Method for evaluating development degree of shale microcosmic fractures based on nanoindentation experiment

Abstract

The invention discloses a method for evaluating the development degree of microscopic fractures of shale based on a nanoindentation experiment. The method comprises the following steps: firstly, carrying out a nanoindentation experiment, and drawing a fitting curve and a theoretical curve of H/Er and Ue/Ut according to obtained related data; calculating a vertical distance from the indentation point to the theoretical curve and an average value of the vertical distance; calculating a first evaluation value; calculating a second evaluation value according to the slope of the fitting curve and the slope of the theoretical curve; then calculating the average value of the vertical distances within the threshold range, and calculating a third evaluation value; and finally, calculating a fracture development degree evaluation value according to the three evaluation values, evaluating the shale microcosmic fracture development degree , and judging that the larger the fracture development degree evaluation value is, the better the shale microcosmic fracture development degree is. The problems of complex internal fracture observation means, long period and difficulty in in-situ monitoring in the existing nanoindentation technology are solved, and the internal fracture of the sample can be evaluated only by acquiring displacement load data through an in-situ indentation experiment.

Description

technical field [0001] The invention relates to the technical field of drilling in soil layers or rocks, in particular to a method for evaluating the development degree of shale microscopic cracks based on nano-indentation experiments. Background technique [0002] As an important unconventional energy source, shale oil and gas can greatly improve the world's energy supply structure. Reservoir structure and mechanical properties play a vital role in the efficient extraction of shale oil and gas. [0003] At present, the research on the structure and mechanical properties of shale reservoirs is generally completed by taking cores to make shale samples for indoor experiments and micro-nano indentation mechanical testing techniques. However, in actual operation, due to the unstable chemical and physical properties of shale, coupled with the development of natural fractures and fissures, cores are easily broken and muddy, and the quality is difficult to guarantee, making it dif...

AI Technical Summary

Problems solved by technology

However, in most cases, only a small number of cracks will cause loading bursts in the image due to fracture, and the existence of most cracks will not change the curve greatly. The apparent mechanical properties of its low hardness and low elastic modulus The properties are similar to clay, so it is often difficult to directly judge the degree of crack development of the sample through the curve shape and mechanical parameters

Moreover, the cost of microscopic observation methods is high and the cycle is long in the actual operation process, and it is difficult to meet the requirements of completing analysis in a short time or even in-situ real-time monitoring

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