SCA2003-03 - Carbonate Rock Wettability Interpreted from Capillary Pressure and Imbibition Resistivity Index Analyses

Aug 27, 2026

Uploaded by Levi

Wettability of carbonate rock samples from five Western Canadian reservoirs ranges from weakly water-wet to mixed-wet and mildly oil-wet. Wettability interpretations were obtained from USBM and Amott analyses on aged samples, supported in one case by live-oil contact angle and in others by restored versus un-restored drainage capillary-pressure behavior. Imbibition resistivity index measurements on aged sister plugs provided the restored Archie saturation exponent n (1.2–3.1). These n values alone cannot uniquely indicate wettability because RI-profile shape is controlled by wettability and pore geometry, confirmed by RI and water relative-permeability comparisons across reservoirs.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages12

Reading Time30 min

AccessFree to download

Abstract

Introduction

Sampling and Analysis

USBM/Amott Wettability Analyses

SCA2003-03: CARBONATE ROCK WETTABILITY INTERPRETED FROM CAPILLARY PRESSURE AND IMBIBITION RESISTIVITY INDEX ANALYSES Dan Potocki, 1 Minghua Ding2,3 and Apostolos Kantzas2,3 1 EnCana Corporation 2 Department of Chemical and Petroleum Engineering, University of Calgary 3 Tomographic Imaging and Porous Media Laboratory This paper was prepared for presentation at the International Symposium of the Society of Core Analysts held in Pau, France, 21-24 September 2003 ABSTRACT The wettability of rock samples from 5 carbonate reservoirs in Western Canada varies from weakly water wet to mixed wet to mildly oil wet. Wettability was determined by USBM and Amott analyses on 17 aged rock samples. Evidence supporting these interpretations was provided in one case by a contact angle measurement of the live oil, and in other instances by relations between un-restored primary drainage and restored secondary drainage capillary pressure curves. Imbibition resistivity index (IRI) measurements were performed on 9 aged sister-plug samples to determine a restored Archie saturation exponent “n”. The saturation exponent measured at the onset of the IRI test provides the most reliable “n” value as it is determined on a restored sample prior to any hysteresis that occurs during increasing Sw. Values for the restored “n” vary from 1.2 to 3.1. Although the imbibition RI tests provide a reliable measure of the saturation exponent, this number cannot be used alone as a valid indicator ofwettability. Wettability and pore geometry principally control the shape of the RI profile during imbibition. Comparisons of imbibition RI profiles and water relative permeability curves were made between an oil wet and water wet reservoir with similar pore geometry. The water wet samples generally exhibit suppressed electrical and hydraulic behaviour during imbibition consistent with a more water wet pore system. In contrast, the oil wet samples exhibit an instantaneous flow of water and electric current with increasing Sw that is consistent with a more oil wet pore system. The wettability interpretations and saturation exponent measurements made for these 5 carbonate reservoirs were used to refine expectations of reservoir performance and enhance petrophysical interpretations. INTRODUCTION Wettability is one of the most important reservoir properties affecting oil recovery. Differences in relative permeability, capillary pressure and electrical properties between water wet and non water wet reservoirs may cause significant differences in reservoir appraisal and oil recovery. Although published studies indicate that most carbonate reservoirs are non water wet, wettability is rarely measured during many routine exploration programs for carbonate reservoirs in western Canada. To better understand reservoir character, this study primarily used USMB/Amott and imbibition resistivity index analyses to determine the wettability and electrical properties of five carbonate reservoirs from Western Canada, treated by some as being simply water wet and evaluated using a standard resistivity index of 2. SAMPLING AND ANALYSIS Twenty six small core plugs (1 ½” diameter and around 2” long) were obtained from the five studied pools (Table 1) . After cleaning, samples for wettability and electrical property analyses were centrifuged to Swi and aged for 40 days in dead uncontaminated reservoir oil. Brine solutions for each pool were composed in the laboratory to mimic the reservoir brine. Wettability was determined using an ultracentrifuge to perform a combined USBM/Amott test. Details regarding the technique can be found in the literature [1] . Relative permeability curves for each sample were constructed using a simulation package which history matches the fractional flow curves from the centrifuge experiments [2] . Wettability was also determined for one oil sample by the dual drop/dual crystal contact angle technique using live oil and a dolomite crystal. Electrical

FAQs

How was rock wettability determined in this study?

Wettability was determined using USBM and Amott analyses on aged carbonate core samples, with additional support from contact angle measurements for one case and drainage capillary-pressure curve relations for others.

What does the imbibition resistivity index analysis provide?

Imbibition resistivity index (IRI) measurements on wettability-restored sister plugs were used to determine the restored Archie saturation exponent n at the onset of the IRI test.

Why can’t the saturation exponent n be used alone to indicate wettability?

Because the RI profile shape during imbibition is governed by both wettability and pore geometry; therefore, n measured from IRI cannot uniquely determine wettability by itself.

Aug 27, 2026

Uploaded by Levi