In Russia many operators are challenged with the goal to increase production on oil and gas fields by drilling new wells or by using enhanced completion designs in the old ones. The latter is significantly less expensive, hence is preferable. The transition from completion to production on new and workover wells requires optimal clean up and the removal of the perforation damage to achieve maximum productivity.Perforating in the low formation pressure West Salym field has historically been performed overbalanced using wireline or with static underbalance using tubing conveyed perforating (TCP) with immediate well kill to remove guns. These perforating techniques, do not provide sufficient cleanup of the perforation tunnels and leave out significant perforation skin. A novel tubing conveyed perforating (TCP) technique using the dynamic underbalance effect combined with an afterperforation inflow testing was applied in the West Salym field. The goal was to achieve maximum productivity and to record the pressure transient. Deep penetrating charges were also used to bypass near wellbore damage and maximize potential results.A customized TCP test string was designed for 7 in. (178mm) casing that had two sets of gauges installed at different depths, and a production valve for the in-flow surge. The test string allowed to conduct a perforation inflow test to estimate post perforation skin, productive zone permeability and reservoir pressure.The operations were performed on 10 wells (5 workover wells and 5 new wells). Inflow pressure data on 5 wells, which allowed us to make conclusive estimates of skin, showed negative values. Improved productivity exceeded expected values by 10% on average.Dynamic underbalanced perforating has enabled us to obtain clean perforation tunnels and resulted in an average 50% production increase in comparison to the average field production.

Exploration has evolved in Western Siberian Fields in recent years, due to demands to maintain production capacity driven in part by increasing energy consumption. The frontiers have therefore extended into the Arctic regions and to the deeper unconventional formations. To ensure a high degree of reliability, safety and efficiency, a more integrated and high-tech approach has been demonstrated to be essential when planning and executing the drilling and testing phases for such complex environments. At the exploration stage the quality of the acquired data must be high to achieve maximium value.Previous exploration work on the Bolshekhetskaya Depression in Yamalo-Nenets Automonomous Area confirmed the geological complexity of the Jurassic and Achimov formations. The deep bedding, low formation permeabilities, abnormally high formation pressures, and complex geomechanics have made the previous well tests with conventional methods unachievable.The 2011P exploration well of the Pyakyakhinskoye field was drilled at 4800 m and featured initial reservoir pressures up to 980 bara with the average permeability of the Jurassic formations less than 0.1 md. Such a combination makes the well unique. As a result of this complexity, an integrated well testing approach was chosen, which included a cased-hole completion with packer and a high-pressure Drill Stem Test (DST) string. This paper presents the 2011P well test planning and execution for the Jurassic and the Achimov Formations of the Pyakyakhinskoye Field, in which four zones were sucessfully tested. The subsurface and surface equipment, well test data quality control (QA/QC), and the pressure-transient analysis are discussed herein. The geological data set included verified initial reservoir pressures and temperatures, horizontal permeability, and downhole fluid sample data. This enabled commercial reserve values to be fully obtained for the first time in the Jurassic and Achimov Formations of the Bolshekhetskaya Depression. The obtained results demonstrate the chosen equipment layout is fully applicable, this selection of equipment and lessons learned will allow execution of more efficient well testing jobs in the future.

The main challenge of perforation completion is to provide communication between the wellbore and the undamaged reservoir through clean perforation tunnels. To achieve this, two key technologies were implemented for tubing-conveyed perforation (TCP) in workover wells in a mature field in Western Siberia. First, the application of dynamic underbalanced perforating achieved clean perforation tunnels, resulting in improved production. Second, the placement of a nondamaging viscoelastic surfactant-based (VES-based) pill after perforation avoided reservoir damage during the well kill operations through clean perforation tunnels. Three wells in the mature Van-Egan oilfield were selected as candidates for the perforating project. Two wells were previously perforated with standard charges, and the third well was to be perforated across a new layer. Deep penetrating charges were used to bypass near-wellbore damage and maximize potential results. A customized TCP test string for 6 5/8-in. (168-mm) casing was implemented with two sets of gauges installed at different depths. The gauges included a downhole shut-in valve for a closed chamber test, a production valve for the inflow surge, and a fill-up valve for improved run-in-hole procedures. The TCP test string was designed to conduct a perforation inflow test to estimate post-perforation skin factor, productive zone permeability, and reservoir pressure. For the third well with 5 3/4-in. (146-mm) casing, a modified toolstring was used due to operational restrictions. After perforation, a novel, nondamaging solids-free VES-based fluid was used as a fluid loss control pill to protect open perforation tunnels during the subsequent workover operations. Several critical parameters such as permeability, bottomhole temperature, possible scale and emulsion formation, specific gravity, and stability time required were assessed to find the best pill formula for each well. This approach successfully protected clean perforating tunnels against damaging kill fluids for 3–5 days of workover operations. Results showed negative skin values for reperforated intervals and slightly positive skin values for the new perforated interval. Improved loss control was reported after spotting the pill. Zero losses were achieved in a low-permeability reservoir; loss rate observed in the reservoir with high permeability was lowered by more than a factor of 4. Post-job production data showed an increase in oil rate of up to 2.5 fold compared with the preworkover rate.

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