Abstract
Casing design an integral part of the well planning is divided into two phases: determination of the optimum casing depth and selection of appropriate casing grade. Conventionally, casing depth is determined using pore-fracture pressure data and an arbitrary kick margin (0.5ppg). This method maybe uneconomical or pose a well control risk since the kick margin may not reflect the actual well condition during fluid influx and subsequent circulation. A gas kick simulator is proposed in this work to aid the drilling engineer to make a good engineering decision during the well planning stage and rig-site well control operation. The kick simulator is derived using the using continuity equation, equation of state, and kick tolerance concept. The effects of temperature, fluid compressibility, annular friction pressure loss, choke line friction pressure loss, gas migration, variable fluid density and two-phase flow are incorporated in the the model. Beggs and Brill correlation is used to describe flow in the two-pase region; while frictional effects in the single-phase region and gas compressibility are modeled using Power Law Model and Peng-Robinson equation of state respectively. The effect of gas migration is modeled using Harmathy, Taylors and Zuber et al bubble rise velocity models. To account for liquid hold up, three types of flow regimes are adopted in the model: single gas bubble, mist and intermittent/transition flow. The results from the simulation study show that determining casing depth using pore-fracture data and an arbitrary kick margin may result to well control incident. Neglecting the effects of temperature, fluid compressibility and use of single gas bubble model is unrealistic and will require deeper casing depth. In offshore wells, choke line friction loss is an important factor that should be considered during the well planning stage.
