Research Of Instability Of The Hole Wall Of Fault Gouge Section And Strategy Of Drilling Fluid System Of Wenchuan Earthquake Fault Scientific Drilling Project

At 14:28 on May 12,2008,it took place 8.0 earthquake shocked the world in Wenchuan of China, and it caused heavy losses to people's lives and property. State Council attaches great importance to it, and set up state council earthquake relief headquarters immediately. In order to study the mechanism of the earthquake and seismic earthquake monitory and prediction, ministry of land and resources joint China Seismological Bureau to organize the earthquake fault scientific drilling project. The content of the earthquake fault scientific drilling project researching is on the basis of five scientific drilling groups on the Beichuan-Yinxiu in the Longmen Mountains and the rupture front of Longmen Mountains Anxian-Guanxian, carried out multi-disciplinary research with geological structure, earthquake geology, rock mechanics, chemical physics, earthquake physics, fluids, rheology and so on. Observation and testing source of the large earthquake and micro multi-disiplinary earthquake, revealing the physical and chemical effects of the controlling faulting and earthquake occurring. Integrated geophysics logging, coring imaging and observation through active source seismic. Indentify active faults of various structural elements, measuring the width of fracture failure and strength, and determine the structural properties of fracture. Established Long-term seismic station by placing instruments in the hole,. The first hole of Wenchuan Earthquake Scientific Drilling Project(WFSD-1)encountered gouge when it is 585 meters deep, hole serious instability, malignant sticking twice accident, forced to sidetrack, seriously hampered the progress of the project.No matter the engineers and technicians who engage in geological core drilling and oil drilling didn't have the experiences about core drilling in fault gauges wall after great earthquake. This is a new subject for drilling technical personnel to solve the problem core in the section of fault gauges during the process of WFSD-1.We analysis the fundamental mechanism, failure criterion of wall, computation of collapse pressure and fracture pressure , the factor affect wall stability of the fault gauges section of the wall. And analysis the constouctional material and Physicochemical Properties of the fault gauges by experiment and reach a conclusion that the fault gauges have low original water Content, strong disparity, low permeability, easy to absorb water and volume expanding. At the same time we test the unconfined compression of the fault gauges in original water content and air-dried condition. Also test the shear strength of the fault gauges in different water content, draw a conclusion that the water content have a great influence on the unconfined compression and shear strength of the fault gauges, with the water content was increasing, the unconfined compression and shear strength decline sharply.We put forward the problems of the fault gauges drilling through analysis the fundamental mechanism about wall stability and study on the Chemistry and physic mechanics of fault gauges, they are:(1) High crustal stress causes fault gauges plastic flow, result for shrinking pathway of hole.(2) Volume expansion by the fault gauges absorbs water result for shrinking pathway of hole.(3) It easy to sticking as high viscosity and high disparity of he fault gauges.To solve these problems, this paper presents the solution and mud technical of the problems, they are:(1) Increase the density and fluid column pressure of the mud to balance high crustal stress.(2) Lower the filtrations of the mud result for achieve low filtration to bring down fault gauges absorbs water.(3) Strong the lubricity and the sticking-Proof capacity of the mud while drilling have good lubrication, if sticking it can solve the problem.Aimed at solve the question, we developed the drilling mud additives can dilute and film-foaming that suit for small hole wire line drilling exploration, And screen out another additives that have the best compatibility proportion with it. Finally we developed the mud system which has good stability, low filtration, heavy density, and apply to the first drilling hole of the Wenchuan earthquake fault science project (WFSD-1) and achieve good results, laid the groundwork for the projects Completed Smoothly.