JOHNSON, WES, Petresim, Houston, TX

ABSTRACT: Permeability and Hydraulic Zone Predictions in Unconsolidated Reservoirs from Log and Core Data

A methodology has been identified for predicting permeability and hydraulic zones in Wilmington field. The method employs well logs to determine porosity at reservoir conditions with overburden stresses. Care is taken to develop log porosity corrections to properly reflect impermeable shale zones with no porosity. Core sample porosities as measured in the laboratory are corrected to agree with log porosities in clean reservoir. A new, theoretical linkage between porosity, pore-throat size, and permeability is used to correct laboratory permeabilities so they are in agreement with corrected laboratory porosity values. The result is a laboratory data set with permeability and porosity values corrected to reservoir-overburden conditions.

Once the corrected laboratory database is completed, hydraulic zones are identified based on pore attributes, including pore-throat size, internal-pore roughness, and flow-path tortuosity. These laboratory hydraulic zones are selected from fluid-flow properties, but offer an accurate reflection of the reservoir facies. A database is constructed from core and log data in a key well and used to predict hydraulic zones in offset wells. Computer-predicted hydraulic zones are then compared to core-facies descriptions to determine whether there is good agreement. When the logs predict facies correctly, a linkage has been found between log response and pore types or hydraulic zones.

When the most useful logs and the number of hydraulic zones have been properly identified, it is possible to perform very accurate permeability predictions. Multidimensional databases of core permeability and logging tool curves are created to uniquely identify individual permeabilities on the basis of log signatures. Permeabilities predicted with this method have different transforms for each of the hydraulic zones present in the reservoir. Results will be presented that show an excellent comparison between overburden-corrected lab permeabilities and those predicted from well logs.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.