Reservoir Characteristics of the Paleogene Mixed Carbonate-siliciclastic Rock or Succession and Its Influencing Factors in the Shizigou Area of the Western Qaidam Basin

Abstract

Abstract:

Western Qaidam Basin belongs to the sedimentary center of the saline lake basin in Qaidam Basin. Salinization stage of the western Qaidam Basin lasts for a long time, and the lake basin is widely distributed. Therefore the Oligocene lacustrine carbonate rock has great exploration potential. Based on core observation, rock slice identification, and the analysis of scanning electron microscope and electron spectrum of the samples of Shizigou area, the features of reservoir lithology,reservoir physical property and reservoir space are studied, and reservoir influential factors and forming mechanism are analyzed. The main conclusions are as follows. (1) The reservoir has characters of mixed deposit. The mineral composition is mainly carbonate and clastic grain, but neither of relative content is over 50%. The genetic type of mixed carbonate-siliciclastic rock or sucession is facies mixed. Fabric mixed is the main type, layer series mixed is the second type, and a few biological mixed type is found. The samples generally contain saline minerals. (2) The results of physical property analysis and X diffraction components testing show that the reservoir is super-low permeable and super-low porous, and its connectivity is poor. The content of carbonate rock composition is in the range of 10.9% to 47.0%, with an average of 32.1%. At the same time, porosity and carbonate content have a good positive correlation. (3) The reservoir space of the samples is mainly saline mineral dissolved pore, dolomite intercrystal pore and fracture. (4) The diagenesis of the reservoir is mainly cementation and dolomitization. Especially the cementation of the saline minerals suppresses the later diagenesis, forming local high pressure. The important conditions of dolomitization are high carbonate content and saline environments. The compaction of reservoir is weak. The reservoir experiences two cementation periods. The saline minerals which cementated in the later period are the main dissolution parts.

Key words: Shizigou of the western Qaidam Basin, saline mineral, mixed carbonate-siliciclastic rock or succession, reservoir influencing factor

CLC Number:

TE122.2

ZHANG Shiming, ZHANG Xiaojun, ZHANG Tingjing, WANG Pu, NAN Xixiang, GOU Yingchun. Reservoir Characteristics of the Paleogene Mixed Carbonate-siliciclastic Rock or Succession and Its Influencing Factors in the Shizigou Area of the Western Qaidam Basin[J]. Geoscience, 2017, 31(05): 1059-1068.

Figures/Tables 9

Fig.1 Structure sketch of Shizigou area, western Qaidam Basin

Fig.2 Comprehensive column of Paleogene in Shizigou area

Fig.3 Triangular diagram of mineral contents of Oligocene reservoir in Shizigou area

Table 1 The result of X-ray diffraction mineral contents of Oligocene reservoir in Shizigou area

样品号	深度/m	岩性	矿物含量/%
样品号	深度/m	岩性	石英	钾长石	斜长石	方解石	白云石	菱铁矿	菱镁矿	石盐	黄铁矿	重晶石	角闪石	硬石膏	钙芒硝	铁白云石	黏土矿物
Shi38-1	2 794.62	含膏粉砂、泥质白云岩	14.8	0.9	6.5	8.4	16.2			0.6	2.4			4.1	2.8	17.5	25.8
Shi38-2	2 796.52	含膏粉砂岩	37.5	7.2	14.7	5.8			0.5	2.6	1.4	1.1	0.9	8.5	4.8	5.1	9.9
Shi38-3	2 796.92	泥质灰岩	10.7	1.1	7.1	12.3	9.8	17.2		0.7	1.6			2.8	1.2	9.4	26.1
Shi38-4	2 800.72	云质灰岩	11.4	1.2	8.4	28.2		6.7		0.5	2.5			3.7	1.1	18.8	17.5
Shi38-5	3 145.86	含膏粉砂质灰岩	11.7	1.1	11.9	35.0	3.3	11.5		0.5	2.8			3.5	3.8		14.9
Shi38-6	3 146.36	含膏泥、粉砂质白云岩	12.8	1.3	8.1	7.7				5.9	8.3			1.1	6.9	31.6	15.7
S37-chc-12	2 692.02	灰质泥岩	12.6	1.1	8.9	25.0				1.1	2.7		1.2	0.9	1.8	17.8	27.0
S37-chc-13	2 697.07	膏质含云粉砂岩	22.9	1.5	11.3	2.7		5.4		1.3	1.7			7.8	19.3	14.9	11.4
S25-chc-1	3 961.39	含膏云质灰岩	11.7	1.6	8.0	7.9	11.6	13.6		0.6	2.9			6.2	13.7	8.4	13.9
S25-chc-2	3 996.71	粉砂质白云岩	11.3	2.4	8.3	4.8	36.6	3.1		0.6	1.4			16.0	11.0		4.6
S37-45	2 695.83	含膏粉砂岩	39.6	3.4	14.4	5.6				3.4	2.1		2.3	4.3	4.4	8.5	12.0

Fig.4 Pore characteristics of Oligocene mixed carbonate-siliciclastic rock or succession in Shizigou of the western Qaidam Basin

Fig.5 Fracture microphotographs of Oligocene mixed carbonate-siliciclastic rock or succession in Shizigou of the western Qaidam Basin

Table 2 Property analysis of Oligocene samples in Shi-zigou area

序号	样号	岩性	深度/m	层位	孔隙度/%	渗透率/ 10^-3μm²
1	S37-chc-12	灰质泥岩	2 692.02	$E 3 2$	13.89	0.013
2	S37-45	含膏粉砂岩	2 695.83	$E 3 2$	3.43	0.009
3	S37-48	含膏粉砂岩	2 696.48	$E 3 2$	13.10	0.006
4	Shi38-2	含膏粉砂岩	2 796.52	$E 3 2$	1.30	0.001
5	Shi38-3	泥质灰岩	2 796.92	$E 3 2$	1.65	0.000 1
6	S25-chc-1	含膏云质灰岩	3 961.39	$E 3 2$	4.45	0.038
7	S25-chc-2	粉砂质白云岩	3 996.71	$E 3 2$	4.49	0.002
8	S23-chc-2	灰质泥岩	4 039.90	$E 3 2$	4.64	0.003
9	S15-chc-3	细砂岩	4 074.60	$E 3 1$	1.62	0.003

Table 2 Property analysis of Oligocene samples in Shi-zigou area

序号	样号	岩性	深度/m	层位	孔隙度/%	渗透率/ 10^-3μm²
1	S37-chc-12	灰质泥岩	2 692.02	$E 3 2$	13.89	0.013
2	S37-45	含膏粉砂岩	2 695.83	$E 3 2$	3.43	0.009
3	S37-48	含膏粉砂岩	2 696.48	$E 3 2$	13.10	0.006
4	Shi38-2	含膏粉砂岩	2 796.52	$E 3 2$	1.30	0.001
5	Shi38-3	泥质灰岩	2 796.92	$E 3 2$	1.65	0.000 1
6	S25-chc-1	含膏云质灰岩	3 961.39	$E 3 2$	4.45	0.038
7	S25-chc-2	粉砂质白云岩	3 996.71	$E 3 2$	4.49	0.002
8	S23-chc-2	灰质泥岩	4 039.90	$E 3 2$	4.64	0.003
9	S15-chc-3	细砂岩	4 074.60	$E 3 1$	1.62	0.003

Fig.6 Main diagenesis of Oligocene mixed carbonate-siliciclastic rock or succession and its effects on reservoir in Shizigou of the western Qaidam Basin

Fig.7 Diagenetic phenomenon microphotographs of Oligocene mixed carbonate-siliciclastic rock or succession in Shizigou of the western Qaidam Basin

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