P-wave and S-wave response of coal rock containing gas-water with different saturation: an experimental perspective

doi:10.1007/s11707-021-0958-x

Front. Earth Sci.

2023, Vol. 17

Issue (1) : 100-108 https://doi.org/10.1007/s11707-021-0958-x

RESEARCH ARTICLE

P-wave and S-wave response of coal rock containing gas-water with different saturation: an experimental perspective

Dameng LIU^1,²(

), Lijing LI^1,², Zheng ZHAO^1,², Wei CHEN³, Yidong CAI^1,², Yongkai QIU^1,², Yingfang ZHOU⁴

¹. School of Energy Resources, China University of Geosciences, Beijing 100083, China
². Coal Reservoir Laboratory of Natural Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing 100083, China
³. Beijing Furuibao Energy Technology Company, Beijing 100176, China
⁴. School of Engineering, King’s College, University of Aberdeen, AB24 3UE Aberdeen, UK

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Abstract

The acoustic response of gas and/or water saturated coal rock is fundamental for establishing the correspondence between the physical properties of the coal reservoir and the characteristics of the well-logging response, which is the technology essential for the geophysical exploration of coalbed methane (CBM). This acoustic response depends on water (S_w) and gas (S_g) saturation among other factors. In this study, we performed acoustic tests on dry and different gas-water saturated coal samples with different degrees of metamorphism and deformation, collected from several coal mining areas in China. These tests enabled us to analyze the influence of coal type and gas-water saturation on the acoustic response of CBM formations. Our results show that the acoustic velocity of P-wave and S-wave (V_p and V_s, respectively), and the relative anisotropy of and V_s, increased with increasing vitrinite reflectance, density, V_p and S_w. WithS_w increasing from 0 to 100%, the growth rate of the acoustic velocity decreased with increasing vitrinite reflectance. The V_p/V_s ratio of tectonic coal was generally higher than that of primary coal. The growth rate of the relative anisotropy in tectonic coal was markedly higher than that in primary coal.

Keywords coal rock gas-water water saturation acoustic velocity relative anisotropy

Corresponding Author(s): Dameng LIU

About author:

^* These authors contributed equally to this work.

Online First Date: 11 April 2022 Issue Date: 03 July 2023

Cite this article:

Dameng LIU,Lijing LI,Zheng ZHAO, et al. P-wave and S-wave response of coal rock containing gas-water with different saturation: an experimental perspective[J]. Front. Earth Sci., 2023, 17(1): 100-108.

URL:

https://academic.hep.com.cn/fesci/EN/10.1007/s11707-021-0958-x
https://academic.hep.com.cn/fesci/EN/Y2023/V17/I1/100

Fig.1 Coal samples (a) and (b) and ultrasonic P-wave and S-wave testing equipment (c).

Tab.1 Basic parameters of selected coals with different vitrinite reflectance

Fig.2 Schematic diagram of displacement experiment.

Fig.3 Variation of the acoustic velocity with the pseudo-azimuth angle of coal sample LHG7-1. (a) P-wave; (b) S-wave.

Sample ID	$V p$ /(m·s^?1)	$V s$ /(m·s^?1)	$V p$ / $V s$	A		B		Relative anisotropy
Sample ID	$V p$ /(m·s^?1)	$V s$ /(m·s^?1)	$V p$ / $V s$	$V p$	$V s$	$V p$	$V s$	$V p$	$V s$
LHG7-1	1707.65	983.86	1.74	80.57	55.82	1699.50	917.55	9.48	12.17
L7	1853.85	1037.66	1.79	72.32	62.68	1892.13	1066.78	7.64	11.75
LL-LL	1931.99	1089.45	1.77	130.98	47.53	1909.72	1075.53	13.72	8.83
LL-YT	2009.65	1119.57	1.80	131.06	125.76	1905.09	1199.63	13.76	20.97
LL-ZJD	2127.75	1186.29	1.79	123.44	130.16	2169.67	1259.53	11.38	20.67
LL-SC	2364.17	1256.35	1.88	188.46	78.33	2448.00	1359.70	15.40	11.52
CC	2385.19	1267.68	1.88	134.29	61.41	2285.35	1183.59	11.75	10.38
YQ-5K	2593.36	1532.80	1.69	172.48	127.09	2451.81	1506.51	14.07	16.87
GJ	2347.41	1246.88	1.88	165.99	115.69	2459.08	1192.04	13.50	19.41

Tab.2 Test results of acoustic parameters of each dry sample

Sample ID	$V p$ at different S_w/(m·s^?1)						$V s$ at different S_w/(m·s^?1)
Sample ID	100%	80%	60%	40%	20%	0	100%	80%	60%	40%	20%	0
LHG7-1	2456	2090	1927	1724	1449	1423	1333	1245	1083	934	824	803
L7	2441	2148	1985	1642	1578	1502	1265	1188	1051	825	758	746
LL-LL	2595	2332	2270	1946	1791	1731	1358	1266	1159	1080	985	970
LL-YT	2657	2494	2212	2021	1927	1825	1443	1297	1263	1125	1085	985
LL-ZJD	2641	2401	2213	2133	2036	1990	1505	1343	1311	1259	1189	1150
LL-SC	2771	2585	2450	2364	2193	2148	1665	1580	1433	1353	1295	1247
CC	2622	2438	2232	2144	2076	2026	1485	1323	1282	1225	1197	1154
YQ-5K	2990	2821	2785	2706	2597	2548	1796	1704	1654	1583	1536	1514
GJ	2886	2712	2433	2176	2064	1911	1401	1357	1216	1088	1001	956

Tab.3 Acoustic velocities at different S_w of coal samples

Sample ID	Relative anisotropy of $V p$ at different S_w/(m·s^?1)						Relative anisotropy of $V s$ at different S_w/(m·s^?1)
Sample ID	100%	80%	60%	40%	20%	0	100%	80%	60%	40%	20%	0
LHG7-1	16.83	15.22	14.71	11.64	10.38	10.12	22.15	24.3	19.24	15.68	15.39	12.07
LL-ZJD	18.03	15.57	13.88	12.79	13.46	11.25	26.79	26.01	25.77	22.26	19.67	20.35
YQ-5K	20.98	19.21	17.33	16.98	14.53	14.07	25.04	22.65	20.52	16.7	18.73	15.46
GJ	19.77	17.44	17.03	15.58	13.87	13.39	28.86	27.48	25.87	23.69	20.46	18.39

Tab.4 Relative anisotropies at different S_w of coal samples containing gas-water

Fig.4 Correlation of (a) vitrinite reflectance and (b) density with wave velocity of coal samples.

Fig.5 Correlation of (a) vitrinite reflectance and (b) density with relative anisotropy and

V p

V s

ratio of coal samples.

Fig.6 Acoustic velocity variations of gas-water saturated coal samples. (a) P-wave; (b) S-wave.

Fig.7 Differences in

V p

V s

ratio of primary coal sample and tectonic coal sample.

Fig.8 Acoustic anisotropy variations of coal samples containing mixed-phase fluid.

Sample ID	Regression expression for 2A/B and S_w
Sample ID	$V p$	R²	$V s$	R²
LHG7-1	2A/B = 0.0730S_w + 9.4971	0.9355	2A/B = 0.1153S_w + 12.3748	0.8500
LL-ZJD	2A/B = 0.0590S_w + 11.2119	0.8436	2A/B = 0.0907S_w + 15.3157	0.8457
YQ-5K	2A/B = 0.0699S_w + 13.6876	0.9588	2A/B = 0.0782S_w + 19.5657	0.8551
GJ	2A/B = 0.0629S_w + 13.0329	0.9838	2A/B = 0.1080S_w + 18.7257	0.9759

Tab.5 Regression analysis results of acoustic anisotropy and water saturation

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