AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Integrating Wireline Pressure Data, Stratigraphy, and Historic Fluid Production to Better Understand the Areal and Stratigraphic Pressure Distribution Prior to Steamflood Operations in the Wafra First Eocene Reservoir, PZ, Saudi Arabia and Kuwait
(1) Energy Technology Company, Chevron, Houston, TX.
(2) Saudi Arabia Chevron, Chevron, Houston, TX.
Since 1956 the Wafra First Eocene Reservoir in Kuwait has produced over 300 million barrels of heavy oil from dolomitized peloidal grainstones and packstones/wackestones interlayered by nodular to tabular evaporites. The current recovery factor for this ramp carbonate is only 3-5%. Currently the operators are evaluating plans for a full field steamflood project to improve oil recovery.
A study was undertaken to assess historic reservoir performance. As the exothermic phase change from steam to water varies with pressure, understanding the vertical and areal pressure levels within the steam targeted formation is critical. This study included the construction of a series of cross sections that combine petrophysical, stratigraphic, and wireline pressure data to evaluate the vertical and horizontal pressure values and discontinuities throughout the reservoir. Wireline acquired pressure data were used to construct well and date specific vertical pressure profiles. Pressure data were extracted from profiles based on stratigraphic intervals. Stratigrahic based pressure data were gridded and mapped to show areal pressure gradients within each stratigraphic interval.
To project recent pressure data to non sampled areas of the reservoir, total fluid production and well spacing values were used to calculate a total produced fluid/acre parameter. Various correlation strengths were observed between this calculated parameter and recently sampled pressure data on an interval by interval basis. For the intervals that exhibited high correlation strengths, the total fluid/acre parameter was used to estimate current pressure levels in the reservoir. The stratigraphic based comparison of correlation strengths of the observed pressure data to the cumulative total fluid per acre grid offered a qualitative indicator of layer fluid contribution.
Apparent high vertical pressure gradients across stratigraphic surfaces suggest significant vertical pressure discontinuities have been induced in the reservoir during primary production. The evaluation of thermal EOR projects in carbonate and evaporite reservoirs offer a different set of challenges compared to siliciclastic counterparts. The inherent heterogeneity of carbonate rocks makes the modeling of steamflood processes in carbonates more complex. This study has shed light on internal pressure/flow discontinuities within a carbonate reservoir; useful information in project design and steamflood optimization.