This work is devoted to the solution of the problem of well drilling on the sediments of the Devonian system known to lots of the world and Russian oil-and-gas regions. The well drilling on the Devonian sediments, especially with the horizontal borehole, is difficult due to the lithological composition and peculiar geomechanic properties of the clay formations composing the drilling intervals. This work covers the approach to solving the problem of keeping the Devonian sediments stability, starting from the integrated study of core of the problem intervals through the end of the testing of the developed technology concepts.

Hydrocarbon-based muds and relating invert emulsions are concerned to be unsurpassed in terms of keeping borehole stability, nevertheless they have got some disadvantages concerning the significant change in their structure-rheological properties during the change in thermobaric conditions. The solution of the stated problems is in the usage of the reagent, described in this report, which is aimed to regulate the rheological profile of the system under high bottom-hole temperature conditions. Due to the nano-size of the polymer particles, contained in the reagent, the filter cake is formed to colmatage micropores and microfractures in the formations as well as to prevent their spread.

The work covers the results of the practical-field testing of the improved invert-emulsion drilling mud formula at Kharyaginskoe oilfield. The leading foreign service company that conducted the drilling mud during the building of the horizontal wells at this oilfield before, has faced the problem connected with the loss of bore hole walls stability while opening the Devonian sediments at the zenith angles more than 60 degrees. The use of the drilling mud formula, presented in the report, has given the opportunity to avoid the problems stated above.

The field testing results, presented in the report, can be useful for the choice and reasoning of the drilling mud formula while constructing horizontal wells on the Devonian sediments by other companies especially those of them working in the Komi Republic and in the Nenets Autonomous District.

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