Rock Characterization in Unconventional Reservoirs: A Comparative Study of Bakken, Eagle Ford, and Niobrara Formations

Cho, Younki; Eker, Erdinc; Uzun, Ilkay; Yin, Xiaolong; Kazemi, Hossein

doi:10.2118/180239-ms

Cited by 41 publications

(19 citation statements)

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“…The tensile strength and permeability were measured in the directions perpendicular to the sedimentary plane, including the fracture propagation direction addressed in the present study (Section 3). As listed in Table 1, the obtained sample was significantly tight (lowpermeable), and other physical parameters were similar to those reported by previous studies (Cho et al 2016). Fig.…”

Section: Samplesupporting

confidence: 88%

Tensile-dominant fractures observed in hydraulic fracturing laboratory experiment using eagle ford shale

Naoi

Chen

Yamamoto

et al. 2020

Geophysical Journal International

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SUMMARY Hydraulic fracturing plays a vital role in the development of unconventional energy resources, such as shale gas/oil and enhanced geothermal systems to increase the permeability of tight rocks. In this study, we conducted hydraulic fracturing experiments in a laboratory using carbonate-rich outcrop samples of Eagle Ford shale from the United States. We used a thermosetting acrylic resin containing a fluorescent compound as a fracturing fluid. Immediately after fracturing, the liquid resin penetrated in the fractured blocks was hardened by applying heat. Then, the crack was viewed under UV irradiation, where the fluorescent resin allowed the induced fracture to be clearly observed, indicating the formation of simple, thin bi-wing planar fractures. We observed the detailed structure of the fractures from microscopy of thin cross-sections, and found that their complexity and width varied with the distance from the wellbore. This likely reflects the change in the stress state around the tip of the growing fracture. The interaction between fractures and constituent grains/other inclusions (e.g. organic substances) seemed to increase the complexity of the fractures, which may contribute to the efficient production of shale gas/oil via hydraulic fracturing. We first detected acoustic emission (AE) signals several seconds before the peak fluid pressure was observed, and the active region gradually migrated along the microscopically observed fracture with increasing magnitude. Immediately after the peak pressure was observed, the fluid pressure dropped suddenly (breakdown) with large seismic waves that were probably radiated by dynamic propagation of the fracture; thereafter, the AE activity stopped. We applied moment tensor inversion for the obtained AE events by carefully correcting the AE sensor characteristics. Almost all of the solutions corresponded to tensile events that had a crack plane along the maximum compression axis, as would be expected based on the conventional theory of hydraulic fracturing. Such domination of tensile events has not been reported in previous studies based on laboratory/in situ experiments, where shear events were often dominant. The extreme domination of the tensile events in the present study is possibly a result of the use of rock samples without any significant pre-existing cracks. Our experiments revealed the fracturing behaviour and accompanying seismic activities of very tight rocks in detail, which will be helpful to our understanding of fracturing behaviour in shale gas/oil resource production.

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Section: Samplesupporting

confidence: 88%

Tensile-dominant fractures observed in hydraulic fracturing laboratory experiment using eagle ford shale

Naoi

Chen

Yamamoto

et al. 2020

Geophysical Journal International

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“…The pore‐size distribution can be detected by a low‐pressure gas‐adsorption experiment using N 2 as a probe gas for pore sizes from ~200 to ~2 nm and CO 2 as a probe gas for pores less than 2 nm . Mercury injection under an ultrahigh pressure enables us to detect a pore throat up to ~3 nm . Small‐angle and ultra‐small‐angle neutron scattering (SANS and USANS) and low‐field nuclear magnetic resonance (NMR) relaxation experiments can be used to provide a pore‐size distribution across various length scales .…”

Section: Introductionmentioning

confidence: 99%

Molecular simulation of CH₄ adsorption behavior in slit nanopores: Verification of simulation methods and models

et al. 2019

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The aim of this study is to select an appropriate method for CH 4 adsorption in organic nanopores for shale-gas development. Molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations were performed. Three comparison studies were included: (i) comparison of the adsorption behavior in kerogen nanopores using different schemes for dispersion correction, (ii) comparison of the adsorption behavior in graphite nanopores using MD and GCMC simulations, and (iii) comparison of the adsorption behavior in kerogen and graphite nanopores using MD simulations. The result was reliable when using a particle-mesh Ewald scheme or a cutoff ≥1.5 nm without dispersion correction. The simulation results were essentially identical for the MD and GCMC simulations. The free-gas CH 4 density inside the nanopores started to deviate from the bulk density at~2 nm for the graphite model and at~7-10 nm for the kerogen model, whereas the total CH 4 density deviates from the bulk density at~20 nm.

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“…Compared to other wellstudied unconventional formations, the Point Pleasant shale generally has a higher carbonate content, higher concentrations of calcium, iron and strontium, and lower concentrations of barium in the produced water. 13,[25][26][27][28][29][30] Additionally, the reservoir depths, pressures and temperatures will differ in comparison to other formations, such as the Bakken with depths between 8,500 and 11,500 ft. (2,931 [31][32][33] On the western side of the UPP play, the depth and thermal maturity of the Point Pleasant shale is such that rich oil deposits are found, forming the UPP Oil Window (OW). A study by Patchen et al…”

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confidence: 99%

Geochemical phenomena between Utica‐Point Pleasant shale and hydraulic fracturing fluid

2019

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This study evaluated geochemistry between the Utica-Point Pleasant shale and reservoir/hydraulic fracturing fluid mixtures under simulated reservoir conditions in a batch reactor system. Analytical techniques were utilized to monitor fluid composition with time along with pre-and post-trial shale microscopy and phase identification analyses. Formation of iron-based precipitate was evident through results from fluid and material analyses. Ferrous iron was the predominant iron form found in the aqueous phase, with oxidation to ferric iron and subsequent precipitate formation. Geochemical modeling further supported ferric iron was the favorable phase for precipitation. K E Y W O R D S crystallization (precipitation), geochemical, hydraulic fracturing, oil shale/tar sands, reaction kinetics 1 | INTRODUCTION U.S. tight oil has had a tremendous impact on stabilizing global oil prices and increasing energy security. Such light crude is recovered from low permeability rock formations, primarily shale, using unconventional methods such as horizontal drilling with hydraulic fracturing. As of March 2019, the Energy Information Association (EIA) reports approximately 60% total U.S. oil production comes from tight oil. 1 While unconventional wells have shown promise in terms of oil production, economic viability is still uncertain due to rapid production decline leading to shorter well life. Peak performance of an unconventional oil well occurs during the first quarter of production, with up to 74% production decline after 1 year. 2 Solutions explored to counteract production decline include refracturing or other enhanced oil recovery methods. Simulation studies have been developed to evaluate the effects of stimulation techniques on production to determine if profitable recovery is feasible. 3-5 Although simulation of refracturing and enhanced oil recovery methods have shown promise, these techniques do not fully account for phenomena encountered in unconventional wells. Various approaches have been utilized to mimic downhole phenomena. 6-8 An approach by Luo evaluated confinement effects on hydrocarbon bubble point. This study found octane and decane confined in nanoporous media possess two distinct bubble point temperatures, with lower/higher bubble point temperatures differing ±15 K in comparison to respective bulk properties. 6 By understanding various in-situ well phenomena, proper recovery analysis can be performed and modifications to hydraulic fracturing processes can be developed to increase well productivity and lifetime. 9 Aqueous phase chemical reactions are another key phenomenon occurring in shale reservoirs. Such reactions occur during well completion, when hydraulic fracturing fluid (HFF) mixes with rock and formation water, potentially causing precipitate formation, more commonly referred to as scale. Scales form when dissolved solid concentrations This contribution was identified by Rameshwar Srivastava (Department of Energy) as the Best Presentation in the session "New Technologies to Enhance the Productio...

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Rock Characterization in Unconventional Reservoirs: A Comparative Study of Bakken, Eagle Ford, and Niobrara Formations

Cited by 41 publications

References 15 publications

Tensile-dominant fractures observed in hydraulic fracturing laboratory experiment using eagle ford shale

Tensile-dominant fractures observed in hydraulic fracturing laboratory experiment using eagle ford shale

Molecular simulation of CH₄ adsorption behavior in slit nanopores: Verification of simulation methods and models

Geochemical phenomena between Utica‐Point Pleasant shale and hydraulic fracturing fluid

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Rock Characterization in Unconventional Reservoirs: A Comparative Study of Bakken, Eagle Ford, and Niobrara Formations

Cited by 41 publications

References 15 publications

Tensile-dominant fractures observed in hydraulic fracturing laboratory experiment using eagle ford shale

Tensile-dominant fractures observed in hydraulic fracturing laboratory experiment using eagle ford shale

Molecular simulation of CH4 adsorption behavior in slit nanopores: Verification of simulation methods and models

Geochemical phenomena between Utica‐Point Pleasant shale and hydraulic fracturing fluid

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Product

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Molecular simulation of CH₄ adsorption behavior in slit nanopores: Verification of simulation methods and models