| Marine carbonate reservoirs is a crucial type of reservoirs in hydrocarbon exploration. However, the micro-pore textures of carbonate reservoirs possess strong anisotropy. It has variety reservoirs spaces, such as pore, vug, hole, fracture and so on, which are very complex. Take Puguang Oilfield for example, the rocks in one layer with same lithology are frequently developed moldic pores, intragranular dissolved pores, intergranular dissolution pore, et al. Another classic sample is Luojiazhai Oilfield. Carbonate reservoirs in Luojiazhai Oilfield have two characters. Firstly, compare to abundant of pores, the throats are rare, which lead to poor permeability of carbonate reservoirs. Secondly, the permeability is a difference of several tens of times while reservoirs character by same lithology, porosity, textures in one area. In one word, reservoir property of carbonate would be deeply influenced by the structure, size, geometry, connectivity of pore and throat. That means new technology and theory should be required to research the pore and throat of carbonate reservoirs.With the development of CT and computer image processing technique, pore and throat of carbonate reservoirs can be descripted finely and quantitatively characterized in 3D space. With the help of CT, fractal and multifractal, this dissertation investigated the pore and throat structure of carbonate reservoirs in 3D space and quantitatively characterized by traditional geometric parameters and fractural and multifractal analysis. Two main conclusions are achieved. One is high-resolution CT technique can be used to descript and character pore and throat of carbonate reservoirs in 3D space. Another is the structure of pore and throat holding the character of fractal and multifractal.Based on the classification of carbonate reservoirs space by Choquette and Pray (1970), Lucia (1983), this dissertation displayed the characterization and alanysis on porous, cavern, fracture individually. Results were listed below.1. For the porous carbonate, the shape of intergranular pore and intercrystalline pore are triangle, which are radial in 3D space. The length of pores is a bit of long with plenty of throat which leads to connect well for whole rock. The shape of moldic pore and gypsum mould pore are regular, these are almostly cycle in 2D space and are sphere in 3D space. The pores of this type are big, correspond to high porosity, and the throats of it are rare which lead to low permeability. The porous have for the type of algal lattice frame pore and mixed pore hold strong heterogeneity. The reservoirs space of this type is influenced by fabric and composition of carbonate rock; Dissolved pore is affected by the late diagenesis which leads to strong heterogeneity. The pore is harbor shape and throat is controlled by dissolution.2. The carbonate reservoirs with vuggy and hole is divided into separated and connected. Vug and hoe of separated are the main reservoirs space. Shape of these pore with different size are isolated and variety. Similar with the separated, the reservoirs space of the connected is dissolved vug and hole. Differently, the vug and hole are connected by dissolved fracture, crack, porous in matrix. Furthermore, the connected channels could be reservoirs space for hydrocarbon.3. The space is small, the length is long, and the angle with different plane, XY, YZ, XZ for fracture. They would be crossed if several fractures are formed in reservoirs.4. In 3D space, the fractal and multifractal are proved by fractal dimension, partition function x(q,δ), the mass exponent T(q) and the singularity exponent, α(q) et al. for carbonate reservoirs pore.The left side of the multifractal spectrum curve of a-f(α) could reflect the size distribution of big pore and the right could reflect the size distribution of small pore. Asymmetry index R could be the index for the distribution of size of pore and quantitatively character whether symmetric of multifractal spectrum curve of a-f(a). Multifractal spectrum curve behaviors as right axis deviat for LJ1-1 with intergranular pore, and Asymmetry index R is less than zero with △αL<△αR. The width of multifractal spectrum curve Aa has high value correspond to big pore and well permeability. Because of the worse porosity and permeability for Sml with intercrystalline pore, the value of △αL is equal to that of △aR and the value of asymmetry index R is closed to zero which means no obvious size difference of pore.4. The Dbox regularity index of pore shapes could have different response characteristics for different pore. The order of Dbox for different types of pore, sorted by value, is moldic pore, intergranular pore, intercrystalline pore and mixed pore, corresponding to1.73～1.88,1.66～1.72,1.58～1.67,1.53～1.61, respectively. More regular of pore, higher value of DboX . For example, the value of Dbox for crycle is 2 in 2D space and 3 in 3D space. Moldic pore with the max value of Dbox have the most regular shape like circular. Mixed pore with the min value of Dbox,1.563, have different types such as intergranular pore, moldic pore, intercrylline pore, et al. The moldic pore sample LJ5 has the highest value of Dbox, up to 2.7834, and shape like sphere in 3D space. According to porosity and permeability analyzing, the porosity could influence Dbox.Base on CT experiment, Grain recognize, volume rendering method of VTK and Seed filling method, the research extract structure of pore and throat, quantitative character with volume of pore and throat, the connective volume ration, the radius of pore and throat, the max and min value of radius, the shape factor, regularity index Dbox, partition function x(q,δ), the mass exponent T(q) and the singularity exponent, a(q), et al. by conventional geometry, fractal and multi fractal. |
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