Study On Brittleness Index And Physical Model Of Muddy Loose Sandstone

Because of the high plastic, high fracture toughness, in muddy loose sandstone it difficult for crack to initiation, fracture morphology is complexity. Performance in the main fracture have large tortuosity, and there appeared shear failure in the fracturing process, shear cracks formed on both sides of the main fracture, sand plugging often happen in the fractures. In order to study the fracturing feasibility evaluation system and mechanism of crack initiation of muddy loose sandstone, in this paper we use the brittleness index to describe the ability to form cracks in muddy loose sandstone, we first summarize the existed brittleness index calculation method, and then proposed a new brittleness index calculation method suitable for muddy loose sandstone. Then based on muddy loose sandstone core production methods and processes, first we measured physical parameters of muddy loose sandstone core, and obtained the brittleness index according stress-strain curves. By compared the experimental phenomena and theoretical results, the new brittleness index can be a good way to describe the destruction of facture. Then study the relationship between pressing pressure, cement content and the clay content with brittleness index. And then analysis the stress-strain curve of muddy loose sandstone core, derived the variation between compacting pressure, cement content and the clay content with Young’s modulus, compressive strength and softening modulus.Based on the above experiment results and phenomena, among loose sandstones, different composition and microstructure of clay have significant effects on the P-wave and S-wave velocities of the rock. By analyzing the different distributions of clay particles of muddy loose sandstones, we divided the reservoir micro structure of muddy loose sandstone into three styles: laminar shale, framework shale and dispersed shale. According to the feature of the reservoir microstructure, we used the improved Backus average model, Xu-White muddy sands mixed model and DEM model to establish some relevant physical models. From this model, we developed the physical model of muddy loose sandstone software, which can obtain corresponding physical model effective elastic parameters and P-wave and S-wave velocities according to the selected physical model. From software we calculated the change regulation with clay content, porosity and pore shape of different reservoir microstructures of P-wave and S-wave velocities of the rock quantitatively. At the same time, analyzed and researched the different reservoir micro structures elastic parameter: the dynamic Young module and the Poisson’s ratio changes with the factors of shale content, porosity and pore shape. By simulating real reservoir environment, the microstructure diagnosis of muddy loose sandstones was carried out: the experiments artificial loose sandstones, clay mainly exist as framework particles, pore structure mainly were spherical pores.