浅层近源扇三角洲砂砾岩沉积充填模式及其对储层分布的影响——以车排子凸起沙一段为例

Sedimentary models for near-source shallow glutenite fan delta and their effects on reservoir distribution:A case of the first member of Shawan Formation in Chepaizi Uplift

车排子凸起沙一段广泛发育浅层近源扇三角洲砂砾岩体,具有沉积规律复杂,岩性、物性以及含油性变化快的特点,导致该类型砂砾岩的勘探工作难以开展,因此需要对研究区近源扇三角洲砂砾岩储层分布特征展开研究。从岩心资料入手,分析砂砾岩体的沉积特征,结合古地貌和地震反射特征等研究,将车排子凸起沙一段近源扇三角洲相划分为退积型和垂向加积型2种沉积充填模式,其中,退积型沉积充填模式中砂砾岩体在空间上呈明显退积样式,纵向整体上具有正韵律特征,且有明显的沉积相变;而垂向加积型砂砾岩体厚度大,垂向上沉积序列与沉积相无明显的变化。同时,通过研究区储层物性的统计,厘定了沙一段浅层近源砂砾岩储层的物性下限,孔隙度为16%,渗透率为21 m D。扇三角洲前缘砂砾岩物性较好,属于有效储层,扇三角洲平原砂体物性差,为非储层,但可作为封堵层对前缘砂砾岩进行侧向封堵。因此,退积型沉积充填模式中,有效储层在空间上呈退积样式相对独立的叠置出现,而垂向加积型沉积充填模式中,有效储层集中叠加发育在扇三角洲砂砾岩的中前部,通常垂向上厚度较大。

Near-source shallow glutenite fan delta is developed wildly in the first member of Shawan Formation in Chepaizi Uplift. Its sedimentary characteristics are complex and the lithology,physical properties and oil-bearing properties can vary significantly. Thus,it’s difficult to carry out the oil and gas exploration in this type of glutenite. Therefore,it is neces？sary to study the distribution characteristics of the glutenite reservoir in the near-source fan delta in the study area. Thesedimentary characteristics of the glutenite were studied by analyzing the core data. Based on the analysis of palaeogeomor？phology and seismic reflection characteristics,the near-source fan deltaic facies in the first member of Shawan Formationof Chepaizi Uplift was divided into two types of sedimentary filling model-the retrogradation type and the vertical aggrada？tion type. For the former type,the glutenite retrogrades backward obviously in space with an overall positive rhythm and ob？vious sedimentary facies transition;while for the latter type,the glutenite aggrades vertically to make its thickness greatwithout obvious change in sedimentary sequence and sedimentary facies. According to the statistical analysis of reservoir physical properties data,the lower limits of the reservoir physical properties for the near-source shallow glutenite reservoirin the first member of Shawan Formation were determined（porosity：16%,permeability：21 mD）. The glutenite in the fandelta front is effective reservoir with good physical properties;while the glutenite in the fan delta plain is not reservoir dueto its poor physical properties,which can act as lateral sealing layer. Therefore,in the retrogradation type,the effective res？ervoirs are superposed retrogradationally and scattered in space,while in the vertical aggradation type,the effective reser？voir,which is very thick in vertical,can be found in the anterior and middle of the fan delta.