风城油田超稠油油藏非均质储集层地应力场特征

Characteristics of In Situ Stress Field in Heterogeneous Ultra Heavy Oil Reservoir of Fengcheng Oilfield

风城油田浅层超稠油油藏非均质储集层具有埋藏浅、非均质性强、隔夹层发育等特点,阻碍SAGD蒸汽腔的发育,需要利用水力压裂建立渗流通道。为指导储集层压裂,分析了非均质储集层沉积特征、地应力场分布,以及隔夹层对地应力场的影响,结合岩石力学室内实验、测井资料解释和地应力测试结果,建立埋藏深度为282~332 m储集层三维应力场模型。模拟结果与小型压裂测试比较显示,建立的三维应力场模型贴合实际地层侧向压力系数和最大水平主应力与垂向主应力的比值,能较好地反映储集层岩性交界面和应力特征。超稠油储集层以垂向主应力为主,利于引导垂向裂缝;岩性交界面地应力突变,储集层砂岩最小水平主应力小于泥岩隔夹层最小水平主应力。泥岩隔夹层具有较高的破裂压力、杨氏模量和最小水平主应力,裂缝扩展能力弱于油砂段。压裂设计应选择隔夹层内或下方射孔,控制缝高,避免砂堵,以达到较好改善渗流能力的目的。

The heterogeneous ultra heavy oil reservoir in the Fengcheng oilfield is characterized by shallow burial,strong heterogeneity and developed interlayers,which are the main obstacles for the steam chamber development during SAGD.In order to form flowing channels by hydraulic fracturing,the paper analyzes sedimentary characteristics,in situ stress field distribution and the influences of interlayers on in situ stress field and establishes a 3D stress field model for the reservoir with the burial depth of 282~332 m based on the results of rock me chanics experiment,logging data interpretation and stress test.The comparison of the simulation results with mini fracturing test shows that the established 3D stress field model accords with the actual lateral formation pressure coefficient and the ratio of the max.horizontal princi pal stress to vertical principal stress,which can better reflect the features of lithology interfaces and stresses in the reservoir.The ultra heavy oil reservoir is dominated by vertical principal stress which is in favor of guiding vertical fractures.The sudden stress changes at lithology interfaces result in the min.horizontal principle stress of sandstone being lower than that of mudstone interlayer.The mudstone interlayer has relatively high breakdown pressure,Young modulus and min.horizontal principle stress,and the fracture propagation capacity of the mud stone interlayer is lower than that of oil sand interval.The positions within interlayers or below interlayers should be selected for perforation during fracturing design,by which fracture height can be controlled,sand plugging can be avoided and reservoir seepage can be improved.