Pore-throat radius and tortuosity estimation from formation resistivity data for tight-gas sandstone reservoirs

Petrophysical rock classification is an important component of the interpretation of core data and well logs acquired in complex reservoirs. Tight-gas sandstones exhibit large variability in all petrophysical properties due to complex pore topology resulting from diagenesis. Conventional methods that rely dominantly on hydraulic radius to classify and rank reservoir rocks are prone to rock misclassification at the low-porosity and low-permeability end of the spectrum. We introduce a bimodal Gaussian density function to quantify complex pore systems in terms of pore volume, major pore-throat radii, and pore-throat radius uniformity. We define petrophysical dissimilarity (referred to as orthogonality) between two different pore systems by invoking the classic “bundle of capillary tubes” model and subsequently classify rocks by clustering an orthogonality matrix constructed with all available mercury injection capillary pressure data. The new method combines several rock textural attributes including porosity, pore-throat radius, and tortuosity for ranking reservoir rock quality in terms of flow capacity. We verify the new rock classification method with field data acquired in the Cotton Valley tight-gas sandstone reservoir located in the East Texas basin. The field case shows that the new method consistently identifies and ranks rock classes in various petrophysical data domains, including porosity-permeability trends, pore-size distribution, mercury injection capillary pressure, and NMR transverse relaxation time ([Formula: see text]) spectra. Relative permeability curves, which are difficult to measure in the laboratory for tight rocks, are quantified with Corey-Burdine’s model using the bimodal Gaussian pore-size distribution and are validated with core data.

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Drainage Efficiency in Naturally Fractured Tight Gas Sandstone Reservoirs

10.2118/39974-ms ◽

1998 ◽

Cited By ~ 1

Author(s):

H. Harstad ◽

L.W. Teufel ◽

J.C. Lorenz

Keyword(s):

Tight Gas ◽

Naturally Fractured ◽

Sandstone Reservoirs ◽

Tight Gas Sandstone

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Experimental determination of dynamic pore-throat structure characteristics in a tight gas sandstone formation with consideration of effective stress

Marine and Petroleum Geology ◽

10.1016/j.marpetgeo.2019.104170 ◽

2020 ◽

Vol 113 ◽

pp. 104170 ◽

Cited By ~ 7

Author(s):

Guangfeng Liu ◽

Hang Yin ◽

Yifei Lan ◽

Shixiang Fei ◽

Daoyong Yang

Keyword(s):

Experimental Determination ◽

Effective Stress ◽

Tight Gas ◽

Pore Throat ◽

Structure Characteristics ◽

Sandstone Formation ◽

Tight Gas Sandstone

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Microscale Pore Throat Differentiation and Its Influence on the Distribution of Movable Fluid in Tight Sandstone Reservoirs

Geofluids ◽

10.1155/2021/6654773 ◽

2021 ◽

Vol 2021 ◽

pp. 1-7

Author(s):

Fengjuan Dong ◽

Xuefei Lu ◽

Yuan Cao ◽

Xinjiu Rao ◽

Zeyong Sun

Keyword(s):

Ordos Basin ◽

Pore Throat ◽

Tight Sandstone ◽

Throat Radius ◽

Thin Sections ◽

Small Pore ◽

Sandstone Reservoir ◽

Sandstone Reservoirs ◽

Classification Evaluation ◽

Better Than

Tight sandstone reservoirs have small pore throat sizes and complex pore structures. Taking the Chang 6 tight sandstone reservoir in the Huaqing area of the Ordos Basin as an example, based on casting thin sections, nuclear magnetic resonance experiments, and modal analysis of pore size distribution characteristics, the Chang 6 tight sandstone reservoir in the study area can be divided into two types: wide bimodal mode reservoirs and asymmetric bimodal mode reservoirs. Based on the information entropy theory, the concept of “the entropy of microscale pore throats” is proposed to characterize the microscale pore throat differentiation of different reservoirs, and its influence on the distribution of movable fluid is discussed. There were significant differences in the entropy of the pore throat radius at different scales, which were mainly shown as follows: the entropy of the pore throat radius of 0.01~0.1 μm, >0.1 μm, and <0.01 μm decreased successively; that is, the complexity of the pore throat structure decreased successively. The correlation between the number of movable fluid occurrences on different scales of pore throats and the entropy of microscale pore throats in different reservoirs is also different, which is mainly shown as follows: in the intervals of >0.1 μm and 0.01~0.1 μm, the positive correlation between the occurrence quantity of movable fluid in the wide bimodal mode reservoir is better than that in the asymmetric bimodal mode reservoir. However, there was a negative correlation between the entropy of the pore throat radius and the number of fluid occurrences in the two types of reservoirs in the pore throat radius of <0.01 μm. Therefore, pore throats of >0.1 μm and 0.01~0.1 μm play a controlling role in studying the complexity of the microscopic pore throat structure and the distribution of movable fluid in the Chang 6 tight sandstone reservoir. The above results deepen the understanding of the pore throat structure of tight sandstone reservoirs and present guiding significance for classification evaluation, quantitative characterization, and efficient development of tight sandstone reservoirs.

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