Understanding the Implications of Multiple Fracture Propagation in Well Productivity and Completion Strategy (original) (raw)
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Integrating Reservoir Geomechanics with Multiple Fracture Propagation and Proppant Placement
SPE Journal, 2020
Summary This paper presents the formulation and results from a coupled finite-volume (FV)/finite-area (FA) model for simulating the propagation of multiple hydraulically driven fractures in two and three dimensions at the wellbore and pad scale. The proposed method captures realistic representations of local heterogeneities, layering, fracture turning, poroelasticity, interactions with other fractures, and proppant transport. We account for competitive fluid and proppant distribution between multiple fractures from the wellbore. Details of the model formulation and its efficient numerical implementation are provided, along with numerical studies comparing the model with both analytical solutions and field results. The results demonstrate the effectiveness of the proposed method for the comprehensive modeling of hydraulically driven fractures in three dimensions at a pad scale.
Strategies for Effective Stimulation of Multiple Perforation Clusters in Horizontal Wells
SPE production & operations, 2017
Increasing the efficiency of completions in horizontal wells is an important concern in the oil and gas industry. To decrease the number of fracturing stages per well, it is common practice to use multiple clusters per stage. This is done with the hope that most of the clusters in the stage will be effectively stimulated. Diagnostic evidence, however, suggests that in many cases, only one or two out of four or five clusters in a stage are effectively stimulated. In this paper, strategies to maximize the number of effectively stimulated perforation clusters are discussed. A fully 3D poroelastic model that simulates the propagation of nonplanar fractures in heterogeneous media is developed and used to model the propagation of multiple competing fractures. A parametric study is first conducted to demonstrate how important fracture-design variables, such as limited-entry perforations and cluster spacing, and formation parameters, such as permeability and lateral and vertical heterogeneity, affect the growth of competing fractures. The effect of stress shadowing caused by both mechanical and poroelastic effects is accounted for. 3D numerical simulations have been performed to show the effect of some operational and reservoir parameters on simultaneouscompetitive-fracture propagation. It was found that an increase in stage spacing decreases the stress interference between propagating fractures and increases the number of propagating fractures in a stage. It was also found that an increase in reservoir permeability can decrease the stress interference between propagating fractures because of poroelastic-stress changes. A modest (approximately 25%) variability in reservoir mechanical properties along the wellbore is shown to be enough to alter the number of fractures created in a hydraulic-fracturing stage and mask the effects of stress shadowing. Interstage fracture simulations show post-shut-in fracture extension induced by stress interference from adjacent propagating fractures. The effect of poroelasticity is highlighted for infill-well-fracture design, and preferential fracture propagation toward depleted regions is clearly observed in multiwell-pad-fracture simulations. The results in this paper attempt to provide practitioners with a better understanding of multicluster-fracturing dynamics. On the basis of these findings, recommendations are made on how best to design fracture treatments that will lead to the successful placement of fluid and proppant in a single fracture, and result in a set of fractures that are competing for growth. The ability to successfully stimulate all perforation clusters is shown to be a function of key fracture-design parameters. Prior experimental work has also clearly shown that the perforation-cluster spacing influences the fracture-growth pattern. When closely spaced multiple fractures were propagated simultaneously, some fractures were much larger than others (El-Rabaa 1982; Abass et al. 1996). It was shown that in some cases, one fracture could become the dominant fracture propagating among the clusters. Bunger et al. (2012) used an analytical model and performed a dimensional analysis to understand the most-important parameters that need to be addressed when optimizing multiple-fracture-growth problems. They considered the deflection patterns that are generated because of interaction of the fractures with existing fractures. They applied their model to a 2D fracture-growth simulator. In a later paper, the Bunger et al. (2012) model was used to understand the effect of viscosity and toughness-dominated regimes on multiple-fracture propagation (Ames and Bunger 2015). The latter used a mathematical model to couple the contributions of fluid flow, rock breakage, and perforation pressure drop to the total power requirement for the growth of multiple hydraulic fractures. Their model predicts that when the stage spacing is less than the created fracture height, the probability of multiple-fracture growth is small. The fundamental understanding their model provides can be very useful in explaining observations from numerical models. Many researchers have used the displacement-discontinuity method to model the stress interference created by hydraulic fractures. Using this method, researchers have attempted to analyze the effect of simultaneous-multiple-fracture growth (
SPE Annual Technical Conference and Exhibition, 2015
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 netw...
Journal of Petroleum Science and Engineering, 1995
A finite-difference, hydraulic fracture treatment simulator that computes fracture dimensions in a layered reservoir is presented in this paper. Each layer can have different mechanical and fluid flow properties. The model allows initiation of the fracture in multiple producing intervals simultaneously. This pseudo-three-dimensional model has been used extensively to study the effects of reservoir mechanical properties, particularly stress distribution, Young's modulus, and fracture toughness of the reservoir layers on the height of the fracture. Effects of fluid properties such as apparent viscosity and injected fluid volume on fracture height have also been investigated. The use of this model for different scenarios illustrates the effects of mechanical properties on fracture dimension and proppant transport. Several examples have been generated for reservoirs with multiple producing zones, in which the fracture is initiated in one or several intervals simultaneously, so that one can illustrate the effects of perforation placement upon the distribution of proppant within the fracture. These examples illustrate that the location of the perforations can substantially affect the final proppant profile. The propped fracture geometry is used in a single-phase finitedifference reservoir simulator to show the production increase and long-term production performance for different scenarios.
Journal of Petroleum Science and Engineering, 2020
For maximum productivity enhancement when targeting low permeability formations, horizontal wells must be made to induce multiple transverse fractures. An orientation criterion for fracture initiation is developed using analytically-derived approximations for the longitudinal and transverse fracturing stresses for perforated wellbores from the literature. The validity of the criterion is assessed numerically and is found to overestimate transverse fracture initiation, which occurs under a narrow range of conditions; pertaining to low breakdown pressure and low formation tensile strength. A three-dimensional numerical model shows that contrary to existing approximations, the transverse fracturing stress from perforated horizontal wells becomes more compressive as wellbore pressure increases. This shrinks the "breakdown pressure window," which is the range of wellbore pressures over which transverse fracture initiation takes place. This creates a second constraint for transverse fracture initiation, which is the "critical tensile strength" value. This determines the maximum formation tensile strength at which transverse fracture initiation is possible for a given in-situ stress state and perforation direction. Sensitivity analyses are performed based on data from seven unconventional shale reservoirs (Barnett, Bakken, Fayetteville, Haynesville, Niobrara, Marcellus and Vaca Muerta) for horizontal wells drilled parallel to S hmin. The frequent longitudinal fracture initiation occurrence indicated suggests fracture reorientation in the near-wellbore region to be a common event, through which the propagating fractures become aligned with the preferred fracture plane (perpendicular to the least compressive principal stress). This induces near-wellbore fluid tortuosity, which in turn can lead to completions and production-related problems, such as early screenouts and poststimulation well underperformance.
Interaction of Multiple Hydraulic Fractures in Horizontal Wells
All Days, 2013
The use of multi-fracced horizontal well technology in unconventional gas and liquid rich reservoirs is one of the key reasons for the recent success in the exploitation of Unconventional Resources. These multiple fractures are placed in many stages along the horizontal well using diverse completion technologies. Yet, the understanding of fracture growth mechanics and the optimum fracture placement design methodology are still preliminary. Recent advances in computational mechanics and the development of appropriate stimulation modeling technology will further nurture innovation and press forward much needed optimization of the Completion and Stimulation technology in multi-fracced horizontal wells. This paper contains two key components. Firstly, an analytical model is used to highlight some of the salient features of multiple hydraulic fractures interaction. The advantage of an analytical model is that it provides immediate insights into the controlling parameters and steer furthe...
Journal of Petroleum Science and Engineering, 2017
This work presents promising results for the application of a novel approach to estimate geopressure to optimize allocation of clusters in a horizontal wellbore in an unconventional shale play using information from logging while drilling (LWD) techniques. In previous publications on this subject, the usefulness of implementing the diffusivity equation in conjunction with information from well logs to estimate geopressure in conventional and complex unconventional geological scenarios was demonstrated. In this new study, a novel approach is applied to characterize reservoir and fracture pressures along the horizontal section of a well drilled in the Southwest part of the Eagle Ford unconventional shale play. To the best of the authors' knowledge, there is no report of estimation of pore pressure in a horizontal wellbore using theoretical principles, such as the diffusivity theory. The recorded rock properties from LWD along the horizontal section of the well serve multiple purposes. Firstly, they were introduced into the solution of the diffusivity equation as "normalized values" to obtain the pore pressure distribution. Secondly, they are employed to generate a synthetic acoustic log along the horizontal section of the wellbore to determine geomechanical properties of Eagle Ford formation. The results documented in this work demonstrate that when using this novel methodology, horizontal wells can be characterized in great detail from the standpoint of reservoir pressure and brittleness. This novel approach is effective, reliable, and can help the completion engineer to decide where to allocate the clusters (perforations) to make more efficient the multistage hydraulic fracturing jobs and improve productivity. Furthermore, geoscientists, reservoir, and production engineers will benefit from knowing reservoir pressure distribution along the path of the horizontal section of the well in more detail. As a result, a more efficient reservoir characterization is obtained to improve horizontal wellbore performance.
SPE Hydraulic Fracturing Technology Conference and Exhibition
This paper presents an analysis of the interactions between stimulation design and two important geomechanical effects: the variation of least principal stress (S hmin) between lithological layers and the stress shadow effect that arises from simultaneously propagating adjacent hydraulic fractures. To demonstrate these interactions, hydraulic fracture propagation is modeled with a 5-layer geomechanical model representing an actual case study. The model consists of a profile of S hmin measurements made within, below and above the producing interval. The stress variations between layers leads to an overall upward fracture propagation and proppant largely above the producing interval. This is due to interactions between the pressure distribution within the fracture and the stress contrast in the multiple layers. A sensitivity study is done to investigate the complex 3-D couplings between geomechanical constraints and well completion design parameters such as landing zone, cluster spacing, perforation diameter, flow rate and proppant concentration. The simulation results demonstrate the importance of a well characterized stress stratigraphy for prediction of hydraulic fracture characteristics and optimization of operational parameters.
Journal of Petroleum Science and Engineering, 2000
Considering the influence of casing, analytical solutions for stress distribution around a cased wellbore are derived, based on which a prediction model for hydraulic fracture initiation with the oriented perforation technique (OPT) is established. Taking well J2 of Z5 oilfield for an example, the predicted initiation pressure with the OPT of our model is about 4.2 MPa higher than the existing model, which neglects the influence of casing. In comparison with the results of laboratory fracturing experiments with OPT on a 400 9 400 9 400 mm 3 rock sample for a cased well with the deviation of 45°, the fracture initiation pressure of our model has an error of 3.2 %, while the error of the existing model is 6.6 %; when the well azimuth angle is 0°a nd the perforation angle is 45°, the prediction error of the fracture initiation pressure of the existing model and our model are 3.4 and 7.7 %, respectively. The study verifies that our model is more applicable for hydraulic fracturing prediction of wells with OPT completion; while the existing model is more suitable for hydraulic fracturing with conventional perforation completion.