Study On Formation Seepage Characteristics Based On Digital Rock And Digital Well

In the process of oilfield exploration and development,in order to accurately evaluate the production capacity,it is particularly important to study the seepage characteristics of the formation.Among them,the absolute permeability determines the amount of produced liquid,the relative permeability reflects the nature of the liquid,and the fluid distribution characterizes the oil content of the formation development stage.Due to the complex geological conditions of most oilfields in China,the seepage characteristics of the formations are quite different.For the study of seepage characteristics of the formation,the petrophysical experimental method is usually adopted,to get results represent the seepage characteristics of the formation which is more realistic,but the experimental period is generally longer.The digital rock technology can quantitatively simulate the seepage characteristics of the formation,and the simulation period is relatively short,but it is still limited to the collected discrete cores;however,the 3D digital well technology is a method that can simulate the characteristics of continuous deep seepage,but at present,there are few research results at home and abroad,which is a challenging new problem.In this paper,the seepage characteristics of the formation are studied from three aspects:petrophysical experiment,small-scale core simulation and large-scale wellbore simulation.Firstly,the measured characteristics of seepage flow in the laboratory are summarized.The three-dimensional digital rocks with different fluid distributions constructed by CT scanning are proposed.Based on the expansion algorithm,an oil-water distribution image restoration method is proposed,and a set of methods for quantitatively characterizing micro-residual oil is proposed,including quantitative characterization of both microscopic residual oil content and structural parameters.For the study of seepage characteristics of nuclear magnetic resonance experiments,a new method for accurately measuring core porosity using MSE pulse sequence is proposed.By using one-dimensional nuclear magnetic resonance and two-dimensional nuclear magnetic resonance experiments of core,saturated oil,saturated water and centrifugal,the distribution law and mode of fluid in organic pores and inorganic pores are reflected,and the method for determining the irreducible water saturation is given,and proposed a new one-dimensional nuclear magnetic experiment to analyze the fluid distribution map and the two-dimensional nuclear magnetic resonance fluid component identification map.The wettability of different types of pores was characterized based on various nuclear magnetic resonance techniques and infiltration process experiments,the nuclear magnetic response range of different components under core oil and water wettability conditions was determined,and the presence of intermolecular homonuclear dipole coupling was verified.Secondly,using the existing data to construct the best three-dimensional digital rock,a multi-mineral component digital rock method based on CT data combined with X-ray diffraction and a multi-scale fusion digital rock method based on rock particle size data and mercury intrusion data are proposed.Through the comprehensive analysis of mathematical morphology method,pore network method and lattice Boltzmann method,the differences in simulation results of rock seepage characteristics are used to determine the applicable methods for seepage simulation under different research purposes and conditions.For fractured reservoirs,the influence of crack tortuosity on seepage is studied,and the seepage coupling between fracture and matrix is found comprehensive permeability model is proposed.The numerical simulation of 3D digital rock can obtain the nuclear magnetic resonance response,combine the nuclear magnetic resonance spectrum with the seepage characteristics of the formation core,and explore the method of studying the seepage characteristics of the formation rock based on nuclear magnetic resonance(NMR).Firstly,the NMR response of the core was simulated by random walk method,and the feasibility of the simulation method was verified.A new method based on voxel finite element method for embedding internal gradient field is proposed.Compared with the traditional dipole summation method,the new method can better capture the magnetic field changes near the pore surface,and the calculated internal magnetic field gradient distribution would be more accurate.The effects of various influencing factors on the internal gradient field of the core are comprehensively analyzed,and the diffusion domain maps of different types of sandstones are drawn.Take the pore radius of the nuclear magnetic resonance T₂ spectrum conversion as the ligament,based on the relationship between the water saturation obtained by the digital rock and the geometric mean of the oil block radius distribution,the microscopic residual oil radius distribution under different saturation conditions is calculated by NMR.A method for spatial distribution of fluid types with different flow velocity equivalents is proposed.The core permeability is calculated by NMR calculation by combining the T₂ spectral coefficient method to solve the irreducible water saturation.The NMR T₂ spectrum was converted into the correlation between capillary pressure and water saturation,and the pore structure index was obtained.The relative permeability was calculated by using the Brooks-Corey model.The calculated results agree well with the experimental results.The porosity data calculated by resistivity imaging log was used as the hard data,and the full-diameter CT data was used as the training image.The multi-point geostatistical method was used to construct the three-dimensional digital wellbore,and the calculated porosities were consistent with the core analysis results.Through the correlation between porosity and permeability,the three-dimensional permeability distribution of the well was constructed,and the permeability value of each layer was calculated by the finite element method.The T2 distributions in well were constructed by 3D pore size distribuitons,and then the relative permeabilities were calculated to realize the continuous seepage characteristics of different layers.