Perforation Spacing Research Articles

Experimental near-wellbore hydraulic fracture initiation and growth for horizontal wells with in-plane perforations

To understand the fracture behavior during different perforation modes on horizontal wells, laboratory-scale hydraulic fracturing experiments with acoustic emission monitoring were conducted on tight concrete samples. The experimental results indicated that the breakdown pressure could be greatly reduced and that a simple fan-like structure was created with in-plane perforations on a horizontal well under the same fracturing treatment conditions. Furthermore, there was a positive relationship between treatment parameters and breakdown pressure for helical perforations. Because of the small pressurization rate and large stress interaction, the breakdown pressure with in-plane perforations is smaller than that of helical perforations. However, the treatment parameters were not sensitive to the breakdown pressure but correlated with the shut-in pressure for the in-plane perforation mode. In general, increasing the pump rate and fracturing fluid viscosity can slightly increase the breakdown pressure and substantially increase the shut-in pressure. The increase in fracture extension pressure in the in-plane perforation mode refers to different fracture initiation orders of individual perforations. Although the deviation and failure of fracture initiation of some perforations can be observed due to the strong stress interaction of in-plane perforations, the existence of perforation tunnels can guide hydraulic fracture propagation within one plane. Thus, hydraulic fractures can connect and create large-scale fractures because of the close perforation spacing. The results of trace length and microscale fracture demonstrate that twisted and curved fractures with smaller widths can be significantly created by the helical perforation mode, but large-scale fractures can be created by the in-plane perforation mode, which is beneficial to sand plugging mitigation.

Hydraulic Fractures from Non-Uniform Perforation Cluster Spacing in Horizontal Wells: Laboratory Testing on Transparent Gelatin

The efficiency of a hydraulic fracturing treatment is directly related to the total surface area of the fractured formation. Development of design guidelines for selecting the optimal perforation cluster spacing, fracturing fluid type, rheology, and flowrate can help maximize well production following a hydraulic fracturing treatment for an arbitrary in-situ stress state, formation type, and other geomechanical properties. The influence of non-uniform spacing of perforation clusters along a horizontal wellbore on simultaneously-induced multiple fracture (multi-frac) growth into a reservoir formation was investigated by a series of laboratory-scale models. The relative geometry of the fluid-driven fractures generated in the models was compared to the relative spacing between three perforations.Uniform perforation spacing is found to yield more homogeneous multi-frac growth, as maximizing the spacing between all perforations minimizes multi-frac growth interference, compared to moving the second (middle) perforation closer to either the toe or the heel of the horizontal well. These results may be associated with parameters not considered by conventional theoretical modeling, such as the relative timing of fracture initiation, dominant (run-away) fracture creation, and inactive perforations. Incorporating these effects may promote more reliable predictive modeling of multi-frac propagation patterns, hence optimizing reservoir stimulation design. Analogue scaling comparing the laboratory conditions used with a typical field-scale hydraulic fracture treatment is then performed to assess the reliability of the conclusions.

Structural parameters analysis for tapered steel section with perforation: effect of shear buckling behaviour

Purpose Due to economic development, tapered members are commonly applied in steel frames, namely, industrial halls, warehouses, exhibition centres, etc. In the design of cantilever steel beam structures in cities building design, tapering is introduced at the web profile to achieve utmost economy and suit the bending moment distributions. The cross-sectional shape of the beam is varied linearly to the moment gradient to achieve the target of higher efficiency with lower cost. Design/methodology/approach The shear deformation pattern and efficiency of the tapered steel section with perforation were investigated using finite element analysis. In addition, I-beam with web opening is studied numerically via LUSAS software for different parameters of tapering ratio, perforation shape and perforation size and perforation layout. Findings The highest contributing parameters for the highest shear buckling capacity and efficiency of the section were due to the small opening size and tapering ratio. Whilst the variation of perforation layout and spacing give a major effect on the shear strength and efficiency of the tapered steel section with perforation. Besides that, the highest efficiency model is found when the section is designed with 0.4 D diamond perforation in Layout 3 under a tapering ratio of 0.3. The critical shear buckling load and efficiency is reduced 14.39% and 13.91%, respectively, when perforations are added onto the tapered steel sections. Originality/value The tapered steel section with perforation has lower critical shear buckling load and efficiency compared to the tapered section without perforation but obtains a higher critical shear buckling load and efficiency compared to the uniform section without perforation.

The Effect of Perforation Spacing on the Variation of Stress Shadow

When the shale gas reservoir is fractured, stress shadows can cause reorientation of hydraulic fractures and affect the complexity. To reveal the variation of stress shadow with perforation spacing, the numerical model between different perforation spacing was simulated by the extended finite element method (XFEM). The variation of stress shadows was analyzed from the stress of two perforation centers, the fracture path, and the ratio of fracture length to spacing. The simulations showed that the reservoir rock at the two perforation centers is always in a state of compressive stress, and the smaller the perforation spacing, the higher the maximum compressive stress. Moreover, the compressive stress value can directly reflect the size of the stress shadow effect, which changes with the fracture propagation. When the fracture length extends to 2.5 times the perforation spacing, the stress shadow effect is the strongest. In addition, small perforation spacing leads to backward-spreading of hydraulic fractures, and the smaller the perforation spacing, the greater the deflection degree of hydraulic fractures. Additionally, the deflection angle of the fracture decreases with the expansion of the fracture. Furthermore, the perforation spacing has an important influence on the initiation pressure, and the smaller the perforation spacing, the greater the initiation pressure. At the same time, there is also a perforation spacing which minimizes the initiation pressure. However, when the perforation spacing increases to a certain value (the result of this work is about 14 m), the initiation pressure will not change. This study will be useful in guiding the design of programs in simultaneous fracturing.

Complexity and tortuosity hydraulic fracture morphology due to near-wellbore nonplanar propagation from perforated horizontal wells

Perforated fracturing enhances single well production in the tight sandstones formations with low porosity and permeability effectively, however, some issues are caused after such achievements, such as high breakdown pressure, short fracture length, and limited proppant migration. All are tightly related to hydraulic fracture complex propagation behavior near wellbore. To understand its mechanism, a 3D near-wellbore fracture propagation model is established based on the combination of finite element method and post-failure damage mechanism. The model is applied on a cased and perforated horizontal well to investigate fracture initiation characteristics, near-wellbore fracture non-planar propagation behavior, and torturous hydraulic fracture morphology. Moreover, the effects of stress shadow and perforation parameters are discussed. Based on induced hydraulic fracture initiation position and propagation speed, three main fracture propagation behaviors are observed under the stress shadow effect in simulation results: limited propagation, nonuniform circular propagation, and opposite direction propagation. These nonplanar propagation behaviors cause complexity and tortuosity hydraulic fracture morphologies near the wellbore, which could be mainly divided into four types: spiral-shaped fracture, multi-spiral shaped fracture, horizontal-vertical crossing shaped fracture, and multi-layered shaped fracture. In addition, the reasonable perforation parameter design could reduce torturous fracture surface, resulting in a near flat fracture. The increase in perforation density or perforation diameter could shorten perforation spacing to provide a small diversion angle for induced fractures to interact with each other and form a small spiral degree fracture geometry. However, increased perforation phase causes many perforations in the same direction to create a longitudinal fracture that has a short fracture length for the horizontal well. Therefore, based on above analyses, high perforation density, small perforation phase, and large perforation diameter are suggested to be an effective perforation parameter combination to conduct the perforated fracturing in tight sandstone formation, in order to create a near flat fracture surface with a minimum tortuosity as well as to increase hydraulic fracture propagation area.

Resolvent Approximations in L2-Norm for Elliptic Operators Acting in a Perforated Space

We study homogenization of a second-order elliptic differential operator Aε = - div a(x/ε)∇ acting in an ε-periodically perforated space, where ε is a small parameter. Coefficients of the operator Aε are measurable ε-periodic functions. The simplest case where coefficients of the operator are constant is also interesting for us. We find an approximation for the resolvent (Aε + 1)-1 with remainder term of order ε2 as ε → 0 in operator L2-norm on the perforated space. This approximation turns to be the sum of the resolvent (A0 + 1)-1 of the homogenized operator A0 = - div a0 ∇, a0 > 0 being a constant matrix, and some correcting operator εCε. The proof of this result is given by the modified method of the first approximation with the usage of the Steklov smoothing operator.

Buckling capacity of cold-formed steel structure column member with perforation section in affordable house framing system

PurposeThe purpose of this study is to know the buckling capacity for cold-formed C-column with perforation. Cold-formed C-column have been used in interior wall construction. The concept of web perforation in the column has been introduced to the construction sector to overcome the issue of material cost.Design/methodology/approachInitially, the determination of the suitable spacing for the space column for the affordable house is investigated. Analysis house frame has been done in STAAD Pro. (Staad Pro, 2003) software using cold-formed C-column without perforation. Perforation with circular shape has been used in this study with the size of 0.4, 0.6 and 0.8 D (D = 180 mm). Perforation spacing is 150, 250 and 350 mm are adopted.FindingsFor the specimen with 0.4 D perforation and the edge distance is 539 mm have the highest buckling capacity (26.59 kN). Reduction of buckling capacity is 5.31% from cold-formed C-column without perforation and reduction of the volume is −2.16%. For the same case with 0.8 D perforation, the buckling capacity reduces with 22.52% and volume is −6.85%.Originality/valueThe conclusion of this analysis, C-column without perforation have higher buckling capacity compare to C-column with perforations.

Phase field characteristic of multizone hydraulic fracturing in porous media: the effect of stress boundary

Multizone hydraulic fracture (HF) helps to enhance the commercial production rate of oil and gas in unconventional reservoirs. However, the efficiency of multizone HF highly depends on the cluster/perforation spacing and in situ stress field. Therefore, this paper investigates the phase field characteristic during multizone HF under different perforation spacing and in situ stress field. The total stress tensor involves the influence of initial stress while the fracture growth is characterised by the evolution equation of phase field. In addition, the numerical simulation is verified by a rectangular domain subjected to internal fluid injection. Then, the hydraulic fracture patterns from a group of pre-existing notches subjected to an identical fluid injection rate are examined. The numerical results show that the hydraulic fractures in multizone HF are the automatic product of the evolution equation of phase field without requiring any external fracture criteria. A diverted fracture scenario is shown in most cases and the fracture growth is inhibited if the stress perpendicular to the perforations increases. The fluid pressure in the fracture and the breakdown pressure increases with the increase in the notch spacing and the stress perpendicular to the perforations. The fluid pressure in the middle notch is larger than that in the upper notch. Reversion of the in situ principal stress direction greatly inhibits the growth of multizone hydraulic fractures, which causes the failure of multizone HF. The numerical investigations in this paper can provide a new perspective for multizone HF design.

DEM numerical simulation study on fracture propagation of synchronous fracturing in a double fracture rock mass

The rational choice of perforation arrangement and injection angle is of great significance to improve the efficiency of synchronous fracturing and to achieve the stimulation of the shale reservoir. In this paper, the influence of perforation angle and perforation arrangement on the crack propagation mechanism and rock failure mode of synchronous fracturing is studied based on the particle discrete element software PFC. Results show that due to the influence of the stress shadow effect, elliptical cutting cracks are produced between perforations during the synchronous fracturing. When the perforations are arranged in alignment, the fracture mode of rock mass between the perforations is single crack cutting failure under low injection angle, and double-crack cutting failure under high injection angle. Meanwhile, when the injection angle tends to the direction of maximum principal stress ( $$\uptheta$$ ≥ 60°), the fracturing effect can be greatly improved. In addition, the small perforation spacing under the high principal stress difference is more conducive to the fracturing of the central rock mass. When the perforation is staggered arrangement and the horizontal distance between the perforation centers is the perforation length, it is easy to form the intersection phenomenon of wing cracks under the high principal stress difference, which is more conducive to the realization of fracturing in the central rock mass. In addition, high injection angle is more conducive to the formation of penetrating cracks, but not easy to achieve the central rock mass fracturing. The findings of this study can help for a better understanding of crack propagation law and rock failure mode under different perforation arrangements, which can provide some theoretical guidance for the field synchronous fracturing construction.

Study on the Interference Law of Staged Fracturing Crack Propagation in Horizontal Wells of Tight Reservoirs.

Horizontal well multistage fracturing technology is a high-efficiency method for tight oil and gas production, which increases the contact area between the wellbore and stratum by forming multiple transverse hydraulic fractures (HFs). The stress interference caused by the created HFs will affect the propagation geometries of the subsequent HFs, and then affect the overall fracturing treatment performance. In order to study the distribution of HFs and law of interference among multiple fractures during horizontal well multistage fracturing in tight reservoirs, in this paper, the effects of horizontal stress difference, perforation spacing, and net pressure in the created fracture on the initiation and propagation of multiple cracks were specially studied through large-scale hydraulic fracturing experiments and numerical simulation. The results showed that under high horizontal stress difference, multiple HFs with small spacing tended to coalesce at a place where the length has extended to a certain level. It was also found that the initiation pressures of HFs within subsequent stages increase with the rise of net pressure in created HFs, which causes the subsequent fractures to deviate from the direction perpendicular to the horizontal wellbore and then to gradually deflect toward it. Moreover, the ratio of fracture spacing to fracture height, and the net pressure are the key parameters to determine the deflection degree of HFs for multistage fracturing. In addition, the deflection degree of subsequent HFs was expected to enhance with the decreasing ratio of fracture spacing to fracture height and increasing net pressure in created HFs. It was useful for mitigating stress interference to lengthen the stage spacing, control the fracture height, and reduce the net pressure. The research results have a reference value for the optimal design of the fracture spacing for multistage fracturing.

CFD study of the effect of perforated spacer on pressure loss and mass transfer in spacer-filled membrane channels

One way to reduce pressure loss in spiral wound membrane modules is via creating holes within the feed spacer matrix, leading to increased channel porosity and reduced flow resistance. This study modifies conventional spacer geometry (i.e., dual-layer non-woven spacer) by perforating spacer filament and analyses the effect of different perforation aspects of spacers on the membrane performance via CFD. The results show that spacers with perforations near the membrane surface demonstrate similar mass transfer and pressure loss to the case where the perforation is in the middle of the channel (i.e., bulk flow) and the case that considers spacers without perforation, for a Reh range of 50 – 200. Moreover, a large perforation size decreases mass transfer by over 10% through weakening of the flow velocity or suppression of vortex shedding. The main finding is that spacer perforation does not improve mass transfer for the cases simulated using conventional spacers.

Numerical study of the effect of natural fractures on shale hydraulic fracturing based on the continuum approach

Because of the complexity of shale reservoirs and multiple physical coupling processes, numerical implementation remains a challenge in engineering applications. Unlike conventional reservoirs, shale reservoirs always contain two main discontinuities: bedding interface and natural fractures. The existence of these discontinuities is the key reason a fracture network is formed. Therefore, the numerical model should contain both bedding interface and natural fractures. In this paper, the fracturing propagation process is described based on continuum theory. In contrast to other research, an anisotropic strength criterion is adopted to consider the anisotropic properties of shale, including the failure of both shale matrix and discontinuities. The criterion is described by the Mohr-Coulomb model combined with tensile failure. When fractures are generated in the shale rock mass, the stiffness and permeability of the fractured rock are homogenized in an element, and volume fracturing is represented by the deformation of three orthogonal fractures in the rock element. Simultaneously, the anisotropic permeability is also enhanced. Hence, based on this continuum approach and finite element method, a three-dimensional model for shale hydraulic fracturing simulation is presented. This model fully considers the direct coupling of fluid flow and rock deformation during hydraulic fracturing. To verify the anisotropic strength criterion, a shale compression test is conducted. Through a comparison of the numerical and experimental results, the applied criterion can describe the shale compressive strength anisotropy. In addition, the KGD analytical model is also adopted to verify the performance of the developed model for hydraulic fracturing. Finally, several cases of shale hydraulic fracturing are simulated, and the results show the geometry of the fracture region under different conditions. Furthermore, the impacts of three factors on hydraulic fracturing geometry are considered, including natural fractures, spacing of perforations and differential in situ stress. The influence of these factors on the complexity and scale of the fracturing region is also discussed.

Experimental investigation of the noise radiated by a ducted air flow discharge though diaphragms and perforated plates

An experimental investigation of the noise radiated by a ducted high pressure flow discharge through diaphragms and perforated plates is carried out for a large range of subsonic and supersonic operating conditions (Nozzle Pressure Ratio (NPR) from 1.2 to 3.6). A parametric study of the geometrical parameters is also conducted to characterize their influence on the acoustic radiation. This covers configurations from single diaphragms to multi-perforated plates with variable hole diameters and arrangements that are placed inside a cylindrical duct. Compared with the free discharge analysed in a first part of the study (perforated plates placed directly at the output of the duct), the discharge into a duct, which is closer to the practical applications, generates strong acoustic modifications. As expected, the broadband noise is disturbed by strong modulations due to acoustic resonances in the output duct (longitudinal resonances and transversal duct modes). However, as in the free configuration, a strong effect of the plate geometries on the mixing noise is observed, allowing to adapt or reduce this source. In particular, the increase of the ratio between the perforation spacing and the perforation diameter allows reducing the maximum amplitude of the mixing noise. Compared to the free-field discharge, the Sound Pressure Level (SPL) in the ducted configuration is on average proportional to the 6-th power of the velocity instead of the 8-th power. Moreover, there are two dominant frequency humps in the sound spectra. The low frequency one is characterized by a constant Helmholtz number, suggesting that the sound is shaped by the duct geometry, whereas the high frequency one is characterized by a constant Strouhal number suggesting that the sound is directly generated by the flow. Finally, for supersonic operating points, the screech radiation appearing with diaphragms in the free configuration is suppressed when the output duct is added but new high amplitude and low frequency tones appear for the largest diaphragms and perforated plates. These lines are due to a coupling between normal shock oscillations and longitudinal resonances.

Below the Data Range Prediction of Soft Computing Wave Reflection of Semicircular Breakwater

Coastal defenses such as the breakwaters are important structures to maintain the navigation conditions in a harbor. The estimation of their hydrodynamic characteristics is conventionally done using physical models, subjecting to higher costs and prolonged procedures. Soft computing methods prove to be useful tools, in cases where the data availability from physical models is limited. The present paper employs adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) models to the data obtained from physical model studies to develop a novel methodology to predict the reflection coefficient (Kr) of seaside perforated semicircular breakwaters under low wave heights, for which no physical model data is available. The prediction was done using the input parameters viz., incident wave height (Hi), wave period (T), center-to-center spacing of perforations (S), diameter of perforations (D), radius of semicircular caisson (R), water depth (d), and semicircular breakwater structure height (hs). The study shows the prediction below the available data range of wave heights is possible by ANFIS and ANN models. However, the ANFIS performed better with R2 = 0.9775 and the error reduced in comparison with the ANN model with R2 = 0.9751. Study includes conventional data segregation and prediction using ANN and ANFIS.

Numerical simulation of foam-based hydraulic fracturing to optimise perforation spacing and to investigate effect of dip angle on hydraulic fracturing

Foam-based hydraulic fracturing has been identified as a promising technique to extract unconventional natural gases such as shale gas and tight gas. However, due to the complex two-phase nature of foam, its use has been limited to a few field-scale applications. Therefore, precise understanding of foam-based hydraulic fracturing is essential in order to optimise fracture treatment processes. The aim of this numerical study is therefore to develop new models to predict and evaluate foam-based hydraulic fracturing. In order to achieve this, two models were developed: 1) a 3-D model to simulate the effect of perforation spacing and 2) a 2-D model to simulate the effect of dip angle on hydraulic fracturing. According to the results, perforation spacing has a direct influence on hydraulic fracturing, and a reduction of spacing from 100 to 25 m, increases the overall strain levels near the perforations by 350%. The numerical results also reveal that the dip angle directly influences the fracture network, and the fracture propagation is limited to only one direction. However, the results suggest that the effect of dip angle on fluid flow is negligible, and the pressure distribution remains almost the same in a direction perpendicular to the dip.

Spectral Approach to Homogenization of Elliptic Operators in a Perforated Space

Let [Formula: see text] be a lattice. For [Formula: see text], we consider the perforated space [Formula: see text] which is an [Formula: see text]-periodic open connected set with Lipschitz boundary. In [Formula: see text], we consider a self-adjoint strongly elliptic second-order differential operator [Formula: see text] with periodic coefficients depending on [Formula: see text]. We study the behavior of the resolvent [Formula: see text] for small [Formula: see text]. Approximations for this resolvent in the [Formula: see text] and [Formula: see text]-operator norms with sharp order error estimates are found. The results are obtained by the operator-theoretic (spectral) approach. General results are applied to particular periodic operators of mathematical physics: the acoustics operator, the elasticity operator, and the Schrödinger operator with a singular potential.

Compressive crushing of novel aluminum hexagonal honeycombs with perforations: Experimental and numerical investigations

The quasi-static compressive behavior of novel aluminum hexagonal honeycombs with perforations on the cell wall is investigated experimentally and numerically. Compressive experiments on the perforated honeycombs with different cell numbers are conducted to study the effect of specimen sizes. The measured collapse stress is almost insensitive to the specimen sizes, while the crushing stress increases with the cell numbers and finally converges to a stable plateau for the specimens beyond 15 × 15 cells. Finite element simulations are performed to study the effects of perforation size, spacing and shape on the mechanical properties of honeycombs. The results reveal that perforation size is a key parameter that affects the compressive mechanical properties and deformation patterns of honeycombs. The perforation number along the height direction of a cell has nearly no influence on the collapse stress, and only affect the crushing stress when the perforation size is large. The perforation shape impacts the collapse of honeycombs but has minor effect on the subsequent crushing stage.

Integrated simulation of multi-stage hydraulic fracturing in unconventional reservoirs

In recent years, the multi-stage hydraulic fracturing technology has been widely applied to unconventional reservoirs. In order to optimize the stimulation performance and achieve economic production rates, the underlying physics and the impacts of different designing parameters must be quantitatively understood prior to the operations. Although many numerical models have been developed for this purpose, few are capable of properly taking into account the interplay of different mechanisms, such as fluid flow in the horizontal wells, fracture propagation, and proppant transport.A novel 3D thermal-hydro-mechanical model entitled UFrac is developed in this paper. This model integrates the various mechanisms to capture the interactions among wellbores, fractures and reservoir rocks. The fluid flow inside the wells and the fractures is simulated with the finite volume method (FVM), the elastic deformations of rock mass are calculated with the 3D displacement discontinuity method (DDM), and fracture propagation is simulated with the fixed grid method. The UFrac model is capable of simulating the combined effects of multiple fracturing operation parameters, elastic interaction between fractures, and temperature redistribution induced by flow exchange.By using the UFrac model, we investigate several key problems in hydraulic fracturing such as fracture height growth, perforation spacing optimization, and thermal effect on proppant placement. Important conclusions are drawn from the simulation results. The strength of stress interaction is found to be related to the fracture geometries. Stress shadow effect does not only affect the flow partitioning and fracture size distribution, but also influence the proppant transport. Friction loss in the wellbore can affect the decisions on spacing optimization. Moving inner fractures closer to the heel of the wells would be beneficial for fracture propagation balancing. Fluid viscosity loss due to heating from the surrounding formations results in longer but narrower fractures and faster settling of proppant. The modeling of proppant distribution aids in better characterization of the fracture conductivity, thus provides more reliable prediction of the well productivity.

Impact of Perforation on Hydraulic Fracture Initiation and Extension in Tight Natural Gas Reservoirs

AbstractIn the exploitation of tight natural gas reservoirs, increasing the number of fractures to enlarge the stimulated reservoir volume is the key point. Furthermore, high breakdown pressure is the primary factor that causes the difficulty of hydraulic fracturing treatment in a tight gas reservoir. Both of these factors are related closely to the perforation strategy. However, the impact of perforation on hydraulic fracture initiation and extension in a tight gas reservoir has not yet been researched in an experimental way. We designed a piece of equipment that we refer to as a mini‐sized true tri‐axial hydraulic fracturing simulation system (8 cm×8 cm×10 cm) for the experiments. By using this equipment, we could simulate hydraulic fracturing using downhole drilling cores, which were acquired from the Erdos basin tight gas reservoir. We mainly examined the influence of the horizontal stress difference and spacing, density, and depth of perforation on the fracture patterns. Experimental results show that, in specimens without perforation, the number of fractures is less than that of the perforation specimens, and the direction of fractures is uncontrollable. In specimens with perforations, fractures initiate at the perforation points, which is conducive to forming fractures uniformly. The perforation spacing and horizontal stress difference strongly influence the interaction among fractures. The interaction among fractures is mitigated as the perforation spacing or the horizontal stress difference increases. The depth of perforation affects the fracture initiation. Factures are easier to initiate and propagate in deeper perforations. The existence of perforation could effectively reduce the breakdown pressure by approximately 18 %.

Perforation spacing optimization for multi-stage hydraulic fracturing in Xujiahe formation: a tight sandstone formation in Sichuan Basin of China

Tight reservoir is characterized with low porosity and ultra-low permeability. Horizontal well with multi-stage fracturing is the key technique to maximize stimulated reservoir volume and achieve commercial production. The spacing between perforations has a significant impact on well production. Perforation spacing is currently optimized from the aspects of reservoir simulation. The methods ignore the fact that fracture will generate induced stress field, which may significantly affect the geometry of subsequent fracture. Based on the displacement discontinuity method, this paper established a multi-fracture stress interference model which is able to simulate non-isometric half-length, unequal fracture spacing and arbitrary angle between fracture and wellbore. Data from a tight sandstone reservoir in Sichuan Basin of China are used to analyze the stress field changes and verify the model. The results show that the induced stress creates the maximum compressive stress on both sides of the fracture, and the maximum tensile stress at the fracture tip by stress concentration. The fracture will change the differential horizontal stress ratio in the surrounding area. Position where the differential horizontal stress ratio is lower than 0.3 will be the optimal site to create the complex fractures. Multi-stage fracturing with multiple perforation clusters in one stage is more favorable for complex fracture formation than single perforation cluster in each stage. Data from field verified the proposed perforation optimization method.