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Novel Assessment of Hydraulic Fracturing with Geomechanical Characteristics in Tight Carbonate Formations


 Hydraulic fracturing in naturally fractured tight formations causes complex fracture geometry corresponding to the existence of natural fracture as well as geomechanical characteristics. It is extremely important when stimulating fluids such as water, brine, and CO2 are injected into tight carbonate reservoirs for increasing recovery. For fracture propagation modeling, several models have implemented multiple planar fracture with only opening mode, which have a problem in representing realistic fracture behavior.
 In this regard, we proposed a hydraulic fracture propagation model implementing multiple planar approach with mixed mode including opening and sliding modes for being able to describe fracture propagation more realistically. When hydraulic fracture encounters natural fracture non-orthogonally, fracture tip slides first along the natural fracture face, and then propagates into rock mass. That is why sliding mode also needs to be considered. With the use of the model, this study analyzed the effects of the brittleness on fracture propagating behavior and gas recovery for tight formations with respect to Poisson's ratio and Young's modulus.
 We investigated the modeling results for examining the importance of the sliding mode newly employed in the hydraulic fracture model. In the case of a formation having a high brittleness index, which presents greater deformation longitudinally rather than transversely, called the formation A, the effect of sliding mode was not critical on the fracture propagation. Meanwhile, in a formation having an intermediate brittleness index, named the formation B, the hydraulic fracture less easily crosses natural fracture because Young's modulus of this formation is lower comparing to the formation A, and consequently, implementation of the sliding mode is more dominant. In a formation representing higher Poisson's ratio and Young's modulus compared to formation A, which denotes a low brittleness index, since it shows larger deformation in transverse direction, hydraulic fracture hardly crosses the natural fracture, and thereafter, the propagating direction of the crossed fracture is highly deviated. The larger brittleness index, the greater in stimulated reservoir volumes by up to 17% because fracture crossing occurred easily.
 Therefore, the model with the mixed mode proposed in this study was found to be extremely important in the analysis of fracture propagation behavior resulting the stimulated reservoir volumes and gas recovery differently in tight carbonate reservoirs.