With today’s economic realities, operators realize the value of attaining information about reservoir potential as soon as possible. The early confirmation of new reservoir potential can translate into time and money savings and can support decisions to optimize the well testing program and plans to drill new wells.
Case studies from appraisal wells in a carbonate gas condensate reservoir located in north Kazakhstan illustrate the importance of real-time information. In these wells, the use of wireline formation tester (WFT) interval pressure transient testing (IPTT) coupled with the latest generation fluid analyzer provided fluid properties and reservoir characteristics and confirmed the presence of additional reserves. When the reservoir was discovered, operational considerations precluded the immediate acquisition of well test data. As a result, the operator had to proceed with significant economic decisions based only on the acquired WFT data. A full year elapsed before the well test results confirmed the initial WFT results.
The IPTT uses two inflatable packers to isolate a borehole interval for testing. A downhole pump is used to clean up invaded filtrate and flow reservoir fluids during fluid cleanup, while composition and gas/oil ratio are measured using a fluid analyzer. After collecting pressure/volume/temperature (PVT) samples, a pressure buildup is performed, and transient pressure data are analyzed for the permeability-thickness product and skin factor.
Two different formations were investigated with WFT IPTT and a full drillstem test (DST). The fluid properties measured in real time matched later PVT laboratory analysis and wellhead production. Reservoir characteristics from both interpretations were in close agreement. The well test, with its deeper depth of investigation, detected a fault boundary that as not seen on the WFT IPTT.
The field examples showed how a judiciously planned and executed WFT acquisition can provide invaluable early information for key investment decisions and complement the design of the well test.