伊拉克HF油田Mishrif组厚壳蛤滩相储层沉积与早期成岩特征

通过岩心观察、薄片鉴定、同位素和微量元素分析,研究伊拉克HF油田Mishrif组富厚壳蛤层MB2-MC1层的沉积微相和早期成岩特征。结果表明,Mishrif组MB2-MC1层发育在开阔台地-台地边缘相。富厚壳蛤层中发育2期厚壳蛤滩以及2套含厚壳蛤风暴层。厚壳蛤滩沉积在台地边缘,Sr/Ba比值为5.74,高于2套开阔台地沉积的风暴层。厚壳蛤滩的发育特征有别于厚壳蛤礁,无原地生长特点,同沉积破碎严重,以厚壳蛤砾屑灰岩、厚壳蛤颗粒灰岩和泥粒灰岩为主要岩相,与开阔台地潮下浅滩交互沉积。同生期厚壳蛤滩相的暴露导致早期大气淡水淋滤作用较强,而胶结作用较弱,形成以粒间孔、粒间溶孔、溶洞、溶缝为主的储集空间。

Reservoir and early diagenesis characteristics of rudist shoal of Mishrif Formation in HF Oilfield of Iraq

Based on observations of cores and thin sections, and measurements of trace elements and isotope, the microfacies and early diagenesis of MB2-MC1 member in Mishrif Formation, HF Oilfield of Iraq were studied. The sedimentary facies of MB2-MC1 member were open platform and shelf margin. There were two layers of abundant rudists deposited in rudists shoal, and two other layers deposited by storm. The rudist shoal was deposited in shelf margin, where the Sr/Ba vaule was 5.74, higher than that of the rudist layers deposited by storm. The rudist shoal shows the characteristics of nonindigenous growth and strong synsedimentary breakup, which are very different from other reefs. The main lithofacies of rudist shoals were composed of rudist rudstone, rudist grainstone and rudist packstone, without reef limestone. The rudist shoals alternate with open shelf shoals. The meteoric water leaching of rudist shoals was strong during exposure, with weak cementation. The pore assembly of rudist shoals was composed of intergranular pores, intergranular dissolved pores, cave and dissolved microfractures.