Solvent-enhanced Spontaneous Imbibition in Fractured Reservoirs

Abstract

Oil recovery in fractured reservoirs by water flooding critically depends on the wetting properties of the matrix blocks between the fractures. The recovery from oil-wet reservoirs is small. In incompletely oil-wet systems, the presence of initial water may change the wettability characteristics so that imbibition and some oil recovery can occur. The hypothesis in this work is that water-soluble solvent (diethyl ether) improve the ultimate recovery and the imbibition rate in partially and completely water-wet cores. The main recovery mechanisms are the wettability change of the partially water-wet cores and oil swelling and the oil viscosity reduction in both partially and completely water-wet cores. This paper reports an experimental study concerning the recovery enhancement by water-soluble solvent (diethyl ether). We used an Amott imbibition cell studying oil saturated samples of various wettabilities, permeabilities using oils of different viscosities and two different diethyl ether (solvent) concentrations in the aqueous phase. In the first stage of the experiment, the completely water-wet core was exposed to brine without solvent. In a second stage, the core was put in a new Amott cell that was filled with solvent/ brine mixture. The extra recovery by solvent/brine mixture strongly depends on the residual oil saturation after brine imbibition and it is relatively insensitive to the permeability of the core or the oil viscosity. Therefore, larger residual oil saturation resulted in a higher extra recovery. For the partially water-wet samples, we also started with exposing the core to pure brine without solvent. Contrary to the completely water-wet samples, there was a significant increase in recovery rate when the sample is transferred to another Amott cell where it is exposed to a mixture of solvent and brine. In view of large values of the inverse Bond number in both partially and completely water-wet cores, the transfer between matrix and fracture capillary driven.

Modeling solvent enhanced gravity drainage from a single matrix block in fractured oil reservoirs

“…In deep reservoirs that are composed of mainly heavy components, use of hydrocarbon gas requires high compression costs to reach miscible conditions. Also in shallow heavy oil reservoirs, use of heavier hydrocarbon solvents are suitable compared to gas injection (Gates 2007;Chahardowli et al 2013;Pathak et al 2013;Mayorquin-Ruiz and Babadagli 2016). Oliveira et al (2009) discussed that oil viscosity and type of the solvent are very important parameters to improve the oil recovery in heavy oil reservoirs.…”

“…The impact of diffusion has been studied by several investigators for enhanced oil recovery from fractured reservoirs (Jamshidnezhad et al 2004;Darvish et al 2006;Karimaei and Torsaeter, 2008). Rich solvents showed important recovery performance in laboratory analysis for fractured rocks (Chahardowli et al, 2013). Hatiboglu and Babadagli (2008) used pentane to understand flow mechanisms in fractured rocks through micro model studies.…”

Construction of an efficient development mode for buried-hill fractured reservoirs in Bohai Bay

“…Naturally fractured reservoirs (NFRs) play an important role in petroleum industry in the world (Yu et al, 2009;Salimi and Bruining, 2010;Chahardowli et al, 2013). In comparison with the conventional reservoirs, NFRs consist of two systems: Fracture and matrix systems (Rangel-German and Kovscek, 2002).…”

Impact of Petrophysical Properties on Hydraulic Fracturing and Development in Tight Volcanic Gas Reservoirs

“…However, field data show that only a fraction of the large water volume used in hydraulic fracturing treatments is recovered during the flow-back operation. The spontaneous imbibition properties of tight sand and shale reservoirs have been investigated by many experts [9][10][11][12][13][14]. However, there is less research related to volcanic reservoirs.…”