METHOD OF HORIZONTAL WELL CONSTRUCTION IN SECTIONS OF UNSTABLE STRATA (VERSIONS) Russian patent published in 2014 - IPC E21B21/14 C09K8/26 C09K8/36 

FIELD: oil-and-gas industry.

SUBSTANCE: proposed method comprises driving the vertical section, initial zenith angle borehole deviation section, and sections of zenith angle increase with outcrop to horizontal, and driving horizontal borehole using techniques of driving and drilling in unstable strata. Vertical section and sections with zenith angle increase to 70° are driven with the help of polymer-emulsion water-based mud (PEWM). Sections with zenith angles over 70° and horizontal borehole composed by stable carbonate and unstable terrigenous deposits are drilled using hydrocarbon-based mud (HCBM). Portion of the latter is replaced by phase inversion with PEWM on reaching the design depth and forced in through borehole. Aforementioned techniques are changing between PEWM and HCBM by phase inversion in drilling. Changing PEWM into HCBM is performed by mixing PEWM with A inverter, that is, the mix of hydrocarbon fluid with inverse emulsion with NAEI making the active component, said NAEI being based on polyglycol ethers of fat acids or alcohols with NLB number not over 10 at hydrocarbon fluid-to-emulsifier ratio making 14-19:1, respectively, A inverter being added in amount of 28-35 vol. %. Subsequent changing HCBM into PEWM is made by adding B inverter to the latter, that is, the mix of direct emulsion emulsifier thereto with NAEI making the active component being based on polyglycol ethers of fat acids or alcohols with NLB number not over 11-14, with dioxane alcohol with weight ratio of hydroxyl groups of 15-36% at emulsifier-to-alcohols ratio of 2-3.5:1, respectively, B inverter being added to HCBM in amount of 1.75-4 vol. %. In compliance with another version, stable carbonate strata horizontal hole driving and drilling are performed using HCBM. Driving the sections in above-productive interval is performed with zenith angles over 70° with the help of PEWM. After reaching the design depth of horizontal hole, PEWM is forced in through borehole.

EFFECT: possibility of drilling over terrigenous Devonian deposits with unlimited zenith angles.

14 cl, 7 tbl