Providing answers for un-testable wells
Antonio Prioletta
Jaime Cadena
Rafael Cachutt
Mateo Sercen
Carlos Ortega
José Flores
Manuel Loli
Juan Watanabe
Carlo Sanabria
Combination tool can give results
Well testing has been a critical step in well evaluation since the 1920s. It has always been the first real measurement of reservoir volumetrics and potential performance.
Described as a temporary completion, well testing gives the industry a chance to flow a well under controlled conditions, allowing it to clean up and stabilize. Total flow rate, as well as the holdup of various phases present, can be measured and representative samples can be taken under PVT conditions for laboratory analysis. Pressure transients can be obtained whose character gives clues about reservoir boundary conditions remote from the well being tested. Reservoir volumes can be calculated along with formation average permeability and near-wellbore formation damage, or “skin.”
Test data
Most subsequent completion decisions are based on information obtained during the well testing phase. The critical inflow performance relationship (IPR) curve is derived from test data, and is the foundation for decisions involving perforating, formation treatment and the sizing of completion hardware and tubulars. Therefore, operators expect well test results to be accurate and of highest quality, because production decisions made from these results can have implications for the life of the well or reservoir.
Although well test data are of high value, operators are constantly evaluating cost versus value. To this end, operators around the world have been working with their service partners to perfect well testing operations and make them as efficient as possible. Traditionally, rig spread costs consume the highest percentage of the well construction budget. Accordingly, the most obvious solution to reducing well test costs is to combine as many operations as possible, or practical, in a single trip.
Testing improvements
The earliest step to improve testing quality and efficiency was the implementation of downhole test tools. With downhole test valves, gauges and sample chambers, well-bore storage effects could be eliminated or greatly reduced, and measurement quality was enhanced. Without wellbore storage, quality pressure data could be obtained in a fraction of the time required using surface testing. At the same time, accurate quartz gauges made significant improvement in test data accuracy.
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Click here to enlarge image
A comparison of test times for the three wells in the order they were run (from left to right) shows dramatic improvement in efficiency when the triple combo test string was run.
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The next step taken was to combine perforating and testing. Using a TCP work sting brought several advantages. Primary among these was the ability to shoot the well underbalanced to take advantage of instant clean-up of the perforation tunnels of any debris, as well as to prevent an influx of completion fluid into the formation creating near-wellbore formation damage.
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Volume 67 Issue 5
May 2007
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