Coiled Tubing - Reverse Circulating Drilling Reverse Circulation Drilling is a technology that is applied to low-pressure, damage-sensitive formations to improve well productivity. Conventional overbalanced drilling can impair well productivity by pushing mud filtrate and drill cuttings into natural fractures and pore throats of the zone. Conventional underbalanced drilling reduces the potential for damage by drilling at pressures lower than the formation pressure. However, it still requires drill cuttings to be circulated past the drilled formation face, which may scour or plug pore throats and cleat systems. Reverse circulation drilling uses a concentric coiled tubing string to place a drilling fluid (typically air or nitrogen) down the annulus between the coiled tubing strings to a bottom hole assembly. The pumped fluid drives a reverse circulating drilling assembly (comprised of a reverse-circulating air hammer with an impact drill bit) which draws exhaust fluid, the drilled cuttings, and any formation fluids back into the inner coiled tubing string. The exhaust fluid, drilled cuttings, and formation fluids are produced back to surface through the inner coiled tubing string without contacting the previously drilled wellbore. Initial target formations are low-pressure, damage-sensitive zones such as shallow gas and coalbed methane opportunities.
Back
