Title

Combined Ionically Modified Seawater and Microgels to Improve Oil Recovery in Fractured Carbonate Reservoirs

Abstract

Modified waterflooding is a process in which the ionic composition of injected water is altered to improve oil recovery. Recently, extensive studies on crude oil, brine, and rock systems reported that the composition of injected water can change rock wettability during waterflooding. Carbonate reservoirs are mixed or oil wet reservoirs and most of these reservoirs are fractured, resulting in low oil recovery. In the last decade, many researchers conducted laboratory experiments to evaluate gel treatment in fractured models. The objective of this study is to examine the effects of sulfate ion concentration and low salinity water (diluted seawater) on improving oil recovery in fractured and nonfractured reservoirs when combined with microgel treatment. Four key parameters were examined: increased sulfate ion concentration, a degree of seawater dilution, fracture width, and matrix permeability. Three models were designed and tested in this work: nonfracture, fully-open fracture, and partially-open fracture model. Three different sulfate ion concentrations (typical seawater and that which was doubled and then tripled in sulfate ion concentration) and low salinity water that had been diluted 10 and 100 times were applied as waterflooding processes in two fracture widths (0.5 mm and 1 mm) with two different matrix permeabilities (20 md and 2.44 md). Microgel (425 µm in size) was swollen in typical seawater and injected in the fractured model to block the fractures and divert the brine into the matrix. The results show that increased sulfate ion concentration and diluted seawater can improve oil recovery by changing core wettability towards water-wet conditions. We also found that diluted seawater can improve both displacement and sweep efficiency while increased sulfate ion concentration only improves displacement efficiency when applied after gel treatment in both fully open fractures and partially open fractures. Therefore, diluted seawater can improve plugging efficiency but sulfate ions cannot. Increased sulfate ion concentration followed by diluted sea water with microgel-filled fractures might be a viable technique to improve oil recovery in fractured carbonate reservoir. The sulfate ion concentration effects decrease as fracture width increases and matrix permeability decreases. Also, the diluted seawater effects decrease as matrix permeability decreases. Combining microgel with sulfate ion concentration results in higher oil recovery than combining microgel with low salinity water in fully open fracture. However, combining microgel with low salinity water showed highest oil recovery in partially open fracture.

Department(s)

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Fractured Reservoir; Improved oil recovery; Low salinity waterflooding; Microgel treatment; Modified seawater

International Standard Serial Number (ISSN)

0920-4105

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2018 Elsevier B.V., All rights reserved.

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