低渗和特低渗油层CO2-N2复合驱研究

针对低渗-特低渗油层CO₂-N₂复合驱提高采收率,以大庆外围YS油田的特低渗透油层为背景,进行了数值模拟和物理模拟两方面的研究。利用CMG数值模拟软件GEM模块,建立了一维长细管、均质、非均质理想模型及五点法井网单元模型,分别对CO₂-N₂复合驱的驱油方式、影响因素、五点法井网单元模型下的段塞组成进行了模拟计算及分析。与此同时,在室内分别选用30 cm长的低渗透、特低渗透天然岩心,各进行了5种不同驱替方案的实验研究,确定了CO₂-N₂复合中CO₂合理段塞尺寸及驱油效果,并验证了数值模拟计算的可靠性。研究结果表明,低渗-特低渗透油层CO₂-N₂复合驱不宜采用CO₂与N₂混合驱方式,而应采用一次注入合理的CO₂段塞(约0.3PV)＋N₂的段塞组合驱方式,这样不仅可以减少CO₂用量,而且可以充分发挥CO₂与N₂各自的优势,获得优于全部注CO₂驱的驱油效果；且油层渗透率越低、渗透率级差越小或长厚比越大,越有利于提高CO₂-N₂复合驱采收率；厚度小于井距1%的油层也有利于CO₂-N₂复合驱提高采收率。

Carbon Dioxide-Nitrogen Compound Floodingin Low Permeability and Ultra-low Permeability Layer

In order to the enhance oil recovery of the CO₂-N₂ compound flooding in low permeability and ultra-low permeability layer, the ultra-low permeability layer in Daqing YS oil field as the research target, both of the numerical simulation and physical simulation experiment have been researched. Using the CMG numerical simulation software GEM model, the one dimensional long slim tube, homogeneous, non-homogeneous ideal model and five-spot well pattern element model have been built. The carbon dioxide-nitrogen compound flooding method, the reason how to influence the recovery, the slug composition in well pattern element model have been calculated and analyzed. Meanwhile, low permeability and ultra-low permeability natural core which size is 30 centimeter have been selected after these five different experiments were completed with selected cores. Through the experiments the suitable size of carbon dioxide slug and flooding effect in carbon dioxide-nitrogen compound flooding has been proved. The experiment result also proved that the numerical calculated result is reliable. The result shows that in low permeability and ultra-low permeability layer, carbon dioxide mixed nitrogen is not a good way but carbon dioxide slug which size is 0.3PV+nitrogen is a better flooding way. It can reduce the carbon dioxide dosage and give full play to the advantage of carbon dioxide and nitrogen to achieve a better effect then carbon dioxide flooding. For low permeability and ultra-low permeability layer, the lower the permeability, or the smaller the permeability ratio, or the bigger the length-thickness ratio is, the more favorable it is for CO₂-N₂ compound flooding; when the layer which thickness is less the 1% of the well spacing, it also suitable to adapt this method.