Well Engineer Guide - Well planning for optimal hole cleaning Pdf

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Annular Velocity and Mud Properties are the two major variables in the process of cleaning solids from the wellbore during drilling and tripping (i.e. hole cleaning). They are however only one part of an integrated process to achieving full hole cleaning optimisation. Other variables if not fully examined, evaluated and considered will result in a damaging effect on other well processes. E.g. Drilling and cost efficiency, bit/bottom hole cleaning, solids removal, wellbore stability, stuck pipe and hole problem prevention. Hole sizes, hole angle, casing setting depths, well conditions and formation characteristics must also be suitably planned, engineered and accounted for. The following guidelines have therefore been compiled to support hole cleaning in the well planning and operational phases of drilling operations. Well Planning : Trajectory - The choice of well trajectory is often limited by other wells in the area, the choice of target and economics. Plan and consider the implications of choosing certain trajectories. e.g. 17.5″ holes at inclinations >55° are best avoided if possible. Hole enlargement - Every effort should be made in well planning to avoid enlargement of the open hole. Mud weights, formation characteristics, fluid and drillstring dynamics are critical considerations to be accounted for in the planning process. Study offset well data for signs of over gauge hole, which may need to be included in minimum flow rate calculations. As a rule of thumb guide, the annular velocity necessary to get cuttings moving in a well inclined at 30 ° is about 20% higher than in a vertical well. Between 50° and 60°, the annular velocity needs to be about twice that in vertical holes. Plan for typical operating conditions - It is recommended that hydraulic and holecleaning simulations are run for each wells. This enables mud properties and flow rates to be optimised to provide adequate hole cleaning in all sections of the well. Hole-cleaning problems do not necessarily occur near total depth, but can occur further up in the hole where enlargement or increase in casing diameters, reduce mud velocities. Simulation of cleaning efficiency at several points in the annulus can determine areas of inadequate cleaning.

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