Author's Reply to Discussion of Brief: Pore- and Fracture-Pressure Determinations: Effective-Stress Approach

摘要

We welcome the opportunity to expand on and challenge some of the comments raised by Dr. Yassir in her discussion. Owing to the constraints of a two-page brief, covering this subject in the detail it deserves is difficult. Essentially, there are two main objections to her arguments. First, she is applying findings from transient laboratory compaction relationships to static equilibrium (classic Terzaghi) natural compaction observations. Second, she is trying to force fit elastic stress/strain rock mechanics theory to a natural compaction process that is essentially plastic to the point of maximum stress loading. There is no documentation of the "gross errors" that can occur when applying the simple methods described in the brief. Rather, the discussion lists a group of possible errors assuming rock response to stress is poroelastic. The two material response coefficients, σ_(max) and α, in the simple porosity/effective stress relationship we use [σ_V = σ_(max) (1 - φ)~α] are derived directly from natural gravitational compaction data observed in sedimentary rocks without prior assumption of any material-response law (plastic or elastic). Gross errors do occur when one tries to force fit poroelastic coefficients to natural processes that do not obey that assumed material-response law.