Coiled Tubing Drilling -A Concept for Directional Drilling in -Pressure Depleted Reserwoirs

摘要

Many gas reservoirs in the north-western part of Germany have been produced for decades. It has become increasingly challenging to start production from conventionally drilled holes in depleted reservoir sections. This can be due to invasion of fluid into the rock matrix causing near wellbore damage, the necessity to stop fluid losses prior to running a completion, or the reservoir pressure being insufficient for producing fluids back after drilling. During the past years a concept has been developed to re-enter carbonate reservoir wells, drill a sidetrack to the top of the reservoir, case-off the section, and run the completion. Afterwards the reservoir section is drilled on coiled tubing using nitrified fluid in order to reduce the overbalance towards the reservoir pressure and to minimize skin related inflow performance issues. This procedure has proven successful in a first step for drilling short open-hole sections without directional control and steering capability. Encouraged by the results, as a second step, a concept for drilling directional hole sections on coiled tubing has been developed using state of the art technology. The goal is to use existing wells that are suffering from severe reservoir damage issues and access virgin reservoir rock by drilling open-hole sidetracks. A portfolio of wells has been screened to find promising candidates for directional coiled tubing drilling. First choice candidates are open hole completed wells with high inclination well paths in carbonate reservoirs.