苏北盆地古近系阜宁组二段页岩油储层岩石力学特征及其控制因素

doi:10.11743/ogg20240214

Abstract

Abstract:

The study aims to determine the fracturability of shale oil reservoirs and post-fracturing variations in pores and fractures in the Subei Basin. The 2^nd member of the Paleogene Funing Formation （also referred to as the Fu 2 Member） is taken as an example to investigate the rock mechanics and fracturing performance and the relevant influencing factors. This process involves three steps： a. Three-dimensional （3D） reconstruction of rock samples using high-resolution computed tomography （i.e.， multi-scale CT scanning） to extract structural parameters of pores and fractures； b. Triaxial mechanical experiments under the confining pressure of the formation to obtain rock mechanical parameters； c. Multi-scale CT scanning of fractured rock samples at the same position and along the same direction to obtain an image of the post-fracturing 3D structures of pores and fractures. Based on the characteristics of stress-strain curves， shales in the study area are categorized into three types. Type 1 is characterized by rupture curves with a wavy downward trend， indicative of intricate post-fracturing reticular fractures. Type 2 shows various rupture curves with both wavy and vertical downward trends， indicating well-developed fracture networks after fracturing. Type 3 exhibits rupture curves with a vertical downward trend， suggesting relative intactness after fracturing with the formation of longitudinal splitting fractures rather than fracture networks. Post-fracturing changes in pores within the three types of shales are as follows. For the first and second types， pores with diameters ranging from 10 to 50 μm represent a decreased proportion， those with diameters between 50 and 100 μm show an increased proportion， and those larger than 300 μm in diameter make a greater contribution to the overall pore volume. In contrast， for the third type， pores with varying diameters demonstrate insignificant changes in proportion and contribution to the overall pore volume after fracturing. The study results reveal that the compressive strength positively correlates with the elastic and shear modulus and exhibits V-shaped relationship with Poisson’s ratio. The mechanical properties of shales in the study area are primarily governed by their carbonate and clay mineral contents， followed by their quartz and organic carbon contents. Furthermore， porosity and lamina development characteristics emerge as significant factors influencing the fracturability of shale reservoirs.

Key words: triaxial stress, CT scanning, rock mechanical parameter, stress-strain curve, reservoir type, shale oil, Paleogene, Subei Basin

CLC Number:

TE 122.2

Hequn GAO, Yuqiao GAO, Xipeng HE, Jun NIE. Rock mechanical properties and controlling factors for shale oil reservoirs in the second member of the Paleogene Funing Formation， Subei Basin[J]. Oil & Gas Geology, 2024, 45(2): 502-515.

Figures/Tables 14

Table 1

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Fig.9

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Fig.13

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井号	样品编号	层位	TOC/%	孔隙度/%	主要矿物含量/%
井号	样品编号	层位	TOC/%	孔隙度/%	石英	黏土矿物	钾长石	斜长石	黄铁矿	方解石	白云石	方沸石
QY1井	1-30	Ⅳ	2.5	1.9	41.5	25.9	0.8	4.2	2.5	21.0	2.4	—
	1-69	Ⅲ-3	1.7	0.9	24.9	17.9	0.6	7.1	1.8	44.7	1.9	—
	1-75	Ⅲ-3	1.5	0.7	26.8	11.3	0.7	6.2	1.7	50.5	1.9	—
	1-126	Ⅲ-1	0.5	5.9	14.5	24.0	1.7	8.8	4.2	5.3	30.4	11.1
	1-218	Ⅱ-2	0.7	3.4	10.2	19.0	0.7	3.7	1.8	0.9	58.6	5.1
	1-238	Ⅱ-1	0.4	4.5	18.2	22.2	1.4	11.4	1.8	15.3	27.6	2.1
	1-282	Ⅰ-8	1.2	1.6	18.4	21.0	2.2	18.9	0.5	12.0	26.4	0.6
	1-303	Ⅰ-7	0.6	3.6	25.1	13.6	1.9	14.3	2.8	10.2	31.2	0.9
	1-323	Ⅰ-6	0.4	5.3	27.1	15.1	0.7	4.5	1.4	48.7	1.5	—
	1-345	Ⅰ-5	1.3	3.1	24.7	23.6	2.7	12.9	2.0	2.8	30.4	0.9
	1-370	Ⅰ-4	1.9	2.9	16.3	12.0	1.5	33.8	5.6	2.7	26.9	1.2
	1-391	Ⅰ-3	0.6	5.0	29.2	28.0	2.8	18.3	3.1	10.0	6.3	2.3
	1-402	Ⅰ-2	0.3	7.1	29.1	31.9	3.3	11.2	1.9	11.1	9.9	1.6
	1-428	阜一段	0.5	—	31.1	44.5	2.0	4.5	1.5	6.0	8.4	2.0
	1-441	阜一段	0.1	1.4	38.9	20.5	2.7	15.0	—	14.2	6.9	1.8
QY2井	2-24	Ⅲ-3	2.2	7.1	27.8	39.4	1.8	3.9	5.6	1.2	18.6	—
	2-43	Ⅲ-2	0.7	3.2	38.9	15.5	8.1	14.5	1.3	10.9	8.7	2.1
	2-61	Ⅲ-1	0.7	3.5	27.9	21.2	2.4	10.8	2.1	6.8	11.4	17.4
	2-62	Ⅲ-1	0.3	4.6	24.0	25.0	2.4	6.6	0.5	6.8	14.9	19.8
	2-76	Ⅱ-4	2.2	—	7.8	6.5	0.1	9.5	1.0	68.0	5.9	1.2
	2-77	Ⅱ-4	1.0	4.9	21.1	31.5	1.6	—	1.8	17.2	21.9	4.9
	2-87	Ⅱ-3	1.6	4.0	15.1	13.4	1.0	5.4	2.9	4.5	56.7	1.0
	2-93	Ⅱ-3	0.8	5.1	27.2	20.7	2.9	11.1	2.2	13.6	20.3	2.0
	2-100	Ⅰ-6	0.4	—	19.2	28.0	1.9	4.9	2.2	8.7	20.5	14.6
	2-104	Ⅰ-6	0.9	4.1	28.7	31.0	2.3	14.0	1.4	7.3	7.1	8.2
	2-110	Ⅰ-5	0.8	4.8	22.6	28.2	3.1	12.5	2.3	6.3	17.6	7.4
	2-112	Ⅰ-4	0.9	4.9	20.9	34.2	2.0	11.5	2.7	6.7	14.1	7.9
	2-121	Ⅰ-4	2.0	2.0	26.1	39.8	2.5	14.5	2.5	3.2	10.0	1.4

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Rock mechanical properties and controlling factors for shale oil reservoirs in the second member of the Paleogene Funing Formation， Subei Basin

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