Minimum Miscibility Pressure Studies in the Bakken

Abstract

The Bakken is among the shale reservoirs which have been discovered to hold a vast amount of oil resource contributing to the production boom in the US. This unconventional reservoir, like most others, displays favorable initial production rates due to stimulation by hydraulic fracturing, but production rates quickly decline after few months. Due to the extremely low permeability and low recovery factors, miscible gas injection is considered for improving the recovery of oil in the Bakken formation. Feasibility of miscible gas injection in the Bakken depends on the analysis of minimum miscibility pressure (MMP) experiments. The Rising Bubble Apparatus (RBA) has been chosen for the purpose of these experiments. The RBA provides results in a short amount of time using small amounts of fluid samples. The RBA consists of a cell gage containing a flat glass tube where oil samples are placed and an injection needle where gas is injected into the flat glass tube. To simulate reservoir conditions, the glass tube is pressurized using de-ionized water and heating plates surrounding the cell are used to regulate temperature. Visual observation of the injected gas bubble behavior is captured by a camera as it rises and moves upward along the oil column. The MMP occurs when the gas bubble dissolves into the oil before reaching the top of the oil column. MMP results from a Bakken crude sample show a range from 2340 to 3000 psia at a temperature of 215 °F using CO2 as the injection fluid. Other injection fluids such as nitrogen and hydrocarbon gases have been tested and provided MMP values from 3500 to over 5000 psia depending on the gas. MMP results from Bakken crude oil samples were compared to existing correlations and more correlations were found to produce unreliable MMP results. Further comparison using an equation of state phase-behavior program has shown similar results with the RBA MMP results. The impact of different injection fluids, inclusive of CO2 and enriched hydrocarbon gases is the subject of this study. MMP results are influenced by the choice of injection fluids, providing valuable information for economic production and increased recovery in the Bakken formation. The results from this study provide MMP data for a range of injection fluids that can be used in planning pilot tests for miscible gas injection in the Bakken.

Use of a CO2-Hybrid Fracturing Design To Enhance Production From Unpropped-Fracture Networks

“…An equation of state developed for CO 2 injection in a separate study was used in this reservoir model. The predicted minimum miscible pressure (MMP) was 2,500 psi, which is consistent with published MMPs for the Middle Bakken (Adekunle and Hoffman 2014). The equation of state had eight (pseudo-)components and yielded a gas/oil ratio (GOR) of 906 scf/bbl, which is a typical value for the Middle Bakken.…”

“…The simulator couples fluid flow and deformation in 2D DFNs. Fracture elements are allowed to slide or open, and the stresses induced by deformation are calculated by use of the boundary-element method (Crouch and Starfield 1983;Asgian 1989). For more information regarding the fracture simulator, the reader may refer to McClure (2012, 2014), and McClure and Horne (2013.…”

CO2 injection for enhanced oil recovery in Bakken tight oil reservoirs

“…Most gases used for injection include carbon dioxide (CO 2 ), 88 nitrogen (N 2 ), natural gas or the mixture of them. Among these 89 gases, CO 2 has received much more attention for enhanced oil 90 recovery in the Bakken formation [7][8][9]. CO 2 has a considerably 91 lower minimum miscibility pressure (MMP) than that of the other 92 gases such as N 2 and CH 4 [10,11].…”

“…CO 2 and trapped oil will become completely miscible and 107 CO 2 will extract light and intermediate hydrocarbons from the oil 108 phase, and the interfacial tension will become zero and capillary 109 pressure disappears, resulting in the oil phase and CO 2 phase, 110 which contains some extracted hydrocarbon components, flow 111 together more easily through the porous media [16][17][18]. 112 Fai-Yengo et al [9] presented that the effect of capillary pressure 190 where / is matrix porosity, q s is matrix density, q ' is density of which is defined as 199 199 200 where k is the formation permeability tensor, k r' is the relative per-201 meability of phase, ', p ' is pressure of phase ' and l ' is viscosity of Sigmund correlation [31] is often used to calculate the oil and gas 211 diffusion coefficients (unit is cm 2 /s) since it is valid for both oil 212 and gas phases [32]. The binary diffusion coefficient between com-213 ponent i and j is calculated by [31,32] 214…”

Reservoir simulation and optimization of Huff-and-Puff operations in the Bakken Shale

“…In this state, CO 2 is 10-25% as viscous as water and 70% as dense, facilitating its dispersion into the matrix [9]. CO 2 develops miscibility with the Bakken oil at pressures between 3000 and 3400 psi [10], allowing it to mix with the reservoir fluids and improve their mobility. A study by Song and Yang [11] concluded that recovery performance in tight rocks is ''significantly enhanced'' by cyclical CO 2 injection over traditional waterflooding.…”