塔里木盆地奥陶系碳酸盐岩储层孔隙特征刻画

Pore characteristics of Ordovician carbonate reservoir in Tarim Basin

塔里木盆地奥陶系碳酸盐岩地层孔隙类型复杂,是地震勘探中孔隙度-纵波阻抗、孔隙度-渗透率关系复杂化的主要因素之一,由于缺乏合适的岩石物理模型,导致其表征一直是一个难题。根据Biot理论,Sun岩石物理模型引入表征碳酸盐岩储层非均质性的研究。与传统岩石物性模型相比,该模型可以更好地刻画碳酸盐岩储层孔隙类型的多样性,其有效性及准确性在岩心及测井尺度得到验证和应用。在这个模型中,孔构参数是一个与孔隙度无关的弹性参数,它能够在孔隙度不变的情况下表征体积和剪切模量的变化,进而表征孔隙的形态变化特征。文中采用该参数表征储层孔隙类型及孔洞特征的变化:首先,通过成像测井的二次处理,实现孔洞储层孔洞段、裂缝段的定性识别及孔洞直径、孔洞数量及孔洞面孔率的定量评价参数,为后续Sun岩石物理模型参数反演提供基础数据;然后,利用Sun岩石物理模型,得到表征储层孔隙类型的孔构参数;最后,在成像测井定量解释参数及薄片资料的刻度下分析了孔构参数与孔洞的大小和充填程度、孔隙类型及裂缝的发育程度的关系。研究结果表明:对于岩溶储层,孔构参数可以表征溶洞储层洞体的规模及充填程度。对于基质孔隙,孔构参数刻画了晶间孔、微晶孔及成岩缝;对于2%以下的非储层段,孔构参数可以刻画裂缝段和致密碳酸盐岩段。利用孔构参数建立的孔隙度类型、孔洞充填程度及直径大小的定量解释图版,为研究区复杂缝洞体优质储层的预测奠定基础。

The Ordovician carbonate formations in the Tarim Basin are characterized by a variety of pore types,which is one of the main factor for the complexity of the porosity-P-wave impedance and porosity-permeability relationships.Due to the lack of suitable petrophysical models,its characterization is always a difficult problem.The heterogeneity of carbonate reservoirs is introduced in Sun petrophysical model according to the Biot theory.Compared with the traditional petrophysical model,this model can better characterize the diversity of pore types in carbonate reservoirs,and its effectiveness and accuracy have been verified and applied in core and logging scales.The pore structure parameter introduced in this model is an elastic parameter independent of porosity,which can characterize the change of volume and shear modulus under the condition of constant porosity,and then characterize the change of pore morphology.This parameter is used in the paper to characterize the change of pore type and vug characteristics for carbonate reservoirs in Tarim.The study firstly realizes the qualitative identification of vug section and fracture section and the quantitative evaluation parameters of vug diameter,vug number and vug surface porosity through the secondary processing of imaging logging,which provides basic data for the subsequent inversion of Sun petrophysical model parameters.Then,using the Sun petrophysical model,the pore structure parameters characterizing the pore types of the reservoir are obtained.Finally,the relationships between pore structure parameters and size and filling degree of vugs,pore types and development degree of fractures are analyzed based on the quantitative interpretation parameters of the imaging logging and the thin-section data scale.The research results show that for karst reservoirs,the pore structure parameters can characterize the size and filling degree of vug in the reservoir.For matrix pores,the pore structure parameters characterize the intercrystalline pores,microcrystalline pores and diagenetic fractures.For non-reservoir section with porosity below 2%,the pore structure parameters can characterize fracture sections and tight carbonate rock sections.The quantitative interpretation chart of porosity type,vug filling degree and diameter based on pore structure parameters lays a foundation for the prediction of high quality reservoir with complex fracture-vugs in the study area.