Amin Nabipour

Steps for conducting a valid hydraulic fracturing laboratory test

Several parameters are involved in a hydraulic-fracturingoperation, which is a technique used mainly in tight formations to enhance productivity. Formation properties, state of stresses in the field, injecting fluid characteristics, and pumping rate are among several parameters that can influence the process. Numerical analysis is conventionally run to simulate the hydraulic-fracturing process. Before operating the expensive fracturing job in the field, however, it would be useful to understand the effect of various parameters by conducting physical experiments in the lab. Laboratory experiments are also valuable for validating the numerical simulations. Applying the scaling laws, which are to correspond to the field operation with the test performed in the lab, are necessary to draw valid conclusions from the experiments. Dimensionless parameters are introduced through the scaling laws that are used to scale-down different parameters including the hole size, pump rate and fluid viscosity to that of the lab scale. Sample preparation and following a consistent and correct test procedure in the lab, however, are two other important factors that play a substantial role in obtaining valid results. The focus of this peer-reviewed paper is to address the latter aspect; however, a review of different scaling laws proposed and used will be given. The results presented in this study are the lab tests conducted using a true triaxial stress cell (TTSC), which allows simulation of hydraulic-fracturing under true field stress conditions where three independent stresses are applied to a cubic rock sample.

Simulation of the cutting action of a single PDC cutter using DEM

Optimization of costly drilling operations is essential to reduce the overall costs of oil and gas extraction. Simulation of these operations can yield a better selection of parameters for maximum drilling efficiency. One of the most cost efficient methods to do so is by computer modeling. Because of the complex nature of the cutting process, no analytical methods can be used for its modeling and the numerical methods are the only option. FEM and Discrete Element Method (DEM) are the most commonly used numerical methods for this purpose. One of the best features of the DEM is that it is very suitable for discontinuous environment and no special treatment or process is required in tracking the produced cracks and fragmentation. Also depending on the depth of cut, it can both simulate ductile or brittle failures. In current study, a 2D computer model was developed using the particle flow code (PFC2D) to simulate the cutting action of a single cutter. PFC uses the DEM to model a rock sample by fine cylinders or disks. The properties of the Berea sandstone were considered in our modeling. A good match of mechanical properties was obtained for the rock model by adjusting micro parameters of the contacts between the constituting balls and the results of the simulation are compared to laboratory data.