Interaction of reservoir oil/water/rock and EOR method of ion matching in low permeability reservoir

Key words:  oil/water/rock  interaction  ion matching  ion exchange  enhanced oil recovery

Abstract:

After conventional water flooding in low-permeability reservoirs, a large number of residual oil films are attached to the rock surface of the reservoir, which restricts the final recovery of water flooding. In this paper, ion exchange/adsorption and differential quantitative evaluation are evaluated by means of photoelectron spectroscopy (XPS). Then adsorption/desorption amount of characteristic polar components in crude oil on rock surface is accurately measured by quartz crystal microbalance (QCM-D). Additionally, the adhesion force and thickness of oil film on rock surface are quantitatively measured by atomic force microscope. The principle of improving water flooding efficiency through ion matching and ion exchange is put forward. Taking Jilin Q60 reservoir as an example, the ion matching oil displacement experiment is carried out to verify the mechanism of ion matching EOR. The research shows that Na⁺ is more easily absorbed on the surface of various minerals than Ca²⁺, and Ca²⁺ on the rock surface can have a large range of ion exchange with Na⁺ in aqueous solution, especially on the surface of kaolinite, chlorite and quartz. After ion exchange, the desorption amount of asphaltene molecules (C5Pe, BisA, PAP) with —COOH, —C₆H₅ and —CH₃ polar functional groups on hydrophilic and hydrophobic rock surfaces increase. On the hydrophilic rock surface, the desorption amount of asphaltene molecule with carboxyl group (C5Pe) increases the most after ion exchange with low salinity water. On the hydrophobic rock surface, the desorption amount of asphaltene molecule (BisA) with symmetrical alkyl chain increases the most after ion exchange. At the same concentration, the order of interfacial tension between solution, crude oil and rock surface from small to large is NaCl solution, Na₂SO₄ solution and CaCl₂ solution, respectively. After the exchange of monovalent ions such as Na⁺ and divalent ions such as Ca²⁺, the thickness of water film on the rock surface increases and the thickness of oil film decreases, which result in effective stripping of oil film. By adjusting the composition of injected water ions in Q60 reservoir, the oil displacement experiment shows that the oil displacement efficiency can be improved by more than 10 percentage points. The pilot test has achieved preliminary results and verified the mechanism of enhanced oil recovery.