基于砾石母岩成分的火山碎屑岩储层评价方法

Evaluation Method of Pyroclastic Rock Reservoir Based on Gravel Parent Rock Composition

某盆地断裂系统复杂,具有“多物源、短物源、相变快”的断陷盆地特点,T组发育一套稳定的砂砾岩,具有较大的勘探潜力。受火山作用、水动力、物源等多方面影响,岩石中普遍含有凝灰质,火山碎屑岩广泛发育。通过岩石薄片实验分析可知,砾石母岩成分多样,主要为花岗岩、流纹岩、安山岩、粗面岩、泥质粉砂岩、玄武岩、凝灰岩等,且不同矿物组分骨架参数变化大。这导致储层孔隙度计算精度低、孔隙结构复杂、流体识别难等问题。以岩石薄片分析及钻井取心精细描述为基础,结合测井响应特征,建立不同砾石母岩成分类型的常规测井识别方法。以地质和电化学实验为基础,确定凝灰质基质部分(泥粒级以下)与黏土具有相似的附加导电性,几乎所有测井响应都在不同程度上受到这部分细粒物质的影响。因此,把凝灰质基质部分和沉积岩中的泥质含量统一,首次提出用“泥质+凝灰质”(下文简称“泥+灰”)含量替代泥质含量,并计算“泥+灰”的含量,消除凝灰质对火山碎屑沉积岩储层导电的影响。该方法可为储层评价、地质建模、压裂方案的制定提供技术支持。

The fault system of a basin is complex and has the characteristics of multiple source,short source and rapid phase transition.T formation develops a set of stable sand conglomerate,which has great exploration potential.Under the influence of volcanism,hydrodynamics,proventology etc.,tuffaceous matter is commonly found in rocks,and pyroclastic rocks are widely developed.According to the experimental analysis of thin sections of rocks,the compositions of gravel parent rocks are diverse,mainly granite,rhyolite,andesite,trachyte,argillaceous siltstone,basalt,tuff,etc.,and the skeleton parameters of different mineral components vary greatly.As a result,the calculation accuracy of reservoir porosity parameters is low,the pore structure is complex,and fluid identification is difficult.Based on the analysis of thin section of rocks and the precise description of drilling core,combined with the logging response characteristics,the conventional log identification methods are established for composition types of different gravel parent rock.On the basis of geological and electrochemical experiments,it is determined that the tuffaceous matrix part(below the muddy level)has similar additional conductivity to that of clay,and almost all logging responses are affected by this part of fine grained material to varying degrees.Therefore,the content of the tuffaceous matrix part is unified with that of the muddy content in sedimentary rocks.For the first time,the content of“mud+tuff”(hereinafter referred to as“mud+ash”)is proposed to replace the content of mud,and its content is calculated to eliminate its influence on the electrical conductivity of volcaniclastic sedimentary rock reservoirs.The method provides technical support for reservoir evaluation,geological modeling and the formulation of fracturing programs.