近岸水下扇岩石相及储层特征分析——以盐家油田盐227区为例

Lithofacies and reservoir characteristics of subaqueous fan: A case from Yan 227 blok in Yanjia Oilfield

研究近岸水下扇的储层内部质量特征及结构特征,对剩余油挖潜及开发方案调整具有重要意义。以盐家油田盐227区为例,依据岩心资料,对其岩石相沉积特征及成因机制进行了分析,认为研究区主要发育6种类型的岩心岩石相。鉴于岩心、测井、录井、地震等资料在研究尺度及分辨率上的差异,在进行岩石相储层质量及分布特征研究之前,考虑岩石相测井定量划分的必要性和可行性,将6种岩心岩石相划分为泥岩相、含砾砂岩相、砾状砂岩相和砾岩相4个亚类,并确定其测井定量划分标准,进而依据实验室分析化验数据,总结了各岩石相亚类的储层质量特征。砾状砂岩相储层以剩余粒间孔为主,物性及含油性好,为Ⅰ类储层;含砾砂岩相储层以剩余粒间孔或粒内溶孔为主,物性及含油性一般,为Ⅱ类储层;砾岩相储层以剩余粒间孔为主,物性相对较差,含油性较差,为Ⅲ类储层;泥岩相物性最差,几乎不含油,为非储层。在此基础上,应用地震反演成果开展了岩石相空间展布研究,认为研究区沙四段下部主要发育砾岩相,其为主水道及侧缘沉积的产物;中部主要发育连续的砂岩相(包括含砾砂岩相及砾状砂岩相),为频繁改道的辫状水道及水道间沉积物的复合体;上部发育稳定泥岩,为湖相泥岩沉积,垂向上整体为正旋回。砾岩相呈带状由北东至南西展布,而砂岩相则呈片状展布。

A full understanding of the internal architecture and quality of subaqueous fan reservoir is significant for remaining oil tapping and development plan adjustment. Taking Yan 227 block in Yanjia Oilfield as an example, this paper summarized 6 types of core lithofacies based on core observation, and analyzed their sedimentary characteristics and origins. Because of the discrepancy of scale and resolution between core data and well log data or seismic data, in consideration of the necessity and possibility of quantitative classification of lithofacies by using well log data, the 6types of core lithofacies were classified into 4 patterns, including mudstone facies, pebbly sandstone facies, gravel sandstone facies and conglomerate facies, and the classification criterion for each pattern was determined. And then,based on lab analysis data, the reservoir quality of each pattern was summarized： gravel sandstone facies mainly has residual pore between grains, the physical properties and oil-bearing character are the best, which makes it the first rank reservoir; pebbly sandstone facies has pores between grains and intragranular dissolved pores, the properties and oil-bearing character are medium and it is the second rank reservoir; conglomerate facies mainly has residual pores between grains but the physical properties and oil-bearing character are relative poor, so it is the third rank reservoir;the physical properties of mudstone facies is the worst, and it is nearly oil-free, so it is non-reservoir in the study area.On this basis, seismic inversion of acoustic impedance was applied to analyze the lithofacies distribution. The result shows that in vertical range, the conglomerate facies is well developed at the bottom of E2s4, which is the deposit of or between the main channel in inner fan; the sandstone facies（including pebbly sandstone facies and gravel sandstone facies） is well developed in the middle of E2s4, which is the complex deposit of multi-stage braided channel in middle fan; the mudstone facies is well developed at the top, and in all the formation shows normal cycle. In horizontal range,the conglomerate facies is ribbon-like and orients northeast-southwest, and the sandstone facies is sheet-like.