碳酸盐岩层序地层格架内组构选择性孔隙分布特征——以塔里木盆地塔中地区上奥陶统良里塔格组台地边缘相为例

Characteristics of fabric selective pore distribution in carbonate sequence stratigraphy framework: A case study from platform margin facies of the Upper Ordovician Lianglitage Formation in Tazhong area,Tarim Basin

组构选择性孔隙是塔中地区良里塔格组台地边缘相油气储集层的重要孔隙类型,目前该类型的孔隙在层序地层格架内的分布特征仍不清晰。作者在前人建立的层序地层格架的基础上,通过大量的岩心、薄片、测井及地震资料的分析,在塔中地区良里塔格组台地边缘相识别出7类主要组构选择性孔隙:粒内溶孔、粒间溶孔、铸模孔、粒间孔、窗格孔、生物体腔孔及格架孔。高频层序中,组构选择性孔隙在90%的礁(丘)滩复合体中上部的大气淡水渗流带—潜流带中成层集中发育,厚度10~40 m,且各类型孔隙纵向上分布特征不同。受研究区湿润的古气候、相对海平面的频繁波动、台地边缘礁滩相较大的沉积速率及较好的初始渗透性等因素控制,组构选择性孔隙的发育具有层位性、旋回性及区块差异性等分布规律。即组构选择性孔隙层主要发育在高位体系域内沉积的良三段—良一段中;纵向上发育5期,主要分布在进积型准层序组6、8及9中,其次是加积型准层序组5、7、10;自东向西,各井区孔隙层数量、厚度及物性均逐步降低,主要孔隙类型由粒内溶孔、铸模孔、粒间溶孔及体腔孔逐渐变为以窗格孔、粒内溶孔及粒间溶孔。

The fabric selective pore is an important pore type of reservoir in the platform margin of the Upper Ordovician Lianglitage Formation in Tazhong area,Tarim Basin. The distribution of fabric pores in the sequence stratigraphy framework is not clear. Based on the analysis of mass data of cores,thin sections,well logging and seismic data,the fabric selective pores in Lianglitage Formation in sequence stratigraphy framework were classified into seven types,including solution interparticle pore,solution intraparticle pore,moldic pore,interparticle pore,fenestral pore,biointraparticle pore and growth framework pore. Within the high-frequency sequences,the fabric selective pores usually develop in the upper part of the reef-bank complex,which is interpreted to be exposed to the vadose zone and phreatic zone during the relative sea level drop. These fabric selective pores usually form a 10-40 m thick layer,and each type of pores displays a distinct vertical distribution pattern. The development of fabric selective pores is controlled by the humid paleoclimate,frequent changes of relative sea-level,high deposition rate and the original high permeability in reef-bank complex in the platform margin. In the third order sequence,the layer of fabric selective pores mainly develop in the high stand system,and are distributed in the Member 3-Member 1 of Lianglitage Formation. Vertical distribution of fabric selective pore can be grouped into 5 stages,most of which are distributed in the progradational parasequence sets of 6,8 and 9 followed by the aggradational parasequence sets of 5,7 and 10. From east to west,the amount,thickness and porosity of the fabric selective pore layers decrease across the study area,with the dominant types of fabric selective pores gradually changing from solution intraparticle pore,solution interparticle pores,moldic pores,biointraparticle pores into fenestral pores,solution intraparticle dissolved pores and solution interparticle dissolved pores.