Fundamental Study of Imbibition in Fissured Oil Fields

Abstract

Abstract Waterflood efficiency of a fissured oil is closely dependent on the volume and speed of water imbibition in the elementary blocks. A large number of laboratory tests have been performed on fluids and porous media taken from a performed on fluids and porous media taken from a field exploited by ELF, and have helped to ascertain the effect of the block height and permeability, and the conditions at their limits as well permeability, and the conditions at their limits as well (some figures may contain water or oil or may be tight), on oil recovery. The results show how important are the physico-chemical bondings between connate water, physico-chemical bondings between connate water, injected brine, oil and rock at any time during imbibition: minor differences in lithology may consideration alter the recovery laws. Similarly, some organic molecules in the fluids influence oil recovery much more than one might expect according to the variations of cos alone. As one does not know how to represent these physico-chemical bondings, it is not permitted to perform laboratory experiments with fluids an/or core different from the real one (except for special cases). Laboratory measurements, together with numerical simulations, have even results which allow to understand the role played by gravity, capillarity, boundary conditions, and end effects an the imbibition. Introduction The development of one of our off shore oil fields which is composed of alternating silt and fissured limestone layers has enabled us to make a detailed study of the effects of imbibition when the field is flooded with sea-water. Since the silt layers contain most of the oil and the limestone layers are continuous and largely fissured, it was possible to represent the situation by the following possible to represent the situation by the following elementary structural model (figure 1-a): a homogeneous matrice containing primarily oil and interstitial water, which is bordered on the top and bottom by two horizontal and parallel fissured Plans, which carry the intrusive water and drain Plans, which carry the intrusive water and drain off the oil displaced from the matrice by imbibition. This model can be itself reduced to the experimental schema (figure 1-b),: a porous medium sample set up vertically and containing initially oil and water at irreductible saturation. Water is brought in contact with the top and bottom of the sample and its hydraulic potential is kept constant by means of a lateral by-pass. The displaced oil is collected selectively in two graduate tubes as shown in the figure 1-b. Such is the elementary schema considered in the present study.