四川盆地下侏罗统大安寨段沉积微相特征及对储层的控制

下侏罗统大安寨段是四川盆地致密油勘探的重点层位,但油气特征复杂。在对大安寨段的岩性特征进行详细研究时,将大安寨段划分为8种岩相:厚层块状重结晶灰岩相、块状亮晶介壳灰岩相、块状—薄层状泥晶介壳灰岩相、薄层状含泥质介壳灰岩相、泥岩与泥质介壳灰岩的薄互层相、薄层状含介壳泥岩相、黑色泥岩相、紫红色到灰绿色泥岩相。总结了大安寨段的沉积模式,划分为5种沉积微相,即滨浅湖泥、滩后、滩核、滩前和浅湖—半深湖泥。最后,通过对比不同岩性的孔渗特性并结合沉积环境进行分析,明确了沉积微相对储集层的控制作用,滩前微相具有较好的致密油成藏条件。

Sedimentary microfacies characteristics and their control on reservoirs in Daanzhai Member,Lower Jurassic,Sichuan Basin

The Daanzhai Member of the Lower Jurassic in the Sichuan Basin is an important exploration target with complicated petrogeologic features. The Daanzhai Member includes eight lithofacies: thick blocks of recrystallized limestone, sparry shell limestone blocks, micritic shell limestone blocks or thin sections, argillaceous shell limestone thin sections, interbedded mudstones and shale shell limestones, shell mudstone thin sections, black mudstones, and red to green mudstones. A depositional model was established, consisting of five sedimentary microfacies: mud from littoral to shallow lake, back beach shell, shell beach core, beach front shell, and mud from shallow to intermediate depth lake. The controls of sedimentary microfacies on reservoir properties were determined according to the relationship between porosity/permeability and depositional environment. The beach front shell facies was favorable for tight oil accumulation.