Hydraulic fracturing initiation and propagation in deep inclined open hole for Enhanced Geothermal System

Energy Science & Engineering

et al. 2020

Geothermal energy has been widely proposed as a potential renewable energy to replace traditional fossil fuel energy. Hot dry rock (HDR) reservoirs were the main geothermal energy resources and usually consist of low‐permeability hard granite without fluid. Developing HDR requires water cyclically flowing between injection and production wells to extract heat energy. Hydraulic fracturing, as a key reservoir stimulation technology, can create the path of fluid cyclically flowing. However, few studies have investigated hydraulic induced artificial fractures in HDR geothermal formations. This paper investigated HDR geothermal reservoir stimulation characteristics and fracture patterns under different injection flow rates. Numerical simulations were conducted to model the laboratory tests. Results showed they were in good agreement, and this indicated the possibility of numerical simulation to predict hydraulic fracturing behavior under different injection flow rates. With the increase of injection flow rate, the fracture initiation pressures and breakdown pressures increased, and the propagation times and postfracturing pressures decreased. The fracture geometries were observed and analyzed, mean injection power was proposed, and results showed that it could be used to roughly estimate the fracture total lengths. Moreover, the fracture permeabilities based on the pressure data were calculated. These results can provide some reasonable advice for implementing reservoir stimulations on application to field‐scale HDR operation.

Section: Discussionmentioning

confidence: 99%

Experimental and numerical studies on hydraulic fracturing characteristics with different injection flow rates in granite geothermal reservoir

Energy Science & Engineering

et al. 2020

“…It will directly influence the hydraulic fracturing method and difficulty in field-scale operations. 48 To find out the time of fracturing initiation, we first analyze the hydraulic fracturing process. Considering the moment at which the wellbore is full of fluids, the pressure will rise quickly.…”

Section: Discussionmentioning

confidence: 99%

“…To properly make sure the fracturing initiation pressure is helpful to analyze the rock properties, such as failure stress, tensile stress, and shear stress in real field hydraulic fracturing, accurate estimation of fracturing initiation pressure is also essential for the hydraulic fracturing system efficient and effective design. It will directly influence the hydraulic fracturing method and difficulty in field-scale operations …”

Section: Discussionmentioning

confidence: 99%

Hydraulic Fracturing Experiment Investigation for the Application of Geothermal Energy Extraction

2020

ACS Omega

As an attractive renewable energy source, deep geothermal energy is increasingly explored. Granite is a typical geothermal reservoir rock type with low permeability, and hydraulic fracturing is a promising reservoir stimulation method which could obviously enhance the reservoir permeability. Previous hydraulic fracturing studies were mostly conducted on artificial samples and small cylindrical granites. The fracturing pressures of artificial samples and small real rock sample were much lower than that of field operation, and it was difficult to observe morphological changes in small rocks. Hence, this paper presents a hydraulic fracturing experimental study on large-scale granite with a sample size of 300 × 300 × 300 mm under high temperatures. Besides, injection flow rate is an important parameter for on-site hydraulic fracturing; previous studies usually only focused on breakdown pressure, and there is a lack of comprehensive analysis about fracturing pressure curves and fracturing characteristics caused by different injection flow rates. This study aims to investigate the influence of injection flow rate on different pressure curve characteristic parameters which are initiation pressure, propagation time, breakdown pressure, postfracturing pressure, fracture geometry, and fracture permeability. The mean injection power was proposed to roughly estimate the fracture total lengths. These results could provide some guidance for field-scale reservoir stimulation and heat extraction efficiency improvement.

“…Accurate estimation of fracturing initiation pressure is also important for the effective and efficient designing of hydraulic fracture schemes. It will directly influence hydraulic fracturing method and difficulty in field-scale operations [42].…”

Section: The Effect Of Flow Rate On the Fracture Initiation Pressurementioning

confidence: 99%

Experimental Study of Fracture Propagation: The Application in Energy Mining

2020

Energies

Hydraulic fracturing has been widely used in recent years as a key technology to improve energy mining efficiency in petroleum and geothermal industries. Laboratory hydraulic fracturing experiments recently were completed in six large-scale 300 × 300 × 300 mm rock specimens to better understand this complex process of hydraulic fracturing. When injection flow rate increases from 5 to 30 mL/min. The fracture initiation pressures and breakdown pressures increase, the propagation times and post-fracturing pressures decrease. The fracture geometries are observed and analyzed, mean injection power is proposed and results show that it could be used to roughly estimate the fracture total lengths. Moreover, the fracture permeabilities based on the pressure data are calculated and linearly ascend with the increase of injection flow rates. These results can provide some reasonable advice for implementing hydraulic fracturing reservoir simulations and improving energy production efficiency on application to field-scale operation.Hydraulic fracturing usually relates complicated solid-fluid coupling processes. Due to the compactness and the low permeability of the granite, an intact large-size granite sample requires a high fracturing pressure to trigger the fracture. To better understand the characteristics of hydraulic fracturing process and fracture network after hydraulic fracturing. In this work, we carried out laboratorial hydraulic fracturing experiments with a true triaxial fracturing apparatus designed by Jilin University. Its cubic specimen fracturing capsule size is 300 × 300 × 300 mm. The granite samples were collected from the Songliao Basin petroleum reservoir field in the northeastern part of China. In order to investigate the injection flow rate on hydraulic fracturing chrematistics, we conducted hydraulic fracturing tests at different injection flow rates for six rocks. The initiation pressure, breakdown pressure, post-fracturing pressure, and propagation time were analyzed based on the fracturing pressure curves. The rock specimens were cut in half after test and the fracture geometry was observed. Based on recorded pressure data and curves, the fracture permeabilities of all specimens were calculated. Results in this study could provide some reasonable advice for implementing hydraulic fracturing reservoir simulations and improving energy production efficiency on application to field-scale operation. Laboratorial Tests BackgroundThe granite samples used in this study are taken from a place nearby YS-2 well (Figure 1) in the Songliao Basin [39]. The YS-2 well (127.25 • E, 52.36 • N) is in the Daqing Oilfield about 78 km from Daqing City, The YS-2 well is a geothermal energy exploration well, and exploration data shows that the geothermal resources here are abundant. As large size intact rock samples cannot be gotten from a wellbore. We use the outcrop rock samples as substitutes (Figure 2a). Three independent triaxial principal stresses are applied on cube-shaped samples to simulate the real field in-situ st...