Abstract
After large-scale sand fracturing of horizontal wells in shale gas reservoir, fracturing fractures will deform in the production process. However, fracture deformation will lead to the decrease in fracture conductivity and then cause the decrease of gas well productivity. Therefore, in order to evaluate the fracturing fracture deformation mechanism of shale reservoirs, the shale proppant-supported fracture deformation evaluation experiments were carried out under different proppant types, particle sizes, sanding concentrations, and closure pressure conditions, respectively, and the variation curves of fracture width was calculated by a stereomicroscope under different experimental conditions. Then based on the experimental results, the fracture sensitivity factors and fracture deformation mechanism were analyzed, and the deformation mechanisms of fracturing fractures affected by proppant embedding and crushing were studied emphatically. The analysis results of fracture sensitivity factors indicate that the larger the particle size and hardness of proppant, the lower the sand concentration, proppant embedded on the shale rock surface. Moreover, the deeper the proppant is embedded, the faster the fracture conductivity decreases. In addition, the greater the closure pressure, the more serious is the proppant embedment, and the faster the fracture width decreases. The analysis results of fracture deformation mechanism show that, on the on hand, under variable closure pressure, the proppant with larger hardness and larger particle size is used for fracturing, and the proppant embedded in the fracture surface is the main cause of fracture deformation. However, if only the sand concentration of the proppant in the fracture is changed, the fracture deformation is jointly dominated by the embedding and crushing of the proppant. On the other hand, under constant closure pressure, the main mechanism of fracture deformation is that the proppant is embedded into the fracture surface when the closure pressure is low, but if the closure pressure is high, the main mechanism of fracture deformation is the crushing and compaction of proppant.
Highlights
There are many factors that cause shale reservoir fracturing fracture deformation, and many scholars at home and abroad (Boyer et al, 2014; Li et al, 2016; Liu et al, 2019; Ao et al, 2020) have carried out related research
The shale rock samples of Longmaxi Formation in Sichuan Basin were taken as the study subjects and through the designed evaluation method of fracture deformation mechanism, a series of fracture conductivity curves and fracture width curves were measured under the conditions of proppant types, proppant particle size, sand concentration, and closure pressure, respectively
3) the prepared shale rock plate is substituted for the steel plate, and the operation in step 2 is repeated to test the Experimental Study on Fracture Deformation conductivity of the proppant-supported fracture under the same conditions
Summary
As one of the unconventional oil and gas resources, shale gas reservoir has the characteristics of low porosity, low permeability, high stress, and so on (Tan et al, 2017; Lei et al, 2018; Zeng 2020; Ao et al, 2021), so the natural productivity of shale gas reservoir is very low. In 2018, based on the research by Guo and Zhang (2011), He et al (2018) used experimental methods to study the effects of closure pressure, proppant particle size and sand laying method on the fracture conductivity of tight sandstone, and the conclusions are consistent. In the production process of shale gas wells, in order to make proppantsupported fractures effectively maintain its high conductivity, it is necessary to fully understand the deformation mechanism of fracturing support fractures under different conditions. The shale rock samples of Longmaxi Formation in Sichuan Basin were taken as the study subjects and through the designed evaluation method of fracture deformation mechanism, a series of fracture conductivity curves and fracture width curves were measured under the conditions of proppant types, proppant particle size, sand concentration, and closure pressure, respectively. The research results are expected to provide some theoretical guidance for the optimization of fracturing parameters in shale gas reservoirs
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