This paper (SPE 52052) was revised for publication from paper SPE 38880, first presented at the 1997 SPE Annual Technical Conference and Exhibition held in San Antonio, Texas, 5-8 October. Original manuscript received for review 21 October 1997. Revised manuscript recieved 22 June 1998. Revised manuscript approved 2 July 1998. Summary We reconstruct three-dimensional (3D) sandstone models that give a realistic description of the complex pore space observed in actual sandstones. The reconstructed pore space is transformed into a pore network that is used as input to a two-phase network model. The model simulates primary drainage and water injection on the basis of a physical scenario for wettability changes at the pore level. We derive general relationships among pore structure, wettability, and capillary pressure for the different pore level displacement mechanisms that may occur in the network model. We present predicted transport properties for three different reconstructed sandstones of increasing complexity: Fontainebleau, a water-wet Bentheimer, and a mixed-wet reservoir rock. Predicted transport properties are in good agreement with available experimental data. For the reservoir rock, both the experiments and the simulated results show that continuous oil films allow low oil saturations to be reached during forced water injection. However, the oil relative permeability is very low. P. 324

A new method for generating realistic homogenous and heterogeneous 3-D pore-scale sandstone models is presented. The essence of our method is to build sandstone models which are analogs of actual sandstones by numerically modelling the results of the main sandstone-forming geological processes-sandgrain sedimentation, compaction, and diagenesis. The input data for the modelling are obtained from image analyses of thin section images of the actual sandstone. The spatial continuity of the sandstone model in the X, Y, and Z directions is determined using a scale-independent invasion percolation based algorithm. The resulting spatial continuity function, which is an ellipsoid, may be used as a heterogeneity descriptor for the sandstone model. Heterogeneity analyses show that compaction reduces the spatial continuity in the horizontal direction more rapidly than in the vertical one. The architecture and geometry of the network representation of the pore space are determined by applying various 3-D image analysis algorithms directly on the fully characterised sandstone model. A 3-D pore network which was generated from thin section data from a strongly water wet Bentheimer sandstone is used as input to a two-phase network flow simulator. Simulated transport properties for the sandstone model are in good agreement with those determined experimentally.

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We reconstruct 3-D sandstone models which give a realistic description of the complex pore space observed in actual sandstones. The reconstructed pore space is transformed into a pore network which is used as input to a two-phase network model. The model simulates primary drainage and water injection based on a physical scenario for wettability changes at the pore level. We derive general relationships between pore structure, wettability, and capillary pressure for the different pore level displacement mechanisms which may occur in the network model. We present predicted transport properties for three different reconstructed sandstones of increasing complexity: Fontainebleau, a water wet Bentheimer, and a mixed wet reservoir rock. Predicted transport properties are in good agreement with available experimental data. For the reservoir rock, both the experiments and the simulated results show that continuos oil films allow low oil saturations to be reached during forced water injection. However, the oil relative permeability is very low.

A reservoir carbonate core plug has been imaged in 3D across a range of length scales using high resolution X-ray microtomography (µ-CT). Data from the original 40-mm diameter plug was obtained at the vug scale (42 µm resolution) and allows the size, shape and spatial distribution of the disconnected vuggy porosity, φ vug = 3.5% to be measured. Within the imaged volume over 32,000 separate vugs are identified and a broad vug size distribution is measured. Higher resolution images, down to 1.1 µm resolution, on subsets of the plug exhibit interconnected porosity and allow one to measure characteristic, intergranular pore size. Pore scale structure and petrophysical properties (permeability, drainage capillary pressure, formation factor, and NMR response) are derived directly on the highest resolution tomographic dataset. We show that data over a range of porosity can be computed from a single plug fragment. Data for the carbonate core is compared to results derived from 3D images of clastic cores and strong differences noted. Computations of permeability are compared to conventional laboratory measurements on the same core material with good agreement. This demonstrates the feasibility of combining digitized images with numerical calculations to predict properties and derive cross-correlations for carbonate lithologies.