Multiple hydraulic fractures growth from a highly deviated well: A XFEM study

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 167770, ’Design Optimization of Horizontal Wells With Multiple Hydraulic Fractures in the Bakken Shale,’ by Luigi Saputelli, SPE, Frontender Corporation; Carlos Lopez, SPE, BP; Alejandro Chacon, SPE, Halliburton; and Mohammed Soliman, SPE, Texas Tech University, prepared for the 2014 SPE/EAGE European Unconventional Resources Conference and Exhibition, Vienna, Austria, 25-27 February. The paper has not been peer reviewed. The ultimate performance of fractured wells in tight reservoirs is affected severely by the interfering effects inside the fracture and interfractures. The most important parameters for determining the optimum fracture length have been shown to be the formation permeability and the stimulated reservoir volume. Although studies have examined the performance of horizontal fractured wells and the fracture-geometry effect, fracture spacing and intersecting angles in vertical and horizontal wells should be investigated further. This study presents the results of a tight-oil-reservoir analogy. Introduction An efficient way to improve the productivity of ultratight shale formations is to increase the density of hydraulic fractures. Decreasing hydraulic-fracture spacing increases the productivity of the well, but the incremental production gain for each additional hydraulic fracture decreases. The current field practice is to develop 640- to 1,280-acre leases with 4,000- to 10,000-ft horizontal wells with multiple fractures. However, the determination of the optimal number of fractures is a challenge. Historically, many of the first horizontal wellbores were drilled using the openhole method in the pay zone. This allowed a significant portion of the wellbore to be in contact with the reservoir. In 2004, a coiled-tubing-deployed jetting assembly was successfully used to focus the stimulation treatments in the openhole wellbore. This further demonstrated that openhole horizontal wells can be successful. Another completion method of that period that is still used is the plug-and-perforation technique in cased holes. The disadvantage of using this completion method, however, is that fracturing fluids can come in contact with the formation for an extended period of time. Near the wellbore, the flow configuration in a transverse fracture intersecting a horizontal well can be of two types. Outside the fracture, the flow from the reservoir into the fracture is linear; inside the fracture, the flow is converging radial. Additionally, turbulence effects, fracture-conductivity impairment, scaling, and unstable wellbore flow regimes can play an important role in creating pressure drops, which affect well performance.

Numerous papers have been published in recent years on the subject of optimization of multiple transverse fractures in horizontal wells (for instance Saputelli et al., 2014). These studies usually focus on searching for an economical optimum based on multiple runs of 3D or 2D numerical simulator, each for certain fixed properties of hydraulic fractures. What we found missing is a systemized approach to calculate a solution to this problem. The objective of this study is to develop a systemized, rigorous mathematical and unified approach to the design of multiple transverse fractures in horizontal well – an extension of Unified Fracture Design (UFD).This paper provides a rigorous methodology to optimize the number of fractures (and consequently, fracture geometry) for a given amount of proppant. We follow the UFD concepts and solve our problem in dimensionless variables. For the case of multiple fractures these are: Proppant Number (NP), Penetration Ratio (Ix), Dimensionless Conductivity (CfD) and Aspect Ratio (yeD) for each fracture, which is inversely proportional to the number of fractures. We used the Direct Boundary Element method to generate the Dimensionless Productivity Index (JD) for a given range of these parameters (28,000 runs) for the Pseudo-Steady state case. Finally we plot total JD as a function of the number of fractures for various NP, which allows optimization. In addition, we generate minimum width curves for various proppants, which represent a practical constraint.Based on our study we found the following:For a given volume or proppant, NP, total JD for multiple fractures increases to an asymptote as the number of fractures increases. This asymptote represents a technical potential for multiple fractures and for high Proppant Numbers (NP ≥ 100) reaches a technical potential of 3πNP. Below this asymptote, the more fractures that are created for a fixed NP the larger the JD In practice however, there's a minimum fracture width (3 proppant grains), which constrains the fracture geometry and therefore maximum JD. It was shown, that for the case when 20/40 sand is used for multiple hydraulic fracturing of 0.01md formation with square total area, optimal number of factures reduces to approximately Np25. Application of horizontal drilling technology with multiple fractures assumes availability of high Proppant Numbers. We show mathematically that the alternative low Proppant Numbers (NP ≤ 20 for the case in p.3) are impractical for multiple fractures because total JD cannot be significantly higher than JD for optimized single fracture in the same area. In practice this means low formation permeability and/or high proppant volumes are necessary for multiple fracture treatments. Our work shows the methodology to determine optimum geometry and required volume to perform multifracture treatments. Total proppant mass (and hence, NP) used for the fracture design must be selected based on economic considerations. For this purpose we constructed a relationship between total JD and the NP, which accounts for the minimum fracture width requirement.Our paper presents a mathematically rigorous, systematic and comprehensive approach to the selection of optimal number of transverse hydraulic fractures in a horizontal well. Using the relationship between Proppant Number and maximum practical JD, the proppant mass should be selected for the treatment. Then, based on the formation and proppant permeability, the maximum number of fractures should be calculated for a given NP using the generated type curves and minimum width restriction.

In unconventional shale reservoirs, the presence of natural fractures is common and widespread. Multi-stage hydraulic fracture treatments are used to generate complex fracture geometry and stimulate reservoirs to unlock hydrocarbon in unconventional reservoirs. Natural fractures further complicate the complexity of the fracture geometry. In this paper, the objective is to investigate the impact of natural fractures on multiple hydraulic fracture propagation using an in-house fracture propagation model. We have developed a complex hydraulic fracture model to simulate multiple fracture propagation in naturally fractured reservoirs. The model can calculate partitioning of fluid between multiple fractures, fracture interaction within a stage and between stages, as well as the interaction between hydraulic and natural fractures. For simultaneous multiple fracture propagation, the exterior fractures generally take the majority of fluid and propagate at the expense of the interior fractures. Natural fractures can retard the growth of hydraulic fractures and change the fluid distribution between fractures and propagation trajectories of hydraulic fractures. In a reservoir with a heterogeneous natural fracture distribution, the interruption of natural fractures can complicate fracture geometry. The higher density or smaller spacing of natural fractures can mitigate stress shadow effects and favor more fluid flowing into the inner fractures. Due to the uncertainty of natural fracture distribution, the reliability of the complex fracture geometry provided by numerical models has been challenged. This paper demonstrates the potential of incorporating diagnostic results to constrain numerical results. Through combining diagnostic results with the fracture model, the accuracy of predicted fracture geometry can be improved.

Drilling horizontal wells to accelerate production and increase recovery efficiency of oil and gas has now become common. With the increasing number of wells, transient well tests have been conducted in many wells with different geological settings. In this paper, we present a number of analytical models for horizontal wells with multiple fractures in homogeneous and laterally composite reservoirs. These solutions are applicable to finite-conductivity transverse fractures, and infinite-conductivity transverse and longitudinal fractures. They may also be used for the fractured reservoirs where the wellbore intersects with multiple fractures. We examine the pressure behavior of horizontal wells with single and multiple fractures in homogeneous systems. It is shown that the wellbore cannot be neglected in the modeling of horizontal wells with fractures unless the fracture conductivity is high. If the fracture permeability (conductivity) variations in different zones are moderate, compared to the formation permeability, the multiple fractures have almost no effect on the pressure behavior of the system; the horizontal well dominates the system's pressure behavior. If the conductivities are high, the intersected fractures will dominate the behavior of the system at early times. It is also shown that multiple finite- and infinite-conductivity transverse fractures may exhibit multiple linear flow regimes before the onset of the first horizontal well radial flow regime.

At present, hundreds of horizontal wells have been drilled in Hassi Messaoud counting for about one fourth of the field's output. Among these, several wells are underperforming and could not yield the expected production. Vertical and areal permeability anisotropies, absence of natural fractures, severe heterogeneity, reservoir damage and wellbore instability are the main factors to blame for poor productivity. To address the problem of poor vertical communication and get past the near wellbore damage, hydraulic fracturing has been thought of as the best solution to improve productivity. This paper describes the candidate selection criteria, the design and execution of the first fracturing job to be carried in a horizontal well. A new openhole completion system is to be deployed in the horizontal section. The system uses a series of mechanical openhole packers that allow for stimulation in each desired interval. The use of mechanical packers provides positive mechanical diversion at high differential fracturing pressures. In this case the horizontal drain has been divided into six sections. Three of them have been hydraulically fractured while the remaining sections characterized by natural fractures are producing naturally by simply opening the frac port. The system has been designed, so the fracturing treatments along the horizontal wellbore can be pumped in one continuous operation, thus minimizing the associated risks and optimizing the efficiencies of both personnel and equipment needed to perform the work. In this case the pumping operation has been successfully performed in less than 48 hours with no operational issue. The first operation has proven the feasibility to set multiple hydraulic fractures in openhole horizontal wells in Hassi Messaoud field. The drastic production increase demonstrates how the multiple fractures allow improving the vertical and areal drainage of the reservoir for this type of wells. The article presents all the project phase from candidate selection, design to job execution. It also highlights the risks involved with regard to many aspects during the project. Finally, the paper summarizes some lessons learned and draws suggestions for prospective candidate wells. Introduction The Hassi Messaoud reservoir has been on stream since 1958. Currently, it produces about 65 Mm3/D of 45°API oil from a thick Cambro-Ordovician sandstone formation. The structure is a flattened anticline with a sequence of horts and grabbens contained by faults in a submeridian direction. The faults are generally oriented SSW to NNE and cross the entire reservoir. The depositional environment is fluvial at the bottom to marine at the top. The shaly sandstone contains silt interbeds which have a thickness between 0.2 and 0.4 m with a metric to kilometric lateral extension. The reservoir is naturally fractured in some parts because of tectonic activity. Fractures are either open or plugged with materials such as shale, silica, anhydrite, pyrite, and bitumen. The reservoir is subdivided into four distinct formations—Ri, Ra, R2, and R3—in addition to a zone of alternance with Ra-Ri and R2 being the main and secondary reservoirs respectively. The producing Ra-Ri is subdivided into six intervals: D5, D4, D3, D2, ID, and D1. The reservoir has a porosity ranging from 6 to 12 %. Overall, the permeability is low with a range from less than 1 to more than 100 md in open-fissures layers. The reservoir was initially undersaturated with an oil saturation of about 80%. The reservoir was subdivided into productive zones. Most zones are under miscible gas flooding. Five zones are under water injection. Up until 1995, the reservoir was developed using vertical wells. Along with matrix treatments, hydraulic fracturing is extensively used with more than 300 wells already treated to compensate for low permeability or to bypass nearby wellbore damage. Gaslift is used for production activation throughout the field.

Multi-stage hydraulic fracturing together with horizontal drilling plays an important role in the economic development of unconventional reservoirs. However, according to field analysis of stimulation effectiveness, only a small percentage of perforation clusters contribute to most of the well production. One reason for this low effectiveness is that multiple fractures do not take the same amount of fluid and proppant due to fracture interaction (i.e., stress shadow effects). Unfortunately, how best to minimize the negative effects of stress shadowing is still poorly understood in the petroleum industry. In this paper, we analyzed this problem in order to promote more uniform fracture growth using our complex hydraulic fracture development model.We employed our fracture propagation model that couples rock deformation and fluid flow in the fracture and horizontal wellbore. Partitioning of flow rate between multiple fractures was calculated by analogizing to the electric circuit network. Fracture development is dominated by flow rate distribution, which is controlled by flow resistance within the fractures. For simultaneous multiple fracture propagation, non-uniform flow rate distribution is induced because stress shadow effects exert additional flow resistance on the interior fractures. To balance the extra resistance introduced by the effects, we investigated two adjustment approaches to promote uniform fracture development. The first approach was to adjust perforation number or diameter to increase flow resistance entering the exterior fractures. The second was to mitigate stress shadow effects through managing non-uniform fracture spacing. We found that decreasing perforation diameter or numbers of the exterior fractures can divert fluid into the interior fractures and promote even fracture growth. Stress shadow effects can be mitigated by moving the two interior fractures away from each other and toward the exterior fractures. The key mechanism is to maintain even flow resistance within each fracture and facilitate fractures to obtain the same amount of injection fluid. Furthermore, flow resistance is affected by near-wellbore fracture tortuosity, natural fractures, and stress heterogeneity in the reservoirs. These factors might also be effectively controlled by adding extra flow resistance to pass perforations, provided that this extra resistance is larger than the extra resistance introduced by the factors.This work analyzes the problem of uneven development of multiple fractures along the horizontal wellbore and provides new insights into how to control simultaneous multiple fracture propagation. It offers potential approaches for engineers to apply in the field to optimize hydraulic fracturing treatment design and thereby maximize well production cost-effectively.

Recently, there has been a heightened interest in the use of horizontal wells to more efficiently drain both oil and gas reservoirs and to compensate for negative producing situations such as coning. The potential applications of horizontal and high-angle wells have led to increased efforts to quantify the expected production increase from these types of completion methods in a variety of geologic settings. Simulation of these alternative completion methods using mathematical models provides a cost-effective method of predicting their performance and allows for sensitivity analysis of reservoir properties. The performance of horizontal and high-angle completions was simulated for marginal marine and lenticular low permeability gas reservoirs of the Upper Cretaceous Mesaverde Formation underlying the east-central Piceance Basin. Results of the simulations show that production from horizontal wells of intermediate length can be expected to be four times higher than that of vertical, stimulated wells draining large areas. The advantages of high-angle wells in lenticular sandstone environments remain unquantified, but a reasonable potential exists, especially when methane from deeply buried coals is considered.

Summary Horizontal wells with multiple hydraulic fractures have become a standard completion for the development of tight oil and gas reservoirs. Successful optimization of multiple-fracture design on horizontal wells began empirically in the Barnett Shale in the late 1990s (Steward 2013; Gertner 2013). More recently, research has focused on further improving fracturing performance by developing a model-derived optimum. Some researchers have focused on an economic optimum on the basis of multiple runs of an analytical or numerical model (Zhang et al. 2012; Saputelli et al. 2014). With such an approach, a new set of model runs is necessary to optimize the design each time the input parameters change significantly. Running multiple simulations for every optimization case might not always be practical. An alternative approach is to develop well-performance curves with dimensionless variables on the basis of the performance model. Such an approach was the basis for unified fracture design (UFD) for a single fracture in a vertical well (Economides et al. 2002). However, a similar systemized method to calculate the optimum for a horizontal well with multiple hydraulic fractures was missing. The objective of this study was to develop a rigorous and unified dimensionless optimization technique with type curves for the case of multiple transverse fractures in a horizontal well—an extension of UFD. The mathematical problem was solved in dimensionless variables. Multiple fractures include the proppant number (NP), penetration ratio (Ix), dimensionless conductivity (CfD), and aspect ratio (yeD) for each fracture, which is inversely proportional to the number of fractures. The direct boundary element (DBE) method was used to generate the dimensionless productivity index (JD) for a given range of these parameters (28,000 runs) for the pseudosteady-state case. Finally, total well JD was plotted as a function of the number of fractures for various NP. The effect of minimum fracture width was studied, and the optimization curves were adjusted for three cases of minimum fracture width. The provided dimensionless type curves can be used to identify the optimized number of fractures and their geometry for a given set of parameters, without running a more complicated numerical model multiple times. First, the proppant mass (and hence, NP) used for the fracture design can be selected on the basis of economic or other considerations. For this purpose, a relationship between total JD and NP, which accounts for the minimum fracture width requirement, was provided. Then, the optimal number of fractures can be calculated for a given NP using the generated type curves with minimum width constraints. The following observations were made during the study on the basis of the performed runs: For a given volume or proppant, NP, total JD for multiple fractures increases to an asymptote as the number of fractures increases. This asymptote represents a technical potential for multiple fractures and for high proppant numbers (NP≥100), with a technical potential of 3πNP. Below this asymptote, the more fractures that are created for a fixed NP, the larger the JD. In practice, minimum fracture width constrains the fracture geometry, and therefore maximum JD. For the case when 20/40 sand is used for multiple hydraulic fracturing of a 0.01-md formation with square total area, the optimal number of factures is approximately NP25. Application of horizontal drilling technology with multiple fractures assumes the availability of high proppant numbers. It was shown mathematically that the alternative low proppant numbers (NP≤20 for the previous case) are impractical for multiple fractures, because total JD cannot be significantly higher than JD for an optimized single fracture in the same area. This means that low formation permeability and/or high proppant volumes are needed for multiple fracture treatments.

The impacts of the fluid type and stress shadow on proppant transport during hydraulic fracturing in a Marcellus shale horizontal well with multiple hydraulic fracture stages were investigated. The available data from a Marcellus Shale horizontal well were utilized to determine the hydraulic fracture properties and to develop a reservoir model. The reliability of the model was confirmed by the close agreement between the predicted production by the model and the well production data. The impact of fluid type and stage spacing on proppant transport during hydraulic fracturing and gas production from Marcellus shale horizontal well were then investigated by employing the reservoir models. Slickwater, compared to crosslinked gels and high viscosity friction reducers (HVFRs), is more efficient in horizontal Marcellus shale wells that are fractured in multiple stages. The application of the HVFRs and crosslinked gels resulted in fracture height growth out of the pay zone. While the use of slickwater directed all stimulation energy towards the pay zone and resulted in improved hydraulic fracture properties in the Marcellus shale and lead to high gas recovery. INTRODUCTION The advancements in horizontal drilling and hydraulic fracturing technologies have made shale production a reality for the past decade. With the technical and economical limitations posed by hydraulic fracturing operations in unconventional reservoirs, it is imperative to create an optimized fracturing design to achieve economic production. A number of treatment design considerations including the type of fluid, proppant type and size, and the additives must be evaluated to achieve successful well stimulation results. In general, proppant transport is dependent on proppant size, density, and type; fluid rheology; temperature changes; pumping rate, among others. The fracturing fluid should be compatible with the formation and promote the increase in the stimulated volume. In order to transport the proppants deep into the fracture, the fluid should be capable of keeping the proppants suspended. With an inherent viscosity, fluid should be able to develop the necessary fracture width to accept proppants. Also, it should have low friction pressure loss and sufficient stability to retain its viscosity throughout the treatment and finally, it should be easy to remove after the treatment. The type of fluid used therefore has pronounced impact on the transport of proppants and the properties of the created hydraulic fracture and consequently the hydrocarbon production. Proppant selection is a contributing factor in the dimensions of a propagating fracture. The most prevalent hydraulic fracturing treatment fluids in shale formations is slickwater with no significant amount of thickening agent. The application of this low viscosity fluid system contradicts conventional fracturing theory. However, slickwater is the preferable fracturing fluid in shale because of its cost-effectiveness and low potential for damaging the shale. In addition, slickwater has the potential to prevent high fracture height growth leading to better fracture containment within the pay zone.

In the last several years, the unconventional gas reservoirs development has grown tremendously. Most of these unconventional reservoirs have very low permeability and are not able to produce an economic flow rate without stimulation treatments. The common method to improve the production is by a horizontal well with multiple hydraulic fractures. Hydraulic fracturing is a stimulation practice to improve the permeability in order to obtain commercial production. Horizontal wells with multiple hydraulic fracture treatments have proven to be an effective method for development of unconventional reservoirs.;The objective of this study is to investigate the interpretation of pressure transient responses from horizontal wells with single and multiple hydraulic fractures using the commercial reservoir simulator. In addition, the research will focus on identifying the impact of the reservoir and fracture properties on the flow regimes of a horizontal well producing from the low permeability reservoirs.;The different flow regimes appear during horizontal-well transient flow. However, the existence of these flow regimes is closely associated with the dimensions of the half length of the fracture, fracture permeability, drainage area, horizontal well length, etc. Hence, it is common that some flow regimes are not present.;The impact of some of the reservoir parameters was analyzed. Drainage area, horizontal well length and reservoir permeability were found to have an impact on flow regimes. In addition to the reservoir parameters, a range of hydraulic fracture parameters was studied. The number of hydraulic fracture, fracture width and fracture half-length were found to have an impact on flow regimes. Fracture permeability and fracture porosity have no major impact on flow regimes.

Hydraulic fracturing is currently the completion of choice in most tight reservoirs; however, the ultimate performance of fractured wells is severely affected by the interfering effects inside the fracture and inter fractures. Previous simulation studies investigated the effects of well spacing and fracture length on well productivity in low-permeability oil and gas reservoirs. It was shown that the most important parameters for determining the optimum fracture length are the formation permeability and the stimulated reservoir volume. Although a number of studies have examined the performance of horizontal fractured wells and fracture geometry effect, fracture spacing and intersecting angles in vertical and horizontal wells should be further investigated. This study presents the results of a tight oil reservoir in the Bakken shale. Reservoir parameters considered include local rock stresses, rock compressibility, absolute and relative permeability, and porosity. The well-completion parameters included fracture length, height, width, conductivity, number and spacing between fractures, fracture intersecting angle, and cased vs. open-hole completion. Fracture modeling considered rigorous description of the hydraulic fracture properties and finite difference reservoir modeling. Economically attractive reserves recovery were modeled through multiple fracture placements in a 10,000 ft horizontal well. Numerical simulation showed that oil recovery increased between 8 to 15% while net present value (NPV) increased 8 to 24%, as the number of fractures increased. Based on the critical assumptions in the study (permeability, natural fracture distribution and stress orientation), an optimum number of fractures was identified. Open hole completions provided better performance in most cases, and recovery was greater for a higher number of contributing perpendicular vs. longitudinal fractures. The results of the study may hopefully be used to improve the understanding of the role of fracture geometry, spacing and open/cased-hole completion strategy to enhance operators optimum completion design.

SummaryThe classic plots of dimensionless fracture conductivity (CfD) vs. equivalent wellbore radius or equivalent negative skin are useful for evaluating the performance of hydraulic fractures (HFs) in vertical wells targeting conventional reservoirs (Prats 1961; Cinco-Ley and Samaniego-V. 1981). The increase in well productivity after hydraulic stimulation can be estimated from the “after fracturing” effective wellbore radius or from the “after fracturing” equivalent negative skin. However, this earlier work does not apply to the case of horizontal wells with multiple fractures. A revision of the diagnostic plots is needed to account for the combination of the resulting radial-flow regime and the transient effect in unconventional reservoirs with ultralow permeability. This paper reviews and extends this earlier work with the objective of making it applicable in the case of horizontal wells with multiple fractures. It also demonstrates practical application of this new technique for fracture-design optimization for horizontal wells.The influence of finite fracture conductivity (FC) on the HF flow efficiency is evaluated through analytical models, and it is confirmed by a 3D transient numerical-reservoir simulation. This work demonstrates that a redefined dimensionless fracture conductivity for horizontal wells CfD,h = 4 is found to be optimal by use of the maximum of log-normal derivative (subject to economics) for HFs in horizontal wells, and this value of CfD,h can provide 50% of the fracture-flow efficiency and 90% of the estimated ultimate recovery (EUR) that would have been obtained from an infinitely conductive fracture for the same production period. This new master plot can provide guidance for hydraulic-fracturing design and its optimization for hydrocarbon recovery in unconventional reservoirs through hydraulic fracturing in horizontal wells.

Extended finite element-based cohesive zone method for modeling simultaneous hydraulic fracture height growth in layered reservoirs

The operator in West Africa embarked upon the "N" field offshore development in 2016 with 13 multi-stage horizontal wells being fracture-stimulated in Phase-I, with further wells being planned in next development phases. Due to the complex nature of the reservoir, which is a multilayered sandstone characterized by high heterogeneity and low permeability, wellbore connections are often located in structurally altered areas with high presence of faults. The unpredictable local re-orientation of the stresses has resulted in complications for the fracturing operations with multiple fractures being induced. This paper presents the challenges and solutions implemented for delivering more consistent fracturing execution and well productivity improvements. The horizontal wells in the "N" field were hydraulically fractured using the "plug-and-perf" method with up to four fractured intervals. The quality of the near-wellbore connection and the observations of complex near-wellbore fracture geometries have hindered far-field proppant distribution and limited maximum proppant concentration inside the fracture. When fracturing this tight formation, controlling the opening of the pressure-dependent multiple fractures was identified as a critical issue. An engineering breakdown process and adapted frac strategy was implemented to minimize the multiple fractures generated at the formation. For the early hydraulic fracture treatments performed, conservative treatment designs were applied in order to avoid premature screenout with the consequence of increasing operative time. Implemented solutions have shown to improve the near-wellbore connections and increase well productivity. The successful outcomes are attributed to the implementation of improved perforating strategies, the optimization of fracturing fluid performance, an engineered fracturing breakdown process, and the development of a frac decision tree for improved decision making. The hydraulic frac strategy has been tailored well-by-well depending on the reservoir conditions (e.g. faults, permeability thickness, contacts), and on the operational conditions interpreted from the diagnostic injection tests (e.g. near wellbore tortuosity, net pressure). The holistic implementation of these new concepts for hydraulic fracturing and field development have delivered positive production results beyond initial expectations. For the horizontal wells intersecting the deep low permeability "D" reservoir, the risk of multiple fractures and influence of tortuosity have been diminished through corrective techniques and unique solutions applied for each fracturing stage.

Summary The post-fracture pressure decay (PFPD) technique is a low-cost method allowing for stage-by-stage hydraulic fracture characterization. The analysis of the PFPD data is complex, with data affected by both hydraulic fracture and reservoir properties. Available analysis methods in the literature are oversimplified; reservoir or fracture properties are often assumed to be constant along the horizontal well, and therefore changes in the trend of pressure decay data are attributed to hydraulic fracture or reservoir properties only. Moreover, methods analogous to those applied to the analysis of conventional diagnostic fracture injection tests (DFITs) are often used and ignore critical mechanisms involved in main-stage hydraulic fracture stimulation. A conceptual numerical simulation study was first conducted herein to understand the key mechanisms involved in main-stage hydraulic fracturing. An analytical model was then developed to account for the dynamic behavior of the hydraulic fracture, leakoff, proppant distribution, multiple fractures, and propped- and unpropped-closure events. The analytical model is cast in the form of a new straightline analysis (SLA) method that provides stage-by-stage estimates of the ratio of unpropped fracture surface area to total fracture surface area. The SLA method was validated against numerical simulation results. Moreover, to account for the variation of reservoir properties along the horizontal well, the PFPD model is integrated with DFIT-flowback (DFIT-FBA) tests, performed at some points along the lateral, to obtain a reliable stage-by-stage hydraulic fracture and reservoir characterization approach. The practical application of the proposed integrated approach was demonstrated using PFPD and DFIT-FBA data from a horizontal well completed in 22 stages in the Montney Formation. The numerical simulation study demonstrated that the use of proppant and injection into multiple clusters (creating multiple fractures) results in multiple closure events. The closure process may start early after the pump-in period at a pressure significantly higher than the minimum in-situ stress. Using DFIT-based analytical models, which ignore the presence of proppant, causes significant errors in hydraulic fracture and reservoir property estimation. The PFPD field data examined herein exhibited a similar pressure trend to the numerical simulation cases. The ratio of unpropped fracture surface area to total fracture surface area was determined stage by stage using the PFPD SLA method, constrained by DFIT-FBA data. Engineers can use this information to optimize the hydraulic fracture stimulation design in real time, optimize the well spacing, and forecast the production. The cost and time advantages of this diagnostic method make this approach very attractive.