The Role of Back Pressure and Perforation Hole Erosion on the Magnitude of the Coefficient of Discharge in Hydraulic Fracturing Stimulation

Yosefnejad, Davood M.; Fricke, Bernd; Loehken, Joern; McNelis, Liam

doi:10.2118/200612-ms

Cited by 9 publications

References 10 publications

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Determination of the Near-Wellbore Pressure Drop for Dual Casing in Hydraulic Fracturing and Refracturing Applications

Loehken

Yosefnejad

McNelis

et al. 2022

Day 2 Wed, January 12, 2022

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Due to the increases in completion costs demand for production improvements, fracturing through double casing in upper reservoirs for mature wells and refracturing early stimulated wells to change the completion design, has become more and more popular. One of the most common technologies used to re-stimulate previously fracked wells, is to run a second, smaller casing or tubular inside of the existing and already perforated pipes of the completed well. The new inner and old outer casing are isolated from each other by a cement layer, which prevents any hydraulic communication between the pre-existing and new perforations, as well as between adjacent new perforations. For these smaller inner casing diameters, specially tailored and designed re-fracturing perforation systems are deployed, which can shoot casing entrance holes of very similar size through both casings, nearly independent of the phasing and still capable of creating tunnels reaching beyond the cement layer into the natural rock formation. Although discussing on the API RP-19B section VII test format has recently been initiated and many companies have started to test multiple casing scenarios and charge performance, not much is known about the complex flow through two radially aligned holes in dual casings. In the paper we will look in detail at the parameters which influence the flow, especially the Coefficient of Discharge of such a dual casing setup. We will evaluate how much the near wellbore pressure drop is affected by the hole's sizes in the first and second casing, respectively the difference between them and investigate how the cement layer is influenced by turbulences, which might build up in the annulus. The results will enhance the design and provide a better understanding of fracturing or refracturing through double casings for hydraulic fracturing specialists and both operation and services companies.

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Determination of the Near-Wellbore Pressure Drop for Dual Casing in Hydraulic Fracturing and Refracturing Applications

Loehken

Yosefnejad

McNelis

et al. 2022

Day 2 Wed, January 12, 2022

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Determination of the Perforation Hole Erosion Characteristics on Single and Dual Casing for Hydraulic Fracturing, in a Laboratory Test Setup Under Realistic Downhole Conditions

Loehken

Fricke

McNelis

et al. 2022

Day 3 Thu, February 03, 2022

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Numerous papers have dealt with the description and measurements of the erosion of perforation holes during a hydraulic fracturing treatment in single casing completions, but not much is known about the erosion of perforations in dual casing setups. This study addresses this topic and compares it to the erosion rate of single casing scenarios and how this is influenced by the backpressure, which is created by the fracture closure pressure. The API 19B norm provides a guideline on how to test perforators under the most realistic downhole conditions. All casings used in our experiments were perforated in such a Section IV test set-up and subsequently installed in a specially designed high pressure flow apparatus. The casing holes were carefully measured, their hydraulic resistance was determined by a flow test and successively eroded by a slurry using high pressure pumping equipment. After each test, the holes were again geometrically measured, and their flow resistance was tested. In addition, the sand grain sizes were analyzed before and after the tests. Our tests revealed a significant difference in the erosion characteristic of dual casing compared to single casing setups. Especially the diameter of the hole in the inner casing is critical for the progress of the erosion and the final hole diameters. Equal holes on both casings provide a better control of the treating pressures, especially after the first minutes of the treatment. The back pressure, which is created by the fluid in the fractures, influences mainly the flow rate through the perforation. For identical flow rates, the pressure differential becomes less with back pressure, however the erosion rate as a function of the cumulative energy pumped through the perforation, remains similar. Finally, the application and design of a bigger test cell was evaluated and will be discussed as well. Although many perforating companies have started testing the charge performance for multiple casing completions, not much is known about the flow and erosion of two radially aligned holes in dual cemented casings during the fracture treatment and the influence of the back pressure created by the reservoir. The results will enhance the completion design and provide a better understanding of fracturing or refracturing through double-casings for hydraulic fracturing specialists and both operation and services companies.

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Modeling Proppant Transport in Perforated Casing Based on Surface Testing

Kollé¹,

Mueller²,

Baumgartner

et al. 2022

SPE Drilling &Amp; Completion

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Summary The results of a series of proppant transport surface tests (PTSTs) were used in conjunction with Eulerian multiphase-computational fluid dynamics (EMP-CFD) modeling to develop an engineering model of proppant distribution. The PTSTs were carried out to evaluate proppant placement through perforated casing. In these tests, sand slurry was pumped at realistically high flow rates through perforated casing, and the distribution of sand and slurry from each perforation cluster was observed. The tests show that gravitational settling in horizontal casing, proppant slip past perforations, and the viscoelastic properties of slickwater fluids strongly affect the distribution of proppant from the heel to the toe of the completion. The EMP-CFD modeling was used to estimate the gravitational settling of sand in fully developed turbulent slurry flow in horizontal casing as a function of casing velocity. A survey of 36 calculations was carried out to generate tables of sand concentration in a cross section through the casing as a function of flow rate and particle size. A single-phase CFD analysis showed how sand exiting each perforation is taken from a limited ingestion area, which is proportional to the ratio of flow through the perforation to total flow in the casing. A detailed EMP-CFD analysis of flow through single perforations showed how sand slips past the perforation. The results of 28 EMP-CFD calculations provided slip factors as a function of particle size, casing flow velocity, and perforation flow velocity in straight and angled perforations. The EMP-CFD settling tables and a parameterization of the slip factors were integrated into an engineering model. The model predicts the distribution of slurry and sand through each perforation based on the proppant size, perforation phase angle, and pump rate. The engineering model was used to predict the sand distributions observed in the PTSTs. The PTSTs were conducted with a range of sand sizes and with friction-reducing (FR) polymer additives, while the EMP-CFD analysis assumed water. A weight factor is introduced in the settling model to account for the increased dispersion of sand in water with FR and to match the observed sand distributions in the PTSTs. The observed slip of 100 and 40/70 mesh sand is consistent with the EMP-CFD calculations in water. The model reflects the PTST observations that fine sand is distributed relatively uniformly throughout the length of a perforated completion, while coarser sand tends to slip past the heel perforations and concentrate at the bottom toward the toe of the completion.

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The Role of Back Pressure and Perforation Hole Erosion on the Magnitude of the Coefficient of Discharge in Hydraulic Fracturing Stimulation

Cited by 9 publications

References 10 publications

Determination of the Near-Wellbore Pressure Drop for Dual Casing in Hydraulic Fracturing and Refracturing Applications

Determination of the Near-Wellbore Pressure Drop for Dual Casing in Hydraulic Fracturing and Refracturing Applications

Determination of the Perforation Hole Erosion Characteristics on Single and Dual Casing for Hydraulic Fracturing, in a Laboratory Test Setup Under Realistic Downhole Conditions

Modeling Proppant Transport in Perforated Casing Based on Surface Testing

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