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Formation of an anomalously high‐porosity zone of a very fine‐grained deep clastic reservoir in the Qiongdongnan Basin, South China Sea
Geological Journal ( IF 1.8 ) Pub Date : 2020-08-03 , DOI: 10.1002/gj.3938
Wei Duan 1, 2 , Chun‐Feng Li 2, 3 , Cheng‐Fei Luo 4 , Jin‐Ding Chen 4 , Xiang‐Sheng Huang 4 , Zuo‐Yu Yan 4
Affiliation  

Development of anomalously high porosities in very fine‐grained deep clastic reservoirs is still largely unknown. The reservoirs in the S13 block of the lower Meishan Formation in the Qiongdongnan Basin, South China Sea, developed a zone of anomalously high porosity up to 28.5%, and thus offers an ideal opportunity to quantitatively study the formation mechanism of the abnormally high porosity but fine‐grained deep clastic reservoir from the diagenetic perspective. Our study demonstrates that the first phase charging of oil and organic acid promoted the early‐stage dissolution. This process, however, restrained the early‐stage compaction, cementation, and transformation of clay minerals in sandstone reservoirs. CO2‐rich thermal fluid at the fourth phase enhanced the dissolution of late‐stage feldspar and early‐stage cements and authigenic clay minerals. The massive Ca2+, Mg2+, Fe2+, and other ions generated by the dissolution facilitated the formation of late‐stage siderite and ankerite, which filled the pore throats and lowered the reservoir permeability. Furthermore, the rapid deposition produced high primary porosities, and the early‐stage overpressure also inhibited the compaction, cementation, and clay transformation in the S13 block. All these processes promoted the preservation of primary pores, and the S13 block developed reservoirs with anomalously high porosity and low permeability. By contrast, the C24 block was only charged by oil and hydrocarbon‐rich gas at the second and third phases, and experienced strong compaction, weak dissolution, and strong cementation. Consequently, fewer primary and secondary pores, but higher contents of cements and authigenic clays were generated in the C24 block. The reservoirs in the C24 block exhibit medium porosity but low permeability.

中文翻译:

南海琼东南盆地一个极细粒深碎屑岩储层异常高孔隙度带的形成

在非常细的深部碎屑岩储层中异常高孔隙度的发育仍是未知之数。南海琼东南盆地眉山组下段S13区块的储集层发育异常高孔隙度区,达28.5%,为定量研究异常高孔隙度的形成机理提供了理想的机会。从成岩角度看,细粒深碎屑岩储层。我们的研究表明,油和有机酸的第一阶段填充促进了早期溶解。但是,这一过程限制了砂岩储层中粘土矿物的早期压实,胶结和转变。一氧化碳2第四阶段富含热流体,增强了后期长石,早期水泥和自生粘土矿物的溶解。块状Ca 2 +,Mg 2 +,Fe 2+,溶解过程中产生的其他离子促进了后期菱铁矿和铁矿的形成,它们填充了孔喉并降低了储层的渗透率。此外,快速沉积产生了较高的初生孔隙度,早期超压也抑制了S13区块的压实,胶结和粘土转变。所有这些过程都促进了初级孔隙的保存,S13区块发育了异常高孔隙度和低渗透率的储层。相比之下,C24区块仅在第二和第三相中充有富含石油和烃类的气体,并且经历了强夯实,弱溶化和强固结作用。因此,在C24区块中生成的初级和次级孔隙较少,但水泥和自生粘土的含量较高。
更新日期:2020-08-03
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