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The existence of gravels in the glutenite formations leads to the complex geometries of hydraulic fracturing propagation and difficult construction in fracturing engineering. To study the hydraulic fracturing propagation law of glutenite formations, this paper establishes a fracture propagation model for the heterogeneous glutenite formations based on discrete element method, and analyzes the effects of gravel content, particle size, distribution, horizontal stress difference, fracturing fluid viscosity and flow rate on hydraulic fracturing propagation behavior. Results show that the complex geometries of hydraulic fractures in glutenite formations can lead to the generation of branched fractures and fracture bifurcation. Small-sized gravels have little effect on the fracture propagation shape which leads to a single main fracture with a flat fracture surface, on the contrary, large-sized gravels may induce hydraulic fractures to deflect along the gravel interface and form branched fractures with distorted fracture surfaces. Hydraulic fractures can propagate around gravels under the condition of high stress difference, high viscosity and medium flow rate. Gravels can prevent the propagation of hydraulic fractures under low stress difference, low viscosity and small flow rate. Hydraulic fracture bifurcation can occur when encountering gravels under high stress difference and large displacement. Properly increasing the high viscosity of fracturing fluids can effectively promote the main hydraulic fracture propagation and reduce the fracture tortuosity, thereby avoiding sand up.

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The composite salt layer of the Kuqa piedmont zone in the Tarim Basin is characterized by deep burial, complex tectonic stress, and interbedding between salt rocks and mudstone. Drilling such salt layers is associated with frequent salt rock creep and inter-salt rock lost circulation, which results in high challenges for safe drilling. Especially, the drilling and completion processes of the salt-gypsum layers of one typical group are found with frequent downhole accidents and complex issues, such as hole shrinkage, sticking, well kick, and lost circulation, which leads to high difficulties in delivering desirable cementing quality and severely hinders the subsequent safe rapid drilling. Reaming while drilling can effectively enlarge the wellbore diameter, provide extra tolerance for creep shrinkage of salt layers, and ultimately help to shorten drilling time, reduce accidents and complex issues, and improve the lifecycle of wells. In this research, a numerical simulation method was developed to invert the creep laws of composite salt layers, based on reaming while drilling. It is generally believed that the dislocation creep mechanism is dominant in coarse-grained salt rocks, while the pressure solution creep mechanism is dominant in fine-grained salt rocks. Here a well in the Dabei area was taken as an example and the numerical simulation of hole shrinkage at the wellbore scale was performed, based on the actual data before and after reaming and also the theoretical analysis of the two salt rock creep mechanisms and corresponding laws. Furthermore, the inversion results were validated using field data. This research discussed the selection of creep parameters and their variation, in cases of the dominance of the dislocation creep and pressure solution creep mechanisms. This presented method can accurately predict the creep behavior of salt layers and can be used as an effective supplement tool for other test methods like laboratory experiments.

Heterogeneity analysis of conventional data, such as geophysical log data, has been still limited to the application of near-wellbore zone, which makes it difficult to optimize the hydraulic fracturing design and may render suboptimal performance. However, the fluctuation of multi-stage pumping data, manifesting nonlinear behavior of physical properties with shale reservoir during hydraulic fractures propagation stage, is usually ignored. In this study, the empirical mode decomposition technique (EMDT) was introduced and applied to the multi-stage pumping data to determine the respective Intrinsic Mode Functions (IMF). By using a relationship between the IMF number and its mean wavenumber, the heterogeneity index associated with far-wellbore shale reservoir was determined. The results indicate that the heterogeneity index from multi-stage pumping data is good coincided with the effective stimulation reservoir volume (ESRV) obtained from micro-seismic events. Not only that, but it also reveals that there is a strong correlation of heterogeneity index, IMF number, ESRV, and degree of heterogeneity within shale reservoir. This work has demonstrated that heterogeneity index analysis combined with EMDT has been significantly important and essential to quantify the degree of heterogeneity within far-wellbore shale reservoir from multi-stage pumping data, which contributes to optimizing the hydraulic fracturing design and improving good optimal performance.