4.6 Article

Restoration of formation processes of dolomite reservoirs based on laser U-Pb dating: A case study of Ordovician Majiagou Formation, Ordos Basin, NW China

Journal

PETROLEUM EXPLORATION AND DEVELOPMENT
Volume 49, Issue 2, Pages 327-338

Publisher

KEAI PUBLISHING LTD
DOI: 10.1016/S1876-3804(22)60027-2

Keywords

U-Pb dating; Ordos Basin; Ordovician; Majiagou Formation; diagenesis; dolomitization; porosity evolution

Funding

  1. National Science and Technology Major Project of China [2016ZX05004-002]
  2. PetroChina Science and Technology Project [2016E-05-14, 2021DJ0503]

Ask authors/readers for more resources

By studying two types of dolomite reservoirs in the Ordos Basin, we found that different diagenetic processes and fillings led to changes in reservoir porosity, which is of great significance for the restoration of porosity evolution in other basins or series of strata.
To address the issue of non-unique interpretation of dolomite reservoir diagenetic and porosity evolution in the previous qualitative or semi-quantitative studies, we investigate two dolomite reservoir types, i.e. weathering-crust karstic reservoirs and mound-beach reservoirs, in the Ordovician Majiagou Formation, Ordos Basin by using in-situ laser ablation U-Pb dating as well as carbon and oxygen isotopic composition analysis. The results show that: (1) According to the dating of 8 reservoir samples, the Majiagou Formation experienced 5 diagenetic stages (Stage 1: deposition of matrix dolomite or penecontemporaneous dolomitization, in 444.0-494.0 Ma; Stage 2: dogtooth- or blade-shaped dolomite cementation, in 440.0-467.0 Ma; Stage 3: dolomitic silt filling, in 316.5-381.0 Ma; Stage 4: crystalline dolomite filling, in 354.0 Ma; Stage 5: crystalline calcite filling, in 292.7-319.0 Ma). (2) Supra-salt weathering-crust karstic dolomite reservoirs went through several diagenetic processes including penecontemporaneous dolomitization, compaction, weathering-crust karstification, packing, and rupturing in succession. Gypsum mold pores formed in the phase of hypergenic karstification and were filled with such minerals as dolomitic silts and calcites, and thus the porosity decreased from 10%-40% to 3%-8 %. (3) Sub-salt mound-beach dolomite reservoirs went through the diagenetic processes including backflow dolomitization, packing, and rupturing. The porosity of reservoirs was originally 10%-30 %, decreased to 0-6% due to seawater cementation, rose back to 5%-15% owing to penecontemporaneous corrosion, and finally declined to 2%-6% as a result of crystalline dolomites and calcites packing. The above methodology for the restoration of dolomitization and porosity evolution may be helpful for the restoration of porosity evolution in other basins or series of strata.

Authors

I am an author on this paper
Click your name to claim this paper and add it to your profile.

Reviews

Primary Rating

4.6
Not enough ratings

Secondary Ratings

Novelty
-
Significance
-
Scientific rigor
-
Rate this paper

Recommended

No Data Available
No Data Available