Now the most prospective objects to perform exploration works are deep horizons of Eastern Siberia. Specific feature of penetration in these conditions is the presence of abnormal reservoir pressures and relatively low reservoir temperatures. Should be noted the presence of rocks of hard drillability as well as heterogeneous rocks interlayered with soft rocks, and also the presence in section of thick halite layers and other unstable chemogenic rocks. Such complex alternation of deposits causes occurrence of various complications (inability to go down and sticking of drilling tools and casing, lost circulation, poor cementing of casing, casing collapse, etc.)
Zheldonskaya parametric borehole is founded in the north-west of the Irkutsk region in the territory of Ust-Ilim region. Purpose of drilling - identifying hydrocarbon reservoirs of fractured and cavernous type at the top of Riphean strata, as well as porous reservoirs in Vendian sandstones; assessment of their prospects for finding oil and gas.
Technological parameters of drilling fluid had been designed taking into account a set of core tasks that must be dealt with during drilling borehole, and taking into account geological features. Task was complicated by presence in section of saline rocks and intercalations of salts of different thickness, excluding the possibility of application of fresh-water drilling fluids, and by presence of cavernous limestone, in which catastrophic absorptions are probable. Composition and properties of drilling mud must also ensure prevention of landslides and sloughing, formation of minimum filtrate invaded zone in promising horizons, while rheology parameters must facilitate optimization of technological process of washover and quality cuttings removal.
In article are proposed technological solutions for conducting deep parametric borehole in difficult conditions of diverse lithologic and stratigraphic section and uncertainty of geological and technical conditions that allowed to drill a borehole with a 5-column construction and to execute a complex of geological, geophysical and technological studies for solving parametric tasks. Also are reviewed issues of cementing of casing and principles of selection of recipes of cement slurries taking into account the lithologic and stratigraphic structure and chemical composition of the rocks and fluids in intervals of cementing.
The proposed systems of drilling fluids and compositions of cement slurries allowed to ensure conduction of deep parametric borehole under conditions of diverse lithologic and stratigraphic section and uncertainty of geological and technical conditions, to ensure execution of geological task and for the first time to study section of sedimentary rocks of Zheldonskaya borehole to a depth of 4500 m.
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