| Autor: |
Kang, Xun, Hu, Wenxuan, Cao, Jian, Jin, Jun, Wu, Haiguang, Zhao, Yang, Wang, Jian |
| Předmět: |
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| Zdroj: |
Geological Journal; Mar2018, Vol. 53 Issue 2, p475-499, 25p |
| Abstrakt: |
Feldspar dissolution resulting from fluid–rock reactions in clastic rocks is common in petroliferous sedimentary basins and significantly affects the quality of reservoirs. The objective of this study is a case study of this phenomenon in the sandy conglomerate reservoirs, based on the Lower Triassic Baikouquan Formation in the Mahu Sag at the northwestern margin of the Junggar Basin in northwestern China, which has obtained exploration breakthroughs recently. In these rocks, orthoclase has undergone dissolution and the dissolution intensity decreases gradually from the basal member (T1b1) to the upper member (T1b3) of the formation, whereas albite remained stable or has even overgrown crystals, displaying a selective dissolution of alkali feldspars. This is interpreted to be mainly controlled by two factors. First, illitization of mixed‐layer illite/smectite in the sandy conglomerates consumed K, thereby increasing Na/K ratios in the formation waters and leading to orthoclase dissolution and albite overgrowths on perthite and microcline. Second, the charge of acidic, hydrocarbon‐related fluids further promoted orthoclase dissolution. These relationships are confirmed by the fact that hydrocarbon charging intensity shows a gradual upward reduction from member T1b1 to T1b3, as does the scale of orthoclase dissolution. This selective dissolution resulted from the influence of different mineral components on diagenesis, the acidic nature of reservoir fluids, and the extent of water–rock interaction. The dissolution significantly improved porosity and permeability of the reservoirs by generating substantial secondary porosity. The results indicate a favorable exploration prospect located in the up‐dip area of the Ma 18 and Aihu 2 wells on the western slope of the Mahu Sag. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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