Low Cost, Low Risk Options for Determining Reservoir Pressures in Newly Drilled Horizontal Wells

Abstract

Understanding ranges of reservoir depletion is essential in optimizing field development within tight gas plays. Unfortunately, determining reservoir pressure in low permeability reservoirs is difficult due the long shut-in times required for conventional pressure transient analysis. Pre-fracture injection tests have successfully been used in low permeability reservoirs, but these tests can add operational complexity restricting their use in many cases. Horizontal wells with reservoir pressure below hydrostatic are particularly challenging since running downhole pressure gauges prior to fracture stimulation is often deemed to be an unacceptable risk. New low cost, low risk measurement methods for determining reasonable approximations of reservoir pressure in horizontal open-hole packer/sleeve (ball actuated) completions have been successfully tested in an East Texas Cotton Valley well. This paper describes two of the methods used in this well which successfully yielded reliable approximations of reservoir pressure. The primary driver for using these methods was well risk imposed by extended deployment of pressure gauges downhole. The first method, port opening observation, is applicable to open-hole packer/sleeve completions where the first port is pressure activated. The second, gas-over-level, can be used on any type of completion on an under-pressured formation where the risk or expense of downhole pressure gauges is prohibitive. It approximates sandface pressure which can then be analyzed using standard DFIT (diagnostic fracture injection test) methods. Both of these methods can be performed with minimal cost and operational interference thus providing an opportunity to routinely obtain reasonable estimates of reservoir pressures during infill horizontal drilling programs.