准噶尔盆地莫索湾地区清水河组深层优质储层特征及其物性控制因素

为了明确准噶尔盆地腹部莫索湾地区清水河组储层特征及其成因,综合利用铸体薄片、扫描电镜、物性、X衍射等多种分析测试手段,并结合钻测井、地层测试资料及区域埋藏史、古地温、沉积体系等相关研究成果,详细分析了清水河组储层成岩作用特征及其物性控制因素,并在此基础上总结成岩模式。研究结果表明:清水河组储层具有低成分成熟度、高塑性岩屑含量及高结构成熟度的"一低两高"特征;尽管储层主体埋深在3 500m以下,但储集空间仍以原生粒间孔为主,平均孔隙度为15.47%,平均渗透率可达226.6mD,为典型的深层优质储层;储层成岩作用总体表现为"中压实中强压实、强溶蚀、弱胶结"的特征,尽管储层埋深较大,但成岩阶段整体仍处于中成岩A1亚期;区域连片的厚层辫状河三角洲前缘水下分流河道及河口坝中细砂岩及中粗砂岩是形成深层优质储层的基础,而成岩过程中储层物性保存主要受控于早期碳酸盐胶结抗压实、绿泥石包壳及后期酸性成岩流体条件下的溶蚀增孔作用;除上述沉积、成岩控制因素外,地层超压的存在使得储层在深埋条件下压实强度显著降低,是储层物性保存的关键,同时在储层成岩演化过程中及现今盆地不断降低的地温梯度也有效延缓了储层的成岩进程。

Characteristics and Controlling Factors on Physical Properties of Deep Buried Favorable Reservoirs of the Qingshuihe Formation in Muosuowan Area,Junggar Basin

For the aim of revealing deep-buried Qingshuihe Formation (K1q) reservoir characteristics and the factors governing reservoir quality, formation test and related researches of regional burial history, paleo-temperature and depositional system were analyzed by casting thin section, SEM, physical properties, X-ray diffraction of clay minerals, together with well drilling-logging data.And on the basis of these data, diagenetic model was proposed.The results demonstrate that K1q reservoir has a typical characteristic of low composition maturity, high plastic lithic content, and high textural maturity.Although buried mostly deeper than 3 500 m, the reservoir still has a mean porosity of 15.47% and mean permeability of 226.6 mD, and the main pore types are intergranular pores.So the Qingshuihe Formation is a typically favorable reservoir with deep buried depth.Moreover, the overall reservoir diagenesis is characterized by medium compaction, strong dissolution and weak cementation.Despite the deep buried depth, the diagenetic stage still belongs to the stage A1 of middle diagenesis phase.For the controlling factors on physical properties, the thick mid-fine sandstones and mid-coarse sandstones originated from underwater distributary channels or mouth bars of regionally distributed braided river delta are the basis for the formation of favorable reservoirs.While during the processes of diagenesis, physical properties are mainly controlled by compaction resistance from earlier carbonate cements, chlorite coats on detrital grains and dissolution attributed to acidic diagenetic fluid in later period.In addition to the sedimentary and diagenesis factors above, formation overpressure is the key factor in preservation of reservoir physical properties, significantly reducing the strength of compaction under the condition of deep burial depth.In the meantime, geothermal gradient continuously decreased during the processes of diagenesis and even at present, which resulting in the delying of diagenesis processes and preservation of physical properties.