Extraction of Hydrocarbons from High-Maturity Marcellus Shale Using Supercritical Carbon Dioxide

Abstract

Shale is now commonly exploited as a hydrocarbon resource. Due to the high degree of geochemical and petrophysical heterogeneity both between shale reservoirs and within a single reservoir, there is a growing need to find more efficient methods of extracting petroleum compounds (crude oil, natural gas, bitumen) from potential source rocks. In this study, supercritical carbon dioxide (CO 2 ) was used to extract n-aliphatic hydrocarbons from ground samples of Marcellus shale. Samples were collected from vertically drilled wells in central and western Pennsylvania, USA, with total organic carbon (TOC) content ranging from 1.5 to 6.2 wt %. Extraction temperature and pressure conditions (80 °C and 21.7 MPa, respectively) were chosen to represent approximate in situ reservoir conditions at sample depth (1920−2280 m). Hydrocarbon yield was evaluated as a function of sample matrix particle size (sieve size) over the following size ranges: 1000−500 μm, 250−125 μm, and 63−25 μm. Several methods of shale characterization including Rock-Eval II pyrolysis, organic petrography, Brunauer−Emmett−Teller surface area, and X-ray diffraction analyses were also performed to better understand potential controls on extraction yields. Despite high sample thermal maturity, results show that supercritical CO 2 can liberate diesel-range (n-C 11 through n-C 21 ) naliphatic hydrocarbons. The total quantity of extracted, resolvable n-aliphatic hydrocarbons ranges from approximately 0.3 to 12 mg of hydrocarbon per gram of TOC. Sieve size does have an effect on extraction yield, with highest recovery from the 250−125 μm size fraction. However, the significance of this effect is limited, likely due to the low size ranges of the extracted shale particles. Additional trends in hydrocarbon yield are observed among all samples, regardless of sieve size: 1) yield increases as a function of specific surface area (r 2 = 0.78); and 2) both yield and surface area increase with increasing TOC content (r 2 = 0.97 and 0.86, respectively). Given that supercritical CO 2 is able to mobilize residual organic matter present in overmature shales, this study contributes to a better understanding of the extent and potential factors affecting the extraction process.

A Review on the Influence of CO2/Shale Interaction on Shale Properties: Implications of CCS in Shales

“…Researchers initially explained the influence of mineralogical composition on the reactivity of shales during CO 2 injection. SCCO 2 has high diffusivity and acts as an organic solvent to extract some organic and inorganic minerals, which may lead to an increase in the porosity of shale [55,71]. Previous studies indicated that the alteration in shale mineralogy after SCCO 2 treatment is mainly caused by the geochemical reaction with the formation brine in the presence of carbonate minerals such as dolomite and calcite [18,30,39,43,51,72].…”

“…CO 2 injection causes a reduction in the intensity of C-O bonds in shales as well as aliphatic hydrocarbon (C-H) groups, which is related to the extraction of organic matter [39,71]. Yin et al [30] suggested that some inorganic vibrational bands of quartz and illite (Si-O, Al-O-H and Si-O-Al bonds) can exhibit high absorption in shales similar to calcite and dolomite.…”

“…This conclusion was based on the results obtained from three different shale formations after being treated with SCCO 2 as shown in Table 2. These relative alterations in oxygen and hydrogen functional groups can be explained by two points, (1) the evaporation and extraction behavior of SCCO 2 [18], and (2) the ability of SCCO 2 to extract organic matter and dissolve the polar kerogen moieties from shale surface [71,80]. As mentioned before, this alteration in surface chemistry and functional species after CO 2 injection could increase the CO 2 adsorption capacity in shales, thus more investigations are required to clarify the impact of chemical properties' alteration on the sequestration potential of CO 2 in shales.…”

Effects of Deep Fluids on Hydrocarbon Generation and Accumulation in Chinese Petroliferous Basins

“…The extraction efficiency is higher than Soxhlet (Akinlua et al, 2008). These features have been used to evaluate hydrocarbon potential (Jaffé et al, 2000), shale oil development (Wang et al, 2012;Jarboe et al, 2015) and hydrocarbon source rocks (Bondar and Koel, 1998).…”

Applied techniques for residual oil recovery from source rocks: A review of current challenges and possible developments

“…Some of the dominant, non-aqueous, and widely discussed techniques such as supercritical fluids (SCFs), microwave, and ultrasonic-assisted extraction methods have recently been reported as potential alternatives for unconventional reservoir stimulation applications and extraction of organic fractions from sedimentary rocks. [10,11] These techniques are considered promising for sustainable production compared to hydraulic fracturing due to their reasonable initial and operation costs and because they have low or nonexistent used and produced water, toxic chemicals, seismic alterations, and environmental hazards, which have been determined as more acceptable and have less of an impact on the environment. The applied SCFs are well recognized as self-propping and dissolving agents with improved intensity.…”