Dynamic underbalance (DUB) is a technique that has been used for many years by many operators to deliver cleaner perforation tunnels so as to achieve better well productivity or injectivity. Its advantage is shown in the laboratory and by many field jobs. Unlike conventional static underbalance perforating, the DUB perforating technique delivers a sharp pressure drop at the time of perforating, which is critical in breaking down the low-permeability zone around the perforation tunnel, commonly known as the crushed zone.
After several years of DUB application in the industry, the technique evolved into the DUB post-perforating technique in which a gun chamber is instantaneously opened at the existing perforations to create a sharp pressure drop to clean the crushed zone. This technique has been successfully applied in both the laboratory and in the field.
Other laboratory work has provided greater insight into the nature of perforating tunnel damage and how effective the standard DUB or post-perforating DUB technique can be in cleaning them. From this understanding and implementation of both DUB techniques, the repeat-DUB technique is proposed.
The repeat-DUB technique delivers perforations by the standard DUB technique and subsequently treats them with the DUB post-perforating technique, all in the same job. Although the DUB techniques produce perforations with a good productivity index (PI), the repeat DUB sequence further enhances the PI. This paper discusses the concepts and why and where this technique enhances the PI, including a review of, the basics of the DUB technique in comparison with various surging techniques. The repeat-DUB technique has been applied to 35 wells in a field in Oman with good results.