A Novel Technique to Characterize Naturally Fractured Reservoirs by Integrating Well Log and Core Data

ELKEWIDY, TAREK I., and DJEBBAR TIAB

This study introduces a new practical and cost-effective technique to in-situ describe the most important petrophysical properties of naturally fractured reservoirs. Cores from naturally fractured formations may not be representative and thus the analysis are not reliable. Well logging interpretation of porosity and resistivity can provide the required in-situ measurements. Here, formation total porosity, which may be estimated from conventional wireline logs, and cementation exponent, which can be determined from crossplotting log porosity versus log resistivity are the only two parameters required to uniquely derive resistivity factor, tortuosity, partitioning coefficient, fracture intensity index, matrix porosity, fracture porosity, and fracture storativity ratio for naturally fractured formations at reservoir conditions. Furthermore, these well log derived parameters are utilized along with correlated core data to express Reservoir Quality Index in terms of partitioning coefficient and fracture intensity index. This reservoir quality index may be, then, used to characterize the different hydraulic (flow) units of naturally fractured reservoirs.

The product of this novel approach is an easy, flexible, and cost effective method that is readily adaptable to different naturally fractured formations including clastics, carbonates, and basement. This study will present the theory, flow chart, application example, and practical charts for estimating the various rock properties. Application of this unique technique may ultimately result in opening new potentials, particularly in carbonates, re-drilling or re-entering hydrocarbon bearing intervals that were by-passed.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.