Jin Zhang

Date of Award

January 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geological Engineering

First Advisor

Richard LeFever

Abstract

This study investigates an idea of chemical imbibition using surfactant formulations to improve oil recovery from Bakken shale. The ultimate objective of this research is to determine the potential for surfactant formulations to imbibe into and displace oil from shale and the mechanisms behind it.

In this study, experiments were conducted to determine the true wetting state of different parts of Bakken Formation using the Amott-Harvey method. Then four surfactant formulations (two anionic surfactants, one nonionic surfactant, and one amphoteric surfactant) investigated previously, have been introduced to identify if the surfactant can alter the wettability of cores from the Bakken Formation with the same method. Phase behavior between surfactants, synthetic Bakken Formation water and crude oil was investigated to achieve optimal salinity. Furthermore, interfacial tensions (IFT) between surfactant solution and crude oil were examined to verify the optimal salinity obtained by phase behavior study by means of a spinning drop tensiometer. Imbibition rate and oil recovery were experimentally investigated in Group 1 with aqueous solutions including fresh water, brine (30% TDS), surfactant solutions, and Group 2 with different type surfactant solutions at optimal salinities.

Bakken shale cores were generally oil-wet or intermediate-wet. Wettability of the cores can be altered toward water-wet by four surfactant formulations tested. Incremental oil recovery (EOR) was obtained from 6.80% to 25.40% OOIP over brine alone, indicating wettability alteration is one mechanism for oil recovery improvement using surfactant imbibition. In most cases, optimal salinity was obtained by phase behavior study and the IFT test. With the optimal salinity, the surfactants that we tested exhibited favorable imbibition rates and good oil recoveries at reservoir temperature, showing that IFT reduction can be taken as another mechanism for increasing oil recovery in the Bakken Formation.

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