Sequence Stratigraphy and Reservoir Architecture of the Lower Cretaceous J Sandstone, Wattenberg Field, Dj Basin, Colorado
Edmund R. Gustason
El Paso Exploration & Production, Denver, CO
The Lower Cretaceous (Albian) J Sandstone has produced nearly 1.0 TCF of gas from Wattenberg Gas Field. PhiH, OGIP and EUR maps reveal broad, regional trends punctuated by an irregular distribution of “sweet spots” and “dead spots”. Recent 32-acre infill drilling has encountered a wide range of bottom hole pressures that indicate small-scale compartmentalization. Results from a core-based, sequence stratigraphic study of the J Sandstone reveal a complex interplay among depositional and erosional processes, pedogenesis, diagenesis, and syndepositional and post-depositional faulting that helps explain both regional and small-scale compartmentalization.
The J Sandstone is divided into the Fort Collins and Horsetooth members. The older Fort Collins Member consists of several upward coarsening marine shoreface deposits comprising a progradational parasequence set. The Fort Collins Member is unconformably overlain by the Horsetooth Member and/or Mowry Shale. During the development of this unconformity, valleys were eroded into the Fort Collins Member and paleosols developed on interfluvial hillsides. The Horsetooth Member consists of fluvial-estuarine valley-fill and retrogradational barrier island deposits.
Most gas in the J Sandstone in Wattenberg Field is trapped within an erosional remnant of two parasequences of the Fort Collins Member bounded by “tite” Horsetooth valley-fill deposits on the west, south, and east. The northern trap appears to be related to an increase in porosity-occluding silica cement--a diagenetic boundary. Smaller sweet spots and dead spots reflect facies architecture on a shoreface clinoform scale as well as small-scale fault compartmentalization.
AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado