AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Geomechanical Controls on the Gas Production in the North Parachute Area, Colorado
(1) Upstream Technology, ConocoPhillips, Houston, TX.
(2) E & P Americas - Development, ConocoPhillips, Midland, TX.
Tight gas plays often need a natural fracture network to provide sufficient system permeability for commercial production rates. Although hydrocarbon production is correlated to higher reservoir porosities and lower water saturation, production is enhanced where the stress state and fracture orientations interact to enhance fracture aperture, and increase the permeability of the natural fracture network. This study shows that geomechanical and structural factors are key controls on gas production in the North Parachute area of the Piceance Basin.
Structural analysis provided the basic framework for this geomechanical study. A systematic workflow was developed to analyze regional and local scale reservoir features in the context of the multiple regional tectonic events and cycles of syn-tectonic sedimentation. This analysis indicates that the thrust fault at depth within the study area was reactivated in compression during the Laramide Orogeny, whereas NW- and NE-striking normal faults at reservoir depth are neo-formed and younger.
To analyze the effect of stress heterogeneity on fractures and reservoir scale faults, geomechanical analysis was conducted at the wellbore- and field-scale. Boundary element modeling (BEM) was used to predict the pattern of sub-seismic fractures associated with faulting. Finite element modeling (FEM) was used to investigate the effect of the topography, faults, and mechanical stratigraphy on local stress variation. Local stress variation was calibrated by stress gradient at the well-scale. A multivariate analysis and prediction approach to permeability modeling is undertaken to integrate geomechanical influences with other effects on permeability. The results indicate that gas production in the North Parachute area is ~82% correlated to geomechanical effects. This correlation can be explained by permeability enhancement due to natural fractures that interact favorably with the present-day stress environment. This study indicates that the first-order geomechanical and lithological modeling can be used to assess the system-scale effect on fracture permeability and therefore can be used to identify sweet spots in tight sand reservoirs.