Examining the Effect of Cemented Natural Fractures on Hydraulic Fracture Propagation in Hydrostone Block Experiments

Abstract

Micro seismic data and coring studies suggest that hydraulic fractures interact heavily with natural fractures creating complex fracture networks in naturally fractured reservoirs such as the Barnett shale, the Eagle Ford shale, and the Marcellus shale. However, since direct observations of subsurface hydraulic fracture geometries are incomplete or nonexistent, we look to properly scaled experimental research and computer modeling based on realistic assumptions to help us understand fracture intersection geometries. Most experimental analysis of this problem has focused on natural fractures with frictional interfaces. However, core observations from the Barnett and other shale plays suggest that natural fractures are largely cemented. To examine hydraulic fracture interactions with cemented natural fractures, we performed 9 hydraulic fracturing experiments in gypsum cement blocks that contained embedded planar glass, sandstone, and plaster discontinuities which acted as proxies for cemented natural fractures. There were three main fracture intersection geometries observed in our experimental program. 1) A hydraulic fracture is diverted into a different propagation path(s) by a natural fracture. 2) A taller hydraulic fracture bypasses a shorter natural fracture by propagating around it via height growth while also separating the weakly bonded interface between the natural fracture and the host rock. 3) A hydraulic fracture bypasses a natural fracture and also diverts down it to form separate fractures. The three main factors that seemed to have the strongest influence on fracture intersection geometry were the angle of intersection, the ratio of hydraulic fracture height to natural fracture height, and the differential stress. Simply put, the most significant finding of this research is that fracture intersection geometries are complex. Our results show that bypass, separation of weakly bonded interfaces, diversion, and mixed mode propagation are likely in hydraulic fracture intersections with cemented natural fractures. The impact of this finding is that we need fully 3D computer models capable of accounting for bypass and mixed mode I-III fracture propagation in order to realistically simulate subsurface hydraulic fracture geometries.

A Laboratory Study of the Effects of Interbeds on Hydraulic Fracture Propagation in Shale Formation

“…Warpinski et al [35] and Wright et al [36] noted the layer material property could impact on the hydraulic fracture propagation and a material property interface could arrest the fracture growth. In the experiments, the three totally different propagation pathways of the main fracture, that are correspondence with the interaction situations pointed out by the scholars [5,6], mainly result from the varying interbed strength. The lower strength interbeds have small resistance to the propagation and extension of fractures under the same conditions of stress and flow rate, so fractures can cross the interbeds, which lead to produce long fractures.…”

“…Therefore, hydraulic fracturing stimulation is one of the key technologies to produce oil and gas in an economical way [1]. Many scholars have undertaken much research on hydraulic fractures through physical experiments, numerical simulations and analytic criteria [2][3][4][5][6][7]. Particularly, conducting physical experiments is not only valuable for validating numerical simulations, but also an efficient way to understand the effects of various factors on fracture propagation.…”

“…The scholars from Delft University of Technology used tri-axial University of Technology used tri-axial test system and acoustic monitoring to study fracture initiation and hydraulic fracture propagation in natural fractures [13,14]. Moreover, the situations of interaction between hydraulic and natural fractures were noted by Beugelsdijk et al [3], Olson and Bahorich [4,5] and Warpinski [9]: crossing, arresting, offsetting, bypass and diversion. Van Eekelen et al [15] studied the hydraulic fracture propagation in layered formation and analyzed the fracture arresting effects.…”

Numerical Investigation of Influence of In-Situ Stress Ratio, Injection Rate and Fluid Viscosity on Hydraulic Fracture Propagation Using a Distinct Element Approach

“…According to laboratory hydraulic fracturing experiments [7,14,42,43], the model dimension was confirmed to be 300 mmˆ300 mm. There is a circular hole that is 20 mm in diameter at the center of the model (Figure 2), from which the fluid was injected at a constant rate.…”

Simulação Numérica Do Processo De Propagação De Fraturas Em Materiais Rochosos Em Condições De Acoplamento Fluidomecânico

“…A partir daí, a trajetória que segue a propagação pode ser modificada devido a que uma descontinuidade torna-se um caminho preferencial para o fluido, impondo pressão de fluido no seu interior e alterando o campo de tensões. Trabalhos experimentais e numéricos mostram que, dependendo do grau de cimentação de uma descontinuidade preexistente, uma fratura propagando-se devidoà injeção de um fluido sob pressão, pode atravessá-la ou ser desviada por esta [3,29]. A capacidade de penetração do fluido na descontinuidade vai depender das suas propriedades de resistência, sendo que, para o fluido poder entrar, precisa do espaço gerado pela abertura da fratura.…”