准噶尔盆地阜康凹陷深层侏罗系砂岩储层差异性成岩演化与烃类充注

Differential Diagenetic Evolution of Deep Sandstone Reservoirs and Hydrocarbon Charge:A Case Study from the Lower Jurassic in the Fukang Sag,Junggar Basin

储层有效性及成因机理是制约目前深层油气勘探的关键地质问题。本文以准噶尔盆地腹部阜康凹陷下侏罗统三工河组砂岩为研究对象,利用岩石薄片、SEM(扫描电子显微镜)、稳定碳和氧同位素、流体包裹体等研究手段,分析储层成岩演化与烃类充注的动态关系,对深层储层有效性及形成过程进行研究。研究发现:三工河组储层主要由富塑性岩屑极细—细砂岩和相对富刚性颗粒中—粗砂岩2类岩石组成,它们在储层砂岩段内相互成层出现,在成岩演化和油气充注方面表现出很大的差异性。在储层深埋成岩过程中,富塑性岩屑极细—细砂岩以泥质塑性岩屑强烈机械压实和新生变形作用为特征,在第一期石油充注之前已变为致密储层,同期和后期烃类均不能充注。相比之下,刚性颗粒体积分数相对较高的中—粗砂岩中机械压实作用较弱,自生矿物类型多样,溶蚀作用亦较为普遍;这类砂岩至少经历了2期石油充注事件,成岩作用与烃类充注交替发生。富塑性岩屑极细—细砂岩构成储层内的隔夹层,可能引起油气运移的不均一性。

Effective reservoir rocks and their genesis in a heterogeneous petroleum reservoir are a critical geological issue of deep exploration.The Lower Jurassic Sangonghe Formation in the Fukang sag,central Junggar basin has been used as a case study to examine the dynamic relationship between diagenetic evolution and oil chargeing in sandstones,and discuss effective reservoir rocks and their formation using an integrated approach of petrography,SEM,stable carbon and oxygen isotopes,and fluid inclusion analyses.The results show the sandstones in the Sangonghe Formation consist mainly of ductile lithic-rich,very fine-to fine-grained,and medium-to coarse-grained petrofacies.The two defined petrofacies are interbeded,and represent demonstrable differences in diagenetic evolution and oil charge.Ductile lithic-rich,very fine-to fine-grained sandstones had a limited diagenetic process in which compaction and neomorphism of easily deformed,clay-rich lithic grains predominated,resulting in a very rapid loss of porosity during burial.They have become relatively nonporous before the first oil arrival and have never been charged later.By contrast,diagenetic events in the relatively coarser-grained sandstones with less abundant ductile-lithic grains included dissolution and cementation as well as ductile compaction.At least two episodes of oil charge occurred.Diagenesis progressed alternately with oil emplacement.The nonreservoir,ductile lithic-rich,very fine-to fine-grained sandstones can constitute impermeable barrier interbeds embedded in permeable reservoir rocks,probably resulting in heterogeneous oil migration.