Investigation of feasibility of alkali-cosolvent flooding in heavy oil reservoirs

Cold production is a challenge in the case of heavy oil because of its high viscosity and poor fluidity in reservoir conditions.Alkali-cosolvent-polymer flooding is a type of microemulsion flooding with low costs and possible potential for heavy oil reservoirs.However,the addition of polymer may cause problems with injection in the case of highly viscous oil.Hence,in this study the feasibility of alkali-cosolvent(AC)flooding in heavy oil reservoirs was investigated via several groups of experiments.The interfacial tension between various AC formulations and heavy crude oil was measured to select appropriate formulations.Phase behavior tests were performed to determine the most appropriate formulation and conditions for the generation of a microemulsion.Sandpack flooding experiments were carried out to investigate the displacement efficiency of the selected Ac formulation.The results showed that the interfacial tension between an AC formulation and heavy oil could be reduced to below 1o-3 mN/m but differed greatly between different types of cosolvent.A butanol random polyether series displayed good performance in reducing the water-oil interfacial tension,which made it possible to form a Type Il microemulsion in reservoir conditions.According to the results of the phase behavior tests,the optimal salinity for different formulations with four cosolvent concentrations(0.5 wt%,1 wt%,2 wt%,and 3 wt%)was 4000,8000,14000,and 20000 ppm,respectively.The results of rheological measurements showed that Type Ill microemulsion had a viscosity that was ten times that of water.The results of sandpack flooding experiments showed that,in comparison with waterflooding,the injection of a certain Ac formulation slug could reduce the injection pressure.The pressure gradient during waterflooding and AC flooding was around 870 and 30-57 kPa/m,respectively.With the addition of an AC slug,the displacement efficiency was 30%-50%higher than in the case of waterflooding.

基于核磁共振二维谱的稠油化学驱孔隙尺度动用规律

为了研究稠油油藏化学冷采技术中复合驱的作用效果,借助二维核磁共振技术对比研究了DJ降黏剂和BHP聚表剂及其复合驱的提高采收率效果、油相流动能力变化及孔隙动用规律。研究表明:复合驱采收率比单一化学驱采收率高,2种药剂的协同作用明显;通过核磁共振测试得到的T2谱和扩散系数与相对幅度的关系,得出2种降黏剂均能不同程度地有效降低稠油黏度,增大油相的流动能力,并且大孔隙的动用程度明显高于小孔隙的动用程度,复合驱在大小孔隙中均有较好的提高稠油动用程度的效果。

中国稠油蒸汽吞吐后提高采收率接替技术前景

针对中国稠油资源特征和蒸汽吞吐开发现状,探索了稠油蒸汽吞吐后接替性技术的研究进展与发展前景。中国稠油普遍埋藏深、黏度大,主要以蒸汽吞吐方式开发。蒸汽吞吐波及半径仅为30~40 m,效益开采为8~12个周期,平均采收率约为20%。蒸汽吞吐转蒸汽驱是国际主流选择,解决了热波及受限问题,但需要克服稠油埋藏深带来的热损失难题。火烧油层作为稠油开发后期的极限接替开发技术,能够解决波及受限、无效热耗等问题,有望成为目前有技术、无经济效益的废弃/半废弃稠油油田的最终提高采收率方法。长远看,由快速热采开发转向低成本持续冷采是稠油开发后期的必然选择。化学复合驱冷采能够大幅度降低成本、扩大波及体积,下一步需要提高低水动力条件下稠油乳化能力。