低渗透油藏常规水驱与二氧化碳驱井距界限研究

为实现吉林油田低渗透油藏井距优选设计,以吉林油田扶余油层为例,通过开展压力梯度测试实验,绘制了水驱和二氧化碳驱启动压力梯度与渗透率关系曲线,结合“一注一采”模式下储层压力分布规律,建立了水驱和二氧化碳驱的合理井距设计图版。结果表明:低渗透扶余油层的最小启动压力梯度与渗透率呈负幂指数关系,在注采压差为15~25 MPa条件下,同一岩心水驱的最小启动压力梯度为二氧化碳驱的2~4倍;储层渗透率低于0.10 mD时,二氧化碳驱的合理井距上限大于水驱,更具效益开发优势,渗透率为0.05~0.10 mD时对应的合理井距为120~380 m;储层渗透率大于0.10 mD时,水驱成本更低,更具开发优势,渗透率为0.10~0.20 mD时对应的合理井距为70~120 m。该研究成果对吉林油田扶余油层不同介质驱替下合理井距选择有借鉴意义。

Study on Well Spacing Limit for Conventional Water Flooding and Carbon Dioxide Flooding in Low-permeability Reservoirs

In order to realize the optimal design of well spacing for low-permeability reservoirs in Jilin Oilfield, based on a case study of Fuyu oil reservoir in Jilin Oilfield, pressure gradient test was conducted, a curve was prepared to indicate the relation between starting pressure gradient and permeability of water flooding and carbon dioxide flooding, and a reasonable well spacing design drawing was drawn for water flooding and carbon dioxide flooding with reference to reservoir pressure distribution law in a mode of "one for injection and one for production". the results of the study show that the minimum starting pressure gradient of the low-permeability Fuyu reservoir had a negative power exponential relation with the permeability, and the minimum starting pressure gradient of the same core water flooding was 2 to 4 times that of carbon dioxide flooding under the condition that the injection-production pressure difference was 15 to 25 MPa; when the reservoir permeability was lower than 0.10 mD, the upper limit of the reasonable well spacing for carbon dioxide flooding was greater than that of water flooding, which was more beneficial for development; when the permeability was from 0.05 to 0.10 mD, the associated reasonable well spacing range was from 120 to 380 m; when the reservoir permeability was greater than 0.10 mD, the water flooding cost was much lower and much favorable for development; when the permeability is from 0.10 to 0.20 mD, the reasonable well spacing range was from 70 to 120 m. The study results provide an important reference for the selection of reasonable well spacing with different medium flooding in Fuyu reservoir in Jilin Oilfield.