Case study: Implementing of sidetrack wells for field development – Sirte Basin-Libya

The Libyan Sirte Basin fields began production more than five decades ago, which led to a decline in production rates in recent years from these mature fields. A number of existing vertical wells have been shut-in or classified as observation wells, as a result of either their bad location - poor quality reservoirs - or the limited production life of these wells. The operating companies of these fields tended to search for economically effective methods that would improve oil recovery. Among these methods is the re-entry drilling technique, on which this paper has focused. This technology was able to convert the old vertical wells into horizontal wells by drilling a horizontal side-track at a lower cost, by save drilling cost from surface to kick-off point and saving well connection cost to surface facilities, therefore, returning them to production. It also used the geosteering technique that maintains the horizontal path of the wells in drilling. The results showed the success of using the re-entry drilling technique (horizontal side-track wells) in increasing production in two wells in the Sirte Basin, the first well in the Mesala oil field, where production increased from 73 to 2474 STB/D (chock size 48/64"), and the second well located in the Sarir oil field from 93 to 2531 STB/D (chock size 24/64") and zero water cut for the two wells. The geosteering technique also succeeded in maintaining a 1, 000-foot horizontal path for the two wells in the target layer. From the above results the practical application of the re-entry drilling technique (horizontal side-track wells) demonstrates an excellent potential to improve oil recovery from existing wells that have an improper reservoir zone.