The Effect Of Temperature And Fluid Composition On Oil Water Capillary Pressure Curves Of Limestone And Sandstones And Measurement Of Contact Angle At Elevated Temperatures

Author : Behrooz Raeesi
Publisher :
ISBN 13 : 9781267591296
Total Pages : 142 pages
Book Rating : 4.5/5 (912 download)

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Download or read book Measurement and Pore-scale Modeling of Capillary Pressure Hysteresis in Strongly Water-wet Sandstones written by Behrooz Raeesi and published by . This book was released on 2012 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Capillary pressure and contact angle hysteresis in porous media are important yet not fully understood phenomena. A fundamental problem in interpretation of the capillary properties of porous media is the effect of the interaction of wetting properties and pore geometry on interface curvature. Contact angles provide a fundamental measure of wetting. However, circumstances under which reproducible and unambiguous values of contact angle are observed are limited to special circumstances. Contact angles commonly exhibit hysteresis between advancing and receding conditions. The origin of the contact angle hysteresis may be related to either chemical or geometric phenomena or a combination of both. Small scale geometric features, such as surface roughness, can have a dominant effect on the effective contact angles at the three phase lines of contact boundaries that are essential to the existence of interfaces and determine their curvature. Hysteresis in drainage and imbibition observed for spreading conditions, when the contact angle is zero and there is no hysteresis in contact angle, is accentuated by the pore geometry and the non-uniform structure of the pore space. In the first part of this thesis, the effect of roughness on the effective contact angle is studied by applying the MS-P (Mayer, Stowe, Princen) method of computing interface curvatures, for the first time, to geometric models of surface roughness that include small scale periodic variation and retained fluid in grooves along the walls of tubes of constant cross section. The theoretical results are shown to be consistent with experimental results on the wetting behavior of combinations of roughened polymeric tubes and pure liquids that give a range of well-defined intrinsic contact angles (contact angles measured at smooth polymeric surfaces or deposited monolayers for pure liquids, usually against air). Most of the investigation reported in this thesis concerns hysteresis in porous media when the contact is zero for advancing and receding conditions. There have been numerous efforts to model hysteresis under this relatively simplified condition. Most of the published hysteresis data is for bead packs. There is a paucity of detailed experimental capillary pressure data for consolidated porous materials, such as porous sandstone and carbonate rocks. In this work, an improved porous plate method was developed to obtain accurate and relatively fast measurement of two-phase capillary pressure-saturation relationships including hysteresis cycles and scanning curves. Extensive sets of capillary pressure data and corresponding equilibration outflow diagrams for various rock and fluid systems including air-brine, mineral oil-brine and crude oil-brine in sandstones are presented and discussed. In order to understand the effects of the pore structure and displacement mechanisms on capillary hysteresis and trapping, a geologically realistic pore network model representing the pore structure of Berea sandstone was adapted and systematically modified to investigate effects of various pore network characteristics. These include pore size distribution, pore-to-pore and pore-to-throat correlations and coordination number, on the shape of capillary pressure curves and the magnitude of capillary pressure hysteresis and non-wetting phase trapping. Using the knowledge from the analysis, the network was then tuned to reproduce capillary pressure hysteresis experimental data for Bentheim sandstone. In order to simultaneously match the hysteresis trends and the residual NWP saturation, a snap-off criterion was introduced to the model based on the theoretical length/diameter ratio at which a cylindrical liquid bubble becomes unstable. The non-wetting phase residual saturation was matched by adjustment of the throat lengths and without further adjustments, the scanning hysteresis cycles at various initial saturations were closely predicted by the model. It is also shown that the predicted distribution of residual nonwetting phase is in close agreement with the reported experimental data for sandstone obtained by 3D micro-CT imaging and other methods of obtaining blob size distribution. The capabilities of the network model are extended to compute fluid-fluid and solid-fluid surface areas as a function of saturation. Comparison of work of displacement from the modeled capillary pressure data with changes in free surface energy from the model are used, for the first time, to calculate the efficiency of conversion of work to surface area and vice versa.