压裂助排工艺优化设计研究

如何提高返排率、减少压裂液对地层的伤害,实现人工裂缝高导流能力,已经成为油气藏增产改造技术面临的重要课题。通过分析氮气、CO2的物理化学特性,研究了液氮、CO2的助排机理,建立气体伴注排液模型,编制了气体伴注设计软件,对影响压裂井气体伴注效果的因素进行了研究,并对助排工艺参数进行了优化设计。结果表明,随着井深增加和压力梯度的降低,液氮伴注比和氮气伴注排量略有增大;井深每增加100 m,液氮伴注比增加约0.3%;压力梯度每增加0.01 MPa/m,液氮伴注比降低约0.6%。随着泵注排量的增加,液氮伴注比增大。井底压力的变化幅度与井口注入压力的变化幅度基本相同;井口注入压力每增加5 MPa,井底压力也增加约5 MPa。随注入流量的增加,井筒压力逐渐减小;注入流量每增加0.5 m3/min,井底压力降低约1.75 MPa。对胜利油田某井进行液氮助排参数优化设计,压裂液返排率达到90%,压裂井产量增加了2.7倍,表明所建立的数学模型准确可靠,可以用于指导油田现场施工。

Optimization of Liquid Nitrogen and Carbon Dioxide Cleanup Technology

The task of how to improve flow back ratio,decrease the formation damage caused by fracturing liquid,and achieve high flow conductivity of artificial fracture had already become a vital question for the reservoir stimulation technology.Through the physical and chemical behavior analysis of nitrogen and carbon dioxide,their cleanup mechanism was researched,the flowing-back model of accompanying gas was built,and the design software of accompanying gas was drawn up.Associating with oilfield examples,the affecting elements of accompanying gas were researched,meanwhile the parameters of flowing back technology were optimized.The results showed that when the well depth and pump injection increased or start-up pressure gradient decreased,the companion ratio and the companion displacement of liquid nitrogen injection increased.The companion ratio of liquid nitrogen injection increased about 0.3% as the well depth increasing per 100 meters,and that decreased about 0.6% as the start-up pressure gradient increasing per 0.01 MPa/m.The change rate of bottom pressure was the same as that of head pressure in a well.The bottom pressure of a well increased about 5 MPa when the wellhead pressure increased 5 MPa.With increasing injection rate,the pressure of the well bore decreased.The bottom pressure of a well decreased about 1.75 MPa when the injection rate increased 0.5 m3/min.When the mathematic model was applied in Shengli oilfield,the fracturing liquid flow back rate achieved 90%,and the fracturing well production increased by 2.7 times.Field application showed that the mathematic model worked reasonably,and accounting parameters were accurate and reliable which could be used to guide field construction.