Prediction of permeability and its anisotropy of tight oil reservoir via precise pore-throat tortuosity characterization and “umbrella deconstruction” method

Abstract

A B S T R A C TThis study aimed to investigate the prediction method of permeability and its anisotropy of tight oil reservoir via precise pore-throat tortuosity characterization and "umbrella deconstruction" method combining the approaches of the field emission SEM imaging, high resolution image processing, fine and large-scale mathematical statistics, nonlinear regression and other technical means.In this paper, the authors proposed the new calculation model of pore-throat tortuosity, the absolute permeability and the permeability anisotropy based on the improved deep understanding of reservoir. Results of the prediction on the tight oil reservoir of "YANCHANG" formation in Ordos Basin show that the errors of the new method in this paper are the smallest among the total five methods, respectively 0.023 × 10 −3 μm 2 and 0.090 × 10 −3 μm 2 ; the average values of other four methods were 0.090 × 10 −3 μm 2 and 0.108 × 10 −3 μm 2 , respectively. The predicted results have higher accordance with the measured results, which proved the practicality of the new method. The samples has the highest permeability at the angle of 0°(180°/360°) and the permeability values are equal to 0.25 × 10 −3 μm 2 . Similarly, the sample has the lowest permeability at the angle of 22.5°(202.5°), 90°(270°), and 112.5°(292.5°), the permeability values are all equal to 0.06 × 10 −3 μm 2 . At the same time, the calculation of permeability anisotropy results shows that the anisotropy of tight oil reservoirs is very significant, and the permeability value in one direction is obviously higher than which in other directions.It is concluded that the precise description of pore throat geometry, especially the calculation of pore-throat tortuosity parameter, is one of the most important parameters affecting the prediction accuracy of permeability theoretically. Meanwhile, there are dominant seepage channels, which would play a very important guiding role in the prediction of hydrocarbon accumulation and seepage capacity.The conclusion will provide a more rigorous theoretical basis for the rapid and accurate evaluation of the physical properties of unconventional reservoirs. distortion of surface roughness into pore throat resulted in the underestimation of permeability. Arash et al. (2016) estimated three-dimensional coordination numbers from two-dimensional cross-sectional images and explored the error of absolute permeability prediction using pore network flow model. An et al. (2016) studied the effects of pore throat ratio, coordination number and pore throat orientation on absolute permeability using a regular network model. Shah et al. (2016) predicted the properties of pore network, such as the number of pore and throat, average pore throat radius and coordination number, and used Lattice Boltzmann (LBM) or pore network (PNM) modeling to simulate single-phase and dual-phase flow. Three-dimensional core image can be obtained after CT scanning, and digital core can be built after filtering and segmentation. Yang et al. (2016) gets the rock

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“…The tortuosity value can be a fitting parameter or taken from literature data. For this study, a tortuosity of 2.0 was assumed initially, as tight carbonates are slightly less tortuous than tight sandstones (Cai et al 2019) with typical values of 2.1 (Du 2019).…”

Nano-Scale Pore Structure and Its Multi-Fractal Characteristics of Tight Sandstone by N2 Adsorption/Desorption Analyses: A Case Study of Shihezi Formation from the Sulige Gas Filed, Ordos Basin, China

“…Energy sources around the world have been changing from solid (firewood and coals) and liquid (petroleum) states to gas state (natural gas) [1], where tight sandstone reservoirs have been playing an important role and exploited industrially in many countries as an effective storage of natural gas, which is a complicated porous material with a highly heterogeneous nanopore structure [2][3][4][5][6][7][8]. Owing to the complexity of the its pore-throat system, pore structure and its fractal characteristics analysis become the core work of reservoir quality evaluation, which includes the research content of specific surface area (SSA), pore volume (PV), pore size distribution (PSD), pore morphology, and anisotropy [9][10][11].…”

A parametric study to numerically analyze the formation damage effect

“…The following parameters were estimated according to the FE-SEM; cement content, porosity, and reservoir fractal dimension are such the essential parameters. Hence, this method would be of significance to estimate the unconventional reservoir characteristics in microscopic scale which would be a beneficial tool for estimating formation damage effect (Du, 2019; Du et al., 2018b).…”