A method for preparing physical simulation samples for fracturing of unconventional natural gas wells

Abstract

The invention provides a method for preparing an unconventional natural gas well fracturing physical simulation sample, comprising the steps of: 1. determining the uniaxial compressive strength and tensile strength of a reservoir shale test piece, and selecting cement that meets the requirements of the strength label; 2. Place two sandstone sheets on both sides of the concrete mold, and pour the mixture of cement, quartz sand, stones, and water between the two sandstone sheets; 3. Remove the mold after curing to obtain a simulated composite layer sample. The bedding surface shear strength test is carried out on the sample to determine the shear strength; 4. Drill a simulated wellbore at the center of the sandstone sheet, cement the simulated wellbore, and obtain a multilayer sample with a simulated wellbore. The present invention combines similar materials with natural sandstone to prepare unconventional natural gas well fracturing physical simulation samples, and prepares fracturing test pieces that are more in line with the conditions of unconventional natural gas, which is conducive to more in-depth research on the fracturing process of unconventional natural gas wells The propagation mechanism of fractures along the direction perpendicular to the bedding.

Description

Preparation method of physical simulation sample for fracturing of unconventional natural gas well technical field The invention belongs to the technical field of rock sample preparation, and is specifically related to the preparation of unconventional natural gas well fracturing physical simulation samples. This method is suitable for fracturing physical simulation of tight gas and shale gas in unconventional natural gas. Background technique At present, the unconventional natural gas resources proven and exploited in my country mainly include tight gas, shale gas, coal seam It is mainly distributed in the Ordos, Sichuan, Songliao, Bohai Bay, Junggar, Qinshui and other gas-bearing basins on land. Our country is very The regulated natural gas has the resource base for large-scale development, with remarkable exploration achievements and important progress in development. In the past ten years, very The proven reserves of conventional natural gas have grown rapidly....

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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