Study On Environmental Scientific Drilling Technology

Environmental scientific drilling is the only technical method to obtain real information or sample in the reaserch on the change of palaeogeography, palaeometeorology and palaeoenvironment and the level of environmental contamination. Based on physical, chemical and biological analyses on the sample, the law of palaeometeorological change and enviommental change can be correctly deduced. Environmental scientific drilling will provide a basis for the decision of regional planning for national economy.Environmental scientific borehole is generally deeper than 5oo meters and full hole coring is needed. The core should be complete, undisturbed, uncontaminated and with good representivity. However, the conventional drilling techniques can not satisfy these requirements because of the stagnant research on coring and drilling fluid techniques.Based on the characteristics of environmental scientific drilling and in accordance with the main problems existed, this research project centres on the coring technique and the borehole wall and core protection technique by drilling fluid.This research project is financially aided by the Ministry of Science and Technology and the Ministry of Land and Resources.Based on a full argumentation, a technical line of taking fluidic type coring technique and environmental protective drilling fluid technique as the main research direction was put forward. That is, high core recovery and borehole wall stability would be mainly realized by new type fluidic coring tools and environmental protective drilling fluid system(Epm).The research on fluidic coring tools included fluidic elements, whirl-proof drill bits and water isolating device.The research on environmental protective drilling fluid system included the biotoxicity inspection method and standard of the environmental protective drilling fluid material, the development and selection of high grade environmental protective treatment materials and the research on the formular of the environmental protective drilling fluid system.Field demonstration application indicated that the fluidic elements were reasonably designed, with compact structure and remarkable results. The fluidic elements had a suspension effect on the core in inner tube. During drilling operations the whirl-proof drill bit realized very good stability, and thus stabilizing the core. Thecontrol of the distribution of drilling fluid flow rate was realized by the water isolating device, and thus the eorsion of drilling fluid to core root was avoided.The environmental protective drilling fluid system(Epm) is simple in component, non-toxic, easy in field preparation and maintenance, and is with remarkable functions of reducing filtrate loss, anti-collapse and lubrication. Thus fracture loss can be effectively sealed. Epm has good thixotropy, conducing to keeping the integrity of core. Field applications indicated that Epm completely satisfied the demands of environmental scientific drilling engineering on comprehensive properties of drilling fluid. The combination of fluidic coring tools and environmental protective drilling fluid system(Epm)increased the core recovery to more than 90 per cent from original 40 per cent by conventional technique, with the results of stable borehole wall during drilling process and smooth tripping.The research on environmental scientific drilling technique provides an effective and timely technical support for the implementation of environmental scientific drilling engineering. The fluidic coring technique and environmental protective drilling fluid technique solved the two main technical problems of low core recovery and poor core and borehole wall protection existed in environmental scientific drilling engineering, filling in the gaps in the country and promoting the progress of environmental scientific drilling techniques.