彭水及邻区龙马溪组页岩气常压形成机制

doi:10.13809/j.cnki.cn32-1825/te.2020.01.002

Abstract

Abstract:

The shale gas reservoirs in Longmaxi formation in Pengshui and its adjacent areas were overpressured in geological history, but nowadays they transformed into normal pressure. Through the simulation of formation pressure evolution in the uplifting process, it is revealed that Longmaxi shale was fractured under excessive pressure in this process, resulting in shale gas loss and therefore overpressure release. By overburden pressure permeability test, it is found that when the normal stress on the mudstone fracture surface of Longmaxi formation is more than 15 MPa, that is to say, when the buried depth is more than 1 000 m, the cracks will be closed, but the degree of fracture closure is affected by overconsolidation ratio（OCR） of shale. For the mudstone or shale under the brittle zones, OCR is relatively small, the closure degree of fracture is relatively high, the overpressure may not be completely released, and a certain degree of overpressure is still maintain. But for those above the brittle zones, the lager the OCR, the worse the fracture closure degree, and it is apt to cause the overpressure released completely, finally transit to normal pressure state. There is a significant correlation between OCR and the pressure coefficient of the formation fluid, that is, the higher the OCR ratio, the more normal the pressure will tend to be.

Key words: shale gas, normal pressure, overconsolidation ratio, brittleness, fracture closure

CLC Number:

TE122

YUAN Yusong,FANG Zhixiong,HE Xipeng,LI Shuangjian,PENG Yongmin,LONG shengxiang. Normal pressure formation mechanism of Longmaxi shale gas in Pengshui and its adjacent areas[J].Reservoir Evaluation and Development, 2020, 10(1): 9-16.

Figures/Tables 12

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References 26

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井名	现今埋深/m	最大古埋深/m	OCR	志留系压力系数实测值	志留系压力系数预测值	误差
PY1	2 153	6 243	2.70	0.96	1.05	0.09
HY1	2 162	6 461	3.00	1.01	0.99	0.02
PY3	3 021	6 216	2.10	1.05	1.21	0.16
DY1	2 050	5 045	2.50	1.15	1.10	0.05
LY1	2 832	5 831	2.10	1.20	1.21	0.01
SY1	3 467	5 462	1.57	1.30	1.43	0.13
NY1	4 405	5 700	1.29	1.40	1.59	0.19
JY1	2 409	5 708	2.20	1.45	1.18	0.27
JS1	4 985	6 904	1.40	1.67	1.52	0.15
DY2	4 359	6 354	1.27	1.78	1.61	0.17

井名	志留系底界最大埋深/m	志留系底界现今埋深/m	脆性带底界/m	保存条件
HY1	6 461	2 162	2 485	较差
PY1	6 243	2 153	2 401
DY1HF	5 545	2 050	2 132
LY1	5 831	2 832	2 242	较好
JY1	5 708	2 409	2 195	较好
DY2HF	6 354	4 359	2 443	好

岩样编号	长度/cm	直径/cm	温度/ ℃	气体黏度/（mPa·s）	造缝前渗透率/10^-3μm²	造缝后渗透率/10^-3μm²
泥-1	3.933	2.487	12	0.017 78	0.002 769	19.503
泥-2	3.239	2.490	12	0.017 78	0.003 701	33.433
泥-3	3.284	2.502	12	0.017 78	0.003 466	18.176
泥-4	2.544	2.493	12	0.017 78	0.003 687	23.588

泥-1		泥-2		泥-3		泥-4
围压/MPa	渗透率/10^-3 μm²	围压/MPa	渗透率/10^-3 μm²	围压/MPa	渗透率/10^-3 μm²	围压/MPa	渗透率/10^-3 μm²
1.00	19.503 000	1.0	33.433 00	1.0	18.176 000	1.0	23.588 000
3.20	9.889 109	9.05	5.639 825	5.4	7.249 812	10.1	12.915 430
5.15	4.742 773	11.5	3.237 930	8.35	2.961 592	12.2	9.766 560
7.15	3.837 527	14.0	1.447 781	11.2	1.574 693	15.2	6.350 846
10.25	2.090 685	19.9	0.443 591	15.2	0.785 671	20.6	2.338 490
15.40	0.832 936	25.2	0.220 236	20.1	0.395 021	25.5	1.168 620
24.98	0.248 925	29.9	0.130 036	25.2	0.238 413	30.4	0.646 946
34.70	0.093 078	39.4	0.056 493	29.9	0.153 105	38.9	0.263 671
44.00	0.042 680	49.8	0.026 599	39.4	0.068 022	50.0	0.108 952
59.50	0.016 512	58.0	0.016 027	50.2	0.032 018	60.0	0.056 485
				59.6	0.021 513

地层层位	样品编号	轴向应力/MPa	围压/MPa	温度/℃	峰值强度/MPa	弹性模量/GPa	泊松比	内聚力C/MPa	内摩擦角Φ/（°）
龙马溪组	1142-3	40.25	1.92	17	38.33	3.54	0.11	11.0	30.0
	1142-38	61.01	7.65	25	53.36	3.48	0.12
	1142-15	93.32	15.49	35	77.83	5.03	0.20
	1142-21	126.35	31.06	55	95.29	6.09	0.22
	1142-46	147.08	48.16	75	98.92	5.33	0.29

Normal pressure formation mechanism of Longmaxi shale gas in Pengshui and its adjacent areas

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