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This summer, ESA entered a cooperative program at California State University, Fullerton to provide instruction, data and research guidance for six students completing their Masters of Applied Mathematics. Our goal was to geostatistically estimate the pore pressure field for the central and western GOM.
From GOM3, we provided two critical data sets: 1) From the Well Activity Report layer (under Map Layers -> Wells), 48,507 observations on mud weight and depth. 2) From the Sands layer (under Map Layers -> Hydrocarbon Accumulations), 13,506 observations on initial reservoir pressure and reservoir depth. The two variables were analyzed separately but both were divided into 21 depth cohorts: from 0-500 feet below mean sea level, then by 1,000-foot intervals to 19,500-20,500 feet.
For each depth interval, ordinary kriging was applied to estimate and map the mean mud weight and reservoir pressure for that interval across the Gulf. For each map of estimated mean, a separate map of kriging standard error (KSE) was also produced. Including the KSE maps with the mean mud weight and reservoir pressure for each 1,000-foot interval allows users to quantitatively assess the confidence they should invest in the statistically estimated means. It also enhances understanding of the natural lateral variability of the pore pressure field across the Gulf within any single 1,000-foot depth interval.
Based on the predicted means at 1,000-foot intervals, additional analysis explored changes in both pressure gradient and mud weight with depth. This identified areas where the pressure gradient changes anomalously with increasing depth: either it increases at a rate greater than the hydrostatic gradient - or actually reverses and goes down between one 1,000-foot depth interval and the next deepest interval. Both conditions can present significant drilling hazards and influence the local distribution of hydrocarbons. Between certain depth intervals, we mapped several contiguous areas with either anomalously high rates of increasing pressure or pressure reversals.
The six students completed their project and graduated in August. We are now revising the final report for publication with the assistance of several experts from our client-companies. By year-end, all final mean mud weight and reservoir pressure maps, along with their corresponding KSE maps, will be placed in GOM3 to provide users with a new source of analysis of pore pressure throughout the Gulf.
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