On the Characterization of Rock/Fluid and Fluid/Fluid Interactions in Carbonate Rocks Using the Ultracentrifuge

ABSTRACT

The ultracentrifuge provides an easy and fast way of estimating the physical properties of reservoir rock/reservoir fluid systems such as wettability information, capillary pressure and relative permeability curves. The ultracentrifuge has been utilized both in routine core analysis and at the research level. In this work, an extensive experimental program was conducted for the characterization of core from the Rainbow Lake Reefs. Numerous plugs were tested for wettability and capillary pressure characteristics. During the experimental procedure, it was found that the conventional use of the centrifuge data introduces uncertainties that may compromise the quality of the results. As a result, a series of improvements was designed and implemented to allow for the collection of more accurate and consistent data using Charged Couple Devices (CCD). Moreover, a series of experiments was performed aiming at producing recovery data for both water imbibition and EOR experiments. A number of interesting and often neglected issues were addressed. The capillary pressure data often showed hysteresis that did not reflect the hysteresis observed in porous plate measurements. This paper summarizes the work completed to date, provides information on the wettability and capillary pressure characterization of the Rainbow Lake Reefs, and presents the results of gravity assisted immiscible gas injection of water flooded plugs. The hysteresis phenomenon observed between primary and secondary drainage is not consistent. The fluid propagation in a three-phase system varies from sample to sample at low Bond Numbers. Amott indices do not change significantly with temperature for strongly water-wet media. There cannot be a consistent correlation among wettability indices and other physical properties for the reef cores. USBM indices on raw centrifuge data are different than the same, indices calculated on fitted curve data but not enough to alter the overall wettability classification.

Introduction Literature Survey

The measurement of reservoir wettability and the assessment of its importance for the recovery of crude oil have been the topic of numerous research papers in the past fifty years. Several reviews have been published that address the methods and options that a researcher has available when measuring wettability. Although simple contact angle measurements are still thought to be the most universal measure of wettability (l), other methods have emerged through the years that take advantage of the changes in capillary phenomena as they are affected by changes in wettability (2). The Amott test (3) and the USBM test (4) and their various combinations have been widely applied in the literature for the determination of the wettability characteristics of given reservoir/crude oil combinations. The initial single wettability characterizations (i.e., oilwet, water-wet, and neutral) were later complemented by new terms such as mixed (5), fractional, etc. In real systems, the distinction between different types of wettability became more and more vague.

One of the tools that has gained considerable popularity in the past decades is the centrifuge and its variations. Starting from the original paper of Hassler and Brunner (6), much effort has been spent on both the experimental part and the interpretation part of centrifuge technology.

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