井震结合分析页岩油“甜点”沉积特征及分布——以吉木萨尔凹陷芦草沟组“下甜点”为例

Sedimentary morphologys and distributions of shale oil"sweet spot"by the data of well to seismic analysis:a case study of the lower sweet pot in Lucaogou Formation of Jimsar Sag

页岩油“甜点”储层多与暗色泥岩薄互层产出,对其沉积形态认识及分布刻画难度大。基于吉木萨尔凹陷二叠系芦草沟组“下甜点”段岩心、测井及地震资料,分析“甜点”沉积相类型,井震结合对比分析“甜点”空间形态及分布。研究表明:1)页岩油“甜点”为湖泊深水扇相成因。其中:中扇亚相主要为细—粉砂岩,发育粒序层理、块状层理及爬升波纹层理等;单层厚度在1.30~3.80 m,平均为2.20 m;核磁孔隙度为6.0%~12.3%,平均为9.0%。外扇亚相主要为粉砂岩及泥质粉砂岩,发育爬升波纹层理及变形构造等沉积构造;单层厚度在0.50~1.40 m,平均为0.92 m;核磁孔隙度为3.5%~7.8%,平均为5.2%。2)在平行物源方向的地震剖面上,见低角度前积地震反射,前积体被沉积坡折带分隔,分别解释为中扇与外扇亚相;在垂直物源方向的地震剖面上,中扇为弱振幅充填地震相,外扇为中振幅亚平行披覆地震相。3)朵叶体从南部J40井区向北推进,发生侧向迁移,在沉积坡折带之下形成多个外扇分支朵叶体,中扇与外扇朵叶体长宽相近,其沉积规模可以超过10 km。研究认为,井震结合分析能够有效指导页岩油“甜点”刻画,提出的“甜点”储层沉积形态及分布对芦草沟组页岩油高效开发有积极意义。

The sweet spot in shale oil reservoirs are often interbedded with dark mudstone,so it is difficult to characterize its sedimentary morphology and distribution.Based on the core,logging and seismic data of the"Lower sweet spot"member in Permian Lucaogou Formation of Jimsar Sag,the sedimentary facies types,spatial morphology and distribution of"sweet spot"were analyzed by combining the data of well to seismic.The results show that the"sweet spot"in shale oil reservoirs is derived from lacustrine deepwater fan facies.Among them,the middle fan subfacies is mainly composed of fine sandstone with grain sequence bedding,massive bedding and climbing ripple bedding.The thickness of single layer is 1.30-3.80 m with an average of 2.20 m.The NMR porosity is 6.0%-12.3%with an average of 9.0%.The outer fan subfacies is mainly siltstone and argillaceous siltstone with climbing ripple bedding and deformation structure.The thickness of the single layer is 0.50-1.40 m with an average of 0.92 m.The NMR porosity is 3.5-7.8%with an average of 5.2%.In the seismic profile of parallel provenance direction,low-angle foreset seismic reflections are observed,and sedimentary break slope seprate foresets,which are interpreted as the middle fan subfacies and outer fan subfacies respectively.In the seismic profile of vertical provenance direction,the middle fan is weak amplitude filling seismic phase,and the outer fan is medium amplitude subparallel covered seismic facies.The middle fan lobe was deposited from the south of well J40 to the north and migrated laterally,forming multiple outer fan branch lobes under the sedimentary break slope.The length and width of the middle fan are similar with the outer fan,and the deposition scale can be more than 10 km.The study show that seismic facies analysis with well-seismic combination can effectively guide the characterization of the sweet spot in shale oil reservoirs,and the proposed sedimentary morphologies and distributions have positive significance for the efficient development of shale oil in Lucaogou Formation.