Effect of Shale Content On Oil Recovery By Alkaline Waterflooding
Authors: Abdel-Waly A.A. , Osman A. , Abdel-Hadi I. 
Published: March 2010

In this work, the effect of shale content on the enhanced oil recovery of Kareem crude oil by alkaline solutions was studied. Kaolinite is the most abundant clay within the mudstone of the Kareem formation and has been used as clay dispersion into the laboratory prepared sandpacks. The acidity, interfacial tension and contact angle of Kareem crude oil were investigated. The present study is concerned with the effect of alkaline slug concentration, slug size, varying shale content and alkali type on oil recovery.

Kareem crude oil is highly acidic (2.7 mg KOH/g). The interfacial tension between Kareem crude oil and sea water decreased with increasing alkaline concentration until it reached a minimum at 6% by weight NaOH concentration, after which no change in interfacial tension was observed with further increase in alkaline concentration. It was found also that sodium hydroxide reduced interfacial tension more than the other hydroxides. Contact angle measurements indicated oil-wetting conditions which increased with an increase in the shale content.

At 2% by weight NaOH and 20% PV slug size, oil recovery decreased with increasing shale content, until it reached the least value at the actual shale content of Kareem formation which is 4% by weight. It was also found out that sodium hydroxide and sodium silicate produced significantly higher recoveries than did potassium hydroxide and sodium carbonate at the same conditions of temperature, shale content, slug size, and at equal equivalent weight percentage of NaOH.

Introduction

Alkaline oil recovery has been attributed to an oil/alkali interaction called "emulsification" and to an alkali/rock interaction called "wettability alteration". Each mechanism requires somewhat different initial conditions with respect to reservoir oil, rock, and injected water properties, and each process is designed to improve oil recovery in a somewhat different manner.

Shale content is a major factor in the overall recovery efficiency within a reservoir due to the large surface area and highly reactive ionic characteristics of the clay particles. The presence of a comparatively small percentage of clay by weight has very little effect on porosity but it may significantly reduce permeability.

The El-Morgan oil field was discovered in February 1965, and put on production in April 1967. The field centre is located at about 15 km north west of El-Tor city, 40 km south east of Ras- Gharib and 20 km from Ras-Shukheir (Figure 1). The El-Morgan oil field produces oil from two reservoir rocks of Miocene age. The upper reservoir is the Belayim formation and the lower one is the major Kareem formation. The two reservoirs are mainly composed of sands interbedded with shales. Kaolinite is the most abundant clay within the Kareem formation.

Therefore, it is important to investigate the recovery behaviour of alkaline flooding at varying percentages of shale content. The experimental work in this study was carried out in order to achieve this objective.

Experimental Work

Fluid Properties

The acidity of Kareem crude oil was determined using the Institute of Petroleum (IP) procedures Nos. 1 and 182(1).