Effect of Acid on Productivity of Fractured Shale Reservoirs

Pournik, Maysam; Tripathi, Divyendu

doi:10.15530/urtec-2014-1922960

Cited by 29 publications

(17 citation statements)

References 9 publications

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“…The second observation is that, although local inhomogeneities in the initial aperture will trigger the development of the localized flow paths and speed up the appearance of instability, the statistical properties of the emerging patterns on the large scale are largely insensitive to the initial geometry of the fracture (Upadhyay et al 2015).…”

Section: Discussionmentioning

confidence: 99%

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Wormhole Formation During Acidizing of Calcite-Cemented Fractures in Gas-Bearing Shales

et al. 2019

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A relatively large number of calcite-cemented fractures are present in gas-bearing shale formations. During hydraulic fracturing, some of these fractures will be reactivated and may become important flow paths in the resulting stimulated fracture network. On the other hand, the presence of carbonate lamina on fracture surfaces will have a hindering effect on the transport of shale gas from the matrix toward the wellbore. We investigate numerically the effect of low-pH reactive fluids on such fractures, and show that dissolution of the cement proceeds in a highly nonuniform manner. The morphology of the emerging flow paths ("wormholes") strongly depends on the thickness of the calcite layer. For thick carbonate layers, a hierarchical, fractal pattern appears, with highly branched wormhole-like channels competing for an available flow. For thin layers, the pattern is much more diffuse, with less-pronounced wormholes that merge easily with each other. Finally, for intermediate thicknesses, we observe a strong attraction between shorter and longer wormholes, which leads to the formation of islands of carbonate lamina surrounded by the dissolved regions. We argue that the wormholeformation processes are not only important for the increase of shale-gas recovery, but also can be used for retaining the fracture permeability, even in the absence of proppant.2019 SPE Journal 1 is the main driving process behind the cave formation in karst systems (Dreybrodt 1990;Hanna and Rajaram 1998;Cheung and Rajaram 2002;Szymczak and Ladd 2011). All these studies show that the dissolution of rock fractures is a strongly unstable process, with spontaneous focusing of the flow in high-porosity channels (wormholes). The instability here is, in fact, stronger than the corresponding instability in the dissolving porous media (Szymczak and Ladd 2011), with much weaker stabilization caused by diffusion. It needs to be stressed that both experimental and numerical studies of fracture dissolution have considered homogeneous soluble samples, in which aperture growth is potentially unlimited. In shales, the situation is fundamentally different, because the amount of soluble cement at a given place is finite and, thus, after a certain time, the cement fully dissolves, and the dissolution front moves farther downstream. As it turns out, a limited amount of soluble material significantly influences the dissolution patterns in fractures. Nevertheless, as we show in the present study, the dissolution front is still unstable, with an intense wormhole formation in the system. Besides serving as a means to increase the fracture-matrix transport, such a nonuniform dissolution is potentially important for retaining the fracture permeability even in the absence of proppant Wu and Sharma 2015). Whereas a uniformly etched fracture may close tightly under the load of overburden once the fluid pressure is removed, the nonuniform etching will tend to maintain the permeability. The less-dissolved regions will then act as supports to keep more-dissolved regions op...

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Section: Discussionmentioning

confidence: 99%

“…Eqs. 20, 21, and 22 are solved using the finite-difference porous package, developed by Upadhyay and Ladd in Upadhyay et al (2015), which uses finite-difference methods with a parallel multigrid linear solver Hypre (Falgout and Yang 2002).…”

Section: Numerical Modelmentioning

confidence: 99%

Wormhole Formation During Acidizing of Calcite-Cemented Fractures in Gas-Bearing Shales

et al. 2019

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“…comparison of values to the study completed by Tripathi and Pournik (2014). The pressure drop across the system is recorded under four different flowrates for each closure stress value.…”

Section: Objectives Of Researchmentioning

confidence: 99%

“…Applying the classification in the Gardner et al study, based on Dunham's classification (1962) for Carbonate rocks and Campbell's classification (1967) for sedimentary structures, a description for each sample used in this study is given in Table 4. Hardness values were not obtained for samples EF_C_4 or EF_D_4, as those samples were used solely for comparison to the Tripathi and Pournik (2014) study.…”

Section: Sample Descriptionmentioning

confidence: 99%

“…Determine the effect of etching pattern, acid concentration, carbonate content, and Brinell Hardness number on the created acid fracture conductivity • Determine potential feasibility of field-scale acid fracturing treatments in the Eagle Ford ShaleUsing the data collected in this study, a comparison to the study ofTripathi and Pournik, 2014, will also be completed using the data from test condition #3. The experimental procedure byWu and Sharma, 2015, varies too greatly to compare to the data collected in this study.The goal of this experimental study is to simulate an acid fracturing treatment in order to determine the effect of etching pattern, acid concentration, carbonate content, and Brinell Hardness Number on the created acid fracture conductivity.Eagle Ford outcrops were obtained and cut to modified API-RP-61 conductivity cell specifications.…”

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Acid Fracturing Carbonate-Rich Shale: A Feasibility Investigation of Eagle Ford Formation

Cash

Zhu

Hill

2016

Day 3 Fri, August 26, 2016

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Due to the extensive technically recoverable shale natural gas resources and an increase in production from shale plays over the last 10 years, it is essential to focus on stimulation techniques to enhance productivity in shale resources. One such stimulation technique is acid fracturing. Similar to hydraulic fracturing, acid fracturing injects acid into a formation at a pressure greater than the fracture pressure, creating fractures and etching the created fracture face. The high carbonate content of the Eagle Ford Shale makes the formation a possible acid fracturing candidate. Minimal research has been completed on the effects of acid fracturing high carbonate-containing shale formations, where various conditions can limit the permeability of petroleum fluids. In this study, eight Eagle Ford shale samples, four from Zone C and four from Zone D, are used to determine the effect of surface etching pattern, acid concentration, calcite content, and Brinell Hardness Number on created acid fracture conductivity in the Eagle Ford shale. The resultant surface etching volume is determined by a pre-and post-surface Profilometer scan to calculate the change in surface profile. Calcite content is determined by X-Ray Diffraction analyses. Conductivity tests are performed on the eight samples up to a closure stress of 4000 psi, sample integrity permitting. Based on the results determined in this study, acid fracturing the Eagle Ford shale could provide optimistic increases in production. Acid fracturing treatments in high calcite containing zones of the Eagle Ford shale are expected to result in an increase in productivity. For the Eagle Ford Shale, the surface etching patterns that result in iii highly sustained conductivity values are channeling and roughness. A direct correlation is shown between calcite content of the shale and resultant surface etching volume. Furthermore, the higher the calcite content of the samples, the more likely the etching pattern will result in channeling and surface roughness. Brinell Hardness tests are completed on Eagle Ford samples determining that, on average, the higher the Brinell Hardness number, the better resulting surface etching pattern and sustained acid fracture conductivity.iv

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Optimization of Criterion for Rock Crack Propagation under Acid Izing Treatment

Sun

Wang

et al. 2021

Chem Technol Fuels Oils

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Effect of Acid on Productivity of Fractured Shale Reservoirs

Cited by 29 publications

References 9 publications

Wormhole Formation During Acidizing of Calcite-Cemented Fractures in Gas-Bearing Shales

Wormhole Formation During Acidizing of Calcite-Cemented Fractures in Gas-Bearing Shales

Acid Fracturing Carbonate-Rich Shale: A Feasibility Investigation of Eagle Ford Formation

Optimization of Criterion for Rock Crack Propagation under Acid Izing Treatment

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