Subscriber access provided by UNIV OF DURHAM
Article
Understanding model crude oil component interactions on kaolinite silicate and aluminol surfaces: towards improved understanding of shale oil recovery Shansi Tian, Valentina Erastova, Shuangfang Lu, Hugh Christopher Greenwell, Thomas Underwood, Haitao Xue, Fang Zeng, Guohui Chen, Chunzheng Wu, and Rixin Zhao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02763 • Publication Date (Web): 18 Dec 2017 Downloaded from http://pubs.acs.org on December 20, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
1
Understanding model crude oil component interactions on
2
kaolinite silicate and aluminol surfaces: towards improved
3
understanding of shale oil recovery
4
Shansi Tian1,2,3, Valentina Erastova4, Shuangfang Lu1,2*, H. Chris Greenwell3*,
5
Thomas R. Underwood3, Haitao Xue1,2, Fang Zeng2, Guohui Chen1,2, Chunzheng
6
Wu1,2, Rixin Zhao1,2
7
1
8
(RIUP&RE), China University of Petroleum (East China), Qingdao 266580,
9
Shandong, PR China
Research Institute of Unconventional Petroleum and Renewable Energy
10
2
11
266580, Shandong, PR China
12
3
13
Kingdom
14
4
15 16 17 18 19 20 21 22 23 24 25
*Corresponding authors: Prof. Shuangfang Lu Research Institute of Unconventional Petroleum and Renewable Energy (RIUP&RE), China University of Petroleum (East China), Qingdao, Shandong, China Phone (or Mobile) No.: +86-18661856596 Email:
[email protected] Prof. H. Chris Greenwell Department of Earth Science, Durham University, Durham, United Kingdom Durham University, South Road, Durham, DH1 3LE Phone (or Mobile) No.: +44-01913342324 Email:
[email protected] School of Geosciences, China University of Petroleum (East China), Qingdao
Department of Earth Science, Durham University, Durham, DH1 3LE, United
Department of Chemistry, Durham University, Durham, DH1 3LE, United Kingdom
1
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 43
26
ABSTRACT: Shale oil is currently of interest for unconventional resource
27
exploration and development. Understanding the mechanism of interaction between
28
the complex mixture of organic compounds in shale oil and minerals making up the
29
reservoir rock-oil interface will assist recovery. In this study, molecular dynamics
30
simulation is used to study the adsorption characteristics of a model oil mixture within
31
nanoscale intra-particle pores of kaolinite minerals, which form pore filling structures
32
in shale rock. To better understand the effects of oil composition, temperature and
33
pressure on the adsorption properties of the model oil mixture, a range of
34
temperatures (298 K, 323 K, 348 K and 373 K) and pressures (1 bar, 50 bar, 100 bar
35
and 200 bar) representing up to reservoir conditions were used. This study shows that
36
adsorption and arrangement of oil molecules is dependent on the surface of kaolinite
37
and the distance away from it. The simulations show polar compounds are likely to be
38
adsorbed on aluminol kaolinite basal surfaces, while alkanes preferentially adsorb on
39
silicate surfaces. In addition, the number of oil molecule bound layers, and total
40
adsorption amount on the silicate surface is greater than the aluminol surface. The
41
density of adsorbed oil is reduced with increase in temperature, while the effect of
42
pressure is not as significant. On the basis of performed molecular simulations, we
43
show the adsorption rate of shale oil on the surfaces of kaolinite sheets and assess the
44
removable capacity of the model oil.
45
Keywords:
shale
oil,
molecular
dynamics,
2
ACS Paragon Plus Environment
clay
mineral,
recovery.
Page 3 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
46
1. INTRODUCTION
47
With increasing demand for energy, and while conventional oil and gas resources are
48
depleting, unconventional oil and gas are receiving more attention as they have
49
become a major contributor to sustained growth in global hydrocarbon production.
50
The exploration and development of shale gas has achieved notable success in North
51
America,1-3 and led a global shale gas research boom.4,5 However, with the lessons
52
learned from initial phases of shale gas extraction and the decrease of natural gas
53
price, investors have now shifted their attention to more profitable shale oil.6-8
54
According to the Energy Information Administration,9 in the last 10 years, the
55
production of U.S. shale oil has increased 12.2 times to an average of 4.57 million
56
barrels per day (MMbbl/d) in 2015, compared to 0.37 MMbbl/d in 2005. Driven by
57
the exploitation of tight sand formations, the United States remained the world's top
58
producer of petroleum and natural gas hydrocarbons in 2015.10 Shale oil is playing a
59
significant role in the global energy industry, and a worldwide shale-oil boom is
60
predicted.11-13
61
Preliminary evaluation has shown that shale oil resources are very rich in China,
62
with the amount of geological resources put at 32 billion barrels, and China ranked
63
third among the 41 countries which have an accumulated total shale oil resource of
64
345 billion barrels.14 At present, in China, a number of reserves in which the amount
65
of geological resources are between 3.5×109 barrels and 7×109 barrels have been
66
discovered, for example in the Triassic Yanchang Formation of the Erdos Basin,
67
Permian Lucaogou Formation of the Junggar Basin, and the Qingshankou Formation
68
of the Songliao Basin. There are also many important discoveries in the lime-shale of
3
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
69
Bohai Bay area and in the Sichuan Basin.15,16 Compared with marine shale oil in the
70
North America, the lacustrine shale oil in China is heavier and has higher amounts of
71
polar components; resin and asphaltene is much more abundant than in the North
72
America reservoirs. The presence of these components in the lacustrine shale oil is
73
thought to result in stronger adsorption of oil within the pores of the shale system,
74
which requires extra effort to remove and makes the reservoir more difficult to
75
develop. These polar components should be accounted for in the assessment of shale
76
oil production in China, as they strongly interact with kerogen, minerals, and the
77
widespread nanopores in the shale rock,17-19 leading to errors in recoverable resource
78
estimation.
79
The adsorption of alkanes on carbonaceous materials, akin to the kerogen, has
80
been studied in recent years. McGonigal et al. directly imaged a two-dimensional,
81
high-degree ordering of the alkane layer at the liquid/graphite interface using a
82
scanning tunneling microscope (STM).20 Castro et al. reported that longer alkanes
83
show a strong preference for adsorption onto graphite.21 Furthermore, Severson and
84
Snurr studied the adsorption isotherms of linear alkanes (ethane, pentane, decane, and
85
pentadecane) on activated carbon and evaluated the functions of pore size, chain
86
length, and temperature on adsorption.22 Recently, Harrison et al. studied the single
87
component preferential adsorption of linear and branched alkanes in pores with
88
different apertures (1, 2, and 4 nm) at 390 K.23
89
A similar issue of accounting for hydrocarbons trapped in narrow pores for shale
90
gas has been discussed by Ambrose et al., who suggested that an adjustment of
91
adsorption phase volume is necessary for gas-in-place (GIP) calculations, leading to a
92
10 to 25% decrease in GIP in comparison with the conventional method for 4
ACS Paragon Plus Environment
Page 4 of 43
Page 5 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
93
assessment.24-26 In addition, Wang reported that the unrecoverable fraction of oil-in-
94
place (OIP) is 13% in Bakken shale,27 when taking the adsorption of alkanes in a
95
graphite model into consideration. Nevertheless, there are relatively few studies that
96
explore the effect of polar component adsorption on the estimation of shale oil-in-
97
place.
98
While the interaction of hydrocarbon molecules with pores and surfaces coated
99
with kerogen like materials has been more extensively studied, conceptually shale
100
consists of two parts: organic matter (kerogen) and inorganic matter (minerals). The
101
inorganic part of shale mainly contains quartz, calcite, feldspar and clay minerals.
102
Each kind of mineral makes up a certain volume fraction of a lacustrine/marine shale
103
and plays an important role in shale systems through presenting intra- and inter-
104
particle pore networks that may hold hydrocarbons. Studying the interface of
105
inorganic pores with oil is challenging, and computational chemistry simulations offer
106
great potential to examine the properties of mineral interfaces and oil mixtures at an
107
atomistic level. Previous simulation studies of mineral-organic interfaces have been
108
widespread and extensively studied in the past, such as quartz,28-30 calcite,31
109
montmorillonite,32 kaolinite,33 and muscovite.34
110
Kaolinite often forms surface coatings in the inorganic pores of shale reservoirs,
111
as well as forming pore filling aggregates and presents inter-particle and intra-particle
112
pore surfaces. Kaolinite is different from certain other clay minerals such as illite,
113
smectite, and chlorite due to the octahedral-tetrahedral structure presenting two
114
different surfaces, the mainly oil-wetting silicate surface and the water-wetting
115
aluminol surface. A significant number of computational studies have been published
116
on kaolinite surfaces,33,35-44 but these have primarily focused on the adsorption 5
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
117
mechanisms of either a single molecule, or a relatively small number of organic
118
molecules to the mineral. As shale oil contains different types and molecular weight
119
alkanes, aromatic hydrocarbons and polar compounds, it is important to study the
120
adsorption of different alkanes in the presence of aromatic and polar compounds to
121
build up a more complete picture of the mineral-oil interface. In addition, temperature
122
and pressure change with depth and maturity in a shale reservoir, therefore it is also
123
important to take these into consideration when considering shale oil adsorption.
124
In this present study, the adsorption behavior of a simple 6-component model
125
crude oil mixture on kaolinite basal surfaces (to represent a shale component) was
126
studied under reservoir conditions using molecular dynamics (MD) simulations. The
127
main objectives were: (1) to provide nanoscale molecular-level resolution for studying
128
the interactions at the hydrocarbon-shale interface; (2) to accurately characterize the
129
adsorption properties of alkanes/polar compounds in the mineral slit-shaped pore
130
space under different temperatures and pressures; (3) to provide improved parameters
131
for the calculation of the unrecoverable fraction for shale OIP (oil-in-place)
132
estimation.
133
2. MODELS AND SIMULATION DETAILS
134
The kaolinite unit cell has the chemical formula Al2Si2O5(OH)4, without isomorphic
135
substitutions. The initial atomic positions were taken from the AMCSD (American
136
Mineralogist Crystal Structure Database).45,46 This was converted to a cubic cell. The
137
model contained three periodically replicated sheets of kaolinite, creating a clay slab
138
of 252 unit cells (12×7×3) as shown in Figure 1g, with dimensions of approximately
139
6.2×6.3×1.9 nm. The kaolinite structures initially occupied the region 0
