A Novel Hydraulics Design Approach Enables Simplified Configuration Offshore Wells

Abstract

The reduction of the number of sections in the construction of an offshore well is a major driver for cost reduction. In order to achieve this goal, the sections must be longer, resulting in additional challenges. A critical aspect is related to the second section (no fluid return to surface) reaching high inclinations and longer extensions. Such sections are drilled with fluids with no carrying capacity, reaching 1500 m and inclinations as high as 65 degrees, resulting in expressive cuttings accumulation in the wellbore annulus. The scope of this article is to present a novel hydraulics design procedure which accounts for the effect of hole cleaning actions during well construction which reposition hydraulic parameters into acceptable criteria. This paper details novel design procedures which include the following steps: Defining cuttings bed height deposited along the wellbore annulus using traditional steady state cuttings transport models. This information is the initial condition for the design of hole cleaning pills pumping. Estimation of the extension of the cuttings bed through a material balance. Estimation of drag efforts for drillstring movement in the presence of a cuttings bed and the maximum well length which can be handled by the rig without carrying extra hole cleaning procedures. Calculation of the solids removal due to the pumping of hole cleaning pills based on a transient solid-liquid model. Optimization of the frequency, volumes and pump rates for the cleaning pills. This way, the proposed methodology allows the creation of a hydraulics design package which incorporates the optimization of hole cleaning actions during the drilling of a deviated well with fluids which do not present cuttings carrying capacity. The procedure was successfully implemented in 4 offshore wells in Campos basin, offshore Brazil, which were built in only 3 sections including a horizontal section. The present methodology is a milestone in hydraulics design for offshore wells, enabling the construction of horizontal wells in 3 phases resulting in a huge well construction time reduction.