Gas hydrates – the firm crystal connections of water and low-molecular waterproof natural gases such as carbohydrates (mainly methane), СО2, N2 and others. At present, time exploitation of the Messoyahsk (Russia) and Mallik (Canada) deposits of gas hydrates is conducted actively. The further perfection of prospecting methods in the field of studying gas hydrate containing sediments in round extent depends on improvement of methods for native-state core sampling from these sediments.
The primary results of the research and engineering work of the Department of Technology and Technique of Well Drilling, carried out and completed in 2000, are presented. The main result of drilling long wells in the ice of Antarctica is the development of the project of environmentally safe opening of the subglacial Lake Vostok, a unique natural phenomenon, the complex study of which is of the greatest interest to the world scientific community. A 505 m long well with full core recovery was drilled on the Academy of Sciences glacier (Severnaya Zemlya archipelago) in the framework of the international environmental program PEGAIS. Geophysical measurements were carried out in the well. A new method of tubeless casing and sealing of anomalous intervals using a fusible binding material and a thermal plugging penetrator was developed. Basic theoretical and technological principles of liquidation plugging of hydrogeological wells with the use of economical and environmentally safe cementing mortar based on cheap mineral waste were developed. Effectively conducted research and experimental developments on the combined heat and hydrodynamic effects on low-productive sands to increase oil and gas production wells, clarified the laws of the hydro and foam core. New applied programs for PC were formed, allowing to increase adequacy of data and to expand the field of application in evaluation of regulation and stabilization of circulation and heat exchange processes during well sinking and development.
Fusion drilling technology is based on unconventional, purely physical methods of destruction and consolidation of rocks associated with changes in their aggregate state as a result of intensive heating in the bottom-hole zone.
The most important and the most effective way to study glaciers is: drilling of boreholes with complete coring, but the processes of ice destruction during rotary drilling are insufficiently studied.
At present, a variety of physical methods of breaking or de-strengthening rocks are increasingly being introduced into the practice of drilling.
Due to the spread of drilling operations in the most diverse geological and natural conditions, constant increase in the depth of exploration and production wells, intensification of traditional and development of new technological methods of drilling, heat and mass exchange processes occurring in the well are becoming increasingly important at all stages of well construction, and the temperature factor in many cases is becoming one of the main technological parameters, determining not only the efficiency of individual operations, but also the very possibility of the well construction.
One of the promising directions of creation and development of new complexes of high-performance technical means for drilling wells in difficult mining and geological conditions is the development of fundamentally new methods of rock destruction, differing both in the type of energy used and the nature of its transfer to the rock massif at the bottom of the well.
With increasing drilling depths, the rheological properties of rocks composing the borehole walls become increasingly important. As a result of unloading on the side of the borehole, passed in a stressed rock mass, a zone of redistribution of normal stresses ...
A new promising direction of increasing the efficiency of well sinking in difficult geological and mining conditions is the development and improvement of physical methods of rock destruction, one of which is melting ...
One of the problems of deep drilling is to maintain the stability of the rocks composing the walls of the borehole, both directly in the process of penetration, and during subsequent studies and works ...
One of the promising directions of further improvement of drilling operations in complex mining and geological conditions is the research and development of the method of drilling wells with changing the aggregate state of the passed rocks ...
With the increase of drilling depths the borehole penetration in the glacial cover becomes sharply complicated, as the borehole continuously narrows due to ice creep under the conditions of increasing mountain pressure and temperature. Thus, during deep drilling at the Vostok station in Antarctica, ice creep became apparent from a depth of 500 m at an ice temperature of -53°C. ...
One of the promising directions for the development and improvement of new drilling methods is the destruction of rocks by melting or vaporizing them under conditions of intense thermal influence in the bottom-hole zone. The efficiency of drilling-melting depends little on the hardness and plasticity of rocks, as well as on external factors, and in this sense has a certain universality, which allows already now to anticipate its advantages over mechanical drilling in some specific conditions of well sinking ...
Prospective reserves of coquina phosphorite deposits in Estonia and the Leningrad Region are estimated at 2-3 billion t. Genetically, they are associated with the thickness of quartz-obol sandy sediments of the Pakerort horizon of the Early Ordovician, spread over almost the entire territory of Estonia and stretching 320 km to the east of it (Leningrad Region). The thickness of the productive strata varies from 1-6 m, with an average thickness of 4 m. Phosphorite-bearing sandy sediments with erosion lie on sandstones, siltstones or clays of Cambrian.
The purpose of simultaneous with the drilling process of freezing of passed melted rocks is to ensure their monolithicity and strength, which makes it possible to avoid complications associated with the instability of loose wet rocks, and to obtain a high core yield.
The most important task of exploratory core drilling is to ensure high yield and quality of core - source material for geological and engineering-geological sampling. Analysis of production data of a number of organizations engaged in drilling in permafrost rocks shows that when drilling with flushing the core yield is 60-70% for bedrock with moisture content of 2 - 5% and 20-30% in rocks with moisture content of 15% and more. In production conditions very often in order to increase the core yield one switches to “dry” drilling. However, the core quality deteriorates sharply. Partial or complete thawing of the core takes place with violation of its structural characteristicsю
Successful testing of technical means and technology of drilling wells with bottom-hole cleaning by cooled compressed air, developed by the department of TTBS of LGI under the contract with the Dalstroyproekt Institute (Magadan), allowed drilling by this method in production conditions and give a preliminary assessment of its economic efficiency in comparison with the method of drilling wells in frozen rocks “dry”, i.e. without bottom-hole cleaning by any circulating agent.
