数值模拟研究原油脱气对混相压力的影响

Numerical Simulation Study on Influence of Crude Oil Degassing Degree on Miscible Phase Pressure

在注气驱油中,最小混相压力MMP是确定注入气体和原油是否能够实现混相的重要参数之一。MMP通常采用细管实验法来确定,花费较大,耗时较长,且必须在压力高于饱和压力条件下进行。而针对驱替压力小于饱和压力的情况,由于需考虑地层原油脱气的影响,情况较为复杂,目前还没有开展对应的细管实验,因此如何获取准确的MMP成为关键。在对地层流体PVT性质进行拟合的基础上,建立一维数值模型模拟细管实验确定MMP,最后,模拟预测不同脱气程度下原油和注入气MMP。结果表明:在准确拟合流体PVT参数场的基础上,利用数值模拟方法建立的细管实验模型能够得到可靠的MMP;当驱替压力大于MMP时,原油采收率随驱替压力的增加并无太大变化;原油脱气程度对MMP有一定的影响,原油脱气越严重,MMP越低。

In the gas injection flooding, the minimum miscible pressure(MMP) is one of important parameters for determining oil and injected gas so as to realize miscible phase. Tubule experimental method is usually adopted to determine the MMP, but adoption of this method needs high cost and long time and this method must be conducted under the pressure condition higher than saturation pressure. If displacement pressure is less than the saturation pressure, crude oil degassing shall be considered, it is more complicated. So far, no corresponding tubule experiment has been conducted, thus how to obtain the accurate MMP becomes the key factor. Fitted are the PVT properties of formation fluid, established is a one-dimensional numerical simulation model for simulating tubule experiment so as to determine the minimum miscible pressure and finally conducted is simulating prediction on MMP of injected crude oil and gas under different degrees of degassing. The results show that: based on accurate fluid PVT parameters, reliable minimum miscible pressure can be obtained from the tube experimental model established by using numerical simulation method, oil recovery remains about the same along with displacement pressure increase if the pressure is higher than the minimum miscible pressure and oil degassing degree has a certain influence on the MMP, the more severe oil degassing, the lower the minimum miscible pressure. The study results can provide some certain theoretical guidance for gas injection miscible flooding.