Modeling And Application Of 3D Digital Core Based On Low Permeability Reservoir

Because the low permeability reservoirs have complex lithologic features and bad physical properties, the conventional petrophysical experiments have difficulties to research them. The petrophysical numerical simulation based on digital core provides a new technical support to the research of low permeability reservoirs.This paper is based on3D digital core constructed by X-Ray CT scanning and process-based method. We use numerical simulation to get the petrophysical properties of pore structure, electrical resistivity, filtration and NMR. We have created three new technologies in the aspects of calculating pore structure parameters, constructing saturation and permeability models and extracting grain-size characteristic by NMR. Then the results of numerical simulation are verified with conventional petrophysical experiment datum, such as physical property, casting thin sections, conventional mercury penetration, grain size and NMR. Finally, we construct the true3D digital cores of SanGongHe formation in Mo Bei oil field and Shi He Zi, ShanXi formation in Su Li Ge gas field. Then we take the practical research in characterizing pore structure, bulding saturation models, calculating permeability and extracting the grain-size distribution. The result is good for the application of digital core in the area of Logging and Geolegy. The conclusions of this paper are as following:(1) The3D digital core by X Ray CT scanning can characterize the pore structure of rock actually. Because the resolution of CT scanning is inverse with the dimensions of digital core, the micron sized and nanometer sized digital cores both have the advantages and disadvantages. Therefore, we propose a new method to construct the high-resolution digital core by micron sized CT scanning combined with mercury penetration and NMR.(2)The maximal ball algorithm can give the paramaters of pore structure quantitatively. The result has a good concordance with mercury penetration, and it is more vivid and direct. The maximal ball algorithm can not only identify the pore and throat respectively, but also overcome the disadvantages of conventional pore structure research which needs multi experiments.(3)Based on the tortuosity model by conductive mechanism of double electrode layer on rock grain, the conventional conductive model of parallel connection is calibrated and we get the new relationship of F-φ; The affection of bound water saturation to relationship between lithology and electricity is simulated by regulating the thickness of bound water on the digital core, then we propose a new non-Archie satyration model with bound water saturation; We also create a new automatic allied electric conduction model of three components according to the conductive forms of different pores in digital core.(4) According to the heterogeneity and content of bound water in the pores of digital core, we propose the concept of effective flow porosity by the similarity of fluid infiltrating and electric current. The effective flow porosity has a good accordance with permeability, so we construct a new method to calculate permeability with formation factor, bound water saturation and effective flow porosity.(5)There is a transformational relationship beteen rock grain radius and NMR T2spectrum, so we propose a method extracting grain size by NMR T2spectrum based on digital core. This approach can help us get the continued formation grain size by NMR logging. It is vary helpful wih the classification of microfacies of deposition.