The Influence of Lamina Density and Occurrence on the Permeability of Lamellar Shale after Hydration

The characteristics of laminae in lamellar shale oil reservoirs have important influences on reservoir parameters, especially permeability. In order to explore the influence of lamina density and occurrence on the permeability of lamellar shale after hydration, we studied the lamellar shale in the Chang 7 member of the Yanchang Formation of Triassic in Ordos Basin. By comparing the permeability of bedding shale and lamellar shale with different densities of laminae, it was found that the permeability anisotropy of lamellar shale was stronger. In the direction parallel to the lamina, the permeability increased approximately linearly with an increase in lamina density. The effect of hydration on rock micropore structure and permeability was studied by soaking shale in different fluids. Most of the microfracture in the lamellar shale was parallel to the lamina direction, and hydration led to a widening of the microfracture, which led to the most obvious increase in permeability parallel to the lamina. Collectively, the research results proved that lamina density, occurrence, and hydration have a significant influence on the permeability anisotropy of lamellar shale.

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Characteristics of Hydration Damage and Its Influence on Permeability of Lamellar Shale Oil Reservoirs in Ordos Basin

Geofluids ◽

10.1155/2021/6646311 ◽

2021 ◽

Vol 2021 ◽

pp. 1-15

Author(s):

Pengfei Zhao ◽

Xiangyu Fan ◽

Qiangui Zhang ◽

Bowei Yao ◽

Mingming Zhang ◽

...

Keyword(s):

Pore Size ◽

Lamellar Structure ◽

Gas Permeability ◽

Drilling Fluid ◽

Ordos Basin ◽

Oil Reservoirs ◽

Rock Surface ◽

Shale Oil ◽

Direction Parallel ◽

Shale Oil Reservoirs

The continental shale oil reservoir has low permeability, high clay content, rich lamellar structure, and strong heterogeneity, which makes the reservoir vulnerable to hydration damage. In order to study characteristics of hydration damage and its influence on permeability of lamellar shale oil reservoirs, a series of experiments such as high-pressure mercury injection, steady gas permeability, rock thin section identification, and scanning electron microscope were carried out with the downhole core in Ordos Basin as the experimental object. The effects of water and water-based drilling fluid on pore size distribution, permeability, and rock microstructure were analyzed. Results show that the pore size of the reservoir is mainly nanoscale, and the pore size of shale changes most dramatically in the stage of hydration for 12-24 hours, while that of tuff changes most dramatically in 24-48 hours. The permeability increases rapidly with hydration time and then tends to be stable, among which the permeability of samples with lamellar structure in the direction parallel to the lamellar structure is most easily affected by hydration and changes fastest. Hydration leads to the formation of new pores, new fractures, and the expansion of existing fractures in rocks, especially in the strata containing large amounts of terrigenous clastic, lamellar structure, and pyrite. The new seepage channel increases the permeability of rock, and the soil powder and plugging particles in drilling fluid are easy to form protective mud cake in these places. These protective mud cakes not only change the microstructure of rock but also inhibit the influence of hydration on the pore space and permeability of rock, which play an effective role in preventing the mineral shedding on the rock surface, reducing the increase of micropores and delaying hydration.

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Evaluation Method of Shale Oil Reservoirs Fracability—A Case from Seventh Member of Triassic Yanchang Formation in Ordos Basin 2018 IFEDC

Proceedings of the International Field Exploration and Development Conference 2018 - Springer Series in Geomechanics and Geoengineering ◽

10.1007/978-981-13-7127-1_52 ◽

2019 ◽

pp. 573-587

Author(s):

L. B Dou ◽

H. Gao ◽

R. Wang ◽

K. Zhao

Keyword(s):

Evaluation Method ◽

Ordos Basin ◽

Oil Reservoirs ◽

Shale Oil ◽

Yanchang Formation ◽

Shale Oil Reservoirs

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Occurrence State of Soluble Organic Matter in Shale Oil Reservoirs from the Upper Triassic Yanchang Formation in the Ordos Basin, China: Insights from Multipolarity Sequential Extraction

Natural Resources Research ◽

10.1007/s11053-021-09959-6 ◽

2021 ◽

Author(s):

Shutong Li ◽

Shixiang Li ◽

Ruiliang Guo ◽

Xinping Zhou ◽

Yang Wang ◽

...

Keyword(s):

Organic Matter ◽

Ordos Basin ◽

Upper Triassic ◽

Oil Reservoirs ◽

Shale Oil ◽

Soluble Organic Matter ◽

Yanchang Formation ◽

Occurrence State ◽

The Ordos Basin ◽

Shale Oil Reservoirs

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The Effect of Hydration on Pores of Shale Oil Reservoirs in the Third Submember of the Triassic Chang 7 Member in Southern Ordos Basin

Energies ◽

10.3390/en12203932 ◽

2019 ◽

Vol 12 (20) ◽

pp. 3932 ◽

Cited By ~ 1

Author(s):

Pengfei Zhao ◽

Xiangyu Fan ◽

Qiangui Zhang ◽

Xiang Wang ◽

Mingming Zhang ◽

...

Keyword(s):

Drilling Fluid ◽

Ordos Basin ◽

Protective Layer ◽

Solid Particles ◽

Oil Reservoirs ◽

Shale Oil ◽

Clear Water ◽

The Third ◽

Initial Stage ◽

Shale Oil Reservoirs

Shale oil is an unconventional kind of oil and gas resource with great potential. China has huge reserves of shale oil, and shale oil resources are abundant in the third submember of the Triassic Chang 7 member in the southern Ordos Basin. At present, this area is in the initial stage of shale oil exploration and development. The reservoir pore is one of the key factors affecting oil accumulation, drilling safety, and oil production. It is also an important reservoir parameter that must be defined in the exploration stage. In general, the clay content in the shale section is high, and is prone to hydration. In order to study the effect of fluid on the pore type, structure, and distribution of shale oil reservoirs, experiments using X-ray diffraction, a porosity–permeability test, mercury porosimetry, rock casting thin section, and scanning electron microscopy were carried out. The experimental results show that the content of clay and quartz is very high in the studied formation. The pore porosity and permeability of the rock is highly heterogeneous because of the obvious stratigraphic bedding and interbeds. Microstructural observation of rocks shows that the main pore types are intergranular pores, intragranular pores, intercrystalline pores, and organic pores. Crack types are dissolution cracks, contraction cracks of organic matter, and abnormal pressure structural cracks. After hydration, the porosity of rock will increase in varying degrees, and pore size, pore content in different sizes, and pore structure will also change. The results show that the pores of tuff mainly changes at the initial stage of hydration, and the pore change of tuff is the most obvious within 6 hours of soaking in clear water. The influence of hydration on the pore of shale is greater than that of tuff, but the main change stage is later than tuff, and the pore change of shale is the most obvious within 12 to 24 hours of soaking in clear water. The soaking experiment of water-based drilling fluid (WBM-SL) shows that it can plug a certain size of holes and cracks and form a protective layer on the rock surface, thus effectively reducing hydration. In actual construction, multisized solid particles should be allocated in drilling fluid according to the formation pore’s characteristics, and the stability of the protective layer should be guaranteed. This can reduce the accident of well leakage and collapse and is conducive to the efficient and safe development of shale oil.

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