特察模型在孔隙性岩石中应用的局限性浅析

地层压实过程中的静力平衡涉及到异常地层压力的形成和地层压力的计算方法。本文认为经典的特察模型不利于表达孔隙性岩石中微观的静力平衡;有效应力并非与孔隙度有直接对应关系;颗粒应力是岩石骨架中传递的真正应力,而且在纵向上颗粒应力变化比较复杂。这些结论影响到地层压力计算模型中的一些基本假设条件。

STADY ON STATIC EQUILIBRIUM EQUATION OF POROUS ROCKS IN COMPACTION PROCESSES

The effective stress has been commonly used to describe the force condition of matrix in underground porous rocks since Hubbert and Rubey(1955) applied the soil consolidation test model of Terzaghi and Peck (1948) to subsurface rock beds. When the test device of Terzaghi model and its mathematical formula was investigated again, however, the authors discovered that the Terzaghi model failed to involve porosity parameter corresponding to the number of spring in that device, so effective stress is not the true support force of grains, but a man-made physical variable. It is not suitable to be dealt with the analysis of static balance. In view of the effect of forcing area on static equilibrium, the authors hold that the total weight per unit area of arock column, namely the overburden stress (S), is actually supported jointly by the pore fluid pressure (P_f) and the grain stress (σ) which act on the area equalling to porosity (φ) and the matrix area (1-φ), respectively. Consequently, the microcosmic static balance equation is newly presented by the authors after simplifying the porous model equivalently accoding to statistics principles. Effective stress is more complicated, which may be smaller than grain stress and the latter is the true support force between grains. It is pointed out at the end of this paper that effective stress can not reflect the compaction degree because it s definition is not related to porosity, thereby the porosities of two rocks may be unequal while their effective stresses are equal to each other.