State Key Laboratory of Oil and Gas Geology and Exploitation

Chengdu, China

State Key Laboratory of Oil and Gas Geology and Exploitation

Chengdu, China
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Liu H.,State Key Laboratory of Oil and Gas Geology and Exploitation
Journal of Applied Geophysics | Year: 2017

The road to understanding the frequency dispersion (relaxation) of permittivity and resistivity in tight rocks remains relatively uncharted. Our team from Da'anzhai Group, Jurassic formation, Sichuan Basin carried out practical research to explore this phenomenon. The research was conducted under laboratory conditions for a selection of low frequencies, with ranges between 0.1 Hz to 1 kHz. Our research has shown that, although both the permittivity and resistivity decrease as the frequency increases, the two individual metrics display different behaviours when compared with each other. While the degree of resistivity variation is minimal, to the point that it is redundant, the permittivity, on the other hand, demonstrates something that is scientifically noteworthy. Permittivity has a distinctive dispersion degree across the entire sample of frequencies and the difference between the minimum and maximum frequencies is several orders of magnitude. An additional, and unexpected, learning from our research is that the level of frequency dispersion increases as the water saturation and concentration increases. In this paper, a collection of equations has been formulated to describe this relationship. These equations particularly shed light on the areas of rock porosity and saturation. They also show that the degree of frequency dispersion of permittivity or resistivity can be used as a function of water saturation and concentration. Two new variables are introduced here, DR and DC, to demonstrate the relaxation law quantitatively. In our practical research, we have characterised the relationship between the saturation and concentration with dielectric relaxation, using three different concentrations of DR and DC and five different saturations of NaCl solution. In difference to conventional Archie's multiple experimental parameters, we have established a new formula to derive the saturation from Rp and Cp, or from DR and DC directly. Two important frequencies were also further investigated for Cp dispersion: first is the critical frequency, which marks the dispersion speed change from steep phase to steady phase, and second is the zero-frequency, which marks the dispersion when it approaches zero. All tight rocks were measured under the same conditions, with the results displaying the same pattern of variations. The results have led us to believe that Cp's frequency dispersion at low-frequencies provides a new methodology to characterise tight rocks. © 2017 Elsevier B.V.


Liu H.,Key Laboratory of Oil and Gas Geology of Sichuan Province | Liu H.,Southwest Petroleum University | Liu H.,Petrochina | Luo S.,Key Laboratory of Oil and Gas Geology of Sichuan Province | And 12 more authors.
Petroleum Exploration and Development | Year: 2015

Based on newly drilled well data in the Gaoshiti area in the central Sichuan Basin, profile data of more than 150 field outcrops of the regional geological survey, and stratigraphic division and correlation of more than 30 wells in the Sichuan Basin and its adjacent areas, combined with regional seismic data, moldic methods are comprehensively used to restore the karst paleogeomorphy of the Dengying Formation, and thus studying the paleogeographic pattern and the significance of oil and gas exploration. The Sichuan Basin was surrounded by paleo-lands/underwater highlands in the late Sininan Dengying period, including Kangdian paleo-land in the west, Songpan paleo-land in the northwest, Hannan paleo-land in the north, Qianjiang-Zheng'an, Zhenba and Wuxi-Jianshi underwater highlands in the southeast and northeast. The Sichuan Basin was adjacent to Jiangnan Basin southeastwards and Qinling paleo-ocean northeastwards respectively. Affected by the separation of NS-striking Zitong-Junlian Aulacogen, NE-striking Langzhong-Tongjiang and Chongqing-Kaixian depressions in this basin, the Sichuan Basin presents the NS-trending framework of "three uplifts (Zhenba, Chuanzhong and Qianjiang-Zheng'an) and two depressions (Langzhong-Tongjiang and Chongqing-Kaixian)", and is divided into two relatively isolated EW-trending paleo-uplift systems (NS-striking Mianyang-Leshan-Xichang paleo-uplift and nearly NE-striking Chuanzhong paleo-uplift). Controlled by karst paleogeomorphy of the Sinian Dengying Formation, the pattern of karst landscape consists of five secondary geomorphic units, such as karst highland, karst platform, karst slope, karst depression and karst basin, of which the karst platform and karst slope are the favorable zones for the development of karst reservoirs, providing advantages for the formation of large gas fields. © 2015 Research Institute of Petroleum Exploration & Development, PetroChina.

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