Influence of the characteristics of fault gouge on the stability of a borehole wall

Abstract

How to find more effective way to stabilize the borehole wall in the fault gouge section is the key technical challenge to control the stability of the borehole wall in the Wenchuan fault gouge section during the process of core drilling.Here we try to describe the characters of deep fault gouge in fracture zones from the undisturbed fault gouge samples which are obtained during the core drilling. The X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and Scanning Electron Microscope (SEM) provided the detailed information of the fault gouge’s microscopic characteristics on the density, moisture content, expansibility, dispersity, permeability, tensile strength and other main physical-mechanical properties. Based on these systematic experimental studies above and analysis of the fault gouge instability mechanism, a new technical procedure to stabilize the borehole wall is proposed — a low water and a low loss low permeability drilling fluid system that consists of 4% clay + 0.5% CMC-HV + 2% S-1 + 3% sulfonated asphalt + 1% SMC + 0.5% X-1 + 0.5% T type lubricant + barite for core drilling in fault gouge sections.