Quantitative identification of diagenetic facies and controls on reservoir quality for tight sandstones: A case study of the Triassic Chang 9 oil layer, Zhenjing area, Ordos Basin

Quantitative characterization of diagenetic facies has great significance for reservoir evaluation and prediction. In order to find out the method to evaluate diagenetic facies, the author took Chang 82 reservoir low-permeability sandstone in Zhenbei area of Ordos basin as research object and divided the reservoir into six types of diagenetic facies by analysis of casting thin section, scanning electron microscope, cathode luminescence, and physical property. According to 14 quantitative evaluating parameters which were related with petrology characteristic, diagenesis strength, pore structure, etc. quantitative evaluation of diagenetic facies of low-permeability sandstone reservoir was done by data envelopment analysis. The result showed that in the Chang 82 reservoir low-permeability sandstone in Zhenbei area of Ordos basin, quantitative representative indexes of diagenetic facies ranged from 0 to 1.00. Various diagenetic facies and their indexes had interval corresponding relation. The diagenetic facies of weak corrosion with chlorite mat and the diagenetic facies of corrosion of unstable components had the best reservoir quality. Their diagenetic facies indexes ranged from 0.66 to 1.00. The reservoir quality of the diagenetic facies filled with kaolinite was not as good as the former. The indexes ranged from 0.50 to 0.66. The diagenetic facies of quartz secondary enlargement and the diagenetic facies of clay mineral cementation replacement had poor reservoir quality. Their diagenetic facies indexes ranged from 0.30 to 0.40. The diagenetic facies of carbonate cementation had the poorest reservoir quality. It hardly possessed fluid storage capability. After comparing diagenetic facies indexes, absorption strength and remaining oil saturability, the perfect corresponding relation between quantitative evaluation results and reservoir quality could be verified.

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The impacts of diagenetic facies on reservoir quality in tight sandstones

Open Geosciences ◽

10.1515/geo-2020-0174 ◽

2020 ◽

Vol 12 (1) ◽

pp. 1060-1082

Author(s):

Dazhong Ren ◽

Liang Sun ◽

Rongxi Li ◽

Dengke Liu

Keyword(s):

Pore Structure ◽

Ordos Basin ◽

Source Rocks ◽

Reservoir Quality ◽

Carbonate Content ◽

Porosity Evolution ◽

Carbonate Cement ◽

Pore Structures ◽

Diagenetic Facies ◽

The Impact

AbstractThe impact of diagenetic minerals and the characteristics of pore structures on reservoir qualities has been studied separately in the past years. However, the difference in the reservoir quality with different pore structures and having same or similar content of diagenesis minerals has not been ascertained. In this study, based on the core samples derived from Chang 6 member in the Ordos basin, various tests were performed to examine the sandstone diagenesis and investigate the pore structure. The results showed that there were five diagenetic facies by diagenetic and pore structure analyses, and the best reservoir quality rocks were found to have relatively low percentage of illite, carbonate cement, pore-filling chlorite, authigenic quartz, and relatively high proportion of intergranular pores. Smectite-to-illite reaction and chemical compaction were main sources for quartz cementation at 60–120°C, and carbonate content was found to increase toward source rocks. The porosity depth trends significantly affected the diagenetic facies. The diagenetic and the pore structure pathways of various diagenetic facies were reconstructed by integrated petrographic, mineralogical, and pore system data. This study provides insights into the porosity evolution and diagenetic pathways of various diagenetic facies of tight sandstones, and the influence of diagenesis minerals and pore structures on their reservoir quality.

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Classification and evaluation of tight sandstone reservoirs based on diagenetic facies: a case study on Chang 6 reservoir in the center-west Ordos Basin

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-021-01383-z ◽

2021 ◽

Author(s):

Gao Zhanwu ◽

Shi Jian ◽

Xie Qichao ◽

Zhou Yan ◽

Zhou Shuxun

Keyword(s):

Ordos Basin ◽

Quality Analysis ◽

Reservoir Quality ◽

Tight Sandstone ◽

Pore Evolution ◽

Sandstone Reservoirs ◽

Four Levels ◽

Comprehensive Classification ◽

Diagenetic Facies ◽

Feldspar Dissolution

AbstractTight sandstone reservoirs dominated by are developed in the Chang 6 oil layer group of the Yanchang Formation in the central-western part of the Ordos Basin. Featuring the lacustrine delta facies, Chang 6 formation in the center-west area of Ordos Basin shows an increasing petroleum reserve expectation. Its exploitation practice, however, has many problems caused by tight sandstone reservoir features. According to diagenetic and pore analysis, the diagenetic facies in the study area are grouped into four types: chlorite-film-intergranular-pore, feldspar-dissolution, clay-cemented-micropore, carbonate-cemented-tightness for their obvious differences in mineral feature and pore evolution. By introducing the comprehensive classification parameter synthesized from 9 other parameters, the reservoir quality is divided up into four levels: I(Feci > 1), II(3 ≤ Feci ≤ 7), III(-2 ≤ Feci ≤ 3), IV(Feci ≤ -2). The reservoir quality division matches well with the diagenetic facies group. To decide the diagenetic type and reservoir quality division in all wells, the logging data are utilized with the Fisher discriminant method, which has obtained a good performance. The method enables the reservoir quality analysis expanding to all wells from samples, which is helpful for exploitation of the study area.

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