The drilling of large oil and gas fields in Eastern Siberia is complicated by the presence of formations in the section that are prone to collapse, scree, loss of drilling mud; characterized in the process of opening by a decrease (for various reasons) of natural porosity and permeability; with low thermobaric parameters (temperature is about 14 °С, reservoir pressure gradient is 0.8-0.95). This makes it necessary to carefully substantiate, develop and use special fluids for drilling in the intervals of occurrence of such formations. Drilling fluids should meet the following requirements: the density is not exceed 1100 kg/m3; rheological characteristics (viscosity, static and dynamic shear stresses) comply with reservoir thermobaric conditions; the dispersed phase of the solution penetrating into the reservoir pore space is physically and chemically inert with respect to the rock-forming minerals and eventually decomposes and can be removed from the reservoir; the drilling mud is not interact with the material composition of the rock cement (is not cause its swelling and destruction), etc. As part of the design of oil-based drilling mud composition a number of experimental studies were carried out. Optimal components concentrations of the hydrocarbon-based solution were selected for the conditions of the Khamakinsky horizon in Eastern Siberia. According to the results of comparative experiments, it can be assumed that the proposed formulations are effective, promising and provides high return permeability. When drilling wells at the Vostochno-Alinskoye field in the interval of the horizontal section (under the shank) at the first stage of pilot-industrial implementation diesel fuel-based mud were chosen because of their increased environmental friendliness in comparison with oil-based and highly mineralized solution. After successful field tests the drilling technology with bottomhole pressure control (equilibrium and depression) were recommended for terrigenous reservoir drilling.
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