济阳坳陷陆相页岩油气藏组合缝网高导流压裂关键技术

A new high-conductivity combined network fracturing technology for continental shale oil and gas reservoirs in the Jiyang Depression

济阳坳陷页岩油气藏具有埋藏深、构造复杂、沉积相变化快、纹层发育、原油黏度高等复杂特征,采用常规缝网压裂技术时改造效果普遍不理想、压后产量低且衰减快,亟待攻关能形成与之相适应的长期高导流能力复杂缝网的压裂新技术。为此,基于地质工程一体化思路,开展了地质—工程双甜点评价、四级组合缝网构建、主裂缝脉冲加砂理论与技术研究,形成了组合缝网高导流压裂关键技术,并实现了规模应用。研究结果表明:①充分考虑页岩油气富集、可动性、页岩纹层发育情况等特征,建立了考虑“岩屑—岩心—井眼—储层”的“地质—工程”双甜点评价模型,井位布置、压裂层位及射孔位置优选更加精准;②构建了CO_(2)与酸液联合降低破裂压力,低黏度压裂液造复杂缝、高黏度压裂液促缝高的组合压裂液新模式,增加了压裂后缝网的复杂性;③形成了多层叠置储层压裂后的“大缝宽主裂缝+分支裂缝+自支撑裂缝+酸蚀蚓孔缝”四级组合缝网体系,提出了主裂缝脉冲加砂、分支裂缝连续加砂的高导流缝网加砂压裂新方法,提升了缝网的长期导流能力。结论认为,“双甜点布缝+CO_(2)与酸液降破促缝+压裂液变黏高黏+主裂缝脉冲加砂”的组合缝网高导流压裂关键技术,促进了济阳坳陷陆相页岩油气藏的高黏度原油经济高效开发,为类似地区页岩油气藏的改造提供了理论与技术参考。

Shale oil and gas reservoirs in the Jiyang Depression have complex characteristics,such as great burial depth,complex structure,rapid sedimentary facies change,developed lamina and high oil viscosity,which make it difficult to implement sufficient stimulation by using the conventional network fracturing technology.As a result,the production rate after fracturing is low and declines fast.Therefore,it is urgent to research and develop a suitable new fracturing technology for the formation of complex fracture networks with long-term high conductivity.Based on the idea of geology-engineering integration,this paper researches geological-engineering double sweet spots evaluation,four-order fracture network construction,and main fracture pulse sanding theories and technologies,and develops and applies the key technologies of high-conductivity combined network fracturing.In addition,a"geological-engineering"double sweet spots evaluation model considering"cutting-core-borehole-reservoir"is established.A new fracturing fluid combination mode is constructed,in which,CO_(2) and acid are combined to reduce fracturing pressure,low-viscosity fracturing fluid is used to create complex fracture networks and highviscosity fracturing fluid is used to promote fracture height growth.A four-order fracture network system of"wide main fracture+branched fracture+self supporting fracture+acidizing wormhole fracture"is formed for multiple-layer superposed reservoirs after fracturing.A new sand high-conductivity network fracturing method is proposed,which conducts pulse sanding in main fractures and continuous sanding in branched fractures.Eventually,a new high-conductivity combined network fracturing technology for shale oil reservoirs is formed,i.e.,"arranging fractures through geological-engineering double sweet spots+combining CO_(2) and acid to reduce fracturing pressure and promote fracture development+increasing fracturing fluid viscosity+performing pulse sanding in main fracture".And the following research results are obtained.First,the 3D"geological-engineering"double sweet spots evaluation model,which fully considers the characteristics of shale oil and shale enrichment,movability and shale lamina,is helpful in the optimization of well location layout,fracturing zone and perforation location.Second,the new fracturing fluid combination mode with combined CO_(2) and acid to reduce the fracturing pressure,low-viscosity fracturing fluid to create complex fractures and high-viscosity fracturing fluid to promote fracture height growth is helpful in increasing the complexity of fracture networks after fracturing.Third,the four-order fracture network system of"wide main fracture+branched fracture+self supporting fracture+acidizing wormhole fracture"is formed in multiple-layer superposed reservoirs after fracturing,and a new sand high-conductivity network fracturing method of pulse sanding in main fractures and continuous sanding in branched fractures is proposed,which is conducive to improving the long-term conductivity of fracture networks.In conclusion,this new technology solves the problem in the economic and efficient development of high-viscosity shale oil in the continental shale oil and gas reservoirs of the Jiyang Depression,and provides theoretical and technical support for the stimulation of similar shale oil and gas reservoirs in the same block.