Chen Liyi

Rheological Properties of Polymer Drilling Fluid Developed for Permafrost Natural Gas Hydrate Drilling

The rheological properties of water-based drilling fluids are heavily influenced by low temperatures and are some of the most important issues for permafrost natural gas hydrate drilling. In this work, we developed a polymer drilling fluid formula and studied its rheological properties at low temperatures. The rheological properties of four different drilling fluids including macro-polymers, amphoteric polymers, sulfonated polymers, and biopolymers were tested. The corresponding rheological-property/temperature response curves were drawn. The response characteristics of the rheological properties with temperature were analyzed. Based on these, a novel research idea was developed to adapt to permafrost drilling a poly-sulfonate drilling fluid system in which sulfonated lignite (SMC) and sulfonated phenolic resin (SMP) were used as the main agents while xanthan gum (XC) served as a flow-pattern modifier. According to orthogonal test results, the optimized drilling fluid formula was base mud + NaCl (20 wt. %) + NaOH (0.1) + SMP (3) + SMC (4) + XC (0.3). Moreover, the rheological-property/temperature response mechanism was analyzed using Fourier transform infrared (FT-IR) spectroscopic tests of the treating agents and scanning electron microscopic (SEM) tests of the mud cakes.

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

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.