Date of Award

6-2002

Document Type

Thesis

Degree Name

Master of Science in Petroleum Engineering (MSPE)

Department

Chemical and Petroleum Engineering

First Advisor

Dr. Hazim AI-Attar

Second Advisor

Abdulrazag Zekri

Third Advisor

John Chatzis

Abstract

Low-salinity water flooding LoSalTM has been used to improve oil recovery for many decades. Historically, the mechanisms behind this improvement in oil recovery were attributed to the pressure maintenance and displacement of oil by injected water, i.e. physical mechanism. Recently, evidence from laboratory and field tests indicated that water flooding also involves chemical processes and that modifying of the injection brine salinity and its ionic composition can significantly impact the oil recovery. Several theories regarding the mechanism of LoSalTM flooding have been discussed in the literature. These include interfacial tension reduction, wettability alteration (cation exchange), change in pH (increase), emulsion formation, and clay migration. It is clear from the literature that there is no agreement among the researchers regarding the mechanism of LoSalTM flooding and although limited work has been done on carbonates, some studies have concluded that LoSal™ have no effect on oil recovery.

This work presents the results of core flooding tests with sea water, and two of Abu Dhabi oil field injection waters UER (197,584 ppm) and SIM (224,987 ppm) to evaluate the effects of brine salinity and ionic composition on the possible interactions of limestone rock/brine/ and oil, and to identify the recovery mechanism. The original injection waters were diluted to salinities of 5000 and 1000 ppm and the optimum salinity system was modified by varying the sulfate and calcium ion concentrations. Wettability alteration is determined by contact angle measurements. Interfacial tensions measurements of the studied systems were also performed in an attempt to evaluate the flow mechanism with LowsalTM flooding.

The experimental results revealed that a significant improvement in the oil recovery can be achieved through alteration of the injection water salinity. Reducing the salinity of UER water from 197,362 ppm to 5000 ppm resulted in an improvement of oil recovery from 63% to 84.5% of OOIP, respectively. Therefore, the salinity of 5000 ppm UER was considered as the optimum salinity to evaluate the effect of sulfate and calcium ion concentrations. Results also indicated that sulfate concentration has a significant effect on the process and increasing the sulfate concentration beyond the optimum concentration (47 ppm) resulted in a negative effect. Contact angle measurements indicated that lowering the solution salinity could shift the wettability of the system toward intermediate wettability levels and that the UER water exhibits higher shift toward intermediate wettability compared to other waters. Results also indicated that there is no clear correlation between the improvements in oil recovery and interfacial tension and the pH of the studied systems.

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