Formation damages caused by the invasion of drilling and workover fluids into the near wellbore area can become a major threat for production. Over the last decades, several techniques have been developed to mitigate this issue in terms of mud cake removal and wellbore stimulation to either dissolve or bypass the damage created. However, the most promising and efficient way would be the elimination of fluid invasion in the first place by underbalanced drilling. Therefore the applicability of this approach in a reservoir located in Hungary will be demonstrated in the following.

The paper reports the challenges as well as the final success of the well Öscöd Eny 1, which was nearly completely lost, until it was recovered by non-damaging Coiled Tubing Drilling.

Due to severe wellbore control issues while conventionally drilling into an over pressured horizon, the well had to be partly cemented to shut of the intense gas influx. Coiled Tubing as the ideal tool for live operations was then used to firstly mill out this cement and secondly deepen the unfinished wellbore significantly into the pay zone – both underbalanced.

Based on the great operational success of this procedure and the impressive production results of a nearly lost wellbore, it was decided to apply this method in an optimized overall procedure for future wells, as it was faster, cheaper and most importantly not damaging to the formation, leading to significantly improved production.

All in all, this paper provides an insight into a successfully applied technology to eliminate formation damage in a Hungarian Gas Field, which led to a rethinking about how to drill and complete these reservoirs in a cost effective and non-damaging way.

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