油砂蒸汽辅助重力排水开发隔层界限及上部剩余油挖潜方法

Standard of Top Interlayers and Exploitation Method of Stranded Reserve in Oil Sand Steam Assistant Gravity Drainage Development

加拿大油砂主要采用双水平井蒸汽辅助重力泄油(steam assistant gravity drainage,SAGD)模式开发,难以动用隔夹层上部的储量。在曲流河沉积中,不同区域隔夹层的岩性、厚度、渗透性各异,造成油砂行业内不同公司所采用的隔层认定标准差别巨大,这给SAGD可动用储量的互认造成很大困扰。通过30组不同渗透率、不同温度(原油黏度)下的油砂启动压力梯度室内物理模拟实验,证实油砂开发过程中存在启动压力梯度现象,启动压力梯度的数值与视流度成幂指数关系,视流度越小,启动压力梯度越大。通过不同厚度、不同渗透率、是否考虑启动压力梯度下的42组数值模拟实验,绘制了隔夹层上部储量采出程度与隔夹层渗透率、厚度的关系图版。结果表明:垂向渗透率小于25 mD的连续物性层可完全封隔上部储量;垂向渗透率25~500 mD的连续物性层可在一定程度上封隔上部储量,此时厚度不同隔挡作用强弱不同;垂向渗透率大于500 mD的连续物性层对上部储量最终采出无明显隔档作用。通过多个方案优化了不同隔夹层隔挡作用下上部剩余油挖潜方式,提出了上部水平加密井的概念:隔挡性较强时可将下部注汽井侧钻为上部采油井;隔挡性较弱时可将下部注汽井侧钻为上部注汽井。初步经济测算表明两种方式下侧钻井均具有较好的经济效益。

Canadian oil sands are mainly developed by horizontal steam assistant gravity drainage(SAGD)well pairs,in which mode reserves above the interlayers(stranded reserve)are hard to be developed.The lithology,thickness and permeability of interlayers in different regions are different in meandering river deposition,which makes the barrier standards vary greatly in oil sands companies.Therefore,it is always hard for companies to reach an agreement of the SAGD exploitable reserves.The phenomenon of potential gradient threshold(PHT)in bitumen flow process was confirmed by 30 sets of indoor physical simulation experiments under different permeability and different temperature(or crude oil viscosity).The PHT is an exponential function of apparent mobility,with a negative exponential index.The relationship chart of stranded reserve recovery factor,the interlayer permeability,and,thickness was drawn based on 42 sets of numerical simulation,which both took or not the PHT into consideration.The results show that the upper oil can be completely sealed by the continuous interlayer with the vertical permeability less than 25 mD,partially sealed by the continuous interlayer with the vertical permeability 25~500 mD,and,hardly sealed by the continuous interlayer with the vertical permeability higher than 500 mD.The influence of thickness is very obviously in the partially sealed mode.The optimized stranded reserve development methods for different kind of interlayers are as below,to sidetrack the lower steam injector into an upper single producer for completely sealed barrier,and to sidetrack the lower steam injector into an upper single injector for partially sealed one.The preliminary economic calculation shows that both recommendations had good economic benefits.