Placement of Permanent Downhole-Pressure Sensors in Reservoir Surveillance

This paper probes the gauge-placement issue with regard to yielding quality formation parameters unaffected by wellbore effects. Nonphysical or biased results may result if the wellbore effects are unaccounted for. We used a well bore/reservoir simulator that conserves mass, momentum, and energy to develop a comprehensive understanding of the gauge-placement issue. First, we reproduced a field example from a deepwater asset to demonstrate the simulator's capabilities. In this example, we matched the bottomhole pressure (BHP) and pressure/temperature monitored about midpoint of the flow string during a multriate-test sequence lasting approximately 60 hours. Calculations show that thermal effects are exacerbated by increasing flow rate and increasing gauge distance from the perforations. Second, we performed a detailed uncertainty analysis with experimental design. Variables included in this analysis were perforation-to-gauge distance, permeability, geothermal gradient, flow rate, fluid viscosity, thermal conductivity of annular fluid and formation, and mechanical skin. This analysis sheds light oil relative importance of these variables on our ability to extract formation parameters. Simple correlations are developed for designing gauge placement in many environments.