Geometry, internal heterogeneity and permeability distribution in turbidite reservoirs, pliocene california

摘要

This paper presents a reservoir model of the geometry, internal heterogeneity and permeability distribution in deep water, unconsolidated turbidite sand reservoirs of Wilmington Field, California. These reservoirs were deposited in a variety of environments associated with a deep-sea submarine fan system. The external form and internal heterogeneity of the reservoirs is controlled fundamentally by depositional environment. Production (rate and volume ) is anisotropic and parallels the depositional trends. Production data indicate relatively high sweep efficiency and preferential permeability in a NE-SW direction (down depositional dip). Permeability and porosity are only wakly related to grain size. Sorting (standard deviation of grain size) and skewness (asymmetry of the grain size distribution) are the fundamental controls on porosity and permeability. Rock-based log models of permeability and internal reservoir heterogeneity are developed based on detailed integration of core and wireline log data, specifically data related to pore geometry. Development drilling demonstrates that areas of the field with the highest values of porosity x thickness (PhixH) and lowest water saturation x thickness (SwxH) do not necessarily have the highest permeability and productivity. Areas with high productivity can have moderate values of PhixH and SwxH, but are characterized by high values of permeability6 x thickness. In high porosity turbidite reservoirs, pore geometry based log models of permeability and reservoir heterogeneity allow for improved petrophysical evaluation, specifically net pay determination and prediction of producibility.