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

Abstract

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...

Ionic Strength and pH Effects on Water–Rock Interaction in an Unconventional Siliceous Reservoir: On the Use of Formation Water in Hydraulic Fracturing

“…One hydrothermal experiment reacted this hydraulic fracturing fluid with samples of core from the Wall Creek at reservoir conditions (115 °C and 35 MPa, Table ); this experiment is designated “Intermediate I” (Table and Figure ). Hydraulic fracturing fluid and rock were added together to the reaction vessel at the outset of the experiment, before heating and pressurizing to reservoir conditions, an approach commonly used to investigate geochemical interactions between hydraulic fracturing fluids and rocks. ,,,− ,, An alternative approach is to inject hydraulic fracturing fluid into an ongoing experiment containing formation water and rock at reservoir conditions. , These two experimental approaches represent a continuum between dry formations and formations that produce significant amounts of water. A water–rock ratio of approximately 20:1 was used to represent conditions present in a large open fracture created during hydraulic fracturing .…”

“…Experiments in many of these studies were conducted using water of one ionic strength (Figure ). A variety of waters were used in the experiments, from ultrapure water ionic strength 8 × 10 –5 mol/kg to saline formation water ionic strength 4 mol/kg . Deionized water and NaCl solution with ionic strength ranging from 5 × 10 –3 to 5 × 10 –1 mol/kg were most often used as proxies for hydraulic fracturing fluids (Figure ).…”

“…Previously we showed that the reaction of reservoir rock with hydraulic fracturing fluid formulated from a natural water (river water with ionic strength 0.05 mol/kg) dissolves feldspar as well as carbonate minerals and precipitates an Mg-aluminosilicate. − Feldspar also began to dissolve in experiments that reacted mudstone with hydraulic fracturing fluid formulated from river water ionic strength 0.005 mol/kg and mixed with saline formation water ionic strength 2 mol/kg . In contrast, the reaction of mudstone with hydraulic fracturing fluid formulated from both a natural spring water (ionic strength 3.1 × 10 –4 mol/kg) and a produced water (ionic strength 0.5 mol/kg) yielded no evidence of silicate reaction. , Five other studies reacted mudstone with hydraulic fracturing fluid formulated from a natural water; one provided temporal water chemistry needed to evaluate fluid-mineral processes and four did not. ,,, Thus, the importance of silicate–fluid equilibria relative to carbonate–fluid equilibria is not known for reactions between reservoir rock and hydraulic fracturing fluid formulated from a natural water.…”

Structural and quantitative evolution of organic matters in oil shale during two different retorting processes

“…Of them, petroleum has been regarded as the principal source of energy for a long time, which alone provided 37.1% of the total energy consumption by the United States in 2017 4,5 . The massive use of petroleum has motivated many countries to explore unconventional oil resources 6‐8 . Oil shale (OS) is a fine‐grain sedimentary rock containing complex solid macromolecular organic matter called kerogen, 9 from which petroleum‐like shale oil can be extracted.…”

Ionic Strength and pH Effects on WaterRock Interaction in an Unconventional Siliceous Reservoir: On the Use of Formation Water in Hydraulic Fracturing

“…Powder River Basin, Wyoming, USA 3 ; the Utica and Point Pleasant Shales of the Appalachian Basin, USA 17 ; and the Baxter Shale of the Green River Basin, USA 8,24 . Although not an unconventional reservoir, experiments have evaluated the Green River Shale of the Green River Basin, USA as a comparator to unconventional shale reservoirs 2,7,22 .…”