CO2 injection for enhanced oil recovery in Bakken tight oil reservoirsby Wei Yu, Hamid Reza Lashgari, Kan Wu, Kamy Sepehrnoori




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13 n 4 5 6 ep 7 8 tin, A 9 10 1 2 h i g h l i g h t s 13 14  The CO2 huff-n-puff for EOR in the Bakken is i 15  CO2 molecular diffusivity is a significant facto 16  Sensitivity studies are performed to quantify t 17 for the 18 2 0 21 22 23 24 25 26 27 28 29 30 31 32 3 3 34 35 36 37 38 39 40 41 42 43 44gnificant role in improving oil recovery from tight oil reservoirs, which cannot 45 46 47 48 49 50 51 52 53 54 55 56 57 58 such as porosity and oil saturation [2]. It has been reported that 59 the Middle Bakken has an estimated average oil resource of 3.65 60 billion barrels and Three Forks has an estimated average resource 61 of 3.73 billion barrels [3]. Horizontal drilling and multi-stage 62 hydraulic fracturing are the two key enabling technologies to make 63 tight oil production commercial from the Bakken formation with 64 low or ultra-low permeability. The key dominant mechanisms for 65 66 67 68 69in a strong 70OR) meth 71improve oil recovery in tight oil reservoirs. It has been re 72that a minor improvement in oil recovery factor such as 1% 73yield 1.6–9 billion barrels of additional oil [6]. The 1% add 74oil recovery factor could bring revenue of $128 to $720 billion with 75an assumption of crude oil price of $80 per barrel. Accordingly, it is 76important to investigate the potential of applying enhanced oil 77recovery methods to improve long-term oil productivity in the 78Bakken formation. 79Although water flooding has been widely used in conventional 80oil reservoirs, it is challenging to be applied in unconventional oil ⇑ Corresponding author. Tel.: +1 512 574 0080.

E-mail address: (W. Yu).

Fuel xxx (2015) xxx–xxx

Contents lists availab ue .e

JFUE 9395 No. of Pages 10, Model 5G 4 July 2015[1], where Middle Bakken and Three Forks are the two primary layers for oil production since they have the best reservoir qualities umes of oil remaining in the reservoir, resulting vation of applying enhanced oil recovery (E 0016-2361/ 2015 Published by Elsevier Ltd.

Please cite this article in press as: Yu W et al. CO2 injection for enhanced oil recovery in Bakken tight oil reservoirs. Fuel (2015), j.fuel.2015.06.092motiods to ported could itionalbe neglected in the reservoir simulation model. Additionally, the tight oil formation with lower permeability, longer fracture half-length, and more heterogeneity is more favorable for the CO2 huff-n-puff process. This work can provide a better understanding of the physical mechanisms and key parameters affecting the effectiveness of CO2 injection for enhanced oil recovery in the Bakken formation.  2015 Published by Elsevier Ltd. 1. Introduction

The Bakken formation with multiple oil-bearing layers is one of major productive tight oil reservoirs in North America (see Fig. 1) the primary recovery are depressurization and solution gas drive.

Although with the advanced technologies, most estimates for primary oil recovery factor remain very low due to tight nature of the Bakken formation [4,5]. Hence, there are still substantial vol-Tight oil

Bakken heterogeneity on the well the CO2 diffusion plays a si More heterogeneity is much favorable a r t i c l e i n f o

Article history:

Received 27 January 2015

Received in revised form 26 June 2015

Accepted 29 June 2015

Available online xxxx


CO2 huff-n-puff

Enhanced oil recovery

CO2 diffusionnvestigated. r. he key parameters.

CO2 huff-n-puff process. a b s t r a c t

The combination of horizontal drilling and multi-stage hydraulic fracturing have boosted the oil production from Bakken tight oil reservoirs. However, the primary oil recovery factor is very low due to the extremely tight formation, resulting in substantial volumes of oil still remaining in place. Hence, it is important to investigate the potential of applying enhanced oil recovery methods to increase oil recovery in the Bakken formation. Although carbon dioxide (CO2) is widely used in conventional reservoirs to improve oil recovery, it is a new subject and not well-understood in unconventional oil reservoirs such as the Bakken formation. In this paper, we use numerical reservoir simulation to model CO2 injection as a huff-n-puff process with typical reservoir and fracture properties from the Bakken formation.

Effects of CO2 molecular diffusion, number of cycle, fracture half-length, permeability and reservoir performance of CO2 huff-n-puff are examined in detail. The results show thatCO2 injection for enhanced oil recovery i

Wei Yu a,⇑, Hamid Reza Lashgari b, Kan Wu a, Kamy S aDepartment of Petroleum Engineering, Texas A&M University, College Station, TX, USA bDepartment of Petroleum and Geosystems Engineering, The University of Texas at Aus

F journal homepage: wwwBakken tight oil reservoirs ehrnoori b ustin, TX, USA le at ScienceDirect l l sevier .com/locate / fuel0.1016/ 81 reservoirs with low permeability because of low injectivity, poor 82 sweep efficiency with fracture networks, and clay swelling prob83 lems. Nevertheless, it is believed that gas injection is more suitable 84 due to lower viscosity and larger injectivity than water injection. 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113has negligible effect on oil recovery in the Bakken formation. The 114extraction of hydrocarbons is highly dependent on the density of 115the CO2, and the CO2 will extract more and heavier hydrocarbons 116with the increasing CO2 density [20–22]. The CO2 density varies 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144


Selected list of acronyms and units

SCF standard cubic feet (ft3)

MSCF 103 standard cubic feet

MMSCF 106 standard cubic feet

RB reservoir barrels

STB stock tank barrels ft  0.3048 m (F-32)/1.8 C psi  6.895 kPa ft3  0.02832 m3 cp  0.001 Pa s md  1e15 m2 lD  1e3 md bbl  0.1589873 m3 2 W. Yu et al. / Fuel xxx (2015) xxx–xxx