scholarly journals Experimental Investigation on the Initiation of Hydraulic Fractures from a Simulated Wellbore in Laminated Shale

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 4) ◽  
Author(s):  
Yang Liu ◽  
Congrui Chen ◽  
Tianshou Ma ◽  
Gongsheng Zhu ◽  
Nian Peng ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Fracture Initiation ◽  
Bedding Plane ◽  
Injection Rate ◽  
Growth Patterns ◽  
Hydraulic Fractures ◽  
Fracture Surfaces ◽  
Shale Rock ◽  
The Impact ◽  
Borehole Size

Abstract Understanding the formation mechanisms of complex fracture networks is vitally important for hydraulic fracturing operations in shale formation. For this purpose, a hydraulic fracturing experiment under a core-plunger scale is conducted to investigate the impact of the bedding plane angle, borehole size, and injection rate on fracture initiation behaviors of laminated shale rock. The results on rock properties demonstrate that the anisotropic characteristics of shale rock are reflected not only in elastic modulus but also in tensile strength. The results of fracturing experiments show that the bedding plane dip angle and borehole size have significant effects on fracture initiation behaviors, in that fracture initiation pressure (FIP) decreases with the increase of those two factors. The impact of injection rate, by contrast, has no obvious variety regulation. The above data is further used to validate our previously proposed fully anisotropic FIP model, which shows better agreement with experimental results than those using other models under various parameter combinations. Finally, a postfracturing analysis is performed to identify the fracture growth patterns and the microstructures on the fracture surfaces. The results show that the hydraulic fractures (HFs) always grow along mechanically favorable directions, and the potential interaction between HFs and bedding planes mainly manifests as fracture arrest. Meanwhile, the roughness of fracture surfaces is physically different from each other, which in turn results in the difficulties of fluid flow and proppant migration. The findings of this study can help for a better understanding of the fracture initiation behavior of laminated shale rock and the corresponding fracture morphology.

scholarly journals An Analytical Model for Fracture Initiation from a Particular Radial Borehole in Hydraulic Fracturing Guided by Multiradial Boreholes

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Yuxin Chen ◽  
Yunhong Ding ◽  
Chong Liang ◽  
Dawei Zhu ◽  
Yu Bai ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Analytical Model ◽  
Fracture Initiation ◽  
Hydraulic Fractures ◽  
Large Radius ◽  
Intersection Angle ◽  
Biot Coefficient ◽  
Depth Difference ◽  
Wellbore Pressure ◽  
The Impact

Radial drilling-fracturing, the combination of the hydraulic fracturing and radial borehole, is a technology that can guide the hydraulic fractures to directionally propagate and efficiently develop low permeability reservoir. In this paper, an analytical model of two radial boreholes (a basic research unit) is established to predict fracture initiation pressure (FIP) from one particular radial borehole and the interference between radial boreholes when the hydraulic fracturing is guided by multi-radial boreholes. The model is based on the stress superposition principle and the maximum tensile stress criterion. The effects of in situ stress, wellbore pressure, and fracturing fluid percolation are considered. Then, sensitivity analysis is performed by examining the impact of the intersection angle between radial boreholes, the depth difference between radial boreholes, the radius of radial boreholes, Biot coefficient, and the number of radial boreholes. The results show that FIP declines with the increase of radial boreholes number and the decrease of intersection angle and depth difference between radial boreholes. Meanwhile, the increase of radial borehole number and the reduction of intersection angle and depth difference strengthen the interference between radial boreholes, which conduce to the formation of the fracture network connecting radial boreholes. Besides, FIP declines with the increase of radial borehole radius and the decrease of Biot coefficient. Large radius and low Biot coefficient can enlarge the influence range of additional stress field produced by radial boreholes, enhance the mutual interference between radial boreholes, and guide fracture growth between radial boreholes. In hydraulic fracturing design, in order to reduce FIP and strengthen the interference between radial boreholes, the optimization design can be carried out by lowering intersection angle, increasing radius and number of boreholes, and reducing the depth difference between boreholes when the conditions permit. The research clarifies the interference between radial boreholes and provides the theoretical basis for optimizing radial boreholes layout in hydraulic fracturing guided by multi-radial boreholes.

Fracture Initiation and Propagation in a Deep Shale Gas Reservoir Subject to an Alternating-Fluid-Injection Hydraulic-Fracturing Treatment

SPE Journal ◽  
2019 ◽  
Vol 24 (04) ◽  
pp. 1839-1855 ◽  
Author(s):  
Bing Hou ◽  
Zhi Chang ◽  
Weineng Fu ◽  
Yeerfulati Muhadasi ◽  
Mian Chen
Keyword(s):  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Fracture Initiation ◽  
Fluid Injection ◽  
Hydraulic Fractures ◽  
Stress Difference ◽  
Gas Reservoirs ◽  
Complex Fracture ◽  
Initiation And Propagation

Summary Deep shale gas reservoirs are characterized by high in-situ stresses, a high horizontal-stress difference (12 MPa), development of bedding seams and natural fractures, and stronger plasticity than shallow shale. All of these factors hinder the extension of hydraulic fractures and the formation of complex fracture networks. Conventional hydraulic-fracturing techniques (that use a single fluid, such as guar fluid or slickwater) do not account for the initiation and propagation of primary fractures and the formation of secondary fractures induced by the primary fractures. For this reason, we proposed an alternating-fluid-injection hydraulic-fracturing treatment. True triaxial hydraulic-fracturing tests were conducted on shale outcrop specimens excavated from the Shallow Silurian Longmaxi Formation to study the initiation and propagation of hydraulic fractures while the specimens were subjected to an alternating fluid injection with guar fluid and slickwater. The initiation and propagation of fractures in the specimens were monitored using an acoustic-emission (AE) system connected to a visual display. The results revealed that the guar fluid and slickwater each played a different role in hydraulic fracturing. At a high in-situ stress difference, the guar fluid tended to open the transverse fractures, whereas the slickwater tended to activate the bedding planes as a result of the temporary blocking effect of the guar fluid. On the basis of the development of fractures around the initiation point, the initiation patterns were classified into three categories: (1) transverse-fracture initiation, (2) bedding-seam initiation, and (3) natural-fracture initiation. Each of these fracture-initiation patterns had a different propagation mode. The alternating-fluid-injection treatment exploited the advantages of the two fracturing fluids to form a large complex fracture network in deep shale gas reservoirs; therefore, we concluded that this method is an efficient way to enhance the stimulated reservoir volume compared with conventional hydraulic-fracturing technologies.

Influence of Oriented Perforation Design on Refracture Reorientation: Simulation and Experiment

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Minhui Qi ◽  
Mingzhong Li ◽  
Tiankui Guo ◽  
Chunting Liu ◽  
Song Gao ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Large Scale ◽  
Simulation Models ◽  
Fracture Initiation ◽  
Simulation Method ◽  
Induced Stress ◽  
Study Results ◽  
Simulation Results ◽  
Fracturing Experiments ◽  
The Impact

The oriented perforating is the essential technique to guide the refracture reorientation, but the influence of the oriented perforation design on the refracture steering radius is still unclear. In this paper, the factors influencing the refracture reorientation were studied by simulation models and experiments. The effects of initial fracture, well production, and perforations on the refracture initiation and propagation were analyzed. Three-dimensional finite element models were conducted to quantify the impact of perforation depth, density, and azimuth on the refracture. The large-scale three-axis hydraulic fracturing experiments guided by oriented perforations were also carried out to verify the fracture initiation position and propagation pattern of the simulation results. The research results showed that perforations change the near-wellbore induced stress distribution, thus changing the steering radius of the refracture. According to the simulation results, the oriented perforation design has a significant influence on the perforation guidance effect and refracture characteristics. Five hydraulic fracturing experiments proved the influence of perforating parameters on fracture initiation and morphology, which have a right consistency between the simulation results. This paper presents a numerical simulation method for evaluating the influence of the refracture reorientation characteristics under the consideration of multiple prerefracturing induced-stress and put forward the oriented perforation field design suggestions according to the study results.

Frac Charge Performance at Downhole Conditions: Assessments and Implications

2021 ◽  
Author(s):  
Brenden Grove ◽  
Jacob McGregor ◽  
Rory DeHart ◽  
Ron Dusterhoft ◽  
Neil Stegent ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Fracture Initiation ◽  
Fracture Network ◽  
Hole Size ◽  
Eagle Ford Shale ◽  
Technical Performance ◽  
Limited Entry ◽  
Surface Test ◽  
The Impact ◽  
Surface Testing

Abstract Hydraulically fractured completions dominate industry perforating activity, particularly in North American land basins. This has led to the development of fracture-optimized perforating systems in recent years. Aside from overarching safety, reliability, and efficiency priorities, the main technical performance attribute of these systems is consistent hole size in the casing, driven by limited entry fracture design considerations. While the industry continues to seek further improvements in hole size consistency, attention is also being directed to the perforations more holistically, from a perspective of maximizing the effectiveness of subsequent hydraulic fracturing and ultimately production operations. To this end, this paper presents two related activities addressing the development, qualification, and optimization of perf-for-frac systems. The first is a surface testing protocol used to characterize perforating system performance, in particular casing hole size and consistency. The second is a laboratory program, recently conducted to investigate perforating stressed Eagle Ford shale samples at downhole conditions. This program explored the influences of charge size, formation lamination direction, pore fluid, and dynamic underbalance on perforation characteristics. Casing hole size was also assessed. For the first activity (surface testing), we find that using cement-backed casing can be an important feature to ensure more downhole-realistic results. For the second activity (laboratory program), perforation casing hole sizes for the charges tested were in line with expectations based on existing surface test data, exhibiting negligible pressure dependency. Corresponding penetration depths into the stressed shale samples generally ranged from 3.5-in to 5-in, which is much shallower than might be expected based on surface concrete performance. Dynamic underbalance was found to exhibit some slight effect on the tunnel fill characteristics, while pore system fluid was found to have minimal influence on the results. An interesting feature of the perforated samples was the complex fracture network at the perforation tips, which appeared "propped" to some extent with charge liner debris. Some of these fractures were formation beds which had delaminated during the shot, a phenomenon observed for perforations both parallel and perpendicular to the laminations. The implications of these results to the downhole environment continues to be assessed. Of particular interest is the impact these phenomena might have on fracture initiation, formation breakdown, and treatment stages which accompany subsequent hydraulic fracturing pumping operations.

Proppant Transport in Hydraulic Fractures by Creating a Capillary Suspension

2021 ◽  
Author(s):  
Ayomikun Bello
Keyword(s):  
Hydraulic Fracturing ◽  
Significant Risk ◽  
High Viscosity ◽  
Hydraulic Fractures ◽  
Main Task ◽  
Low Viscosity ◽  
Fracturing Fluids ◽  
Geological Conditions ◽  
Fracture Development ◽  
The Impact

Abstract Slick water fracturing fluids with high viscosity and minimal friction pressure losses are commonly employed in hydraulic fracturing nowadays. At the same time, high injection rates can be used to perform hydraulic fracturing to get the calculated fracture sizes. The conventional algorithm for conducting a standard proppant hydraulic fracturing includes performing a pressure test using a linear gel without a trial proppant pack to determine the quality of communication with the formation and the initial parameters of the fracture; and performing a mini-hydraulic fracturing on a cross-linked gel with a trial proppant pack (1000 - 2000 kg) to assess the parameters of the fracture development used to correct the design of the main hydraulic fracturing operation. However, in complex geological conditions associated with the presence of small clay barriers between the target formation and above or below the water-saturated layers, as well as in low-productive formations, this conventional method of conducting hydraulic fracturing operations using high-viscosity fluids is not always suitable. Hydraulic fracturing in thin-layer formations is associated with a significant risk of the tightness established by the fracture being broken, as well as fluids contained in the underlying or overlying layers being involved in the drainage process. Hydraulic fracturing in low-productive formations creates fractures that are similar in shape to radial fractures, reducing the efficiency and profitability of the impact due to inefficient use of materials and reagents. The main task in this situation is to limit the height of the fracture development and increase their length. It is necessary to use low-viscosity fracturing fluids with a high ability to transfer proppants to reduce the specific pressure in the fracture and control the height of the rupture. The goal of this research is to develop such fluid.

scholarly journals A multi-perforation staged fracturing experimental study on hydraulic fracture initiation and propagation

2020 ◽  
Vol 38 (6) ◽  
pp. 2466-2484
Author(s):  
Jianguang Wei ◽  
Saipeng Huang ◽  
Guangwei Hao ◽  
Jiangtao Li ◽  
Xiaofeng Zhou ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Oil And Gas ◽  
Fracture Initiation ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Breakdown Pressure ◽  
Tight Sandstone ◽  
Heterogeneous Samples ◽  
Initiation And Propagation

Hydraulic fracture initiation and propagation are extremely important on deciding the production capacity and are crucial for oil and gas exploration and development. Based on a self-designed system, multi-perforation cluster-staged fracturing in thick tight sandstone reservoir was simulated in the laboratory. Moreover, the technology of staged fracturing during casing completion was achieved by using a preformed perforated wellbore. Three hydraulic fracturing methods, including single-perforation cluster fracturing, multi-perforation cluster conventional fracturing and multi-perforation cluster staged fracturing, were applied and studied, respectively. The results clearly indicate that the hydraulic fractures resulting from single-perforation cluster fracturing are relatively simple, which is difficult to form fracture network. In contrast, multi-perforation cluster-staged fracturing has more probability to produce complex fractures including major fracture and its branched fractures, especially in heterogeneous samples. Furthermore, the propagation direction of hydraulic fractures tends to change in heterogeneous samples, which is more likely to form a multi-directional hydraulic fracture network. The fracture area is greatly increased when the perforation cluster density increases in multi-perforation cluster conventional fracturing and multi-perforation cluster-staged fracturing. Moreover, higher perforation cluster densities and larger stage numbers are beneficial to hydraulic fracture initiation. The breakdown pressure in homogeneous samples is much higher than that in heterogeneous samples during hydraulic fracturing. In addition, the time of first fracture initiation has the trend that the shorter the initiation time is, the higher the breakdown pressure is. The results of this study provide meaningful suggestions for enhancing the production mechanism of multi-perforation cluster staged fracturing.

scholarly journals Investigation of the Fracturing Effect Induced by the Disturbing Stress of Hydrofracturing Using the Bonded-Particle Model

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-24
Author(s):  
Xin Zhang ◽  
Yuqi Zhang ◽  
Bingxiang Huang
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Zone ◽  
Fracture Propagation ◽  
Bedding Plane ◽  
Particle Model ◽  
Hydraulic Fractures ◽  
Bedding Planes ◽  
Geological Conditions ◽  
Hydraulic Fracture Propagation

Hydraulic fracturing applications have shown a stress disturbance effect during hydraulic fracture propagation, which is often ignored. Using laboratory and discrete element numerical simulation tests, hydraulic fracture propagation under this stress disturbance is systematically studied. The results show that during hydraulic fracturing, the bedding plane is damaged by the stress disturbance, forming a bedding fracture zone (BFZ). The nonlinear fracture characteristics of the formation process of the disturbed fracture zone are revealed, and two indexes (the number of fractures in the disturbed fracture zone and the size of the disturbed fracture zone) are proposed to evaluate the fracturing effect of the stress disturbance. Based on these indexes, multifactor sensitivity tests are conducted under different geological conditions and operational factors. When the principal stress ( σ 1 ) difference is large, the number of hydraulic fractures gradually decreases from many to one, and the direction of the hydraulic fractures gradually approaches the vertical direction of σ 3 , but the change in the in situ stress condition has no obvious effect on the stress disturbance effect. The weaker the bonding strength of the bedding plane, the more significant the stress disturbance effect is, and the easier it is for the fractures to expand along the bedding plane. With increasing injection rate, the stress disturbance effect first increases and then decreases, and the hydraulic fracture propagates from along the bedding plane to cross the bedding plane. With increasing relative distance between the injection hole and bedding plane, the stress disturbance effect presents a linearly increasing trend, and the hydraulic fractures along the bedding planes extend. Based on the experimental results, the relationship between the fracturing effect of the stress disturbance and the extension mode of the hydraulic fracture is determined, and an optimization method for hydraulic fracturing in composite rock reservoirs is given. The research results can provide a theoretical basis for controlling the formation of complex fracture networks in composite rock reservoirs.

Research on hydraulic fracture initiation and vertical propagation behavior in laminated tight formation

2020 ◽  
Author(s):  
anan wu
Keyword(s):  
Hydraulic Fracture ◽  
Vertical Plane ◽  
Fracture Initiation ◽  
Bedding Plane ◽  
Vertical Stress ◽  
Hydraulic Fractures ◽  
Research Knowledge ◽  
Propagation Behavior ◽  
Vertical Propagation ◽  
Tight Formation

<p>Research on hydraulic fracture initiation and vertical propagation</p><p>behavior in laminated tight formation</p><p>Anan Wu<sup>1</sup>, Bing Hou<sup>*1</sup>, Fei Gao<sup>2</sup>，Yifan Dai<sup>1</sup>，Mian Chen<sup>1</sup></p><ul><li>(1. State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum-Beijing, Beijing, China No.1 Cementing Company, Bohai Drilling Engineering Company Limited, CNPC, China. Renqiu,062550)</li> </ul><p> </p><p><strong>Abstract: </strong>The extent of hydraulic fracture vertical propagation extent is important in evaluating simulated reservoir volume for laminated tight reservoirs. Given that it is affected by the discontinuities (beddings, natural fractures, and other factors), fracture geometry is complex in the vertical plane and is different from a simple fracture in a homogeneous formation. Because the tight formation bedding is very developed, hydraulic fracture is difficult to spread vertically. Now,the propagation mechanism of hydraulic fracture in the vertical plane has not been well understood. To clarify this mechanism, several groups of large-scale tri-axial tests were deployed in this study to investigate the fracture initiation and vertical propagation behavior in laminated tight formation. The influences of multiple factors on fracture vertical propagation were studied.</p><p>we carried out the indoor hadraulic fracturing physical simulation experiments of the bedding-developed rocks. Tight cores obtained from the core well were wrapped with cement into 30 cm cubes, and samples were drilled and cemented. Before the experiment ,three-dimensional axial stress was applied to simulate the stratigraphic environment. When the stress was balanced, a certain flowing rate was set for hadraulic fracturing. After the fracturing work was completed, the cement block was opened to observe the hydraulic fracture propagation pattern.</p><p>The results showed that the ultimate fracture geometries could be classified into three categories: simple bedding fracture, slight turning fracture, stair-like fracture, and multilateral fishbone-like fracture network. Here comes some research knowledge:(1)When the difference between the vertical stress and the minimum horizontal principal stress is less than 12Mpa, the hydraulic fracture will only expand along the rock bedding plane Furthermore. (2)when the vertical stress difference is close to 14 MPa, hydraulic fractures will generate vertical fractures that will communicate multiple beddings of the rock. (3)Increasing flowing rate will cause a slight turning or jumping fractures and improve the complexity of fractures to a certain extent. (4)because of the influence of beddings and lithology,the fracture pressure is usually high.</p><p><strong>Key words:</strong> Hydraulic fracturing, tight reversior Bedding plane, fracture morphology.</p>

scholarly journals Diffusivity-dependent fracturing processes and microseismic activity in granite

2020 ◽  
Vol 205 ◽  
pp. 02009
Author(s):  
Catarina Baptista-Pereira ◽  
Bruno Gonçalves da Silva
Keyword(s):  
Hydraulic Fracturing ◽  
Fluid Pressure ◽  
Injection Rate ◽  
Hydraulic Fractures ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Rock Matrix ◽  
Hydraulic Oil ◽  
Permeability Enhancement ◽  
Microseismic Activity

Enhanced Geothermal Systems have relied on hydraulic fracturing to increase the permeability of rock reservoirs. The permeability enhancement depends on the connectivity between new and existing fractures. This, in turn, depends to a large extent on the interaction between the rock and the fracturing fluid, which not only pressurizes existing and new fractures but also diffuses into the rock matrix. In this research, the effect of the diffusivity of hydraulic oil on the fracturing processes and microseismicity of unconfined prismatic granite specimens was experimentally evaluated using visual and acoustic emission monitoring. The tests consisted of injecting hydraulic oil into two pre-fabricated flaws at two rates (2 ml/min and 20 ml/min), kept constant in each test. The fluid pressure inside the flaws was increased until hydraulic fractures propagated and the fluid front growing from the pre-fabricated flaws was visually monitored throughout the tests. It was observed that the fracturing pressures and patterns were injection-rate-dependent, which shows that diffusivity and poro-elastic effects play an important role in the hydraulic fracturing processes of granite. A smaller fluid front was observed for the 20 ml/min injection rate, associated to a lower volume injected and to a higher fracturing pressure when compared to the 2 ml/min injection rate. This was interpreted to be caused by the different pore pressures that developed inside of the rock matrix, which are function of the fluid front size. Microseismic activity was observed throughout the tests, becoming more intense and localized near the flaws as one approached the end of the test (i.e. visible crack propagation). While microseismic events were observed outside the fluid front region, their density was significantly larger within this area, showing that fluid diffusivity may contribute to an intensification of the microseismic activity.

scholarly journals Complexing the hydraulic fracturing simulation results when hybrid acid-propant treatment performing and with the simultaneous hydraulic fracture initiation in separated intervals

2021 ◽  
pp. 103-111
Author(s):  
I. G. Fattakhov ◽  
◽  
L. S. Kuleshova ◽  
R. N. Bakhtizin ◽  
V. V. Mukhametshin ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Hydraulic Fracturing ◽  
Qualitative Data ◽  
Three Dimensional ◽  
Fracture Initiation ◽  
Data Series ◽  
Hydraulic Fractures ◽  
Data Generation ◽  
Data Preparation ◽  
New Approach

The purpose of the work is to substantiate and formulate the principles of data generation with multiple results of hydraulic fracturing (HF) modeling. Qualitative data for assessment, intercomparison and subsequent statistical analysis are characterized by a single numerical value for each considered hydraulic fracturing parameter. For a number of hydraulic fracturing technologies, uncertainty may arise due to obtaining several values for the parameter under consideration. The scientific novelty of the work lies in the substantiation of a new approach for evaluating the obtained data series during hydraulic fracturing modeling. A number of data can be obtained both during the formation and modeling of several hydraulic fractures, and for one fracture when calculating in different modules of the simulator. As a result, an integration technique was developed that allows forming a uniform data array regardless of the number of elements in the hydraulic fracturing modeling results. Keywords: hydraulic fracturing; acid-proppant hydraulic fracturing; hydraulic fracturing of layered rocks; hydraulic fracturing modeling; pseudo-three-dimensional fracture model; data preparation; statistical analysis.

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