Near Wellbore Hydraulic Fracture Propagation from Perforations in Tight Rocks: The Roles of Fracturing Fluid Viscosity and Injection Rate

Abstract

Abstract:Hydraulic fracture initiation and near wellbore propagation is governed by complex failure mechanisms, especially in cased perforated wellbores. Various parameters affect such mechanisms, including fracturing fluid viscosity and injection rate. In this study, three different fracturing fluids with viscosities ranging from 20 to 600 Pa.s were used to investigate the effects of varying fracturing fluid viscosities and fluid injection rates on the fracturing mechanisms. Hydraulic fracturing tests were conducted in cased perforated boreholes made in tight 150 mm synthetic cubic samples. A true tri-axial stress cell was used to simulate real far field stress conditions. In addition, dimensional analyses were performed to correspond the results of lab experiments to field-scale operations. The results indicated that by increasing the fracturing fluid viscosity and injection rate, the fracturing energy increased, and consequently, higher fracturing pressures were observed. However, when the fracturing energy was transferred to a borehole at a faster rate, the fracture initiation angle also increased. This resulted in more curved fracture planes. Accordingly, a new parameter, called fracturing power, was introduced to relate fracture geometry to fluid viscosity and injection rate. Furthermore, it was observed that the presence of casing in the wellbore impacted the stress distribution around the casing in such a way that the fracture propagation deviated from the wellbore vicinity.

Experimental Study of Fracture Propagation: The Application in Energy Mining

“…Guo et al [11] showed that breakdown pressure could be used to calculate the horizontal stresses, and the breakdown pressure was influenced by injection flow rate, in situ stresses, reservoir size, fracturing fluid, etc. Similar results also were found by other researchers [22][23][24][25], the injection flow rate could influence the hydraulic fracturing pump pressure and fracture patterns. Fallahzadeh et al [25] performed hydraulic fracturing tests in 150 mm synthetic cubic samples and show that with the increasing of flow rate, the initiation angle of fracture increased and resulted in a more curved plane.…”

“…In order to optimize reservoir stimulation, several researchers have conducted studies about the mechanism of hydraulic fracturing. They have shown that, in the fracture initiation and propagation process, the flow rate and fluid pressure play important roles [15][16][17][18][19][20][21][22][23][24][25][26][27]. Hubbert and Willis [16] first studied the hydraulic fracturing mechanism, and proposed a stress formula for hydraulic induced fracture initiation, and they found that fracture and breakdown pressures are affected by the pre-existing regional stresses.…”

Numerical Simulation of Hydraulic Fracture Propagation Guided by Single Radial Boreholes

“…In order to verify the feasibility of directional propagation of hydraulic fracturing guided by the single radial borehole, two sets of true triaxial hydraulic fracturing simulation experiments were carried out for large-size artificial cores (300 mm 3 ) [36]. The rock mechanics test results of the artificial cores show an average Young modulus of 14 GPa, average Poisson's ratio of 0.22, and average tensile strength of 2.7 MPa.…”

Heat Transfer Characteristics and Prediction Model of Supercritical Carbon Dioxide (SC-CO2) in a Vertical Tube

“…Since the high-pressure liquid and supercritical regions are the main concern of this work, the Span and Wagner (SW) EOS was used because it is considered to be the most accurate EOS for CO 2 and is used as a benchmark for other models [42].…”

“…In 2000, shale gas only accounted for 1% of U.S. natural gas production, but fifteen years later, it accounted for nearly 50% [1]. The boom of shale gas production is mainly due to the wide use of hydraulic fracturing, a well-stimulation technique in which rock is fractured by a pressurized fluid (primarily water containing sand or other proppants suspended with the aid of thickening agents) [2][3][4]. However, more and more studies have argued that hydraulic fracturing may raise a number of environmental problems: (1) a large amount of water is required for one shale gas well [5]; (2) more than 20 types of additives are added in the injection water, such as hydrochloric or muriatic acid, gelling agents, and chemical modifiers, which may contaminate groundwater [6,7]; (3) large-scale water disposal via deep re-injection has been linked to trigger seismicity that results in low-level earthquakes [8][9][10]; (4) other issues include accidental chemical spills, waste disposal, air pollution, and the land footprint of drilling activities [11].…”