灰屑砂岩在须家河组沉积相研究中的应用

ROLE OF CALCARENACEOUS SANDSTONE IN SEDIMENTARY FACIES OF XUJIAHE FORMATION

利用岩心薄片、岩屑薄片、测井和地震资料对四川盆地须家河组砂岩类型开展研究,明确了川西至川中地区须一、须三、须五段内大面积发育灰屑砂岩,属于三角洲前缘水下分流河道沉积,具有成熟度低、灰质胶结重、粒间孔少、物性差等特征,局部发育相对高孔"甜点"砂体。电性上表现为"三低两高"特征,即低自然伽玛、低声波时差、低补偿中子、高电阻、高密度;地震上表现为高阻抗特征。以灰屑砂岩作为典型标志层,提出在剑阁—蓬莱地区发育大型三角洲体。该三角洲体具有继承性发育特征,在须一、须三、须五段沉积时期,与优质泥质烃源岩共生,生储盖组合好,具备形成大规模致密气的成藏条件。

Xujiahe sandstone reservoir,Sichuan Basin,was studied by means of thin-section identification,and well-logging and seismic data.Results show that calcarenaceous sandstone is widely developed in the Xujiahe 1,Xujiahe 3,and Xujiahe 5 members,western and central Sichuan Basin.For the sandstone,the content of limeclast is more than 30 percent;and it is developed in the whole Xujiahe Formation of Jiange-Penglai area.Xujiahe Formation not only belongs to the deposition of deltaic front underwater distributary channel facies,but also is characterized by low maturity,high calcite cementation,a few intergranular pores,and poor physical property.It is also found that some sweet spots with relatively high porosity are developed.In view of electric property,it appears a character of three lows and two highs,namely,low GR,low interval transit time,low CNL,and high resistivity,high density.Seismically,it assumes a feature of high impedance.In addition,an idea that a large-scale deltaic body is developed in Jiange-Penglai area is presented.This body is featured by inherited development.In particular,during the deposition of Xujiahe 1,Xujiahe 3,and Xujiahe 5 members,not only the intergrowth between the body and high-quality argillaceous source rock but also good source-reservoir-caprock assemblage were conducive to forming large-scale tight gas reservoirs.