Diagenesis and porosity development in the First Eocene reservoir at the giant Wafra Field, Partitioned Zone, Saudi Arabia and Kuwait
Diagenesis and porosity development in the First Eocene reservoir at the giant Wafra Field, Partitioned Zone, Saudi Arabia and Kuwait
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DOI：
10.1306/12021313040
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发表时间：
2014-06
期刊：
影响因子：
3.5
通讯作者：
A. Saller;D. A. Pollitt;J. Dickson
中科院分区：
文献类型：
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作者：
A. Saller;D. A. Pollitt;J. Dickson
沃夫拉油田的第一个始新统油藏从古新统-始新统Umm Er Radhuma组（300 - 400 m）深度的非常多孔的泥岩中生产重油。孔隙度一般为30- 50%，渗透率一般为100-2000 md，这些储层特征在很大程度上由成岩作用决定。早期成岩作用主要为碳酸盐化、碳酸盐化的溶解作用和硫酸盐的沉淀作用。岩相学和稳定同位素特征支持浅埋过程中蒸发海水中的硫酸盐沉淀和石化作用。最高的渗透率出现在潮下相。低渗透潮坪相使储层分层。重油优先填充高渗透率的泥岩;而低渗透率的潮坪相通常充满水，因为它们的孔喉太小，不允许粘性油迁移到岩石中。储层孔隙度高可能与埋藏浅、油侵位早有关。晚期成岩作用以细菌硫酸盐还原作用（BSR）为主，导致硫酸盐结核溶解、方解石胶结、硫沉淀和石油生物降解。BSR由非常低的方解石胶结物组成（至Peedee Belemnite标准）指示，其需要有机碳源;可能是油。方解石的氧同位素组成支持从地层沃茨沉淀类似于那些在水库现在。BSR可能在最初的石油侵位期间开始并持续到现在。BSR是非均质的，导致产出的油具有14-21° API的重力。甚至存在在初级生产期间不能流动的更重的油。初级生产可能是最大的地区和间隔较轻，粘度较低的石油。
The First Eocene reservoir at the Wafra Field produces heavy oil from very porous dolomites at depths of (300 to 400 m) in the Paleocene–Eocene Umm Er Radhuma Formation. Porosity is commonly 30–50%, permeability is commonly 100–2000 md, and those reservoir characteristics were determined largely by diagenesis. Early diagenesis is dominated by dolomitization, dissolution associated with dolomitization, and precipitation of sulfates. Petrographic and stable isotopic characteristics support dolomitization and sulfate precipitation in evaporated (refluxing) seawater during shallow burial. The highest permeabilities occur in subtidal facies. Low-permeability tidal-flat facies stratify the reservoir. Heavy oil preferentially filled high-permeability dolomites; whereas, low-permeability tidal-flat facies are commonly filled with water because their pore throats are too small to allow migration of viscous oil into the rock. This reservoir’s very high porosity is probably related to its shallow burial and early oil emplacement. Late-stage diagenesis is dominated by bacterial sulfate reduction (BSR) that caused dissolution of sulfate nodules, calcite cementation, sulfur precipitation, and oil biodegradation. The BSR is indicated by very low compositions of calcite cements ( to , Peedee Belemnite standard), which require an organic carbon source; probably oil. The oxygen isotopic compositions of the calcites support precipitation from formation waters similar to those in the reservoir now. The BSR probably started during initial oil emplacement and continues to the present. The BSR was heterogeneous resulting in produced oils with gravities of 14–21° API. Even heavier oils are present that could not flow during primary production. Primary production was likely greatest in areas and intervals with lighter, less viscous oil.