Effect of flow rate and viscosity on complex fracture development in UFM model

Abstract

A recently developed unconventional fracture model (UFM*) is able to simulate complex fracture networks propagation in a formation with pre-existing natural fractures. Multiple fracture branches can propagate at the same time and crisscross each other. The behaviour of a hydraulic fracture when it intersects a natural fracture, whether being arrested, crossing, creating an offset, or dilating the natural fracture, plays a key role in predicting the resulting fracture footprint, microseismicity, and improving production evaluation. It is therefore critical to properly model the fracture interaction in a complex fracture model such as UFM. A new crossing model, called OpenT, taking into account the effect of flow rate and fluid viscosity on the hydraulic/natural fracture crossing behaviour is integrated in UFM simulator. The previous fracture crossing model is primarily based on the stress field at the approaching hydraulic fracture tip and its interaction with the natural fracture. A new elasticity solution for the fracture contact has been developed. The new OpenT semi-analytical crossing model quantifies the localized stress field induced in the natural fracture and in the rock and evaluates the size and length of open and shear slippage zones along the natural fracture. The natural fracture activation and stress field near the intersection point are strongly dependent on the contacting hydraulic fracture opening and thus on fluid flow rate and viscosity. This new model is validated against laboratory experimental results and an advanced numerical model. In this paper we present the results of several test cases showing the influence of injection rate and fluid viscosity on the generated hydraulic fracture footprint in formations with pre-existing natural fractures. The influence of the stress field anisotropy, intersection angle, as well as natural fractures properties are also important and are discussed. The results are then compared with the simulations using the previous crossing model which does not account for the influence of fluid properties.