Pore Throat Structures and Fluid Occurrences of Reservoirs in Fengcheng Formation, Mahu Sag

doi:10.7657/XJPG20240305

Abstract

Abstract:

In order to reveal and compare the microstructures of sandstone and shale reservoirs, and the fluid occurrences within different sizes of pores in the Fengcheng formation of the Mahu sag, the experiments including high-pressure mercury intrusion (HPMI), nuclear magnetic resonance (NMR), and large-view splicing SEM were conducted to quantitatively characterize the pore throat size and fluid occurrence characteristics of the two types of reservoirs. The NMR experimental results and the HPMI experimental results before and after extraction of the original samples and the pressurized oil-saturated sample were compared to reveal the distributions of bound and movable fluids within pores of different sizes. The results indicate that sandstone and shale do not differ significantly in the sizes of pores and throats, which are dominantly 0.01-10.00 μm in pore diameter and <10.00 nm in throat radius, respectively, indicative of mesopores and fine throats. Shale has slightly larger pore diameters but smaller throat radii than sandstone. Shale mainly develops tubular pores such as intercrystalline pores and honeycomb-like dissolution pores. Sandstone has an equal distribution of tubular and spherical pores, with the proportion of spherical pores such as intergranular pores and intergranular dissolution pores increasing as the pore size increases. Fluid occurrence and mobility are controlled by multiple factors such as mineral composition and pore size. The oil-wet properties of organic matter, dolomite and pyrite, and the strong capillary confinement of intergranular pores in clay minerals, reduce the mobility of shale oil, and the movable fluids are mainly distributed in mesopores-macropores with diameters greater than 300 nm. Combining the reservoir physical properties and movable fluid distribution, it is determined that the favorable shale oil block in the study area is the Ma 51X well block, both shale and sandstone in the well block are favorable targets for development.

Key words: Mahu sag, Fengcheng formation, reservoir, shale oil, pore throat structure, fluid occurrence

CLC Number:

TE122

ZHU Yue, WU Shunwei, DENG Yusen, LIU Lin, LEI Xianghui, NIU Youmu. Pore Throat Structures and Fluid Occurrences of Reservoirs in Fengcheng Formation, Mahu Sag[J]. Xinjiang Petroleum Geology, 2024, 45(3): 286-295.

Figures/Tables 11

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Table 2.

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样品编号	井名	深度/ m	岩性	孔隙度/ %	渗透率/ mD	大视域电镜扫描	高压压汞	核磁共振
1	夏203井	4 711.6	极细粒长石砂岩	3.900	0.032		√	√
2	夏203井	4 711.5	极细粒长石砂岩	2.500	0.029		√	√
3	夏203井	4 729.6	极细粒长石砂岩	4.900	0.050		√	√
4	夏203井	4 718.5	白云质泥页岩	6.300	0.053		√	√
5	夏203井	4 721.3	砂质泥页岩	2.300	0.016		√	√
6	夏203井	4 881.0	白云质泥页岩	5.700	0.030		√	√
7	夏203井	4 812.0	石灰质泥页岩	6.900	0.040		√	√
8	夏203井	4 746.7	极细粒长石砂岩	2.600	0.021		√	√
9	夏203井	4 740.8	砂质泥页岩	1.900	0.007	√		√
10	玛页1H井	4 564.1	白云质泥页岩	1.100	0.001			√
11	玛页1H井	4 572.1	白云质泥页岩	1.900	0.009		√	√
12	玛49井	4 669.6	极细粒长石砂岩	1.940	0.005		√	√
13	玛49井	4 821.2	极细粒长石砂岩	2.900	0.010	√	√	√
14	玛51X井	4 997.1	含白云石粉砂岩	3.700	0.024		√	√
15	玛51X井	4 998.0	砂质泥页岩	3.745	0.020		√	√
16	玛56X井	5 948.6	含白云石泥页岩	7.400	0.060		√	√
17	玛56X井	5 950.1	含白云石泥页岩	3.800	0.055		√	√

样品编号	井名	岩性	束缚油占比/ %	可动流体占比/%
1	夏203井	极细粒长石砂岩	83	31
2	夏203井	极细粒长石砂岩	83	25
3	夏203井	极细粒长石砂岩	88	33
4	夏203井	白云质泥页岩	72	37
5	夏203井	砂质泥页岩	91	33
6	夏203井	白云质泥页岩	69	54
7	夏203井	石灰质泥页岩	20	56
8	夏203井	极细粒长石砂岩	88	36
9	夏203井	砂质泥页岩	52	11
10	玛页1H井	白云质泥页岩	95	22
11	玛页1H井	白云质泥页岩	92	21
12	玛49井	极细粒长石砂岩	34	38
13	玛49井	极细粒长石砂岩	57	72
14	玛51X井	含白云石粉砂岩	32	44
15	玛51X井	砂质泥页岩	61	45
16	玛56X井	含白云石泥页岩	93	18
17	玛56X井	含白云石泥页岩	91	36