压实与出砂双重作用下疏松砂岩稠油油藏产能变化实验

Experimental study on productivity change of unconsolidated sandstone heavy oil reservoir under the dual effect of compaction and sand production

渤海绥中36-1油田疏松砂岩稠油油藏开发注水不及时,地层压力下降快,压实作用明显改变油藏储层孔径结构和渗流特性,同时对岩石骨架造成破坏导致出砂而进一步影响油井产能,因此如何评价压实和出砂双重作用下油井产能变化是开发的关键。制备了4块岩心(渗透率分别为1 071、1 291、2 170、2 479mD),在保持围压不变、改变内压(地层压力)条件下模拟了实际储层压力变化过程,采用连续测试的方法开展了不同含水率(低、中、高)下储层压实和出砂对稠油产能(用采油指数衡量)影响的研究。实验结果表明:低含水阶段压实对产能下降起主要作用,出砂的作用相对很弱;中、高含水阶段存在出砂增渗,对产能的快速下降有所缓解,产能变化受出砂与压实双重作用的影响;随着地层压力的下降,各个含水阶段采油指数整体呈下降趋势,储层越疏松,其下降幅度越大,地层压降初期(小于4 MPa)压实作用导致产能下降程度明显。因此,疏松砂岩稠油油藏开采过程中必须保持较高的压力水平,以充分保护储层并释放油藏产能。

Compaction has a great influence on reservoir pore structure and percolation characteristics due to quick reservoir pressure drop caused by inappropriate water injection for unconsolidated sandstone heavy oil reservoirs in Bohai SZ36-I oilfield. Rock framework is also destroyed which leads to sand production and further influences on productivity. So how to evaluate well productivity variation under the dual effect of compaction and sand production is the key for development. Four cores with permeabilities of 1 071, 1 291, 2 170 and 1 291 mD are used to simulate the process of reservoir pressure change under constant confining pressure and variable internal pressure （formation pressure）. The effect of compaction and sand production on heavy oil productivity （measured by productivity index） under different water contents （low, medium and high） is studied by continuous testing method. Results show that compaction has prior effect on productivity decline than sand production at low water content; Sand production increases the permeability at medium and high water contents which slows down productivity decline, and productivity change is affected by the combination of compaction and sand production. Productivity index decreases with formation pressure drop, and the looser the reservoir sandstone is, the greater the reduction will be. It shows obvious productivity decline in early stage of formation pressure drop （less than 4 MPa）. So high formation pressure must be kept during the development process for unconsolidated sandstone heavy oil reservoir to fully protect reservoir and release the reservoir capacity.