An Integral Approach Boosts the Value of Heavy Oil Core Analysis

Carreras, Patricia Elva (Consultant) | Barge, David Lee (Chevron Corp.) | Burger, Jon Edward (Chevron Corp.) | Inouye, T. Art (ChevronTexaco Energy Research)

OnePetro 

Abstract
The Large Scale Steamflood Pilot (LSP) is a project aimed to determine the feasibility of economically steamflooding the Wafra First Eocene carbonate reservoir. The field is located in the Partitioned Neutral Zone, between Kuwait and Saudi Arabia. The reservoir is a dolomite, with 14-20*API oil. The LSP consists of sixteen inverted 5-spot injection patterns. A fully integrated workflow was matured to maximize the value of information provided by four full cores that were collected when drilling the LSP wells. Core work will support reservoir characterization and dynamic simulation, essential tools for project decision-making. High-level workflow consisted of the following phases: (i) define field, laboratory and office activities, (ii) identify and prioritize stakeholders, (iii) delineate project schedule and assign responsibilities. Coring and core
analysis for heavy oil involves short, mid and long term activities, that may require several years of planning and execution. Planning and frequent communication engaged core experts very early in the work process. Their input was used to shape the project, assuring reliable execution of dependent and independent tasks as work progressed. Synergies between subject matter experts were promoted, and proved to add value to the project. Due to the organizational efforts, the project schedule was not affected by personnel changes. Concerning lab measurements, the operator's heavy oil experts recommend Best Practices for the determination of relative permeability. Long equilibrium times, crude oil instabilities, and viscous fingering are challenges unique to heavy oil systems. Limited capability for such measurements exists in the industry. Heavy oil tests are not routine and should be carefully assessed. We hope that the integrated workflow proposed in this paper provides guidance to similar projects on planning and execution of heavy oil coring programs and analysis.

Introduction
The Large Scale Steamflood Pilot (LSP) is the third in a series of staged tests conducted to validate the feasibility of applying the enhanced oil recovery technology of steamflooding to unlock the production potential of the heavy oil Eocene reservoir in the onshore Partitioned Neutral Zone (PNZ). Refer to Fig. 1 for the PNZ location. Previous tests included the Small Scale Steamflood Test (SST), which was successfully completed in 2008, and simple steam stimulation testing, conducted in the
late 1990s. The LSP consists of sixteen inverted 5-spot injection patterns. The project is expected to lead to full-field steamflooding of the First Eocene reservoir, marking the first commercial application of a conventional steamflood in a carbonate reservoir anywhere in the world.

The First Eocene is the shallowest reservoir at Wafra field. Average depth to the top of the reservoir is about 1,000 feet. The stratigraphic interval averages 750 feet thick with a gross average porosity of 35% based on well log and core data, and a gross average permeability of 250 md based on core plug measurements. Based on current field practice a porosity cutoff of 35% is used to define net reservoir. The average porosity in the net reservoir is 43% and the net average permeability is about 280 md. The reservoir was discovered in 1954. Full field development and production commenced in 1956. Current oil cumulative from the reservoir is over 300 MMBO. Oil production exceeds 25,000 BOPD of 14-20 ºAPI high-sulfur oil. The First Eocene is a depletion drive reservoir, with partial solution gas drive and limited aquifer support. The aquifer support is not sufficient to maintain the reservoir pressure at current production rate.


A fully integrated workflow was matured to maximize the value of information provided by four LSP cored wells. Core work will support reservoir characterization and dynamic simulation, essential tools for project decision-making. The purpose of this paper is to describe the approach that was followed to maximize the value of heavy oil core analysis and support the LSP development with appropriate petrophysical data.