基于岩石电阻率参数研究致密砂岩孔隙结构

STUDY ON PORE STRUCTURE OF TIGHT SAND BASED ON RESISTIVITY

低孔低渗致密砂岩储层孔隙结构特征是影响其油气储集能力和采收率的重要因素,故对其孔隙结构特征进行研究具有重要的意义。文章主要探讨了利用电阻率参数开展该类储层孔隙结构特征研究的方法。基于铸体薄片和压汞实验数据反映出的此类储层孔隙结构的特征,选取毛细管束模型推导并建立了致密砂岩储层孔隙结构特征参数计算模型,并结合岩电实验数据对模型进行了验证。结果表明:从电阻率参数计算得到的岩石孔隙结构参数能较好地反映岩石的孔隙结构特征,利用电阻率计算得到的岩石孔隙结构参数是随含水饱和度变化而变化的量,其变化量及变化的速率能够反映出储集层开采过程中油气藏内部流体的分布变化;利用井下不同时刻实测电阻率参数计算得到的岩石的孔喉半径,仅代表测井时刻地层内导电流体所占据的孔隙空间的半径,而计算得到的岩石迂曲度也只反映了当前状态下导电流体的分布状况。

Pore structure of tight sand reservoirs with low porosity and low permeability is an important factor influencing the storage capacity and recovery ratio, thus study of pore structural features is of great significance. This paper mainly discusses the methods to study the pore structural features of reservoirs with low permeability and porosity. Based on the pore structural features of this kind of reservoirs derived from the experimental data of cast thin section and mercury penetration, a model for calculating the pore structure parameters of tight sand reservoirs is built by using the bundle of capillary tubes pack, and is verified with the experimental data of lithology and electric properties. The pore structure parameters derived from resistivity parameters are variable with water saturation, and the magnitude and rate of their variations can reflect the change of fluid distribution in reservoirs in the recovery process. The pore throat radius calculated by using the measured resistivity downhole at different times can only reflect the radius of pore spaces that are occupied by conductive fluids at the time of logging, and the calculated tortuosity also can only reflect the current distribution of conductive fluids.