A Unified Approach To Optimize Fracture Design of a Horizontal Well Intercepted by Primary- and Secondary-Fracture Networks

SPE Journal ◽  
2019 ◽  
Vol 24 (03) ◽  
pp. 1270-1287 ◽  
Author(s):  
Junlei Wang ◽  
Yunsheng Wei ◽  
Wanjing Luo
Keyword(s):  
Performance Optimization ◽  
Horizontal Well ◽  
Fracture Network ◽  
Network Size ◽  
Productivity Index ◽  
Single Fracture ◽  
Fracture Conductivity ◽  
Secondary Fracture ◽  
Fracture Spacing ◽  
Fracture Complexity

Summary The classical optimization design dependent on a single-fracture (SF) assumption is widely applied in performance optimization for hydraulically fractured wells. The objective of this paper is to extend the optimal design to a complex fracture network to achieve the maximum productivity index (PI). In this work, we established a pseudosteady-state (PSS) productivity model of a fractured horizontal well, which has the flexibility of accounting for the complexity of fracture-network dimensions. A semianalytical solution was then presented in the generalized matrix format through coupling reservoir- and fracture-flowing systems. Subsequently, several published studies on the PSS productivity calculation of a SF were used to verify this model, and a 3D transient numerical simulation of an orthogonal fracture network was used to perform further verification. We show that results from our solutions agree very well with those benchmarked results. On the basis of the model, we provide a detailed analysis on the productivity enhancement of the fracture-network/optimization work flow using unified fracture design (UFD). The results show the following: The PI is determined by fracture conductivity and complexity (network size, spacing, and configuration), and it is a function of fracture complexity and conductivity when the influence of proppant volume is not considered. Under the constraint of a given amount of proppant known as UFD, the maximum PI would be achieved when the best balance between network complexity and conductivity was obtained. It is more advantageous to minimize fracture complexity by creating relatively simple-geometry fractures with smaller network size and larger fracture spacing in the condition of small and intermediate proppant numbers. It should be the design goal to generate a complex network by creating relatively complex-geometry fractures with larger network size and smaller fracture spacing in the condition of a large proppant number. Increasing fracture complexity could reduce the optimal requirement of fracture conductivity. The proposed approach can provide guidance for a network-hydraulic-fracturing design for an optimal completion.

scholarly journals Productivity analysis for a horizontal well with multiple reorientation fractures in an anisotropic reservoir

2020 ◽  
Vol 75 ◽  
pp. 80
Author(s):  
Mingxian Wang ◽  
Zifei Fan ◽  
Lun Zhao ◽  
Guoqiang Xing ◽  
Wenqi Zhao ◽  
...  
Keyword(s):  
Horizontal Well ◽  
Productivity Index ◽  
Finite Conductivity ◽  
Productivity Analysis ◽  
Well Productivity ◽  
Fracture Conductivity ◽  
Fracture Angle ◽  
Fracture Spacing ◽  
Anisotropic Factor ◽  
Anisotropic Reservoir

Reorientation fractures may be formed in soft and shallow formations during fracturing stimulation and then affect well productivity. The principal focus of this study is on the productivity analysis for a horizontal well with multiple reorientation fractures in an anisotropic reservoir. Combining the nodal analysis technique and fracture-wing method, a semi-analytical model for a horizontal well with multiple finite-conductivity reorientation fractures was established to calculate its dimensionless productivity index and derivative for production evaluation. A classic case in the literature was selected to verify the accuracy of our semi-analytical solution and the verification indicates this new solution is reliable. Results show that for a fixed fracture configuration the dimensionless productivity index of the proposed model first goes up and then remains constant with the increase of fracture conductivity, and optimal fracture conductivity can be determined on derivative curves. Strong permeability anisotropy is a negative factor for well production and the productivity index gradually decreases with the increase of anisotropic factor. As principal fracture angle goes up, horizontal well’s productivity index increases correspondingly. However, the effect of reoriented fracture angle on the productivity index is not as strong as that of principal fracture angle. When reoriented fracture angle is smaller than principal fracture angle, reoriented factor should be as low as possible to achieve optimal productivity index. Meanwhile, well productivity index rises up with the increase of fracture number and fracture spacing, but the horizontal well has optimal reorientation fracture number and fracture spacing to get the economical productivity. Furthermore, the influence of the rotation of one central reorientation fracture on productivity index is weaker than that caused by the rotation of one external reorientation fracture. In addition, the asymmetrical distribution of one or more reorientation fractures slightly affects the productivity index when fracture conductivity is high enough.

Evaluating the Performance of Horizontal Multi-Frac Wells in a Depleted Gas Condensate Reservoir in Sultanate of Oman

2022 ◽  
Author(s):  
Josef R. Shaoul ◽  
Jason Park ◽  
Andrew Boucher ◽  
Inna Tkachuk ◽  
Cornelis Veeken ◽  
...  
Keyword(s):  
Horizontal Well ◽  
Horizontal Wells ◽  
Gas Condensate ◽  
Integrated Analysis ◽  
Single Fracture ◽  
Reservoir Pressure ◽  
Well Test ◽  
Vertical Wells ◽  
Fracture Conductivity ◽  
Half Length

Abstract The Saih Rawl gas condensate field has been producing for 20 years from multiple fractured vertical wells covering a very thick gross interval with varying reservoir permeability. After many years of production, the remaining reserves are mainly in the lowest permeability upper units. A pilot program using horizontal multi-frac wells was started in 2015, and five wells were drilled, stimulated and tested over a four-year period. The number of stages per horizontal well ranged from 6 to 14, but in all cases production was much less than expected based on the number of stages and the production from offset vertical wells producing from the same reservoir units with a single fracture. The scope of this paper is to describe the work that was performed to understand the reason for the lower than expected performance of the horizontal wells, how to improve the performance, and the implementation of those ideas in two additional horizontal wells completed in 2020. The study workflow was to perform an integrated analysis of fracturing, production and well test data, in order to history match all available data with a consistent reservoir description (permeability and fracture properties). Fracturing data included diagnostic injections (breakdown, step-rate test and minifrac) and main fracture treatments, where net pressure matching was performed. After closure analysis (ACA) was not possible in most cases due to low reservoir pressure and absence of downhole gauges. Post-fracture well test and production matching was performed using 3D reservoir simulation models including local grid refinement to capture fracture dimensions and conductivity. Based on simulation results, the effective propped fracture half-length seen in the post-frac production was extremely small, on the order of tens of meters, in some of the wells. In other wells, the effective fracture half-length was consistent with the created propped half-length, but the fracture conductivity was extremely small (finite conductivity fracture). The problems with the propped fractures appear to be related to a combination of poor proppant pack cleanup, low proppant concentration and small proppant diameter, compounded by low reservoir pressure which has a negative impact on proppant regained permeability after fracturing with crosslinked gel. Key conclusions from this study are that 1) using the same fracture design in a horizontal well with transverse fractures will not give the same result as in a vertical well in the same reservoir, 2) the effect of depletion on proppant pack cleanup in high temperature tight gas reservoirs appears to be very strong, requiring an adjustment in fracture design and proppant selection to achieve reasonable fracture conductivity, and 3) achieving sufficient effective propped length and height is key to economic production.

scholarly journals Pressure Transient Performance for a Horizontal Well Intercepted by Multiple Reorientation Fractures in a Tight Reservoir

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4232 ◽  
Author(s):  
Guoqiang Xing ◽  
Shuhong Wu ◽  
Jiahang Wang ◽  
Mingxian Wang ◽  
Baohua Wang ◽  
...  
Keyword(s):  
Horizontal Well ◽  
Flow Behavior ◽  
Flow Equation ◽  
Finite Conductivity ◽  
Transient Pressure ◽  
Pressure Derivative ◽  
Fracture Conductivity ◽  
Fracture Spacing ◽  
Economic Production ◽  
Tight Reservoir

A fractured horizontal well is an effective technology to obtain hydrocarbons from tight reservoirs. In this study, a new semi-analytical model for a horizontal well intercepted by multiple finite-conductivity reorientation fractures was developed in an anisotropic rectangular tight reservoir. Firstly, to establish the flow equation of the reorientation fracture, all reorientation fractures were discretized by combining the nodal analysis technique and the fracture-wing method. Secondly, through coupling the reservoir solution and reorientation fracture solution, a semi-analytical solution for multiple reorientation fractures along a horizontal well was derived in the Laplace domain, and its accuracy was also verified. Thirdly, typical flow regimes were identified on the transient-pressure curves. Finally, dimensionless pressure and pressure derivative curves were obtained to analyze the effect of key parameters on the flow behavior, including fracture angle, permeability anisotropy, fracture conductivity, fracture spacing, fracture number, and fracture configuration. Results show that, for an anisotropic rectangular tight reservoir, horizontal wells should be deployed parallel to the direction of principal permeability and fracture reorientation should be controlled to extend along the direction of minimum permeability. Meanwhile, the optimal fracture number should be considered for economic production and the fracture spacing should be optimized to reduce the flow interferences between reorientation fractures.

Production Performance Evaluation of Multifractured Horizontal Wells in Shale Oil Reservoirs: An Analytical Method

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Xingbang Meng ◽  
Jiexiang Wang
Keyword(s):  
Production Rate ◽  
Analytical Method ◽  
Oil And Gas ◽  
Production Performance ◽  
Single Fracture ◽  
Shale Oil ◽  
Affecting Factors ◽  
Gas Reservoirs ◽  
Fracture Conductivity ◽  
Fracture Spacing

Hydraulic fracturing stimulation has become a routine for the development of shale oil and gas reservoirs, which creates large volumes of fracturing networks by helping the hydrocarbon to transport quickly into the wellbore. However, the optimal fracture spacing distance and fracture conductivity are still unclear for the field practice, even though the technique has improved significantly over the last several years. In this work, an analytical method is proposed to address it. First, the analytical production rate for a single fracture is proposed, and then, we apply Duhamel principle to obtain the production rate of a horizontal well with multifractures. Based on this model, the flow regimes and essential affecting factors including fracture spacing, fracture conductivity, and skin factor are analyzed in this work. The optimal values and suggestion are provided based on the simulation results.

Productivity-Index Optimization for Hydraulically Fractured Vertical Wells in a Circular Reservoir: A Comparative Study With Analytical Solutions

SPE Journal ◽  
2016 ◽  
Vol 21 (06) ◽  
pp. 2208-2219 ◽  
Author(s):  
Yunhu Lu ◽  
Kang Ping Chen
Keyword(s):  
Steady State ◽  
Analytical Solution ◽  
Performance Optimization ◽  
Ad Hoc ◽  
Drainage Area ◽  
Productivity Index ◽  
Steady State Flow ◽  
Fracture Conductivity ◽  
State Flow ◽  
Shape Approximation

Summary Productivity-index (PI) optimization by means of optimal fracture design for a vertical well in a circular reservoir is a canonical problem in performance optimization for hydraulically fractured wells. Recent availability of the exact analytical solution for the pseudosteady-state (PSS) flow of a vertically fractured well with finite fracture conductivity in an elliptical drainage area provides an opportunity to re-examine this fundamental problem in a more-rigorous manner. This paper first quantitatively estimates the shape-approximation-induced error in the PI when the exact solution for an elliptical drainage area is applied to a circular drainage area. It is shown that the shape-approximation-induced error in the PSS-flow PI is less than 1% for fracture penetration ratios up to 53%, and this error decreases significantly as the fracture conductivity is increased. PI optimization is then performed with the highly accurate analytical solution for this range of the penetration ratios. The results show that the optimal fracture conductivity increases linearly from 1.39 to 1.71 when the proppant number is increased from 0.0001 to 0.6. PI for the steady-state flow and a popular ad hoc PSS-flow PI are compared with the analytical PSS-flow PI. It is found that both the steady-state and the ad hoc PIs deviate significantly from the analytical PSS-flow PI. In particular, the optimal fracture conductivity for the steady-state flow and the ad hoc PIs decreases with the proppant number, opposite to the trend observed for the optimal fracture conductivity for the PSS flow. It is suggested that the ad hoc PI should be abandoned in favor of the more-rigorous analytical PSS-flow solution.

scholarly journals Numerical simulation on the simultaneous stress interference of parallel multiple hydraulic fractures

2021 ◽  
pp. 014459872110019
Author(s):  
Weiyong Lu ◽  
Changchun He
Keyword(s):  
Principal Stress ◽  
Hydraulic Fracture ◽  
Stress Ratio ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Fracture Spacing ◽  
Induced Stress ◽  
Minimum Principal Stress ◽  
Fracturing Process ◽  
Stress Ratios

During horizontal well staged fracturing, there is stress interference between multiple transverse fractures in the same perforation cluster. Theoretical analysis and numerical calculation methods are applied in this study. We analysed the mechanism of induced stress interference in a single fracture under different fracture spacings and principal stress ratios. We also investigated the hydraulic fracture morphology and synchronous expansion process under different fracture spacings and principal stress ratios. The results show that the essence of induced stress is the stress increment in the area around the hydraulic fracture. Induced stress had a dual role in the fracturing process. It created favourable ground stress conditions for the diversion of hydraulic fractures and the formation of complex fracture network systems, inhibited fracture expansion in local areas, stopped hydraulic fractures, and prevented the formation of effective fractures. The curves of the maximum principal stress, minimum principal stress, and induced principal stress difference with distance under different fracture lengths, different fracture spacings, and different principal stress ratios were consistent overall. With a small fracture spacing and a small principal stress ratio, intermediate hydraulic fractures were difficult to initiate or arrest soon after initiation, fractures did not expand easily, and the expansion speed of lateral hydraulic fractures was fast. Moreover, with a smaller fracture spacing and a smaller principal stress ratio, hydraulic fractures were more prone to steering, and even new fractures were produced in the minimum principal stress direction, which was beneficial to the fracture network communication in the reservoir. When the local stress and fracture spacing were appropriate, the intermediate fracture could expand normally, which could effectively increase the reservoir permeability.

High-Resolution and Multimaterial Fracture Productivity Calculator for the Successful Design of Channel Fracturing Jobs

2021 ◽  
Author(s):  
Dimitry Chuprakov ◽  
Ludmila Belyakova ◽  
Ivan Glaznev ◽  
Aleksandra Peshcherenko
Keyword(s):  
High Resolution ◽  
Effective Conductivity ◽  
Productivity Index ◽  
Hydraulic Fractures ◽  
Total Production ◽  
Fracture Conductivity ◽  
Hindered Settling ◽  
Accurate Evaluation ◽  
Skin Factor ◽  
Fracture Closure

Abstract We developed a high-resolution fracture productivity calculator to enable fast and accurate evaluation of hydraulic fractures modeled using a fine-scale 2D simulation of material placement. Using an example of channel fracturing treatments, we show how the productivity index, effective fracture conductivity, and skin factor are sensitive to variations in pumping schedule design and pulsing strategy. We perform fracturing simulations using an advanced high-resolution multiphysics model that includes coupled 2D hydrodynamics with geomechanics (pseudo-3D, or P3D, model), 2D transport of materials with tracking temperature exposure history, in-situ kinetics, and a hindered settling model, which includes the effect of fibers. For all simulated fracturing treatments, we accurately solve a problem of 3D planar fracture closure on heterogenous spatial distribution of solids, estimate 2D profiles of fracture width and stresses applied to proppants, and, as a result, obtain the complex and heterogenous shape of fracture conductivity with highly conductive cells owing to the presence of channels. Then, we also evaluate reservoir fluid inflows from a reservoir to fracture walls and further along a fracture to limited-size wellbore perforations. Solution of a productivity problem at the finest scale allows us to accurately evaluate key productivity characteristics: productivity index, dimensional and dimensionless effective conductivity, skin factor, and folds of increase, as well as the total production rate at any day and for any pressure drawdown in a well during well production life. We develop a workflow to understand how productivity of a fracture depends on variation of the pumping schedule and facilitate taking appropriate decisions about the best job design. The presented workflow gives insight into how new computationally efficient methods can enable fast, convenient, and accurate evaluation of the material placement design for maximum production with cost-saving channel fracturing technology.

scholarly journals Experimental and Numerical Investigation of Preferential Flow in Fractured Network with Clogging Process

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Xiaobing Chen ◽  
Jian Zhao ◽  
Li Chen
Keyword(s):  
Velocity Field ◽  
Cross Sections ◽  
Preferential Flow ◽  
Pressure Head ◽  
Fracture Network ◽  
Navier Stokes ◽  
Single Fracture ◽  
Navier Stokes Equation ◽  
Physical Experiments ◽  
Fractured Network

In this study, physical experiments and numerical simulations are combined to provide a detailed understanding of flow dynamics in fracture network. Hydraulic parameters such as pressure head, velocity field, Reynolds number on certain monitoring cross points, and total flux rate are examined under various clogging conditions. Applying the COMSOL Multiphysics code to solve the Navier-Stokes equation instead of Reynolds equation and using the measured data to validate the model, the fluid flow in the horizontal 2D cross-sections of the fracture network was simulated. Results show that local clogging leads to a significant reshaping of the flow velocity field and a reduction of the transport capacity of the entire system. The flow rate distribution is highly influenced by the fractures connected to the dominant flow channels, although local disturbances in velocity field are unlikely to spread over the whole network. Also, modeling results indicate that water flow in a fracture network, compared with that in a single fracture, is likely to transit into turbulence earlier under the same hydraulic gradient due to the influence of fracture intersections.

scholarly journals Factors affecting reorientation of hydraulically induced fracture during fracturing with oriented perforations in shale gas reservoirs

2021 ◽  
Vol 15 (58) ◽  
pp. 1-20
Author(s):  
Qingchao Li ◽  
Liang Zhou ◽  
Zhi-Min Li ◽  
Zhen-Hua Liu ◽  
Yong Fang ◽  
...  
Keyword(s):  
Shale Gas ◽  
Injection Rate ◽  
Single Fracture ◽  
Fluid Viscosity ◽  
Fracture Conductivity ◽  
Factors Affecting ◽  
Controllable Factors ◽  
Initiation Pressure ◽  
Shale Reservoirs ◽  
Induced Fractures

Hydraulic fracturing with oriented perforations is an effective technology for reservoir stimulation for gas development in shale reservoirs. However, fracture reorientation during fracturing operation can affect the fracture conductivity and hinder the effective production of shale gas. In the present work, a numerical simulation model for investigating fracture reorientation during fracturing with oriented perforations was established, and it was verified to be suitable for all investigations in this paper. Based on this, factors (such as injection rate and fluid viscosity) affecting both of initiation and reorientation of the hydraulically induced fractures were investigated. The investigation results show that the fluid viscosity has little effect on initiation pressure of hydraulically induced fracture during fracturing operation, and the initiation pressure is mainly affected by perforation azimuth, injection rate and the stress difference. Moreover, the investigation results also show that perforation azimuth and difference between two horizontal principle stresses are the two most important factors affecting fracture reorientation. Based on the investigation results, the optimization of fracturing design can be achieved by adjusting some controllable factors. However, the regret is that the research object herein is a single fracture, and the interaction between fractures during fracturing operation needs to be further explored.

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