The Role of Gravity in Capillary Pressure Measurements

1972 ◽  
Vol 12 (02) ◽  
pp. 85-88 ◽  
Author(s):  
Miklos T. Szabo
Keyword(s):  
Capillary Pressure ◽  
Gravitational Effect ◽  
Test Sample ◽  
Gravity Drainage ◽  
Pressure Curve ◽  
High Permeability ◽  
Technical Literature ◽  
Capillary Pressure Curve ◽  
Capillary Pressures ◽  
Capillary Pressure Curves

Abstract This paper shows on a theoretical basis how saturation profiles are influenced by gravity during the measurement of profiles are influenced by gravity during the measurement of capillary pressures in porous samples. A precise method is suggested for calculating the realistic capillary pressure curves from the data obtained in either the "diaphragm" or the "gravity drainage of long vertical core" method. A capillary pressure curve, free of the influence of gravity, can be determined by the equations developed in this paper from measurement of the pressures applied in the nonwetting phase and from the average saturations corresponding to capillary equilibria. The same equations may also be used for the evaluation of centrifuge data, provided the increase in capillary pressures is achieved by gradual lengthening of end-effect absorbers set up under the test sample, using the same constant speed of rotation at each run. Introduction The disc method is usually referred to in the technical literature as a standard method for determining capillary pressure curves. This study shows that using this method a certain pressure curves. This study shows that using this method a certain saturation distribution can be observed in the samples when the viscous fluid flow has ceased. The description of this phenomenon led to equations that offer a more precise formulation of the results obtained by the disc method. In addition, this formulation simplifies the "gravity drainage of long vertical cores" method because it is now sufficient merely to determine average saturations. Thus, it is unnecessary to determine saturations by electric methods or by the weighing of sectors of the drainage column. EXAMINATION OF SATURATION DISTRIBUTIONS IN POROUS MEDIA In order to study deviations that appear in the capillary pressure curve of high permeability porous samples due to gravity, pressure curve of high permeability porous samples due to gravity, a study of saturation distributions in a test sample is necessary. The horizontal pipet arrangement shown in Fig. 1 is the most suitable to study this effect because there is no need to correct the pressures with the rising meniscus in the pipet. Curve 1 in Fig. 2 represents a capillary pressure curve of a very thin porous disc. This curve can be considered a true capillary pressure curve of a porous material because of its short length; no gravitational effect is involved in that curve. Curve 1 in Fig. 2 will be used throughout for determining saturation distributions in a longer sample. In the example, a 30-mm long sample will be studied. SPEJ P. 85

Experimental Validation of a Pore-Scale-Derived Dimensionless Capillary Pressure Function for Imbibition Under Mixed-Wet Conditions

SPE Journal ◽  
2017 ◽  
Vol 22 (05) ◽  
pp. 1338-1348 ◽  
Author(s):  
Y.. Zhou ◽  
J. O. Helland ◽  
D. G. Hatzignatiou ◽  
R.. Ahsan ◽  
A.. Hiorth
Keyword(s):  
Capillary Pressure ◽  
Reservoir Simulation ◽  
Simulation Models ◽  
Pressure Curve ◽  
Pore Scale ◽  
Pressure Function ◽  
Capillary Pressure Curve ◽  
Mixed Wettability ◽  
Dimensionless Function ◽  
Capillary Pressure Curves

Summary We validate experimentally a dimensionless capillary pressure function for imbibition at mixed-wet conditions that we developed recently on the basis of pore-scale modeling in rock images. The difference from Leverett's traditional J-function is that our dimensionless function accounts for wettability and initial water saturation after primary drainage through area-averaged, effective contact angles that depend on the wetting property and distribution of oil- and water-wet grain surfaces. In the present work, we adopt the dimensionless function to scale imbibition capillary pressure data measured on mixed-wet sandstone and chalk cores. The measured data practically collapse to a unique curve when subjected to the dimensionless capillary pressure function. For each rock material, we use the average dimensionless curve to reproduce the measured capillary pressure curves and obtain excellent agreement. We also demonstrate two approaches to generate different capillary pressure curves at other mixed-wettability states than that available from the data used to generate the dimensionless curve. The first approach changes the shape of the spontaneous- and forced-imbibition segments of the capillary pressure curve whereas the saturation at zero capillary pressure is constant. The second approach shifts the vertical level of the entire capillary pressure curve, such that the Amott wetting index (and the saturation at zero capillary pressure) changes accordingly. Thus, integrating these two approaches with the dimensionless function yields increased flexibility to account for different mixed-wettability states. The validated dimensionless function scales mixed-wet capillary pressure curves from core samples accurately, which demonstrates its applicability to describe variations of wettability and permeability with capillary pressure in reservoir-simulation models. This allows for improved use of core experiments in predicting reservoir performance. Reservoir-simulation models can also use the dimensionless function together with existing capillary pressure correlations.

scholarly journals Revisiting the applications of drainage capillary pressure curves in water-wet hydrocarbon systems

2016 ◽  
Vol 8 (1) ◽  
Author(s):  
István Nemes
Keyword(s):  
Capillary Pressure ◽  
Water Saturation ◽  
Pressure Curve ◽  
Initial Water ◽  
New Approach ◽  
Capillary Pressure Curve ◽  
Side Track ◽  
Relationship Of ◽  
Capillary Pressure Curves ◽  
The Relationship

AbstractThe main focus of the paper is to introduce a new approach at studying and modelling the relationship of initial water saturation profile and capillarity in water-wet hydrocarbon reservoirs, and describe the available measurement methods and possible applications. As a side track it aims to highlight a set of derivable parameters of mercury capillary curves using the Thomeer-method. Since the widely used mercury capillary pressure curves themselves can lead to over-, or underestimations regarding in-place and technical volumes and misinterpreted reservoir behaviour, the need for a proper capillary curve is reasonable. Combining the results of mercury and centrifuge capillary curves could yield a capillary curve preserving the strengths of both methods, while overcoming their weaknesses. Mercury injection capillary curves were normalized by using the irreducible water saturations derived from centrifuge capillary pressure measurements of the same core plug, and this new, combined capillary curve was applied for engineering calculations in order to make comparisons with other approaches. The most significant benefit of this approach is, that all of the measured data needed for a valid drainage capillary pressure curve represents the very same sample piece.

A Technique for the Determination of Capillary Pressure Curves Using a Constantly Accelerated Centrifuge

1963 ◽  
Vol 3 (03) ◽  
pp. 227-235 ◽  
Author(s):  
Robert N. Hoffman
Keyword(s):  
Capillary Pressure ◽  
Pressure Curve ◽  
Barrier Method ◽  
Centrifuge Method ◽  
Permeable Barrier ◽  
The Core ◽  
Capillary Pressure Curve ◽  
Fluid Saturation ◽  
Time Required ◽  
Capillary Pressure Curves

HOFFMAN, ROBERT N., MISSOURI SCHOOL OF MINES, ROLLA, MO. JUNIOR MEMBER AIME Abstract A new technique for determining capillary pressure curves has been developed and tested. The technique differs from previously reported centrifuge techniques in that the centrifuge is slowly accelerated from zero to the maximum desired speed rather than being held constant at particular, progressively higher speeds. An important advantage of this technique over other methods of determining capillary pressure curves is the short time required to obtain the desired amount of data over the chosen pressure range. For example, to obtain 30 data points between 1.2 and 104 psig with a 1.55-in. long, 3/4-in, diameter core using a brine-air system, 6. 6 hours were required with this technique. An equally important development of this paper is an analytic method for the conversion of the data from the centrifuge experiment to capillary pressure curve data. Previously there has been only an approximate conversion available.Although the capillary pressure curves determined by this technique appear to be as accurate as those determined by other techniques, the accuracy could be improved if certain variables, not treated in this experiment, were investigated. Among these are the dynamic distortion of the centrifuge equipment and imperfect initial saturation of the cores. Introduction Pirson defines capillary pressure in a porous medium as "the differential pressure that exists between two fluid phases at their interfaces when they are distributed under static equilibrium within a porous material". Capillary pressure in rocks is known to be a function of fluid saturation, among other things, and a capillary pressure curve is defined for the purposes of this paper as a plot of the capillary pressure-wetting phase saturation relationship for a particular rock sample.Several methods are used for determining capillary pressure curves for small rock cores. Prominent among these are the semi-permeable barrier, mercury injection, and, to a lesser extent, centrifuge methods. The semi-permeable barrier method is currently the most popular. It features simplicity in both execution and the mathematical conversion of the experimental data into a capillary pressure curve. The main disadvantages of the semi-permeable barrier method are the time required - as long as two months - to obtain several points for the curve, and a fairly low maximum pressure before breakthrough of the non- wetting phase into the barrier occurs, for example, about 32 psig for a brine-air system.It is for these reasons that other methods such as the centrifuge method have been introduced. High accelerations and the absence of a barrier result in quicker attainment of saturation equilibrium at a given pressure. However, the centrifuge method involves much more expensive equipment and more difficult procedures and calculations than does the barrier method. The purpose of this investigation has been to improve the equipment and procedures of the centrifuge method and to develop an analytic method for the conversion of the experimental data into a capillary pressure curve.Hassler and Brunner did the original work in the determination of capillary pressure using a centrifuge. In their work the centrifuge speed was increased in a step-wise manner, each speed being held constant until saturation equilibrium was reached in each core. Saturation equilibrium was indicated when the volume of liquid collected in the graduated pipette of the core holder remained constant. According to Hassler and Brunner, equilibrium was reached in "a few minutes to one-half hour or more".In the centrifuge method, as opposed to the barrier method, the fluid saturation of the core is not a constant throughout the length of the core, but varies with the radius of centrifugation. Also, the capillary pressure cannot be read directly but must be calculated from a knowledge of the centrifuge speed and other parameters. SPEJ P. 227^

Fractal Capillary Pressure Curve Models

Fractals ◽  
2017 ◽  
pp. 29-54
Author(s):  
Behzad Ghanbarian ◽  
Humberto Millán
Keyword(s):  
Capillary Pressure ◽  
Pressure Curve ◽  
Capillary Pressure Curve

Characterization of Fluid Drainage Mechanism at Core and Pore Scales: an NMR Capillary Pressure–Based Saturation Exponent Prediction

2021 ◽  
Author(s):  
Abubakar Isah ◽  
Abdulrauf Rasheed Adebayo ◽  
Mohamed Mahmoud ◽  
Lamidi O. Babalola ◽  
Ammar El-Husseiny
Keyword(s):  
Electrical Resistivity ◽  
Capillary Pressure ◽  
Oil Recovery ◽  
Gas Storage ◽  
Pressure Curve ◽  
Pore Scale ◽  
Resistivity Index ◽  
Capillary Pressure Curve ◽  
In Series ◽  
Saturation Exponent

Abstract Capillary pressure (Pc) and electrical resistivity index (RI) curves are used in many reservoir engineering applications. Drainage capillary pressure curve represents a scenario where a non-wetting phase displaces a wetting phase such as (i) during gas injection (ii) gas storage in reservoirs (e.g. aquifer or depleted hydrocarbon reservoirs). The gas used for injection is typically natural gas, N2, or CO2. Gas storage principally used to meet requirement variations, and water injection into oil-wet reservoirs are drainage processes. Resistivity index (RI) curve which is used to evaluate the potential of oil recovery from a reservoir, is also an important tool used in log calibration and reservoir fluid typing. The pore drainage mechanism in a multimodal pore system is important for effective recovery of hydrocarbon reserves; enhance oil recovery (EOR) planning and underground gas storage. The understanding of pore structure and drainage mechanism within a multimodal pore system during petrophysical analysis is of paramount importance to reservoir engineers. Therefore, it becomes inherent to study and establish a way to relate these special core analyses laboratory (SCAL) methods with quick measurements such as the nuclear magnetic resonance (NMR) to reduce the time requirement for analysis. This research employed the use of nuclear magnetic resonance (NMR) to estimate saturation exponent (n) of rocks using nitrogen as the displacing fluid. Different rock types were used in this study that cover carbonates, sandstones, and dolomites. We developed an analytical workflow to separate the capillary pressure curve into capillary pressure curve for macropores and a capillary pressure curve for the micropores, and then used these pore scale Pc curves to estimate an NMR - capillary pressure - based electrical resistivity index - saturation (NMR-RI-Sw) curve for the rocks. We predicted the saturation exponent (n) for the rock samples from the NMR-RI-Sw curve. The NMR-based saturation exponent estimation method requires the transverse (T2) relaxation distribution of the rock - fluid system at various saturations. To verify the reliability of the new workflow, we performed porous plate capillary pressure and electrical resistivity measurements on the rock samples. The reliability of the results for the resistivity index curve and the saturation exponent was verified using the experimental data obtained from the SCAL method. The pore scale Pc curve was used to ascertain the drainage pattern and fluid contribution of the different pore subsystems. For bimodal rock system, the drainage mechanism can be in series, in parallel, or in series - parallel depending on the rock pore structure.

scholarly journals A New Method for Predicting the Permeability of Sandstone in Deep Reservoirs

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Feisheng Feng ◽  
Pan Wang ◽  
Zhen Wei ◽  
Guanghui Jiang ◽  
Dongjing Xu ◽  
...  
Keyword(s):  
Support Vector Regression ◽  
Capillary Pressure ◽  
Prediction Models ◽  
Reservoir Rock ◽  
Support Vector ◽  
Pressure Curve ◽  
Pore Throat ◽  
Capillary Pressure Curve ◽  
Mercury Injection ◽  
Mercury Injection Capillary Pressure

Capillary pressure curve data measured through the mercury injection method can accurately reflect the pore throat characteristics of reservoir rock; in this study, a new methodology is proposed to solve the aforementioned problem by virtue of the support vector regression tool and two improved models according to Swanson and capillary parachor parameters. Based on previous research data on the mercury injection capillary pressure (MICP) for two groups of core plugs excised, several permeability prediction models, including Swanson, improved Swanson, capillary parachor, improved capillary parachor, and support vector regression (SVR) models, are established to estimate the permeability. The results show that the SVR models are applicable in both high and relatively low porosity-permeability sandstone reservoirs; it can provide a higher degree of precision, and it is recognized as a helpful tool aimed at estimating the permeability in sandstone formations, particularly in situations where it is crucial to obtain a precise estimation value.

New Methods for Measuring Imbibition Capillary Pressure and Electrical Resistivity Curves by Centrifuge

1974 ◽  
Vol 14 (03) ◽  
pp. 243-252 ◽  
Author(s):  
Miklos T. Szabo
Keyword(s):  
Electrical Resistivity ◽  
Gravitational Field ◽  
Capillary Pressure ◽  
Water Reservoir ◽  
Pressure Curve ◽  
Resistivity Index ◽  
Rotary Axis ◽  
New Methods ◽  
Capillary Pressure Curve ◽  
Filter Disc

Abstract Three new techniques have been developed for measuring the imbibition capillary pressure curve of small porous samples by centrifuge. The paper shows the capillary pressure and saturation distributions in the cores subjected to different speeds of rotation by each of the techniques. Combination of these methods with measurements of electrical resistivity also makes it possible to obtain numerous resistivity-index/saturation curves or capillary-pressure/resistivity-index curves relatively quickly in either the drainage direction or the imbibition direction of saturation change. INTRODUCTION TO THE CAPILLARY PRESSURE MEASUREMENTS It has been known for more than 2 decades how to obtain the drainage capillary pressure curve by means of a centrifuge. Recently others have attempted to explain the mechanism of the gravity drainage of porous samples in the gravity field of a centrifuge by demonstrating the saturation distributions along the samples at different speeds of rotation. These works have led to both new methods and new evaluation techniques. However, there is still no method known by which the centrifuge can be used to obtain the capillary pressure curve in the imbibition direction. pressure curve in the imbibition direction. This paper reports the technical and theoretical considerations for thus obtaining such a curve. SHORT, SINGLE-CORE METHOD Both in this and in the following methods a system had to be chosen that would permit the quantity of fluid entering the sample to be controlled and regulated. A system in which the sample is simply surrounded by water could be neglected unless the sample is intermediately wet or oil wet; however, only in the negative capillary pressure interval could it be used. The applicability of this system to the case of water-wet samples may be explained very simply. From a partially oil-saturated sample the oil will be displaced by water, and subjecting this system to a multiplied gravitational field will only accelerate this displacement process. Therefore, there is no chance to regulate the degree of imbibition. A theoretical solution cannot be considered when the side of a sample farthest from the rotary axis is in contact with water or with a water-saturated porous disc because the imbibition occurs against the centrifugal force. Although it is true that imbibition will take place, the rate of imbibition will be slower than would be expected in the disc method in the earth gravitational field. Consequently, a method had to be chosen in which the direction of phase exchange occurs as a result of the natural fluid differences. That is, the water must enter the sample moving off the rotary axis and the quantity of imbibed water must be controllable. Fig. 1 illustrates a test cell that meets the requirements noted above. The cell can be used to obtain both imbibition and drainage data. For imbibition tests the sample is placed in contact with the filter nearest the rotary axis as shown. A fine porous filter paper is placed between the sample and the filter disc to provide good capillary contact. The water reservoir above the filter disc is partially filled. JPT P. 243

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