Historical Assessment of Volumetric Uncertainty for the Humma Marrat Reservoir in the Partitioned Neutral Zone (PNZ)

W. Scott Meddaugh¹ and Stewart Griest^2
1 ChevronTexaco Energy Technology Company, Bellaire, TX
² ChevronTexaco Exploration and Production Technology Company, Bellaire, TX

A consistent design of experiments (DoE) based evaluation process was used to assess the magnitude of OOIP uncertainty as well as the relative contributions from several uncertainty sources as a function of the historical development of the Humma Marrat reservoir in the Partitioned Neutral Zone (PNZ). The Jurassic-age limestone and dolomite reservoir was discovered in 1998 and currently has 5 producers. Average porosity within the productive intervals is 8-14%. Average permeability (core plug) in productive zones is 10-30 md. Porosity and permeability is generally best developed in the dolomitized lowermost Marrat “E” interval

The uncertainty sources used in the DoE-based evaluation were structure (includes both time-to-depth conversion and interpretation uncertain), original oil-water contact (OOWC), facies occurrence and distribution, porosity and water saturation histograms, and porosity semivariogram (range and azimuth). High, mid, and low-case values were determined for each of the uncertainty sources listed using well log, core, and seismic data as well as analog information available after the discovery, third, and fifth wells were drilled (corresponding to year 1999, 2001, and 2004 respectively). Preliminary analysis of the DoE-based results showed that the significant contributors to OOIP uncertainty changed only slightly as additional wells were drilled. The analysis also showed that the OOWC and porosity histogram uncertainties remain the largest contributors to the overall OOIP uncertainty. The results of the historical analysis were subsequently used in a Monte Carlo-based evaluation of delineation drilling scenarios to determine which and how many locations should be drilled to minimize the OOIP uncertainty.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005