Connectivity of Channelized and Other Reservoirs

D.K. Larue¹ and J. Hovadik^2
1 Chevron Energy Techology Company, Bakersfield, CA
² Chevron Energy Technology Company, San Ramon, CA

Connectivity represents one of the fundamental properties of a reservoir that directly affects recovery. If a portion of the reservoir is not connected to a well, it cannot be drained. Geobody connectivity is defined as the percentage of the reservoir that is connected, and reservoir connectivity is defined as the percentage of the reservoir that is connected to wells. Reservoir connectivity can also be defined relative to producing and injecting wells: if a portion of the reservoir is not connected to both a producer and injector wells, it can be considered not to be connected. In the current study, the stratigraphy of connectivity is characterized using simple, conceptual 3D geostatistical models. Based on these modeling studies, stratigraphic connectivity is good, usually greater than 90%, if the net to gross ratio, or sand fraction, is greater than about 30%. At net to gross values less than 30%, there is a rapid diminishment of connectivity as a function of net to gross. Non-stratigraphic factors that can influence connectivity are well density, well orientation (vertical or horizontal; horizontal parallel to channels or perpendicular) and length of completion zones. Reservoir connectivity as a function of net to gross can be improved by several factors: presence of overbank sandy facies, deposition of channels in a channel belt, deposition of channels with high width/thickness ratios, and deposition of channels during variable floodplain aggradation rates. Connectivity can be substantially reduced as well associated with two-dimensional reservoirs, in map view or in cross section, and stratigraphic heterogeneities. Volume support issues occur when the reservoir element size represents a substantial fraction of the reservoir gross rock volume, and can increase uncertainty of reservoir connectivity. Most of the stratigraphic factors that affect reservoir connectivity can be addressed by careful geologic studies of available core, well log and seismic data.