced terminology to describe certain features of the pressure fluctuations that we describe in the next section. In 1971, Gaulierio published similar techniques for depicting vug volume, although his sensitivity was very low. In this report, we show the significance of resolving the pore space of a rock sample by deriving petrophysical parameters from mercury capillary curves, which lead to a better understanding of properties of porous media.
Experimental Considerations and Terminology
Experimental. The key feature of the APEX system is automated data acquisition coupled with high-precision pressure measurement, which enables very small pressure fluctuations to be resolved. The experimental setup is shown in Fig. I @ A stainless-steel sample cell. constructed so that it gives rise to negligible pressure fluctuations upon the injection of mercury, is attached to a motorized pressure intensifier. A Bell and Howell CEC 1000 sputtered-gauge pressure transducer is attached to the cell, and a shaft encoder is attached to the end of the asynchronous motor to determine volume. For the experiments reported here, a pressure transducer with a range of 700 kPa [101 psi] was used.
The pressure-transducer signal is amplified and the high-level signal is fed into a Phoenix data 16-bit analog-to-digital (A/D) converter. The pressure resolution is better than 0.014 kPa [0.002 psi]. The shaft encoder is supplied with a 5-V excitation from an interface board in the computer, which also counts the pulsed output of the shaft encoder.
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Отправлено: 29.10.11 09:14. Заголовок: Ага Видел две статьи в SPE и еще
