鄂尔多斯盆地陕北地区长10_1低孔低渗储层孔隙演化及其定量模式

Pore evolution and its quantitative model of low porosity and low permeability reservoir of Chang 10_1 in Shanbei area,Ordos Basin

孔隙演化是储层评价和油气成藏研究的重点和难点,低渗透储层中成岩作用是控制孔隙演化的主要原因。通过钻井岩心、薄片鉴定、扫描电镜等资料,系统研究了鄂尔多斯盆地陕北地区长10_1储层的基本特征、成岩作用及其与物性的响应关系,建立成岩演化序列;结合埋藏史、地热史以及生烃充注史,定性和定量分析了长10_1储层孔隙演化模式,恢复了油气成藏关键时期的古孔隙度。研究表明:陕北地区长10_1储层以长石砂岩和岩屑长石砂岩为主,孔隙度平均为10.21%,渗透率平均为2.88×10^(-3)μm^2,属于典型的低孔低渗储层,储集空间以粒间孔和次生溶蚀孔为主。成岩作用类型主要包括压实作用、胶结作用和溶蚀作用,综合判断储层处于中成岩A期。砂岩原始孔隙度平均值为35.71%,经历4个典型的演化阶段:强压实减孔阶段(-19.42%)、早期胶结减孔阶段(-6.46%)、溶蚀作用增孔阶段(+3.38%)和晚期胶结减孔阶段(-2.84%)。压实减孔率为54.38%,胶结减孔率为26.04%,溶蚀增孔率为9.46%,表明早期强压实作用是储层低孔低渗的主要原因,胶结作用则进一步强化低孔低渗特征。

Porosity evolution of reservoir is a key and difficult point of the study on hydrocarbon accumulation and regional reservoir evaluation.Diagenesis of low permeability reservoir dominates pore evolution.Through cores,thin sections,SEM and other methods,reservoir characteristics,diagenesis and relationship with physical property of Chang 101 reservoir in the Shanbei area of Ordos Basin were systematically studied,and the diagenetic evolution sequence was established.Combined with burial history,geothermal history and hydrocarbon filling history,pore evolution model were qualitatively and quantitatively studied and porosity of the critical period of hydrocarbon accumulation were restored.The results show that types of reservoir sandstone are arkose and lithic arkose.It is a typical low porosity and low permeability reservoir with an average porosity of 10.21%and an average permeability of 2.88×10^-3μm^2The types of pores are inter-partical and dissolution pores with strong heterogeneity.The main diagenesis includes compaction,cementation and dissolution which belong to stage A of middle diagenesis phase according to comprehensive analysis.Original unconsolidated porosity is 35.71%.The process of pore evolution was summarized as:Strong compaction and pore reduction(-19.42%),early stage of cementation and pore reduction(-6.46%),stage of dissolution and pore increase(+3.38%)and late stage of cementation and pore reduction(-2.84%).Also,the reduction rate of porosity by compaction is 54.38%,the reduction rate of porosity by cementation is 26.04%,and the increment rate of porosity by dissolution is 9.46%,indicating early strong compaction is the main reason of low permeability and cementation further strengthens characteristics of low permeability.