厚层块状冲积扇沉积演化特征及其对油气富集的控制作用——以百口泉油田百21井区百口泉组油藏为例

The Evolution Characteristic of Massive Alluvial Fan and Its Controlling Effect on the Hydrocarbon Accumulation:A Case of Baikouquan Formation in B21 Block,Baikouquan Oilfield

综合应用研究区丰富的密井网资料、取心分析化验资料及开发实践认识,通过取心井单井沉积相标定、平剖面沉积特征解剖,结合油层展布特征分析,明确了百口泉组厚层块状砂砾岩的沉积演化规律,并在此基础上了探讨了其油气差异富集机理。研究表明:(1)研究区百口泉组为干旱型冲积扇沉积,根据其内部沉积特征的差异可进一步划分为扇根及扇中2个亚相和7个微相单元,扇根以主槽微相发育为主,扇中以辫流水道微相发育为主。(2)百口泉组冲积扇整体呈不断退积的特征,B3砂组以扇根主槽块状砂砾岩发育为主,整体呈连片分布特征;B2砂组为扇根主槽向扇中辫流带过渡沉积,砂砾岩体由块状向近层状演化;B1砂组以扇中辫流水道发育为主,辫流水道砂体呈层状展布特征。(3)研究区油气富集平面呈现断裂处连片富集、近断裂处条带状富集和远断裂处富集较差的特征,剖面上呈现底部B3砂组富集较差,中部B2砂组最为富集,顶部B1砂组富集稍差的特征。研究区油气差异富集整体受构造及沉积特征的共同控制,断裂为油气运移路径,后期起到遮挡作用,加之断裂处扇根主槽块状砂砾岩储集层发育,导致其油气较富集;近断裂处受扇中辫流水道优势储层条带状分布的控制,油气富集亦呈条带状分布特征;远离断裂处扇中外缘有利储层发育较差,油气富集程度较低。

Based on the abundant data of wells and core analysis and the development experience,through the calibration of core well,anatomy of plane and profile facies distribution,the evolution characteristic of massive alluvial fan in Baikouquan Formation was clarified.Combined with the oil layer distribution,the mechanism of the different hydrocarbon accumulation in Baikouquan Formation was discussed.The research shows as follows.（1）Baikouquan Formation develops arid alluvial fan,it can be further divided into two subfacies and seven microfacies.The inner fan mainly developed main trench,while middle fan mainly developed braided river.（2）The alluvial fan of Baikouquan Formation is characterized by continuous regression.B3 sandy group develops main trench,with the character of continuous massive conglomerate.B2 sandy group characterizes by the transition of inner fan to middle fan,the conglomerate has the layer-like distribution.B1 sandy group develops middle fan,with the character of braided river well develops.（3）The hydrocarbon accumulation in the study area is characterized by well accumulation in the fault zone,band-like accumulation near the fault and poor accumulation in the far fault zone.In the profile,the distribution is characterized by poor accumulation in B3 sandy group,well accumulation in B2 sandy group and slightly well accumulation in B1 sandy group.The hydrocarbon accumulation is controlled by the tectonic and sedimentary characteristics.The fault is the best migration path and plays the role of blocking in the latter stage,thus,the fault zone accumulates abundant hydrocarbon.The high quality reservoir developed in the middle fan has the shape of stripe,because of the high quality reservoir controlled by braided river.The reservoir is not well developed in the outer middle fan far from the fault,so the hydrocarbon accumulation is poor.