Dynamic Underbalanced Perforating Application Increases Productivity in the Mature High-Permeability Gas Reservoirs of Santa Ana Field, Venezuela

Abstract

Located in Eastern Venezuela the Santa Ana Field is part of the most important gas province of Venezuela: Anaco District. Its main productive zones are the Merecure and San Juan formations, which are sandstones characterized by their high permeabilities (100 - 500 md) and low pressures (1200 - 2200 psi). The wells in Anaco District are normally perforated using conventional static underbalanced techniques. The productivity of these wells was evaluated using nodal analysis techniques coupled with perforating performance simulations. The quality and amount of data was recognized to be limited. However, a qualitative diagnosis of these results indicated that the static underbalanced condition and the shaped charges used were not enough to effectively clean the perforation tunnel and surpass the near wellbore damaged zone. Dynamic underbalanced perforating coupled with high performance charges was selected as the technology that would improve productivity in the challenging wells of Santa Ana. This technology has been applied in similar scenarios across the industry in recent years, although no documentation was found on its use in such low pressure environments. This paper describes how dynamic underbalanced perforating was deployed successfully, while pushing the limits of its application envelope. To obtain a dynamic underbalanced condition in such a low pressure environment, the shot density had to be reduced to 2.5 spf, raising concerns about its effect on well productivity. Two wells were selected for this field trial. They were perforated using a TCP/DST string, which allowed the well to be tested immediately after perforating. Details of the diagnosis, planning, execution and evaluation phases of this project are described. The resulting gas production and zero perforation skin represented more than a two-fold productivity increase compared with the target reservoir average well production. These results demonstrate the effectiveness of the technique under borderline conditions, and promote its application in similar scenarios worldwide. This project shows the importance of production and perforating diagnosis, leveraging technology application and pushing the limit of dynamic underbalanced perforating in order to increase productivity in mature/low pressure assets. Introduction Perforating can be defined as the process of connecting the well with the reservoir by creating a tunnel which goes through the casing, cement sheath and the reservoir rock. The main objective of perforating is to create a clean tunnel sufficiently long that it reaches the undamaged reservoir. This process is fundamental to the productivity of the well; however, its importance is often overlooked during completion operations. It was recognized that perforating was an area that could be improved in Anaco District well completions. As a result, a qualitative evaluation of conventional perforating performance was done. This evaluation confirmed the link between poor well productivity and perforating and justified the field trials of new technology in this area. Most of the perforating technology developments have been focused on obtaining deeper penetrations. However, few breakthrough advances have been achieved relating to tunnel quality. The industry has relied solely on static underbalance, which is now a well recognized technique for perforation cleanup. The appropriate level of static underbalance has been extensively researched1,2,3; however, more recent investigations4,5 have presented relevant evidence indicating that static underbalance is not the only governing factor in effective perforation cleanup.