Early Jurassic Gypsum within Eastern African Continental Marginal Basins and Its Significance for Gas Play
Early Jurassic Gypsum within Eastern African Continental Marginal Basins and Its Significance for Gas Play
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DOI：
10.3390/jmse12010093
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发表时间：
2024-01
影响因子：
2.9
通讯作者：
Jun Cai;Rong Guo
中科院分区：
文献类型：
--
作者：
Jun Cai;Rong Guo
东非大陆边缘盆地虽然发现了大型气田，但与主要烃源岩伴生的早侏罗世石膏是否控制了天然气的作用尚不清楚。本文综合利用测井、地震反射、有机地球化学等资料，综合分析了该区石膏矿床的分布、成因及其对气藏的控制作用。结果表明，在201 ~ 183 Ma期间，由于海水分层作用，南部海湾海开始形成一套厚层薄层石膏泥岩。自183ma以来，随着海平面的下降，在一些地堑中沉积了一套厚厚的石膏，这些地堑的沉积环境变成了泻湖。石膏提高了下侏罗统烃源岩的成熟阈值深度，延缓了生气高峰期，导致东非天然气储层持续充注，形成巨大储量。此外，石膏不仅控制着常规气的分布，而且由于其良好的封闭性，使得断裂不发达的下侏罗统页岩成为未来页岩气勘探的重要场所。
Although the eastern African continental marginal basins have discovered giant gas fields, it is not clear whether the Early Jurassic gypsum associated with the main source rocks controls the gas play. In this paper, we use well logging, seismic reflection, and organic geochemistry data to synthesize the distribution and origin of the gypsum deposits and their control over the gas play. The results show that from 201 Ma to 183 Ma, a thick suite of mudstone with thin-layered gypsum began to form in the southern gulf-like sea due to water stratification. With the sea level falling since 183 Ma, a thick suite of gypsum was deposited in some grabens, where the sedimentary environment changed to lagoons. The gypsum increases the maturity threshold depth of Lower Jurassic source rocks and delays the peak time of gas generation, resulting in the ongoing filling of East African natural gas reservoirs and the formation of giant reserves. In addition, the gypsum not only controls the distribution of conventional gas but also makes the Lower Jurassic shale, where the faults are not developed, an important place for shale gas exploration in the future due to the good sealing properties of the gypsum.