| Popis: |
The requirements to the drilling fluid weight, determined by the geomechanical modeling results, without taking into account all the factors affecting the wellbore stability, cannot guarantee accident-free well drilling in the intervals of unstable terrigenous deposits. The composition and properties of drilling fluid have a significant impact on the wellbore stability. This article has developed an approach to minimizing the problems associated with loss of wellbore stability, combining modern achievements in geomechanical modeling and physical and chemical studies of the effects of oil-based drilling fluids on core properties, which seems more effective in reducing the probability of the above problems compared to the separate use of geomechanical models and the results of physical and chemical studies. The proposed approach is based on the joint application of geomechanical modeling, hydraulic calculations and physical and chemical studies with the use of natural core from the intervals of the most unstable deposits, which allows developing a set of requirements to the composition and properties of drilling fluid to penetrate unstable rocks of a particular field. The specified set of requirements includes: requirements for weight, plastic viscosity, dynamic and static shear stresses of drilling fluid, providing mechanical stability of the borehole walls and effective cuttings transport; requirements for aqueous phase composition, the value of voltage stability of the mud, providing minimization of fracturing (according to the X-ray tomography results), softening and swelling of the rocks under consideration due to the hydration process; requirements for the fractional composition of microcolmatants corresponding to the fracture size in the rocks under consideration; requirements for the inhibiting and bridging abilities of the drilling fluid. This approach has been successfully applied when drilling a well with horizontal completion at one of the fields in the Perm Territory in the interval of unstable Carboniferous terrigenous deposits, which are prone to collapse and are penetrated at inclination angles of more than 70 degrees. The set of requirements for a hydrocarbon-based drilling fluid is established based on the results of geomechanical modeling and the above detailed studies. A drilling fluid formulation that meets the specified requirements has been developed. Engineering and technological support was carried out for the drilling of the considered well using the developed drilling fluid and monitoring of compliance with the specified requirements, which avoided problems associated with the wellbore instability. |
