Overview of an Integrated Process Model to Develop Petrophysical Based Reservoir Descriptions
Authors: Gunter G.W. , Pinch J.J. , Finneran J.M. , Bryant W.T. 
Published: December 2007

Quality reservoir descriptions require calibration of rock, pore and fluid data against production performance decline and pressure information. This paper presents a powerful three-stage integration process for building reservoir descriptions that has been successfully applied to over 80 reservoirs since 1994.

The first stage defines rock types by relating geologic framework, lithofacies and petrology to porosity, permeability and capillarity. Rock types represent reservoir units with a distinct porosity-permeability relationship and a unique water saturation for a given height above the free-water level. Relative permeability coupled with rock type data predicts production fluid ratios and residual hydrocarbon saturation. The products of stage one are rock, pore, and fluid models.

The second stage integrates rock type models with formation evaluation data to define reservoir compartments and flow units. Formation evaluation extends the rock type models and builds data transforms to compute storage capacity, flow capacity and reservoir speed. The products of stage two are petrophysical models.

The third stage uses the petrophysical models to calibrate seismic data and/or geostatistics to build a 3D reservoir description. Production tests, pressure transient data and decline curve analysis calibrate these descriptions for flow simulation.

This integrated process results in reservoir descriptions and flow models that are synergistic and powerful reservoir management tools. Over 500 BCF of gas and 45 MMBO of additional resources were identified by applying this process in the last four years. An additional 11.4 TCF of gas and 500 MMBO of recently discovered resources have been evaluated in key business areas.

This process is the focus for a year-long training program at Amoco. The training helps geologists, geophysicist, engineers and formation analysts become expert integrators of multidiscipline data to produce reservoir descriptions which are used to solve business problems.

Introduction

The business impact of applying the petrophysical integration process model (PIPM) and petrophysics project management is significant. The influence diagram (Figure 1) clearly shows front-end-loading project design reduces costs, because the ability to change decreases with time and the cost of change increases dramatically with time. Additionally, collection of some forms of reservoir data must be completed early to be representative of reservoir performance.

Our definition of petrophysics is "the synergistic process of integrating multiple disciplines to characterize and quantify rock, pore and fluid systems." This nineties' version of Archie's definition maintains the fundamental truths established in 1950.

To integrate the study of petrophysics, the PIPM is taught at Amoco as an intensive year long training program. This successful program hinges on our ability to teach, integrate and apply technologies to business problems. Working on a chosen technical project, participants receive technical training and apply techniques and interpretation methods to solve a business problem. To complete the project phase of the program they must use progress principles such as business process improvement and project management. Participants learn the fundamentals of PIPM through 80 classroom lectures, field trips, and applied workshops taught by world class consultants and in-house professionals (Figure 2). These seminars are organized around the fundamental keystones of rock, pores, fluids and project management (Figure 3).

The petrophysical integration process (Figure 4) focuses on key wells to build the basis for extrapolation to the larger field. The key well concept allows for the necessary depth of investigation and reduces cycle time. P. 475^