Unique Underbalanced Perforating Technique Reveals Unexpected Remaining Oil in Shut-In Wells in Libya

Abstract

The fundamental objective of well perforating is to launch an optimum wellbore to reservoir communication. Unfortunately, not all perforating jobs deliver ideal communication quality. In this paper the rudiments of apposite perforating operations, from data integration and job design to safe implementation, are summarized to produce practical guidelines for high productivity perforating jobs. Reviving oil production in mature fields is a major challenge around the globe. In Libya, there are several mature oil and gas fields that requires production enhancement. In some of these fields the challenge was to come up with a methodology that improves the oil production with minimal well intervention while testing the wells in a much quicker way than the conventional wireline conveyed perforating, well kill, swab, and test techniques. Producing zones in Libyan oil fields have lost productivity over the years due to various activities associated with workover operations. Damage was mainly caused by existence of high salinity formation water and unfiltered brine usage to kill or control the wells. Research has proven that wellbore dynamics have a substantial impact on the success of perforating activities during this very high-paced and short-lived event. We have used a technique that combines the static and the dynamic underbalanced perforating techniques to ultimately improve the hydrocarbon production in such mature fields. Advanced downhole gun and charge system designs and downhole tools are combined to enhance oil production. Debris, scale, and crushed rock removal from the perforation tunnels by applying static underbalanced perforating techniques works very successfully in many cases. Numerous field examples and research have also shown that dynamic underbalance can greatly enhance the tunnel clean up and well productivity. In this paper we are showing that combining static and dynamic underbalanced perforating ensures the optimum perforation tunnel structure. We have applied this technique on numerous wells for the purposes of perforating and re-perforating. Several wells were reperforated to improve the well to reservoir communication quality of existing plugged and damaged perforating zones. In most of the cases new perforating intervals were also added based on production logging and reservoir saturation log results. We have gained extraordinary oil production for several wells. This methodology with improved design increased oil production more than 400% in some wells. Results of this study are presented in an easy to follow way to ensure learnings are passed on to the industry for achieving improved results elsewhere. The techniques outlined in this paper will permit enhanced perforation designs via utilizing available software packages in challenging environments where conventional approaches can be inadequate. The methodology described in this paper is unique in terms of combining the existing techniques in an accessible way.