Investigation Performance of Underbalanced With Overbalanced Drilling: A Case Study In South Of Iran

Difficulties often experienced in drilling wells using conventional overbalanced drilling methods have encouraged operators to look for alternative techniques. So we can state that general and beneficial purposes of underbalanced drilling (UBD) such as decrease formation damage and drilling cost has not achieved and not use of sufficient , modern tools and maintain drilling condition in underbalanced station during the whole time of operation. On the basis of this study, UBD has not been successful significantly by way of performance in the selected oilfield except of few cases. In this paper by comparison of performance of underbalanced and overbalanced performance in terms of the amount of mud loss cost, Rate of penetration, lost time and drilling cost, productivity index in some of drilled wells in any oilfield in south of Iran, the success rate of underbalanced drilling, has surveyed and evaluated. Also the reasons and problems which lead to unsuccessful UBD have considered. This subject has been implemented by collect and study of all drilling operation information of all wells which drilled with UBD method and select their nearby wells have a reasonable comparison

Underbalanced, productivity index , rate of penetration, drilling cost