Abstract: Geochemical Variability in Reservoirs: Examples from Exxon Experience

Richardson, Mark; Glenn B. Hieshima and Ron J. Hill - Exxon Production Research Co.; Lloyd M. Wenger and Gary H. Isaksen - Exxon Exploration Co.

Petroleum geochemistry, when integrated with available engineering and geologic frameworks, plays an active role at Exxon in solving production, reservoir and development problems. Recognizing and understanding both vertical and lateral variability in hydrocarbon composition can impact field development and production strategies. Integrated and high-resolution geochemical data are often required to recognize subtle variability in hydrocarbon compositions. Several examples of different causes and impacts of hydrocarbon variability will be presented.

A common development and production-related issue is the recognition of compartmentalized reservoirs using geochemistry. Different compartments frequently contain petroleum with subtle chemical differences arising from variable hydrocarbon-rock-water interactions, biodegradation, charge, leakage, or gas fractionation. Identification of these differences and their integration within an engineering and geologic framework has, in some cases, resulted in the addition of significant reserves, lowered production costs, increased production rates and accelerated earnings. Our experience has also shown that identification of reservoir compartments through geochemical variability can influence well completion strategies.

Systematic geochemical variability has also been observed both horizontally and vertically in continuous reservoirs. This geochemical variability includes changes in asphaltene concentrations due to gravity settling, hydrocarbon recharge, or gas deasphaltening. Such variability can affect the physical properties of oil and hence significantly impact producibility and field development. This systematic, vertical variability in the geochemistry of some reservoirs can be used to optimize the location of well perforations.

Integrated studies of geochemical variability within individual fields have proven useful to help define targets for step-out development and infill drilling, to explain unusual production histories, and to recognize bypassed and deeper pay zones. Potential step-out targets (satellite structures) around producing fields can be high-graded by the integration of reservoir-scale geochemistry, maturation assessment and migration analysis. The integration of reservoir geochemistry into production and development issues requires careful but straightforward hydrocarbon sample collection and utilizes low cost, conventional analytical instrumentation.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil