Identification of productive layers in low-permeability gas wells

This paper presents new guidelines for determining net pay thickness in typical low permeability, multilayered gas wells, such as the Devonian Shale wells. These criteria were developed from a sensitivity study performed using an analytical solution for complex multilayered reservoirs. The reason for this study was to determine whether many layers which are now considered to contribute to net pay actually have transmissibilities which are too low for the layer to be productive, causing performance projections to be too optimistic using current single-layer descriptive models. Devonian Shale wells have appeared to respond less than effectively to stimulation treatments, with shorter fracture half-lengths than designed being calculated from post-fracture buildup tests. This paper illustrates with the analytical solution how layering may be the cause of the apparent lack of stimulation. The outcome of this study is new criteria in the form of cutoff values for transmissibilities to determine when a given layer contributes to production. This paper shows that to obtain accurate performance projections for these low permeability layered gas wells, the projections must be based on a model which more nearly describes the actual formation and fracture conditions.

Identification of productive layers in low-permeability gas wells Conference Paper