Understanding hydraulic fracture mechanisms: From the laboratory to numerical modelling

Hydraulic fracturing technology is the main method to develop low-permeability reservoirs. Fracture conductivity is not only the basis of fracture optimization design but also one of the key parameters to determine the effect of hydraulic fracturing. However, current methods of calculating fracture conductivity require a lot of time and labor cost. This research proposes a fracture conductivity prediction model based on machine learning. The main controlling factors of fracture conductivity are determined using the Pearson coefficient method and gray correlation analysis. Example application shows that the R 2 values of the BP neural network model based on a genetic algorithm for predicting the fracture conductivity of block A and block B are 0.981 and 0.975, respectively, indicating that the machine learning model can accurately predict fracture conductivity.

Section: Introductionmentioning

confidence: 99%

Fracture Conductivity Prediction Based on Machine Learning

Wang,

Zhang,

et al. 2024

“…Hydraulic fracturing is widely used for exploiting low-permeability oil and gas reservoirs. − A proppant is injected to support the fracture and prevent the fracture from closing under in situ stress. The placement of a proppant in a hydraulic fracture will directly affect the fracture conductivity and thus affect the stimulation effect of hydraulic fracturing. − …”

Section: Introductionmentioning

confidence: 99%

Proppant Settlement and Long-Term Conductivity Calculation in Complex Fractures

Wang,

Zhang,

Zhang

et al. 2024

The current research on fracture conductivity ignores the placement of the proppant in fractures and relies on single-fracture conductivity testing and calculation, which cannot represent the overall conductivity of complex fracture systems. This research proposes a calculation method for the long-term conductivity of complex fractures based on proppant placement. This method considers fracture morphology, proppant placement, proppant embedment, and deformation under high closing pressure. The research results show that fracture conductivity decreases with increasing time, which can be divided into three stages: the embedding stage, the creep stage, and the stabilization stage. The long-term conductivity of the main fracture is higher than that of the branching fracture. With increasing closing pressure, the conductivities of both the main fracture and the branching fracture decrease. This is because increasing closure stress accelerates proppant embedment and creep, compressing the fluid flow space and further reducing fracture conductivity. Fracture conductivity is related to the placement of the proppant and sand concentration. Increasing the sand ratio can significantly increase the placement of the proppant in the main fracture and branching fractures, thereby improving fracture conductivity. Increasing the fracturing fluid viscosity can increase its proppant migration capacity. The proppant does not easily settle prematurely in high-viscosity fracturing fluid and can enter more into branching fractures, thereby improving their conductivity.

“…Hydraulic fracturing is an important technology for developing low-permeability oil and gas reservoirs. The transport and placement of the proppant in fracturing fractures directly affects fracture conductivity, further affecting the productivity of oil and gas. − Clarifying proppant transport in fractures is of great significance for optimizing the fracturing design.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Proppant Transport in Major and Branching Fractures Based on CFD-DEM

Zuo,

Li,

Han

et al. 2024

This research investigated the effect of branching fracture, proppant, and fracturing fluid on proppant transport based on the CFD-DEM coupling model. The obtained results show that the balance height of embankment in the major fracture decreases gradually with increasing angle between major and branching fractures, while it increases gradually in the branching fracture. This is because the additional resistance of fracturing fluid flow at the joint increases with increasing angle, leading to the decrease of the fracturing fluid velocity. The proppant is prone to settling in branching fractures, resulting in the increase of embankment height in the branching fracture. At angles of 45, 60, and 90°, as the diameter of the proppant increases from 0.8 to 1.1 mm, the balance height of embankment increases slightly in the major fracture, while it decreases in the branching fracture. The frictional resistance of the fracture wall enhances the difficulty of large proppant entering the branching fracture, resulting in a decrease in the amount of proppant entering the branching fracture and a decrease of the balance height of embankment in the branching fracture. In the low-viscosity fracturing fluid, the proppant quickly deposits at the bottom of the fracture as it enters the fracture. Improving the viscosity of the fracturing fluid can significantly enhance its ability to transport the proppant. The proppant is less likely to quickly settle in high-viscosity fracturing fluids, especially when the fracturing fluid viscosity exceeds 50 mPa·s.