Abstract
The microflow equipment monitored with micro X-ray computerized tomography (CT) is employed to investigate the microoccurrence of the irreducible water in a low-permeability sandstone core. By means of image segmentation and the three-dimensional (3D) image reconstruction technique, the visual microdistribution characteristics of irreducible water in two-dimensional (2D) slices and the 3D pore-throat system are quantitatively evaluated. Some interesting findings are list as below. Firstly, due to the variant micro geometric structures of the pore-throat systems, specific core slices showed significantly different irreducible water saturation even though these slices had same areal porosity. Secondly, due to the influence of capillary trapping and the existence of oil-wetting clay (main chlorite), the irreducible water saturation in the throat system (64%) is much larger than that in the pore system (36%). Furthermore, the wetting phase (irreducible water) did not spread all over the surface of the pore-throat network which caused a much more complicated oil-water two-phase interface. Thirdly, in micro scale, the main irreducible water occurrence mode in the pore system is much different from that in the throat system. In the pore system, the irreducible water principally existed in the corner of the pores which are linked through a water film. While in the throat system, the irreducible water occurrence is dominated by the water film. However, 25.5% of the throats are blocked by the irreducible water which cut off the crude oil drainage channels.
Highlights
With the increasing worldwide demand for crude oil, lowpermeability reservoirs are considered to overcome the energy deficit in developing countries [1, 2]
This section of the current study mainly emphasizes on three aspects: irreducible water distribution characteristics in 500 Two dimensional 3D (2D) slices, 3D pore-throat network, and microoccurrence modes in the pore and throat system
Irreducible water distribution and its exact content in 500 2D core slices are evaluated by areal porosity and irreducible water that is contained in the porethroat space
Summary
With the increasing worldwide demand for crude oil, lowpermeability reservoirs are considered to overcome the energy deficit in developing countries [1, 2]. Many geological factors determine the efficiency of water drives, such as rock permeability, porethroat structure, irreducible water saturation, and crude oil viscosity [4,5,6] Among these factors, the microdistribution of irreducible water confined in the pore-throat system is one of the critical factors affecting the ultimate recovery [7]. How to obtain the quantitative visualized information about the irreducible water microdistribution is necessary to Geofluids investigate the mechanisms of irreducible water on microflow behaviors in low permeable porous media. For this purpose, specific techniques are currently employed which will be discussed in the below paragraphs
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