Computational Fluid Dynamics Applied to Investigate Development and Optimization of Highly Conductive Channels within the Fracture Geometry

SPE International Conference and Exhibition on Formation Damage Control

Hudson

Nelson

et al. 2016

Self Cite

A conventional proppant pack can lose up to 99% of its conductivity due to gel damage, fines migration, multiphase flow, and non-Darcy flow. Consequently, pillar fracturing was developed to generate highly conductive paths for hydrocarbon flow. This paper describes experimental results and numerical models of a new method of generating stable proppant pillars. The proposed treatment method depends on fingering phenomena observed when a less-viscous fluid, which does not carry proppant, is injected to displace a more-viscous fluid that carries proppant. The low-viscosity fluid channels through the high-viscosity fluid and creates isolated proppant pillars. This method promises to reduce proppant costs, pumping horsepower, and gel damage, when compared to conventional treatments.A computational fluid dynamics (CFD) model using commercial CFD software was constructed to simulate the fluid flow inside a full-scale fracture dimensions. The objective of this study was to further evaluate the treatment design parameters during the generation of stable pillar-propped fractures. This study focused on gravity effects on the created channels' characteristics. The study also performed detailed investigation of the channel pattern as a function of treatment design (injection rate (1 to 120 bpm), and pulse stage time (5 seconds to 5 minutes), viscosity ratio (2 to 200)), and fracture geometry (width and height). Finally, horizontal proppant covering efficiency was calculated.Numerical modeling results confirmed that the gravity effect can be minimized either by increasing the injected fluid viscosity or by increasing the fluid injection rate. A strong linear relation was found between the minimum required viscosity to eliminate gravity effect and the density ratio between the two injected fluids. As an example, for a fracture width of 0.2 in. and injection rate of 4 bpm, the minimum viscosity needed to eliminate the gravity effect was 50 cP, 150 cP and 300 cP for density ratios ( R ) of 1.05, 1.25 and 1.5, respectively. The optimum channel pattern has small channel sizes, remain opened under closure stress, more channels throughout the entire fracture area and good communication between unpropped areas. Increasing fracture height or width during injection shifted the created channel pattern toward an optimum shape. Reducing the injection rate and/or stage pulse time moved the created channel pattern toward an optimum shape.A new dimensionless term, Dimensionless Stage Volume (VSD), is presented to describe the channel pattern inside the fracture. Smaller the VSD number resulted in the smaller and more distributed channels. Therefore, it is highly recommended to select and design a proppant pillar fracture treatment to achieve the lowest VSD possible and create the optimal channel pattern. For each viscosity ratio, the horizontal proppant coverage efficiency was independent of the VSD. However, a power-law relationship was defined between the horizontal proppant coverage efficiency and viscosity ratio between the two injected f...

Section: Effect Of Gravity On Fluid Flow Inside the Fracturesupporting

confidence: 88%

Section: Numerical Model Constructionsupporting

confidence: 77%

Section: Effect Of Gravity On Fluid Flow Inside the Fracturementioning

confidence: 66%

Section: Concept Of Creating ؆Pillar-propped؆ Fracturementioning

confidence: 99%

Section: Numerical Model Constructionmentioning

confidence: 99%

See 3 more Smart Citations

Improving Fracture Conductivity by Developing and Optimizing Channels within the Fracture Geometry: CFD Study

SPE International Conference and Exhibition on Formation Damage Control

Hudson

Nelson

et al. 2016

Self Cite

Fractured Well Productivity: Proppant Pack vs. Pillar Fracture - Numerical Study

Day 3 Wed, April 26, 2017

Alerigi

Alnoaimi

et al. 2017

Proppant selection and placement have been significantly discussed in the literature as the key parameters to measure the success of a hydraulic fracturing treatment. Conventional proppant pack may suffer a significant reduction in conductivity due to gel damage, fines migration, multiphase flow, and non-Darcy flow. To mitigate these adverse effects, an alternative posits to substitute the porous proppant pack in the fracture with an isolated structure made of propped pillars surrounded by a network of open channels. However, recent field data has not shown improvement in the productivity of the well due to channel creation within the fracture geometry. The objective of this study is to understand the effect of proppant permeability, placement, and channel creation on the well productivity using the numerical technique. A 3D numerical model was constructed to simulate the hydrocarbon flow from the reservoir through the fracture towards the wellbore. Production rate, well productivity index (PI), and dimensionless well productivity index (Jd) were evaluated as a function of the following parameters: -Reservoir effective permeability (0.1–1000 mD),-Vertical to horizontal permeability ratio (0.1-1),-Reservoir drawdown pressure (500-5000 psi),-Proppant conductivity in the near wellbore region (1–5000 mD-ft),-Proppant conductivity in the far-field region (1–5000 mD-ft),-No. of the created channels and their distribution. For conventional proppant pack, numerical results agreed with Cinco-Ley and Samaniego-V (1981), and it showed that dimensionless fracture conductivity (CFD) values higher than 30 maximize Jd. Also, the numerical model revealed that pillar fracturing technology with highly conductive channels could significantly improve well productivity if the used proppant conductivity is low. However, for high proppant conductivity and high CFD values, the maximum increase in well productivity index due to channel creation will be only 20%. For low CFD values, pillar fracturing technique with highly conductive channels is highly recommended, particularly if the vertical to horizontal permeability ratio is low. Statistical analysis of the numerical results evinced that reservoir permeability and near-wellbore proppant conductivity have a major effect on the well productivity; whereas proppant conductivity in the far-field region has limited effect. The statistical analysis revealed that any number of channels greater than 2 has marginal influence on the well productivity and that the derived, dimensionless, variables can be used to create conditional decision models to maximize it. The results suggest that there is an interplay between the dimensionless fracture conductivity and the near-to-far-field permeability ratio that has a significant influence on the results.

Parameters Affecting the Fractured Well Productivity: Proppant Pack vs. Pillar Fracture - Numerical Study

Day 1 Mon, November 13, 2017

Alerigi

Alnoaimi

et al. 2017

Gel damage, fines migration, multiphase flow, and non-Darcy flow are the primary effects that reduce the conductivity of the conventional proppant pack. Therefore, a recent technology was introduced to mitigate those impacts by substituting the porous proppant pack in the fracture with propped pillars surrounded by a network of open channels. In this technique, the fracture is held open by discrete conglomerations of propping materials, known as proppant pillars. Consequently, the flow capacity of the open channel is several orders of magnitude higher than that of a proppant pack. Another advantage of this method is the reduced proppant mass because more area is left open for flow. Most of the available literature investigates the formation of proppant pillars the stability at subsurface conditions. This study aims to characterize the impact of the technology in hydrocarbon production and identify key optimization parameters. Therefore, a 3D numerical model was constructed to simulate the hydrocarbon flow from the reservoir through the fracture towards the wellbore, Gomaa et al. 2017. The model is used to investigate the relation between the fracture well productivity and different fracture and reservoir properties: reservoir effective permeability, vertical to horizontal permeability ratio, reservoir drawdown pressure, proppant conductivity in the near wellbore region, proppant conductivity in the far-field region, the radius of last proppant stage, and channel width. The results showed that for conventional proppant pack a CFD value of 30 maximizes the Jd value; this agrees with the previous findings by Cinco-Ley and Samaniego-V (1981). In the case of pillar fracture technology with highly conductive channels, the numerical model showed a significant improvement in well productivity, even when the proppant conductivity was low. In the case of high proppant conductivity and high CFD values, the maximum increase in well productivity index was approximately 25%; however, for low CFD values, the channel fracture had a significant impact on productivity, improving it up to 120%. Statistical analysis of the results evinced that the proppant conductivity in the near wellbore region had a major effect on the well productivity; whereas proppant conductivity in the far-field had little impact. The analysis also revealed that for every reservoir type, there are different combinations of CFD and proppant conductivity that maximize Jd, even if CFD < 0.1. These results suggest that there is a relationship between the dimensionless fracture conductivity and the near-to-far-field permeability ratio, which has a significant influence on the results.