Multi-fracture Propagation Research Articles

The effect of rock mechanical heterogeneity on induced stress and initiation pressure of multi-cluster fracturing

The stress interference between fracturing clusters in horizontal wells is key in affecting the initiation and propagation of multi-cluster fractures. However, in reservoirs such as shale, there are often changes in the mechanical properties of the rock along the direction of the wellbore. Such changes are often not considered in models for multi-fracture propagation. As a result, the impact of rock mechanical heterogeneity on induced stress is not fully understood. Therefore, in this paper, a prediction model of the three-dimensional induced stress field of hydraulic fractures is established, taking into account mechanical heterogeneity. Combined with the prediction model of fracturing pressure, the changes in induced stress and initiation pressure under different conditions are analyzed. The results indicate a significant difference between the induced stress results considering mechanical heterogeneity and those considering only a single homogeneous region. The change in elastic modulus has a profound influence on induced stress and initiation pressure. Perforating at locations with low elastic modulus in situ can help reduce initiation pressure. Additionally, temporarily blocking the wellbore and reducing the flow rate to decrease the net pressure in the fractures can facilitate more fractures to initiate.

Research on Horizontal Well Multi-Fracture Propagation Law under the Synergistic Effect of Complex Natural Fracture and Reservoir Heterogeneity

Conventional fracturing design generally only considers the propagation of a single fracture in homogeneous storage, but the heterogeneity characteristics of the reservoir and the development of complex natural fractures will affect the fracturing effect. In order to study the horizontal well fracture propagation law under the synergistic effect of complex natural fracture reservoir heterogeneity, the globally embedded cohesive element finite model is established, and the heterogeneous reservoirs are built by Python programming. The influencing factors of multi-fracture propagation with heterogeneous reservoirs are analyzed, including the in situ stress difference, the injection rate of fracturing fluid, the perforation spacing, and the perforating clusters number. The results show that the heterogeneity and the natural fracture of the reservoir will affect the in situ stress distribution and propagation direction. When the in situ stress difference is low, the reservoir heterogeneity and natural fractures have a great influence on the fracture morphology. With the increase in injection rate, the fracture length and fracture width increase. With the in situ stress difference increase, the fracture deflection angle decreases. With the increase in fracturing fluid injection rate, the fracture length increases. The number of hydraulic fractures communicating with natural fractures increases with the natural fracture number and the number of perforation clusters under the synergistic effect of complex natural fracture and reservoir heterogeneity.

Research on the Interaction Mechanism of Multi-Fracture Propagation in Hydraulic Fracturing

During the hydraulic-fracturing process, stress interference occurs among multiple wells and fractures, potentially affecting the trajectory of hydraulic fracture propagation. Previous studies have largely overlooked the influence of proppant support stresses on the trajectories of fracture propagation. This paper establishes a mathematical model, grounded in the boundary element method, designed to compute the propagation of multiple fractures, considering both proppant support on the fracture surface and dynamic perturbations within the local stress field. The findings of this research reveal that the stress field induced by hydraulic fracturing exhibits dynamic evolution characteristics, necessitating a comprehensive study of the fracture initiation and extension across the entire fracturing time domain. The effect of the residual fracture width under proppant action on the in situ stress field cannot be ignored. During simultaneous fracturing, hydraulic fractures are inclined to propagate in the direction of the maximum horizontal principal stress, particularly as the in situ differential stress escalates. Staggered fracturing between wells has been proven to be more effective than head-to-head fracturing. Simply increasing the well spacing cannot solve the problem of inter-well fracture interference. In zipper fracturing, adjusting the fracturing sequence can inhibit the fracture intersections between wells, thereby controlling the trajectory of fracture propagation. The aforementioned research has considerable significance in guiding the control of fracture morphology during hydraulic-fracturing processes.

Numerical Simulation of Stress Disturbance Mechanism Caused by Hydraulic Fracturing of Shale Formation

Characterizing changes in rock properties is essential for the hydraulic fracture and re-fracture parameter optimization of shale formations. This paper proposed a hydraulic fracturing model to investigate the changes in rock properties during hydraulic fracturing using SPH, and the changes in the stress field and rock properties were quantitatively characterized. The simulation results indicated that the minimum horizontal principal stress increased by 10 MPa~15 MPa during fracture propagation, which is the main reason for the uneven propagation in multi-fracture propagation. Affected by the stress disturbance, the stimulated area was divided into four parts based on the changes in Young’s modulus and permeability; the more seriously the stress disturbance was affected, the higher the permeability of the stimulated zone was, and the smaller the stimulated zone was. Meanwhile, a zone with reduced permeability appeared due to the compression effect caused by the high injection pressure, and this increased with the increase in stress disturbance. The main reason for this was that strain formed because of the compression effect from the high injection pressure. The higher the stress disturbance, the higher the accumulated strain. This new model provides a new method for fracture parameter optimization, which also provides a foundation for the re-fracture parameter optimization of shale formations.

Study on the Influence of Perforating Parameters on the Flow Rate and Stress Distribution of Multi-Fracture Competitive Propagation

It is of great significance to investigate the flow rate and stress distribution of multi-fracture propagation for the optimization of perforation parameters and fracture parameters. Considering the coupling of rock deformation, fracture direction and fluid flow in multi-fracture scenarios, a mathematical model and solution program for the flow and stress distribution of multiple fractures are established, and the analytical model is used for comparison and verification. The effects of perforation cluster number, cluster spacing, perforation diameter on fracture extension trajectory, fracture width, flow rate of each fracture and stress field are studied by the model. The results show that, as the number of perforating clusters increases, the inner fracture is inhibited more severely with less width, length and flow distribution, as well as lower bottom hole pressure. With the increase in cluster spacing, the stress interference between whole fractures is weakened and the flow distribution of the inner fracture is increased with lower bottom hole pressure. With the decrease in perforation diameter, the inhibition effect of inside fractures is weakened, while the inhibition effect of outside fractures, the flow distribution of inside fractures and the bottom hole pressure are increased. The uniform propagation of multiple fractures can be promoted by decreasing the perforation clusters’ number and perforation diameter or increasing fracture spacing.

Multi-Fracture Propagation Considering Perforation Erosion with Respect to Multi-Stage Fracturing in Shale Reservoirs

Shale gas is considered a crucial global energy source. Hydraulic fracturing with multiple fractures in horizontal wells has been a crucial method for stimulating shale gas. During multi-stage fracturing, the fracture propagation is non-uniform, and fractures cannot be induced in some clusters due to the influence of stress shadow. To improve the multi-fracture propagation performance, technologies such as limited-entry fracturing are employed. However, perforation erosion limits the effect of the application of these technologies. In this paper, a two-dimensional numerical model that considers perforation erosion is established based on the finite element method. Then, the multi-fracture propagation, taking into account the impact of perforation erosion, is studied under different parameters. The results suggest that perforation erosion leads to a reduction in the perforation friction and exacerbates the uneven propagation of the fractures. The effects of erosion on multi-fracture propagation are heightened with a small perforation diameter and perforation number. However, reducing the perforation number and perforation diameter remains an effective method for promoting uniform fracture propagation. As the cluster spacing is increased, the effects of erosion on multi-fracture propagation are aggravated because of the weakened stress shadow effect. Furthermore, for a given volume of fracturing fluid, although a higher injection rate is associated with a shorter injection time, the effects of erosion on the multi-fracture propagation are more severe at a high injection rate.

Study on rock fracture mechanism and hydraulic fracturing propagation law of heterogeneous tight sandstone reservoir.

Hydraulic fracturing technology is an effective way to develop tight sandstone reservoirs with low porosity and permeability. The tight sandstone reservoir is heterogeneous and the heterogeneity characteristics has an important influence on fracture propagation. To investigate hydraulic fracture performance in heterogeneous tight reservoir, the X-ray diffraction experiments are carried out, the Weibull distribution method and finite element method are applied to establish the uniaxial compression model and the hydraulic fracture propagation model of heterogeneous tight sandstone. Meanwhile, the sensitivity of different heterogeneity characterization factors and the multi-fracture propagation mechanism during hydraulic fracture propagation is analyzed. The results indicate that the pressure transfer in the heterogeneous reservoir is non-uniform, showing a multi-point initiation fracture mode. For different heterogeneity characterization factors, the heterogeneity characteristics based on elastic modulus are the most sensitive. The multi-fracture propagation of heterogeneous tight sandstone reservoir is different from that of homogeneous reservoir, the fracture propagation morphology is more complex. With the increase of stress difference, the fracture propagation length increases. With the increase of injection rate, the fracture propagation length increases. With the increase of cluster spacing, the propagation length of multiple fractures tends to propagate evenly. This study clarifies the influence of heterogeneity on fracture propagation and provides some guidance for fracturing optimization of tight sandstone reservoirs.

Investigation and Application of Perforation Optimization Method on Shale Gas Horizontal Well with Numerical Simulation of Multicluster Fracturing under Dense-Segment Pattern

Investigation and Application of Perforation Optimization Method on Shale Gas Horizontal Well with Numerical Simulation of Multicluster Fracturing under Dense-Segment Pattern

Promoting the uniform propagation of multi-fracture through adjusting the injection rate and perforation parameter: A numerical study

The strong stress interference and fluid competitive distribution result in the non-uniform propagation of multiple fractures during horizontal well multi-stage hydraulic fracturing (HWMHF). The uniform stimulation effect can be effectively improved by adjusting the injection rate and perforation scheme. In this work, a two-dimensional fluid–solid fully coupled multi-fracture propagation model is established to investigate the pattern of multi-fracture propagation and the flow distribution. The considering factors include the fluid injection rate, the perforation parameters, and the reservoir heterogeneity. The pipe element is developed to realize the free fluid distribution among multiple fractures. The results show that multiple fractures are more likely to initiate simultaneously and propagate uniformly with a higher fluid injection rate. The stress interference among multiple fractures can be balanced and the equilibrium propagation degree of multiple fractures can be greatly improved by reducing the perforation number. In the homogeneous reservoir, when the fluid injection rate is 12 m3/min and the perforation number per cluster is reduced to 10, the difference coefficient of fluid distribution can be reduced to 3.31%. In the heterogeneous reservoir, multiple perforation clusters with different tensile strengths can generate nearly uniform fractures by increasing the fluid injection rate and reducing the perforation number. When the fluid injection rate is 12 m3/min and the perforation number per cluster is 6, the difference coefficient of fluid distribution can be reduced to 3.26%. This work is of great significance in clarifying the propagation pattern and optimizing the fluid injection rate and the perforation number to improve the uniform propagation degree of multiple fractures.

Numerical simulation of multi-fracture propagation in staged multi-cluster SC-CO2 fracturing of horizontal wells

Numerical simulation research on fracture propagation in SC-CO2 (supercritical carbon dioxide) fracturing mainly focuses on a single fracture, and the multifracture propagation law of SC-CO2 fracturing under the influence of multiple factors is ambiguous. In this study, based on the boundary element method, a three-dimensional, plane propagation model of multicluster SC-CO2 fracturing in multifractured horizontal wells, which considers the three-dimensional, elastic deformation of the reservoir rock mass, the two-dimensional flow of SC-CO2 fracturing fluid in fractures, the change in SC-CO2 physical parameters during fracturing and the flow distribution of each cluster fracture, is established. The influence of geological factors and construction factors on the propagation law of SC-CO2 fracturing in multifractured horizontal wells is explored. The results show that compared with slick water fracturing, the hole friction of SC-CO2 fracturing effectively balances the negative effect of induced stress between two fractures, inhibits the liquid entry advantage of heel-end fractures, and increases the reconstruction area in the reservoir. SC-CO2 fracturing in multifractured horizontal wells minimizes the energy loss of the fracture tip in different ways with different reservoir stress differences. Increasing the displacement and crack spacing are conducive to promoting the uniform expansion of SC-CO2 multicrack propagation. Based on the liquid volume distribution index, the construction parameters are optimized. The construction displacement of SC-CO2 multicluster fracturing should be greater than 10 m3 min−1, the hole diameter should be less than 14 mm, and the number of boreholes in each perforation cluster should be less than 16.

Numerical simulation of proppant migration in horizontal wells with multi-fracture fracturing

For horizontal wells fracturing in unconventional reservoirs, the fracture morphology and proppant migration are severely affected by the interfering effects among multiple fractures propagation. Current numerical simulation for proppant migration did not reveal the interrelation among flow distribution, fracture length and sandbank shape during multiple fractures propagation. In this study, a proppant migration model is proposed by combining the displacement discontinuity method (DDM) and the Eulerian-Lagrangian method (E-L M), which implement dynamic multiple fractures propagation simulation as well as the changing state of flow distribution for each fracture. The accuracy of the numerical model is verified by laboratory experiments. The sensitivity parameters of proppant settlement are analyzed, and two dimensionless parameters, height ratio γ and area ratio η are proposed for proppant migration evaluation. The results show that with a lower fracturing fluid flow rate, fluid viscosity, the height ratio γ is lower, and the area ratio η is higher, which also results in the proppant being more likely to accumulate at the fracture entrance. As the proppant particle size increases from 100 μm to 500 μm, the dimensionless height ratio γ and the dimensionless area ratio η decrease significantly. Increase in fracture spacing during horizontal well multi-cluster fracturing results in a limited improvement for proppant settlement. Formation elastic modulus has an appreciable impact on proppant migration in multi-fracture propagation, high elastic modulus formation leads to an ununiform proppant placement over long distances.

Numerical Study on Simultaneous Propagation of Multiple Fractures: A Method to Design Nonuniform Perforation and In-Stage Diversion

Summary The uneven propagation of multifractures is a key factor restricting production growth due to stress shadow and heterogeneity. To date, limited-entry fracturing techniques, nonuniform perforation, and in-stage diversion have been commonly used to promote even multifracture growth. In this study, a fully coupled multiple pseudo-3D (P3D) fracture simulator has been developed to examine the competitive propagation of multifractures during multicluster fracturing in a horizontal well. The present model considers stress interaction among multiple fractures, perforation erosion, fluid distribution among clusters, and in-stage diversion. The results of the model are validated against the reference data. Using the model, a series of numerical simulations are performed to investigate multifracture propagation with nonuniform perforation and in-stage diversion fracturing. We estimate the value of stress interaction for different fractures and time based on the approximate solution of Perkins-Kern-Nordgren (PKN) fracture in the viscosity-dominated regime and improve the dimensionless parameter that characterizes the competition between stress interaction and perforation friction. The fluid distributes evenly when the dimensionless parameter is less than unity (perforation friction is larger than stress interference). Based on this dimensionless parameter, a method to design nonuniform perforation and in-stage diversion is proposed. Results show that in the case of homogeneous in-stage stress, the perforation parameters should be selected under the condition that the dimensionless parameter is less than unity. In the case of heterogeneous in-stage stress and based on the perforation parameters selected under homogeneous stress conditions, the perforation holes in the high-stress cluster should be increased, making the reduction of perforation friction equal to the value of the in-stage stress heterogeneity. The stress heterogeneity can be balanced by decreasing the perforation friction of the high-stress clusters. In this way, nonuniform perforation under heterogeneous in-stage stress conditions can be designed quantitatively without numerical simulation. For in-stage diversion treatment, a method to design the number of ball sealers is proposed based on the results of nonuniform perforation, and only several or even zero groups of simulation are necessary to find the optimal number of ball sealers. A series of numerical simulations shows that the proposed design method is reliable and achieves a satisfactory result in an actual field case. The results can be helpful for nonuniform perforation and in-stage diversion design for multicluster fracturing in a horizontal well.

A Fully Coupled Hydro-Mechanical Approach for Multi-Fracture Propagation Simulations

Hydraulic fracturing is a complex nonlinear hydro-mechanical coupled process. Accurate numerical simulation is of great significance for reducing fracturing costs and improving reservoir development benefits. The aim of this paper is to propose an efficient numerical simulation method for the fracturing-to-production problem under a unified framework that has good convergence and accuracy. A hydro-mechanical coupled fracturing model (HMFM) is established for poroelastic media saturated with a compressible fluid, and the local characteristics of the physical field are fully considered. Each fracture is explicitly characterized using the discrete fracture model (DFM), which can better reflect the physical characteristics near fractures. Based on the extended finite element method (XFEM) and the Newton–Raphson method, a fully coupled approach named Unified Extended Finite Element (UXFEM) is developed, which can solve the nonlinear system of equations that describe the solution under a unified framework. UXFEM can accurately capture the local physical characteristics of different physical fields on the orthogonal structured grids. It realizes the grid-fracture decoupling, and fractures can propagate in any direction, which shows greater flexibility in simulating fracture propagation. The fully coupled approach can better reflect the essential relationship between pressure, stress, and fracture, which is beneficial to studying hydro-mechanical coupled problems. To validate the UXFEM, UXFEM is compared with the classical KGD model, analytic solution, and COMSOL solution. Finally, based on UXFEM, the interference phenomenon and fracturing-to-production study are carried out to prove the broad practical application prospect of this new fully coupled approach.

A multi-fracture balanced extension control method for horizontal wells in anisotropic shale

Shale has anisotropy in elastic parameters and permeability coefficient in parallel and perpendicular directions to the bedding plane. In the study of fracture propagation during hydraulic fracturing, it is necessary to consider the influence of shale anisotropy. Through the development of fluid pipe element, fluid pipe connector element, cohesive damage element, and rock matrix element with pore pressure, a fluid–structure coupling numerical model with comprehensive consideration of dynamic flow distribution, dynamic fracture propagation and extension, and stress interference are established. The anisotropic characteristic parameters of shale reservoirs are given to study the balanced propagation control method of multi-fracture in horizontal shale Wells. The results show that under anisotropic conditions, hydraulic fractures are easy to expand in the direction parallel to the bedding plane but not in the direction perpendicular to the bedding plane. Finally, It forms a long extension in the length direction and a short extension in the height direction. The stress interference along the direction of the minimum horizontal principal stress is gradually intense with the increase of the degree of anisotropy. During multi-fracture propagation in horizontal shale wells, the stress interference generated in the direction of minimum horizontal principal stress can be balanced by effectively controlling the perforation friction so as to promote the balanced extension of multiple fractures. At the same time, with the increase of injection flow and the decrease of the distance between clusters, the stress interference degree gradually becomes serious. Therefore, it is necessary to strictly design how to control the perforation friction in the multi-fracture fracturing process of shale horizontal Wells with large flow rates and small cluster distances. The research conclusions provide a theoretical reference for the efficient development of shale petroleum resources.

Competition growth of biwing hydraulic fractures in naturally fractured reservoirs

Hydraulic fracturing, combined with horizontal wells, is one of the key technologies that enables production from shale gas reservoirs. However, data from several fields in the United States verified that the total production is only contributed by a small portion of designed fractures (Miller et al., 2011). In this paper, we aim to provide an explanation about this phenomenon and propose corresponding suggestions to improve stimulation efficiency. Here, a multi-fracture propagation model in reservoirs containing cemented natural fractures (NFs) is presented based on phase field method. The fracture growth resistance of each wing for varying properties of NFs is quantitatively investigated. We found that NFs toughness, roughness and intersection angle play a vital role on the fracture growth resistance. It was demonstrated that the discrepancy of fracture growth resistance of each wing can suppress fracture propagation in heterogeneous reservoirs. Fracture propagation in mixed-regime was found to favor creation of biwing fractures, which can be used to improve stimulation performance. The simulations of simultaneous fracturing in naturally fractured formations demonstrated that the existence of NFs alters the extending paths of hydraulic fractures (HFs), which may result in fracture coalescence. In this case, the presented model can be utilized to improve stimulation efficiency through optimizing design parameters.

Numerical Simulation of Multifracture Growth under Extremely Limited Entry Fracturing of Horizontal Well

The multifracture competitive growth from a horizontal well is an essential issue in multi-cluster fracturing design. In recent years, extremely limited entry (ELE) fracturing has been implemented to promote uniform multifracture growth. However, the mechanism of multifracture growth and ELE design remain unclear. Based on the planar three-dimensional multifracture propagation model, a multi-cluster horizontal well fracturing model that considers ELE design has been developed. The model considers flow in the wellbore and fluid filtration loss in the fracture. The simulator enables the simulation and analysis of non-uniform in situ stress, filtration loss, and fracture properties. Using this program, we simulated the propagation process of multiple clusters of fractures in ELE fracturing of horizontal wells. The results show the following: The perforation friction in the ELE fracturing can counteract the difference in fluid allocation caused by stress interference, allowing all clusters of perforations to have even fluid allocation but to differ significantly in fracture geometry. The in situ stress profile and 3D fracture stress interference determine the fracture geometry, and the fracture of the middle cluster could cross through the layer with relatively higher in situ stress, resulting in a decrease in effective fracture area in the pay zone. Furthermore, an increase in perforation diameter causes the flow-limiting effect of the perforations to decrease. The fluid volumes entering different clusters of perforations become less uniform. The difference in fracture toughness within a perforated stage has a minor influence on the fluid allocation between different clusters, while the in situ stress distribution within a perforated stage has a significant impact on the fluid allocation between different perforation clusters in the stage. Fractures preferentially propagate at the perforation points with lower in situ stress and stress interference. This study can be helpful to understand multifracture competitive growth and the optimization of ELE fracturing design.

Study on multi-fracture propagation based on the uniform coefficient of fracture propagation

Multi-cluster fracturing is one of the most critical technologies for the efficient exploitation of unconventional reservoirs, and fracture uniform propagation during synchronous multi-fracture propagation is the goal of hydraulic fracturing. Most of the current studies on the simultaneous propagation of multiple fractures characterize the degree of uniform fracture propagation by the difference in fracture length or width, while the uniformity of multiple fractures is affected by multiple fracture parameters simultaneously, which makes such a characterization method biased. In this article, the stress interference of multiple fractures, fluid flow in fractures, flow distribution, and fracturing fluid filtration are comprehensively considered to establish the synchronous propagation model of multiple fractures in horizontal wells, and the fracture propagation patterns are simulated for different parameters. Then, the propagation uniformity coefficient of multiple fractures is proposed to represent the propagation uniformity of multiple fractures. The fracture uniformity coefficient is the result of the combination of fracture length, fracture width, inlet volume and fracture deflection angle, which can more comprehensively represent the uniformity of fracture propagation. Based on the uniformity coefficient of multi-fracture propagation, the law of multi-fracture interference is studied, and the parameters of multi-fracture propagation are optimized combining with an engineering background.

Numerical Simulation of Fracture Propagation of Multi-Cluster Perforation and Fracturing in Horizontal Wells: A Case Study of Mahu Oilfield

Mahu oilfield is a typical tight gravel oil reservoir. At present, long-stage multi-cluster fracturing is widely used for reservoir stimulation, and multiple-clusters treatment is realized through cluster perforation. Field monitoring indicates that not all perforation clusters produce hydraulic fractures in the fracturing process, and each cluster of hydraulic fractures in the section will expand unevenly. The unbalanced expansion of multiple clusters of fractures in the section seriously affects the effect of reservoir reconstruction of horizontal wells. Aiming at the long-stage multi-cluster fracturing of horizontal wells, a multi-fracture propagation calculation model considering wellbore flow, performance friction, different fracture criteria at the tip, and the interaction stress among multiple fractures is established in this paper. In order to improve the calculation efficiency, an explicit Runge Kutta Legendre algorithm is proposed to solve the structural mesh, and the solution program is compiled, which provides a basis for the theoretical analysis and rapid solution of the mechanism of multiple fracture growth. Finally, taking Mahu oil field as an example, we calculate the multi fracture propagation and flow distribution under different geological conditions, perforation conditions, and construction parameters. The research results will help to improve the fracturing efficiency of long-stage multi-cluster fractures.

Parametric effects on fracture geometries from multi-fracture propagation emanating from neighbouring wellbores in quasi-brittle rocks

An integrated approach is presented using field data input from measured geological information into numerical simulation for understanding effects of induced stress on geometries of multiple fracture propagation. We establish a benchmark study based on comparison of field result with numerical computations. The comparison then acts as reference measures for studying effects of changing in-situ stress, fracturing fluid viscosity and fracture spacing on propagation and geometries of multiple fractures between neighbouring wellbores in an undisclosed gas field. This leverages understanding of more complexities associated with inter-well multiple fracture growth that are idealized as straight from certain perspectives. Although some studies focus on stress interference from pre-existing fractures, actual fracture propagation geometries may be far from the idealized scenarios. Therefore, the stress shadow effects between growing multiple hydraulic fractures, if not taken into account, can lead to unrealistic estimation of hydraulic fracture trajectories. Consequently, more attention should be paid to the actual propagation of hydraulic fractures. Actual field geologic information is provided through well-logging and field mapping data. Very short fractures were propagated in these wells before the operation was terminated due to technical problems. The reservoir depth in the area is about 2170 m. At such depth, quasi-brittleness of shale should be accounted for by using relevant methods that capture rock ductility such as traction separation law. Abaqus commercial software is used to conduct the numerical computation using extended finite element method based on cohesive zone modeling. Application of this technique is further validated using Kristianovich-Geertsma-de Klerk analytical solution. This study is important in field implementation of infill drilling with well-informed mechanism of fracture interference in the inter-well region.

Quantitative investigation of multi-fracture morphology during TPDF through true tri-axial fracturing experiments and CT scanning

Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing (TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows: (1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage (IFS) for most tests. (2) The perforation cluster effectiveness (PCE) has increased from 26.62% during the IFS to 88.86% after using diverters. (3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage (DFS) but is positively correlated with water-work. (4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.