Preparation method of unconventional natural gas well fracturing physical simulation sample

Abstract

The invention provides a preparation method of an unconventional natural gas well fracturing physical simulation sample, which comprises the following steps: 1, determining the uniaxial compressive strength and tensile strength of a reservoir shale test piece, and selecting cement satisfying the strength grade requirements; 2, placing two sandstone sheets on the two sides of a concrete mold, and pouring the stirred mixture of the cement, the quartz sand, the stones and the water between the two sandstone sheets; 3, removing the mold after curing and molding to obtain a simulated multi-layer sample, and performing bedding surface shear strength test on the sample to determine the shear strength; and 4, drilling a simulated borehole in the center of the sandstone thin plate, and cementing the simulated wellbore to obtain the multi-layer sample with the simulated wellbore. The unconventional natural gas well fracturing physical simulation sample is prepared by combining the blended similar material and the natural sandstone, the fracturing test piece more conforming to the unconventional natural gas condition is prepared, and the expansion mechanism of cracks in the direction perpendicular to the bedding direction in the unconventional natural gas well fracturing process can be more deeply studied.

Description

technical field [0001] The invention belongs to the technical field of rock sample preparation, in particular to a method for preparing an unconventional natural gas well fracturing physical simulation sample, which is suitable for the fracturing physical simulation of tight gas and shale gas in unconventional natural gas. Background technique [0002] At present, my country's proven and developed unconventional natural gas resources mainly include tight gas, shale gas, coalbed methane, etc., and are mainly distributed on land in Ordos, Sichuan, Songliao, Bohai Bay, Junggar, Qinshui, etc. basin. my country's unconventional natural gas has a resource base for large-scale development, with remarkable exploration results and important progress in development. In the past ten years, the proven reserves of unconventional natural gas have grown rapidly. Among the cumulative proven geological reserves of natural gas, unconventional natural gas accounts for about 41%, and it shows a...

AI Technical Summary

Problems solved by technology

At present, if natural sedimentary rock samples are used to prepare layered samples for laboratory experiments, the bedding is well developed, the various sedimentary layers are interlaced, and the physical properties are quite different, which makes it difficult to control the bedding plane, and there are many factors that affect fracture propagation. The expansion mechanism is difficult to grasp, resulting in large dispersion of experimental results

Therefore, the comparative study of experimental variables cannot be realized by using the current sample preparation method, and it is difficult to grasp the law of fracture penetration and propagation

[0004] The invention patent with the application publication number CN105334090A discloses a method for preparing a coal-bearing formation group fracturing physical model sample. The preparation method has the following disadvantages: the physical model sample is taken from rocks with similar mechanical properties to the area where the simulated formation is located. The outcrop rocks are characterized by high degree of weathering, well-developed joints and fissures, and high content of water-sensitive clay minerals. However, when drilling the simulated wellbore, a rock sheet with high strength and no fractures is selected. Here, the outcrop rock The method cannot achieve the effect of prefabricated wellbore; it is necessary to select the coating layer to pour the coal-bearing layer combination externally to form the fracturing model sample of the coal-bearing layer group, and the material of the coating layer should be selected to be similar to all materials. However, the middle layer is a thin rock plate, and the coal and rock thin plates are cemented on both sides. The physical properties of the rock and coal rock are relatively different, and the nature of the wrapping layer is difficult to determine; Large, in the true triaxial fracturing process, it is easy to cause stress concentration, which seriously affects the accuracy and reliability of the simulation test results; the fracturing phantom sample of the coal-bearing formation group is a cube, and its side length is 400-440mm , the sample size is large and heavy, it is difficult to move and carry out indoor fracturing experiments

[0007] The invention patent with the application publication number CN103883302A discloses a method for making a physical simulation test piece for hydraulic fracturing of a coalbed methane well. Consider the influence of the surface morphology of the roof and floor on the crack propagation, that is, the roughness of the bedding surface is uncontrollable

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