Unconventional reservoirs are multivariate problems requiring integration of data across multiple disciplines. Microseismic data recording hydraulic fracture treatments in the Niobrara Formation in the Denver Basin are no exception. Microseismic data are the real time recording of the subsurface reaction to stimulation and the stimulation is affected by the lithology and structure penetrated by the wellbore. Microseismic data are often not studied at the wellbore scale, yet this is where the stimulation initiates. Integrating both cluster analysis and horizontal borehole imagery can aid in the interpretation of microseismic data.
Due to the complex stratigraphy and structure in the Denver Basin, horizontal wells rarely target a single lithology. The varying lithology targeted by the wellbore could lead to stimulation heterogeneity and recorded via microseismic data. Vertical well cluster analysis was applied to one horizontal well to quantify the number of stage locations per lithology and how microseismic magnitude is affected by the lithology at each stage location. The number of natural fractures in each lithology was also quantified. In addition, horizontal borehole imagery identified natural and drilling induced fractures which aided in the interpretation of microseismic data heterogeneity. These interpretations can help understand how lithology and structure control stimulation heterogeneity and thus recorded by microseismic data.
Microseismic magnitude was found to be 43% higher in stage locations within higher Young's Modulus (chalk) rock compared to stage locations within lower Young's Modulus (marl) rock. In addition, chalk was found to be more naturally fractured than marl, although the marl still contains natural fractures. Finally, image log analysis showed linear microseismic trends are due to lack of natural fractures and are affected by and parallel maximum horizontal stress (σH) whereas clustered microseismic trends are due to abundant, conjugate natural fractures.
The research presented is a part of a joint research effort between the Reservoir Characterization Project and Anadarko Petroleum Corporation. The Wattenberg Project, Phase XV, began July 1, 2013 with the main objective of the Wattenberg Project is to guide well spacing and completions to improve ultimate hydrocarbon recovery. Unconventional reservoir development is dependent upon integration of data and multiple disciplines to solve multivariate problems. This research focuses on integrating both vertically derived, horizontally applied cluster analysis and horizontal borehole imagery to identify how geological heterogeneity influences completions and thus microseismic data recording the stimulation along the wellbore.