INVESTIGATING THE EFFECT OF CLAY MINERALS ON A SANDSTONE RESERVOIR: A ROCK PHYSICS ANALYSIS OF MAGNOLIA FIELD GULF OF MEXICO

Petrophysical and Rock physics approaches have been used to investigate the effects of clay minerals within delineated reservoirs from the Magnolia field, offshore Louisiana. It is generally known that reservoir sandstones are rarely deposited alone rather they occur alongside finer clay minerals which are often of varying mineralogy, morphology, and distribution. Clay minerals are members of the hydrous aluminous phyllosilicates that dominate the fined-grained fractions of reservoir rocks (Worthington, 2003). A well-known approach often used to unravel clay mineral distributions within a clastic reservoir is through special core analysis. This process is capital intensive and usually gives non-continuous down-hole measurement. This study employs rock physics models to understand clay distribution within Magnolia field in the deep-water Northern Gulf of Mexico. The Thomas–Stieber model is used to predict and describe the porosity-shale volume relations resulting from various mode of sandstone–shale mixing. The Dvorkin and Gutierrez model predicts the associated P-wave velocities. The combination of Thomas-Stieber and Dvorkin-Gutierrez models gives a higher degree of confidence while evaluating formation properties. From the above approach, dominant clay distribution pattern observed in the reservoirs delineated in Magnolia field are laminated clay. Dispersed and structural clays are rarely observed within the reservoirs. Findings from this research show that rock physics analysis can be used as an alternative to core analysis in determining clay distribution patterns and local reservoir studies.