Fundamentals of reservoir surface energy as related to surface properties, wettability, capillary action, and oil recovery from fractured reservoirs by spontaneous imbibition Page: 3 of 42
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The objective of this project is to increase oil recovery from fractured reservoirs through
improved fundamental understanding of the process of spontaneous imbibition by which oil is
displaced from the rock matrix into the fractures. Spontaneous imbibition is fundamentally
dependent on the reservoir surface free energy but this has never been investigated for rocks. In
this project, the surface free energy of rocks will be determined by using liquids that can be
solidified within the rock pore space at selected saturations. Thin sections of the rock then
provide a two-dimensional view of the rock minerals and the occupant phases. Saturations and
oil/rock, water/rock, and oil/water surface areas will be determined by advanced petrographic
analysis and the surface free energy which drives spontaneous imbibition will be determined as a
function of increase in wetting phase saturation. The inherent loss in surface free energy
resulting from capillary instabilities at the microscopic (pore level) scale will be distinguished
from the decrease in surface free energy that drives spontaneous imbibition.
A mathematical network/numerical model will be developed and tested against experimental
results of recovery versus time over broad variation of key factors such as rock properties, fluid
phase viscosities, sample size, shape and boundary conditions. Two fundamentally important,
but not previously considered, parameters of spontaneous imbibition, the capillary pressure
acting to oppose production of oil at the outflow face and the pressure in the non-wetting phase
at the no-flow boundary versus time, will also be measured and modeled. Simulation and
network models will also be tested against special case solutions provided by analytic models.
In the second stage of the project, application of the fundamental concepts developed in the first
stage of the project will be demonstrated. The fundamental ideas, measurements, and
analytic/numerical modeling will be applied to mixed-wet rocks. Imbibition measurements will
include novel sensitive pressure measurements designed to elucidate the basic mechanisms that
determine induction time and drive the very slow rate of spontaneous imbibition commonly
observed for mixed-wet rocks. In further demonstration of concepts, three approaches to
improved oil recovery from fractured reservoirs will be tested; use of surfactants to promote
imbibition in oil wet rocks by wettability alteration: manipulation of injection brine composition:
reduction of the capillary back pressure which opposes production of oil at the fracture face.
01/01/06 - 06/30/06
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Morrow, Norman R.; Fischer, Herbert; Li, Yu; Mason, Geoffrey; Ruth, Douglas; Seth, Siddhartha et al. Fundamentals of reservoir surface energy as related to surface properties, wettability, capillary action, and oil recovery from fractured reservoirs by spontaneous imbibition, report, June 8, 2006; Wyoming. (digital.library.unt.edu/ark:/67531/metadc887825/m1/3/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.