Digital Rock Reconstruction Of Complex Reservoir And Numerical Simulation Of Acoustic And Electrical Properties

With the increasing development of oil exploration,China's major oil exploration and development becomes more and more difficult and the exploration object is transferring from conventional reservoirs to complex reservoirs.Because of the complexity of the reservoir has characteristics of complex lithology,complex pore structure,thin formation layer,strong heterogeneity,etc.,they lead to difficult to carry out complex reservoir core petrophysical experiments,thus limits the logging evaluation of complex reservoir.Digital core technology as a new numerical simulation method has gradually play an important role in the study of the physical properties of complex reservoir rocks.The main objective of this thesis is a complex reservoir with a fracture and a layered structure,we use the digital technology to build the core containing fractures and layered sandstone,and then we study the electrical and acoustical characteristics of complex reservoir rocks.The digital rock technology makes up the deficiencies of traditional petrophysical experiments.The study of electrical and acoustic characteristics of complex reservoir rocks can lay the foundation on the research of new methods and theories.This paper describes the construction of porosity digital core with X-ray CT method and process-based method.Then according to the study,we use the fractional Brownian motion model constructed a rough self-affine fractal fractures and then superimpose the fracture on the matrix to build a fractured digital core;then we use a modified process-based method to construct a layered sandstone,and then based on the digital core,we use a two-phase immiscible lattice Boltzmann method to simulate oil-water separation process in the pore space and determine the oil/water distribution,they lay a foundation for simulating electrical and acoustic properties of complex reservoir rock.We extended the digital core technology to the study of electric properties of complex reservoir and studied the effect of fracture aperture on the formation factor and cementation exponent by using finite element method,we further studied the relationship between the water saturation and the resistivity index under different fracture aperture and studied the effect of fracture aperture and fracture angle on the electrical anisotropy.The results show that: the presence of the fracture has an effect on fluid distribution in pore space.The formation factor decreases with the increasing of whole porosity,but in the double logarithmic coordinates the formation factor and porosity still show a linear relationship.The cementation exponent decreases with increasing of fracture porosity.When the fracture aperture is narrow,it has no significant influence on the relationship between RI and Sw.The main reason is that the fracture is at a pore scale.When the fracture's scale is larger than pore scale(the rock matrix pore and fracture form a dual-porosity system),a non-linear characteristic between RI and Sw occurred on a double logarithmic scale.At the same water saturation,the resistivity index is bigger,when the fracture aperture is wider.The presence of fracture caused the difference of in horizontal and vertical resistivity and fractured core electrical anisotropy coefficient is affected not only by the fracture porosity,but also affected by the fracture angle.Traditional Archie equation cannot well describe the electrical characteristics of layered sandstone core,when the current flows parallel to the sandstone layer,the relationship between water saturation and resistivity index shows a nonlinear relationship in the double logarithmic coordinates.Layered sandstone electrical anisotropy coefficient is a function of water saturation,the relationship curve is the "S" type.We also extended the digital core technology to the study of acoustic properties of transversely isotropic(TI)medium.We studied the influence of fracture aperture and fluid properties on elastic parameters of TI medium.The results show that: In dry rocks,the stiffness elements in the vertical to fracture direction and parallel to fracture direction deviate gradually with the increasing of fracture aperture.The stiffness elements that parallel to the fracture plane changes smaller compared to that vertical to the fracture plane with the increasing of fracture aperture.With the increase of the fracture width,P-wave and shear wave velocity decreases.When the fracture aperture is large enough,the P-wave and shear wave velocity tend to 0.In fluid saturated fractured rocks,with the increase of fluid bulk modulus,the shear wave velocity showed an increasing trend,but the change is very small.The P-wave velocity increases gradually with the increase of fluid bulk modulus.When the reservoir spaces contain oil or water,Vp/Vs changed little,but if the reservoir space containing gas,Vp/Vs decreases sharply,this phenomenon indicates that we can use Vp/Vs to identify gas of fractured reservoir.Both rock particle size and porosity should be considered in dry layered sandstone.When the layered sandstone fully saturated with fluid,the p-wave and s-wave velocity changes little with the fluid modulus and almost parallel with each other.