Quantification of Fracture Surface Roughness and Its Insights to Mechanical Rock Properties Determination Using Image Analysis Techniques

Abstract

During the hydraulic fracturing process, the rough surface of fractures and the viscous proppant suspension flow bring great challenges to the distribution of proppants evenly at the fracture thin apertures. As a result, a detailed understanding of the effect of surface roughness on proppant sedimentation seems essentially indispensable. Apart from that, how the roughness of Nano-scale conduits and their orientations, such as microfracture channels, affect the flow through the damaged fracture process zone (FPZ) have not been well understood. A newfangled developed algorithm using image analysis software (ImageJ) is applied to characterize the morphological features of the damaged fracture system, including surface roughness, microcrack types and microcrack density indicators. Hydraulic fracturing experiment is conducted on a Tennessee sandstone core using a triaxial loading system. The fractured samples are ion milled, and its cross section plane images are recorded by scanning electron microscope (SEM). Statistical analysis of surface roughness, the degree of damage at FPZ, the density of microcracks and effective connection indicator of microfractures to the main fracture are quantitatively investigated, in addition to Young's modulus and Poisson's ratio. We found that the higher roughness of microfracture network significantly enhances the effective conduits open to fluid flow while taking the density of the microfracture within FPZ into account within the fracture processed region, depending upon how much damage is presented. In other words, the overall ease of fluid delivery to the main fracture essentially depends on the level of the damage in FPZ. The heavily deformed rock grains cause a partial blockage at the fracture surface and will be detached on the main fracture. The leftover is the induced intercrystalline microfracture network in the vicinity of the main fracture. Additionally, mechanical moduli were interpreted by image analysis, where a novel approach was developed to calculate the mechanical rock properties. The results from image analysis were compared to other failure criteria and fracturing pressure data interpretation. We also validated the obtained mechanical properties by collating the literature records. The microfracture network creates the significant incremental amount of fluid conduits to hydrocarbons. The better understanding of the fracture network serves as a valuable guide to the fracturing job design and managing the damaged FPZ. This novel approach will commit to supporting the lab measurements, gives field preliminary mechanical property assessment and lower the cost needed for hydraulic fracturing design.