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塔里木盆地碳酸盐岩属于低孔隙度低渗透率,且孔隙形状复杂,常规岩石物理模型不能很好的描述塔里木地区碳酸盐岩孔隙度-速度关系。本文提出一种新的岩石物理模型-多孔颗粒上界限(PGU)模型来估计低孔隙度下碳酸盐岩的速度-孔隙度关系。在这个模型中,将岩石视为压实的弹性多孔斑块介质,从沉积过程角度把岩石中孔隙类型分为孤立孔隙和连通孔隙。这个模型是多孔颗粒硬砂岩(PGST)模型的改进,将临界孔隙度修改为更接近于实际的连通孔隙度。首先采用差分等效介质模型(DEM)来计算含孤立孔隙的岩石沉积晶体等效模量,利用改进的Hashin-Shtrikman上界限来估算含有连通孔隙的干岩模量。本文将该模型在塔里木地区测井数据应用,模型预测与测井数据匹配很好。与其他几种常用的速度-孔隙度模型对比,结果显示PGU模型预测结果更稳定,误差更小。
The carbonate rocks in the Tarim Basin are characterized by low porosity and low permeability and complex pore shapes. The conventional petrophysical models do not describe well the porosity-velocity relationships of carbonate rocks in Tarim Basin. In this paper, we propose a new petrophysical model called the Upper Boundary of Porous Particle (PGU) model to estimate the velocity-porosity relationship of carbonate rocks with low porosity. In this model, the rock is regarded as a compacted elastic porous patch medium, and the pore types in the rock are divided into isolated pores and communicating pores from the depositional process. This model is an improvement of the PGST model, which modifies the critical porosity closer to the actual connected porosity. The differential equivalent medium model (DEM) is first used to calculate the equivalent moduli of isolated rock-deposited crystals, and the improved Hashin-Shtrikman upper bound is used to estimate the dry rock modulus with connected pores. In this paper, the model is applied to well logging data in Tarim area, and the model prediction and well logging data are well matched. Compared with several other commonly used velocity-porosity models, the results show that the PGU model predicts more stable and less error.