超稠油油藏溶剂辅助重力泄油机理物理模拟实验

Scaled physical experiments on drainage mechanisms of solvent-expanded SAGD in super-heavy oil reservoirs

针对国内超稠油双水平井蒸汽辅助重力泄油(SAGD)油区原油高温黏度大、蒸汽腔扩展慢、产油量水平低、油汽比偏低等问题,在溶剂加速降黏特征实验基础上,建立溶剂辅助SAGD(ES-SAGD)泄油理论模型,开展ES-SAGD大型二维比例物理模拟实验,分析纯蒸汽、两种辅助溶剂配方的重力泄油开发效果。研究表明,轻烃溶剂对原油具有较好的降黏效果,50℃条件下原油中添加5%正己烷,降黏率可达96.5%;蒸汽中添加轻烃溶剂(实验中加量为10%)后,可发挥“溶剂溶油降黏+蒸汽高温降黏”的双重作用,加快蒸汽腔横向扩展速率和泄油速率,提高采出程度;蒸汽-溶剂体系中添加1%二甲苯,可以充分发挥其对沥青的溶解作用,减少沥青沉淀,有效降低渗流阻力,进一步提高采出程度;重复利用溶剂,采用ES-SAGD方式开发,可实现利用少量溶剂替代蒸汽,虽目前成本略有偏高,但其具有提高泄油速度、缩短生产周期、提高采出程度等优势,应用潜力巨大;引入轻烃溶剂溶油降黏特征,对SAGD进行修正后建立的ES-SAGD泄油理论模型,经实验数据拟合证实是可靠的,可用于ES-SAGD生产动态预测。

In view of high oil viscosity at high temperatures,slow steam chamber expansion rate,low oil rate,and low oil/steam ratio of domestic super heavy oil blocks developed with dual-horizontal well steam assisted gravity drainage(SAGD),the solvent-aided oil viscosity reduction tests were carried out,based on which the analytical equations and similarity laws of solvent-expanded SAGD(ES-SAGD)were deduced.The large 2-D ES-SAGD scaled physical simulation experiments were conducted to compare the SAGD performances of the conventional steam and two formulas of solvent-steam system.The experimental results show that the light hydrocarbon solvents have good viscosity reduction effects to oil,and the oil reduction ratio can reach 96.5%by adding 5%N-hexane at 50℃.Moreover,adding light hydrocarbon solvent(10%in the experiments)into the steam can bring the oil viscosity reduction effect of solvent and high temperature steam into play,speed up the lateral steam chamber expansion rate,increase the oil drainage rate and enhance the oil recovery degree.Adding 1%of xylene into the steam-solvent system can dissolve the asphalt to reduce asphalt precipitation,reduce the porous flow resistance and further enhance the oil recovery factor.The ES-SAGD recovery by reusing the solvents can realize replacement of the steam with small amount of solvents.Although currently higher in cost,the technology has the advantages of higher oil drainage rate,reduced production period,and enhanced oil recovery.The ES-SAGD theoretical model by modifying the SAGD model based on the oil viscosity reduction characteristics of solvents has been validated by the experiments and can be applied in ES-SAGD production predictions.