Subscriber access provided by University of Sunderland
Fossil Fuels
Characteristics of hydrogen and oxygen isotopes in produced water and productivity response of CBM wells in western Guizhou Congcong Wu, Zhaobiao Yang, Yong Qin, Jie Chen, Zhengguang Zhang, and Yangyang Li Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02185 • Publication Date (Web): 08 Oct 2018 Downloaded from http://pubs.acs.org on October 9, 2018
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 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 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.
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 30 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
Characteristics of hydrogen and oxygen isotopes in produced water and
2
productivity response of CBM wells in western Guizhou
3
4 5
Congcong Wu1,2, Zhaobiao Yang1,2*, Yong Qin1,2, Jie Chen3, Zhengguang Zhang1,2, Yangyang Li1,2
(1.Key Laboratory of CBM Resources and Dynamic Accumulation Process, Ministry of Education of China, China
6
University of Mining and Technology, Xuzhou
7
University of Mining and Technology, Xuzhou
8
Engineering Thechnology, Guiyang
221008, China; 2.School of Resource and Geosciences, China 221116, China; 3.Guizhou Research Center of Shale Gas and CBM
550009,China)
9
10
Abstract: The characteristics of hydrogen (H) and oxygen (O) isotopes in produced
11
water of coalbed methane (CBM) wells have abundant geochemical indication
12
information. Based on the tests of conventional ions and H and O isotopes of 20 water
13
samples produced from CBM wells in western Guizhou, the characteristics of H and O
14
isotopes and productivity response of the wells in the study area have been analyzed in
15
combination with the geological background. The research shows that, if the H and O
16
isotopic compositions of produced water from a CBM well have obvious D drift (D drift
17
means that when δ18O takes the same value, the measured value of δD that is higher than
18
the theoretical value of δD obtained from the regional atmospheric precipitation line
19
equation.), the well is likely to get high production, if the H and O isotopic compositions 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
20
have O drift (O drift means that when δD takes the same value, the measured value of
21
δ18O that is higher than the theoretical value of δ18O obtained from the regional
22
atmospheric precipitation line equation.), the well is not likely to get high production. As
23
drainage goes on, the water-rock interaction gradually strengthens, and the H and O
24
isotope compositions tend to become heavier, but seasonal rainfall can cause their values
25
to decrease. From shallow to medium-deep formations, δD and δ18O values increase
26
continuously, and the wells with the lowest δD and δ18O values in the shallow formation
27
have the highest average daily gas production. The d', of D drift comprehensive index, is
28
proposed, which is of universal significance. With the increase of d', the average daily
29
gas production decreases, and combined with productivity performance, the high
30
production wells and low production wells can be distinguished. d' of less than 0
31
indicates high production, which can be used as a geochemical index to evaluate potential
32
productivity. It is proposed that δD=-50‰, d'=0, and Cl-=2 000 mg/L can be used as a
33
criterion for judging whether produced water of CBM well is polluted, and δD=-25‰,
34
Cl-=4 000 mg/L can be used to distinguish the degree of formation water pollution.
35
Moreover, the identification template of produced water source based on δD, d' and Cl-
36
has been established preliminarily, and three ranges, coal seam water, light polluted water
37
and severe polluted water can be identified according to the template. Moreover, it is
38
considered that the CBM production will drop as the pollution degree of produced water
39
increases.
2
ACS Paragon Plus Environment
Page 2 of 30
Page 3 of 30 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
40
Key words: CBM wells; produced water; hydrogen and oxygen isotopes; productivity response; water
41
source identification
42
Introduction
43
Drainage production of CBM well is achieved through water drainage and pressure reduction.
44
Under the reductive environment of coal measures, there are various physical, chemical and biological
45
reactions between the discharged formation water and minerals in the coal seams and surrounding
46
rocks, which result in large differences in hydrogen and oxygen isotope composition and properties of
47
produced water from different CBM wells.1-4In thin and medium thick coal seam groups of Western
48
Guizhou area, multiple independent CBM-bearing systems superimpose in the vertical direction,5,6so
49
commingled production of multi-layers has become an popular way to increase single-well production
50
and save development costs in this area.7 Therefore, it is of great significance for achieving high
51
yields to systematically study the chemical characteristics of hydrogen and oxygen isotopes in the
52
produced water from CBM wells, identify the source of multi-layer drainage water, and accurately
53
predict CBM productivity.
54
The characteristics of H and O isotopes in produced water of CBM well have abundant
55
geochemical indication significance. According to previous studies on the characteristics of produced
56
water from CBM wells in the south of Qinshui Basin, it is found that there is a positive correlation
57
between δD and δ18O, and the δD/δ18O of less than 0.5 is conducive to high yield, and their
58
distribution characteristics are related to the evolution of groundwater environment, so their values
59
can be used as hydrological indexes to judge the runoff condition of coal seam and favorable area for 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
60
CBM development.8-12 Chen et al. proposed that the distribution of H and O isotopes in deep
61
groundwater was related to the flow field of groundwater, and had a tracer function of water
62
circulation.13,14Examining the produced water source, Guo et al. reached the conclusion that the water
63
contaminated by fracturing fluid had higher δD, δ18O and d of D drift index, and established the
64
identification template of produced water source using the δD, δ18O and d as response indexes.15But
65
most previous studies focused on the Qinshui Basin and Ordos Basin where CBM exploration and
66
development are more mature, however, for the western Guizhou blocks, where the geological
67
conditions are extremely complex, there are no detailed reports on the H and O isotopic characteristics
68
of produced water and their control on productivity of CBM wells.2,12,16-20
69
Therefore, in this study, the H and O isotopic characteristics and productivity response were
70
analyzed, based on the produced water samples systematically collected from 20 CBM wells in
71
western Guizhou in 2017, in the hope to provide theoretical basis for the CBM exploration and
72
development in this area.
73
1. Geological background of CBM development
74
The Upper Permian coal-bearing strata in western Guizhou, contain abundant CBM resources,
75
accounting for approximately 10% of the total in China.21The CBM reservoirs there have the
76
geological characteristics of multiple thin coal seams, high stress, slightly high water content, and
77
complex coal structure.22,23
78
Development wells in production test in western Guizhou are mainly distributed in Songhe, 4
ACS Paragon Plus Environment
Page 4 of 30
Page 5 of 30 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
79
Zhijin and northern Guizhou blocks (Figure 1) and the main coal-bearing strata producing CBM are
80
the Late Permian Longtan Formation and Changxing Formation (Figure 2). The GP well group in
81
Songhe block includes 8 CBM wells, of which wells GP-1 and GP-2 were put into production in
82
January 2014, and wells GP-3 to GP-8 were put into production in January 2015. All the wells are
83
developed by staged fracturing and commingled drainageof multi-layers. Each well generally has 3 to
84
4 fracturing stages of about 20 m thick each, and the span of production layers of about 200 m
85
straddling 3 main coal seams. By December 2017, the highest daily gas production reached about 3
86
000 m3, but stabilized at around 500 m3 in late stage. The cumulative water production was about 2
87
400-4 300 m3, and the average cumulative water production of single well was over 2 000 m3.
88 89
The Zhijin well group in Zhijin block includes 6 vertical CBM wells, of which wells Z-X-1,
90
Z-X-2, Z-X-3 and Z-X-4 were put into production in February 2015, while wells Z-X-5 and Z-X-6 in
91
May 2015. Each well has 2 to 4 fracturing stages. These wells are developed by fracturing the III coal
92
group (the main coal seams of No. s 20, 23, 27 and 30) and commingled multi-layer drainage. By
93
December 2017, the highest daily gas production reached about 3 000 m3, and stabilized at above 1
94
000 m3 later. The cumulative water production was about 500-3 000 m3, and the average cumulative
95
water production of single well exceeded 1 000 m3.
96
Wells B-8, N-9 and N-10, located in the Bide syncline, are developed by staged fracturing and
97
commingled production of 2-3 layers, of which Well B-8 was put into production in April 2015, and
98
Well N-9 and N-10 in February 2016. Well Z-7, located at the Dahebian syncline was put into 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
99
production in June 2016, by fracturing 2 stages and commingled multi-layer drainage. Well D-11
100
located in the Huangnitang syncline is developed by 5 stage fracturing and commingled multi-layer
101
drainage. Well F-12 located in the Changgang syncline in northern Guizhou is produced by 3-stage
102
fracturing and commingled multi-layer drainage. By December 2017, they had a highest daily gas
103
production of about 1 500 m3, stable production of about 1 000 m3 later, and cumulative water
104
production of about 500-3 000 m3.
105
2. Sample collection and testing
106
Samples of produced water from 20 CBM development wells in western Guizhou were collected
107
five times on the following dates: January 2017, March 2017, May 2017, August 2017 and November
108
2017, respectively. A total of 92 water samples were collected for testing, among them, 91 were CBM
109
produced water samples from the 20 wells and the other sample was surface water from Jichangping
110
river near the Songhe block, in May 2017.
111
Before sample collecting, clean plastic containers, 2.5 L pure water bottles, were flushed three
112
times with sample water, samples were collected directly from the outlet of CBM wells without
113
contact between the outlet and the plastic containers during sampling. The containers were filled to the
114
brim and the lids were carefully closed to minimize headspace air in the sample container, then the
115
containers were sealed using paraffin wax. All the collected samples were sent to the State Key
116
Laboratory of Environmental Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou
117
Province, China, within 72 h for tests of conventional ions and hydrogen and oxygen isotopes. The
118
instruments used for testing anion concentration, cation concentration, and hydrogen and oxygen 6
ACS Paragon Plus Environment
Page 6 of 30
Page 7 of 30 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
119
isotope compositions were Diane ICS-90, inductively coupled plasma emission spectrometer Vista
120
MPX, and Finnigan MAT253 mass spectrometer with an analytical precision of
