Abstract
Modelling the process of induced fracture initiation, propagation and interaction with natural fractures is a very challenged task. Significant progress has been made in recent years in the development of complex fracture models to address the needs for more suitable design tools than the conventional planar fracture models. However, some aspects of this complex process are not still fully understood in terms of their impact or importance to the overall fracture geometry, or the complexity of simulating them is beyond the current modelling capabilities or requires computation effort that is not practical for engineering purpose. A technique that has been developed to represent the process of fracture propagation is the Continuous Approximation of Strong Discontinuities, which introduces a special kinematics, capable of representing the process of degradation of the material. One way to implement this approximation is to introduce the effects of a very narrow band of localized deformations within the existing finite elements. In this paper was used a finite element procedure that performs numerical analysis of fluid flow in a deformable porous media in a fully coupled scheme. In this analysis the propagation of the hydraulic fracture occurs specially along the pathway of the natural fractures, due to their lower tensile strength and greater permeability.
Highlights
Hydraulic fracturing is an evolving technology that has been used to increase oil recovery in naturally fractured reservoirs [1], usually all reservoirs are fractured to some degree
The network pattern of fractures resulting from a hydraulic fracturing operation depends on several factors, among them, the strength, deformability and permeability of the rock mass and the in-situ stress state [3], because natural fractures are formed within geological time scale and the formation itself may have gone through multiple tectonic events, the distribution and orientation of the natural fractures do not necessarily relate to the current insitu stresses [2]
There are two competing forces that govern the general trend of hydraulic fracture propagation path: one is the propensity to propagate along the direction of the weak planes resulting from the natural fracture sets, and the other is the tendency to propagate along the direction of maximum principal stress and open against the minimum principal stress
Summary
Hydraulic fracturing is an evolving technology that has been used to increase oil recovery in naturally fractured reservoirs [1], usually all reservoirs are fractured to some degree. When a hydraulic fracturing operation is being done in a naturally fractured reservoir it is possible to have two scenarios, on one hand, the stimulated natural fractures, if-well connected, can enlarge the reservoir contact area, expand the fluid flow path and enhance productivity. The reactivated natural fracture and weak planes may divert fluid flow from the main hydraulic fracture channel and lead to an unreasonably high proppant concentration and early screenouts. There are two competing forces that govern the general trend of hydraulic fracture propagation path: one is the propensity to propagate along the direction of the weak planes resulting from the natural fracture sets, and the other is the tendency to propagate along the direction of maximum principal stress and open against the minimum principal stress. The directions of natural fractures sets are not aligned with in-situ principal stresses, so the fracture propagation has to balance these two forces to find the path that has lesser fracturing energy, which is why the hydraulic fracture propagates along a zig-zag path [2]
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