Practical Modeling of Complex Depositional Systems, from Carbonate Diagenesis to Shale Resources

Yarus, Jeffrey M.; Chambers, Richard L.
Halliburton, Houston, TX.

Geostatistical simulation of facies and petrophysical properties is now mainstream technology for building stochastic geocellular models. However, modelers encounter many challenges when attempting to reconstruct complex depositional systems due to diagenesis. Diagenetic changes occur rapidly or seemingly unpredictably as in carbonate systems or shale resource plays. Many commonly used algorithm implementations generally lack control over facies relationships or cannot model significant subtle relationships, which could result in improperly distributed petrophysical properties when conditioned to the facies model. For example, sequential indicator simulation cannot control known facies interactions. Truncated Gaussian simulation provides for only simple facies transitional boundaries; object simulation is not well suited to model diagenetic features or subtleties of shale facies. Although multipoint statistics seems promising in the future, current methods for integrating training images and trends introduce a significant level of modeling complexity. A powerful combination of methodologies is the use of a multiple lithotype proportion curve matrix (LPM) with plurigaussian simulation (PGS for facies modeling, then condition the petrophysical (and/or mechanical) properties to the facies. PGS with a LPM has been used worldwide in many reservoir studies for nearly two decades and provides many advantages over the more commonly used techniques. The LPM consists of hundreds of high resolution trend maps accounting for vertical and lateral facies associations, ensuring that Walter's law is preserved. Trends for each facies within each layer and every reservoir interval in the model are calculated. The PGS methodology captures most inter- and intra-facies relationships, including post depositional overprinting, such as diagenesis, or subtle changes in organic composition of shale facies. This is particularly powerful when tied to mechanical and petrophysical properties using traditional collocated (co)simulation. Although some of the challenges of traditional algorithms may be overcome through the intervention by experts, the implementation of a LPM, PGS, and Cosimulation workflow can be presented simply and intuitively, making it available to experts and non-experts alike.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012