Geological Significance and Logging Identification of Triassic and Jurassic Unconformity in Dingbian-Jingbian, Ordos Basin
The Triassic and Jurassic unconformity face has an important influence on low permeability reservoirs above Chang3. At present, core observation, core geochemical analysis, conventional logging and seismic methods are the most commonly used methods to identify unconformity. However, the cost of core...
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| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | zho |
| Published: |
Editorial Office of Well Logging Technology
2023-10-01
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| Series: | Cejing jishu |
| Subjects: | |
| Online Access: | https://www.cnpcwlt.com/#/digest?ArticleID=5532 |
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| Summary: | The Triassic and Jurassic unconformity face has an important influence on low permeability reservoirs above Chang3. At present, core observation, core geochemical analysis, conventional logging and seismic methods are the most commonly used methods to identify unconformity. However, the cost of core and core geochemical analysis is high, the sampling degree is high, and the longitudinal resolution of seismic methods is low. It restricts the accurate identification of unconformity. Therefore, the conventional logging response characteristics of unconformity surface are clarified by combining core observation, analysis and testing data with logging data, and the unconformity interface is determined based on principal component analysis. the thickness of weathered and semi-weathered zones on the unconformity of the Triassic and Jurassic in Dingbian-Jingbian area is about 15m, and the weathering of rocks in the strata above 15m below the unconformity interface is very weak or no weathering. Conventional logging parameters such as natural gamma ray, spontaneous potential, sonic time difference, compensated neutron and compensated density can be used to identify weathered strata, semi-weathered strata and unweathered strata by principal component analysis, so as to determine the unconformity interface. The results show that, the unconformity of different palaeogeomorphic units in the Dingbian-Jingbian area of the Jurassic was mainly caused by water intakes, and a complete three-layer unconformity structure was usually developed in the bevel and slope. Weathering or erosion products are not easy to preserve in the highlands and river valleys, generally there is a lack of weathered clay layer, and mainly eluviated sediments and semi-weathered rocks. At the same time, the bevel is the key position to control oil and gas enrichment. The study of the unconformity during Triassic and Jurassic is of significance to the analysis of oil and gas distribution and the prediction of favorable areas in Chang3 and Yan9 member. |
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| ISSN: | 1004-1338 |