四川盆地大安寨段介壳灰岩致密油储层特征

四川盆地侏罗系大安寨段油藏是一种未经过大规模长距离运移的源内或近源聚集的非常规致密油,其中大一亚段、大二亚段和大三亚段储层以介壳灰岩为主,大面积连续分布,是一类典型的近源型湖相介壳灰岩致密油。致密油储层岩性复杂、储集空间类型多、孔隙结构复杂,组构选择性微孔隙和微裂缝是重要的有效储集空间。岩石物理实验揭示,储层连通基质孔隙度平均值约为2.13%,虽然低于国内外其他致密油,但高于前期单一酒精法确定的有效孔隙度平均值(0.97%)。生产动态资料证实,大安寨段介壳灰岩致密油不是简单的孔隙型或裂缝型,其具有复杂的孔、喉、缝组合特征或储渗模式;较发育的介壳控制型微裂缝使储层内流体难进易出,虽然孔喉细、分选差、排驱压力高,但储层可动流体饱和度和退汞效率仅略低于部分储渗模式,且好于鄂尔多斯盆地长7油层组,大安寨段是少数具有较高自然产能的致密油储层之一。介壳灰岩致密油具有较大的开发潜力,但其规模有效开发仍面临基质渗流阻力大、单一开发方式效果差等问题,需要借鉴北美Bakken组和中国鄂尔多斯盆地长7油层组致密油的开发经验,研究基于体积压裂和精细施工的有效开发技术以实现规模效益开发。

Reservoir characteristics of Da'anzhai shell limestone tight oil in Sichuan Basin

Jurassic Da'anzhai oil reservoir in Sichuan Basin is one type of unconventional tight oil, accumulated in source or near source, which has not yet experienced a large-scale long-distance migration. Da 1, Da 2 and Da 3 sub-members are all typical near-source shell limestone tight oil distributed extensively. These reservoirs are characterized by complex lithology, multi-type strorage spaces and complicated pore structure. In them the micro-pores and micro-fractures with strong fabric selectivity are important and effective strorage space. The newest petrophysics experiments show that the average connected porosity is about 2.13%, lower than that of other tight oil fields but far higher than 0.97% which is obtained by single alcohol-saturated method previously. Practical performance shows that the reservoirs are expressed as complex pore-throat-fissure assemblage or storage-percolation modes, neither simple pore types nor fractured types. Fluid in the reservoirs is difficult to enter but easy to escape because of the developed shell-controlled micro-fractures. The movable fluid saturation and mercury removal efficiency are only slightly lower than, or even partially higher than that of Chang 7 reservoirs in Ordos Basin, though shown as fine pore-throat, poor sorting and high replacement pressure. Da'anzhai member is one of the few tight oils with high natural productivity. New researches revealed the greater development potential of Da'anzhai shell limestone tight oil but the large-scale effective development still faces challenges including large matrix seepage resistance and single development mode which is low efficiency in such a complex reservoir. Therefore, it is necessary to learn experiences of Bakken group in the North America and Chang 7 in Ordos Basin, China to develop effective developing technologies based on volume fracturing and fine construction. The technology breakthrough will lay the foundation for the high-efficient development in large scale.