Volumetric Swelling of Bakken Crude Oil with Carbon Dioxide and Hydrocarbon Gases at 110 °C and Pressures of up to 34.5 Megapascals

Abstract

Volumetric swelling tests were performed using a typical crude oil produced from the Middle Bakken formation to compare the ability of pure carbon dioxide, methane, ethane, propane, and a typical Bakken produced gas (ca. 68/22/10 mole fraction methane/ethane/propane) at the reservoir temperature (110 °C) and pressures of up to 34.5 MPa (5000 psi). Crude oil swelling factors at 34.5 MPa for the individual hydrocarbon gases were quite low for methane (1.13), moderately higher for the produced gas (1.39), and much higher for ethane (2.50). Propane caused dramatically higher crude oil swelling than any of the test gases and reached a volumetric expansion of 2.6 at 4.2 MPa (the highest degree of swelling that could be observed in the test cell). The presence of water had no significant effect on oil swelling for the hydrocarbon gases. However, carbon dioxide showed a moderate increase in oil swelling at higher pressures when water was present in the high-pressure cell and achieved oil swelling factors at 34.5 MPa of 1.60 with water and 1.42 without water. The crude oil swelling results show the same trend as that of the individual gas' solubility in the crude oil. The oil swelling results were compared to earlier experimental results that used the same injected gases, temperature, and pressure ranges to determine each gas' minimum miscibility pressure (MMP) and ability to dissolve oil hydrocarbons with the same crude oil as was used in the swelling tests, as well as the ability of the same test gases to recover residual oil from siltstone samples collected from the Middle Bakken target drilling zone. Oil swelling, MMP, crude oil solubility in each gas, and residual oil recovery tests all showed that propane is the superior EOR fluid, followed by ethane, then carbon dioxide and the produced gas (which are similar), and finally methane, which is the poorest in each lab test of the five gases investigated.

Measured Sorption Isotherms for Bakken Petroleum System Shales Using Carbon Dioxide and Produced Gas Hydrocarbons at 110 °C and Pressures up to 34.5 MPa

“…Table shows a summary of the experimental results from exposing Bakken produced crude oil and rock samples to the five test gases at reservoir pressures and at a temperature of 110 °C, including crude oil MMP, solubility, and volumetric swelling as well as the recovery of crude oil hydrocarbons and the sorption isotherm behaviors with LBS rock samples. − Table gives a ranking of each gas from the most effective to the least effective, with the most effective based on having the lowest MMP, the highest ability to dissolve bulk crude oil, causing the most oil swelling and yielding the highest recovery of oil hydrocarbons from rock core samples, and achieving the highest molar gas sorption on the LBS rock samples at reservoir pressure (34.5 MPa), and the having the lowest Langmuir pressure.…”

“…The work reported here is the fifth in a series of experimental studies conducted at reservoir temperature (110 °C) and pressures (up to 34.5 MPa, 5000 psi) that compare rich gas hydrocarbons (methane, ethane, propane, and an approximately 70/20/10 mol ratio of methane/ethane/ propane typical of BPS produced gas) and CO 2 for their abilities to interact with BPS materials, including measured minimum miscibility pressures (MMP) with Bakken crude oil, 23 recovery of liquid hydrocarbons from rock samples collected from the MB producing zone as well as the LBS source shale, 24 and their respective abilities to dissolve crude oil hydrocarbons 25 and to swell bulk crude oil. 26 In order to augment those previous investigations, the present study reports sorption isotherms using three organic-rich LBS source shale samples obtained from three different wells that represent low, mid, and high thermal maturity oil-producing regions. Isotherms were measured using a magnetic suspension balance (MSB) at reservoir conditions.…”