Georesursy (Dec 2018)
The safe operations modes substantiation for water source wellbores of the Vadelypskoye deposit
Abstract
The sand production problem for the water sources wellbores at the Vadelypskoye oilfield that is located in Hanty-Mansy region of Russia is considered. The serious issue during field operations is the open wellbore wall destruction even if low drawdown rates (4-6 bar) are applied to the water-bearing pay at one kilometer depth. Petrophysical analysis of high permeable (0.6-2.5 D) sandstones of water-bearing pay is presented. The effectiveness of the sands prevention methods used at the deposit is discussed and the practical recommendations for drilling and operations are given. To identify the conditions of safe fluid extraction the three-dimensional poroelastic software was used for modeling of the vertical borehole section located in the water saturated sandstone. We consider the mudcake is stripped and disappeared due to the wellbore technological operations but the plugging zone persisted. The colmatage zone was taken into account in the modeling as the radial area with reduced relative to formation permeability. Along with this, the axial sandstone permeability is non-uniform and assigned according to the core data. Different horizontal stresses ratios and values are considered in the simulations. The medium-clogged and high‑clogged damage zone influence on the formation effective stresses was studied for minimal and maximal drawdown values. It was established that the most stable borehole relative to the draw-down is located in the homogeneous horizontal stress field within the medium-clogged damage zone. Special attention was given to the damage zone permeability and thickness influence on the wellbore wall failure while pumping. It was determined that rock failure is more possible when the thin and low-permeable colmatage zone is built in formation. The near-wellbore zone colmatage effect on rock destruction can be definitely seen for conditions of equal horizontal stresses but decreases when horizontal loads are unequal. The analysis of different in-situ conditions showed that the difference between horizontal stresses has more effect on destruction than colmatage zone parameters changes. The water-pumping admissible drawdown pressure ranges are specified for each horizontal stresses regime and the recommendations were given for sanding screen characteristics. For wellbore planning at the Vadelypskoye deposit the preferable drill mud composition was described that will contribute to subsequent safe water pumping.
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