Hydrocarbon Recovery from Williston Basin Shale and Mudrock Cores with Supercritical CO₂: Part 1. Method Validation and Recoveries from Cores Collected across the Basin

Abstract

Rock core samples (51) from multiple lithofacies and depths were collected from 10 wells located throughout the Bakken Petroleum System. Each 11.2 mm diameter core was exposed to CO 2 for 24 h at reservoir conditions of 34.5 MPa (5000 psi) and 110 °C in a pressurized apparatus designed to mimic the fracture-dominated flow expected to occur during a CO 2 injection into hydraulically fractured tight unconventional formations. The oil recovered from the rock samples was collected hourly by slowly depressurizing the CO 2 into a collection solvent, while maintaining both CO 2 pressure and temperature constant in the extraction chamber. Recoveries of light and heavy oils were validated by comparing rock samples before and after CO 2 exposure using the extended slow heating Rock-Eval analysis. Extractions of replicate core samples from Middle Bakken (MB) tight nonshale, Upper Bakken shale (UBS), and Lower Bakken shale (LBS) gave reproducible results, demonstrating that the 11.2 mm diameter cores represent the original 10.2 cm (4 in.) core, and that the extraction and associated analysis procedures are reproducible. Recoveries of oil from the Three Forks (TF) and all MB cores ranged from 65 to >99% after 7 h of exposure and exceeded 94% for all cores at 24 h, despite median pore throat radii of only about 13 nm (MB) to 26 nm (TF). Surprisingly, significant oil was obtained from UBS and LBS cores despite the median pore throat radii of only ca. 3.5 nm, sizes that approach molecular dimensions. Although all TF and MB reservoir rocks showed high oil recoveries, the oil obtained in 24 h from UBS and LBS source rocks varied greatly for different well locations and ranged from as low as 11% to as high as 80%. Data analysis of mineralogical components, including clays, carbonates, evaporates, feldspars, and pyrite, showed that these factors were not useful to predict oil recoveries. Both total organic carbon (4−15 wt % for shales and 0.1−0.4 wt % for TF and MB) and the pore throat radii appear to control oil recovery, though they were not predictive for individual UBS and LBS cores. Results from the 51 rock core samples demonstrate that CO 2 is capable of penetrating oil-bearing pores and displacing crude oil from the UBS and LBS source rocks as well as the MB and TF reservoir rocks.

CO2-Enhanced Oil Recovery Mechanism in Canadian Bakken Shale

“…In this approach, the fractured reservoir is soaked in the injected fluid. Diffusion (which is driven by the concentration gradient) is expected to be the dominant mode of transport under a waning pressure gradient [7]. EOR through huff-n-puff is affected by several parameters, such as injection plan, gas injection rate and volume, pressure, cycle time, reservoir heterogeneity, pore space, and shale characteristics, some of which are design parameters whereas others are simply reservoir properties.…”

“…Among the lab studies, Hawthorne et al [7] studied the use of CO 2 -EOR on 51 shale samples from the Bakken Petroleum System in the US. The shale samples were exposed to supercritical CO 2 for 24 h under reservoir conditions.…”

“…In conventional systems, CO 2 penetrates the matrix and causes swelling, viscosity reduction or sweeping of the in-place oil [15]. In shales, the concentration gradientdriven diffusion of hydrocarbons from the interstitial pore spaces in the rock to the surface and into the bulk-injected fluid in the fractures is considered to be the main recovery mechanism [7,8,16,17]. The minimum miscibility pressure (MMP) may not be as important in CO 2 -EOR in shales as it is in conventional systems.…”

Estimation of efficiency of oil extraction with supercritical CO2 in a low-permeability reservoir

“…Одним из хорошо изученных примеров закачки CO 2 в плотные нефтяные пласты и сланцы является месторождение Баккен, расположенное на территории нефтегазоносного бассейна Уиллистон в Северной Америке [4][5][6]. В работах [7][8][9] авторы экспериментально исследовали параметры, влияющие на эффективность извлечения нефти закачкой CO 2 на образцах сланцевых и глинистых пород-коллекторов нефти формации Баккен. Показано, что площадь, а также время контакта породы с CO 2 являются основными факторами, влияющими на нефтеот-дачу пласта.…”

Experimental study of enhanced oil recovery by CO2 huff-n-puff in shales and tight sandstones with fractures

“…In recent years, the effects of mechanistic factors (e.g., soaking time, cycle number, pressure) on the CO 2 huff-npuff in shale cores have been studied by many researchers (Wang et al 2013;Wan et al 2013;Li et al 2017a, b;Sheng 2017;Du et al 2018). Besides, the effects of heterogeneity (Chen et al 2014), water saturation (Huang et al 2020), permeability (Su et al 2020), pore throat radii and total organic carbon (TOC) content (Hawthorne et al 2019) on the CO 2 huff-n-puff in the shale were also studied. The recovery factor varies widely (25%-100%), which is caused by different experimental methods and samples.…”