Laboratory Study of the Influence of Fluid Rheology on the Characteristics of Created Hydraulic Fracture

Abstract

In the last decade, the negative impact of hydraulic fracturing fluids on the reservoir properties has been noted, which has led to the new trend of improving characteristics and developing new hydraulic fracturing fluids. As an alternative option to the traditionally used cross-linked fluids based on guar solution, in our laboratory we have tested fluids having a branched spatial structure, which allowed them to hold and transport proppants, despite the low viscosity of this kind of fluids (100–200 mPa·s measured at 100 s−1). Existing theoretical models of hydraulic fracture (HF) propagation have some limitations in predicting the influence of fracturing fluids on reservoir properties. Unfortunately, in situ experiments in the target reservoir are difficult and expensive. Thus, laboratory experiments can be considered as a reasonable alternative for testing new fluids, since they can provide comprehensive information about the properties of the created HF before the application of a new hydraulic fracturing technique in the field conditions. This paper presents the results of an experimental study of hydraulic fracturing of granite samples in laboratory conditions. The injection of water- and oil-based unconventional fracturing fluids was performed to study the influence of fluid rheology on the dynamics of the hydraulic fracture propagation process and parameters of the created HF. We have found that the fracturing fluid viscosity affects the parameters of the created HF, such as aperture, propagation velocity, breakdown pressure, and HF surface tortuosity. The obtained relationships can be taken into account for Hydraulic Fracture modelling, which may increase the efficiency of the hydraulic fracturing in the field conditions.

Assessment of Saturation Effect on Hydraulic Fracturing in Sandstone and Thermally Treated Granite

“…An injection of lower viscosity OG induced a less symmetrical spread of the radial fracture front in the sandstone samples (Figure 25, middle illustration) and narrow-sector fracture propagation in the granite samples (Figure 25, lower illustration). These findings are consistent with the results of the previous study [25], conducted on another granite with a low-viscosity fluid injection. A comparison of normalized densities of localized AE events in the GM5-101, GM4-101, and TG-715h samples at the moment when HF approached the sample boundary is shown in Figure 26.…”

“…The injection of the fluid into the TG-701 sample caused the onset of AE activity much earlier than the moment when the HF approached the rock surface, and upon approaching the surface it showed a significantly larger number of AE signals (Figure 14i), a larger deformation of the sample (Figure 14j), a larger volume of fluid injected into the fracture (Figure 14k), and a significantly lower speed of the HF propagation (Figure 14p). We attribute the difference in all parameters, observed by several independent recording systems, to the influence of the viscosity of the injected fluid, in accordance with the results of earlier studies [25,39,41].…”

“…In addition, during our experimental study, Newtonian viscous silicone oil (SO) with viscosities of 1000 cP, 10,000 cP, and 100,000 cP and non-Newtonian OilGel 40/40 (OG) with a viscosity decreasing from 1220 cP at 100 rpm to 310.81 cP at 300 rpm (a detailed description of which was published in [25]) were injected into the specimens to induce a hydraulic fracture. Mineral oil Multitherm PG-1 (with a viscosity of 46 cP) was used as a fluid for the saturation of samples in the pseudo-triaxial cell.…”

“…Meanwhile, hydraulic fracturing in the laboratory can be used to characterize the geometry of fractures that occur under different conditions (e.g., stress state) [24]. Reliable assessment of the characteristics of created hydraulic fractures, such as fracture geometry, surface roughness, etc., in field conditions is a very complicated task, while the geometrical characteristics of created hydraulic fractures can be directly determined in a laboratory test, e.g., by computed tomography [25] or by laser scanning technique [26]. Knowledge of the roughness and the aperture of the created hydraulic fractures is crucial for arranging successful proppant delivery.…”

“…Knowledge of the roughness and the aperture of the created hydraulic fractures is crucial for arranging successful proppant delivery. However, in the field, the aperture of hydraulic fractures can be estimated very roughly, while in the laboratory it is possible to directly measure the deformation of the sample related to the opening of hydraulic fractures [25,27]. Similarly to microseismicity recorded in the field, acoustic emissions (AE) can also be monitored in the laboratory using sensitive, high-frequency data acquisition systems [28].…”