Core Driven Hierarchical Facies Modeling of Shoreface Environments: A Case Study from Offshore Sabah

Sharma, Sachin K.; Chin, Michael; Basu, Tanwi; Bhargava, Ram Oruganti; Henson, Richard; Jiang, Long; Shuhaimi, Mimi Azura B.; Vizzini, Luca

A novel approach focused on facies association for static modeling has been pioneered for the Samarang field, offshore Sabah. Facies modeling provides the framework to control the fluid flow behavior during dynamic simulation by determining the distribution of porosity, permeability, and initial water saturation constrained to facies. In a shoreface environment, additional challenges are involved in the characterization of lateral facies variation within apparently sheet-like continuous depositional units. Though these depositional units are correlatable over a large distance, the variation within the units is the key to understanding the dynamic behavior of the reservoir and using that to build a representative dynamic model.

Lithofacies associations (sands, shales,) and their vertical and lateral distribution within each depositional unit (upper, middle, lower shoreface, and offshore) are the main focus of this paper. It is essential to capture these facies associations properly at the well level to provide the detailed input for facies modeling. Core description, routine core analysis (RCA), and special core analysis (SCAL) provide the ground truth for the depositional and lithofacies descriptions, which can then be used to propagate facies in the non-cored wells using the supervised classification based on principal component analysis and other adaptive methods with petrophysical logs as input.

This novel approach is based on using hierarchical truncated Gaussian-based methodologies. To capture the depositional facies and transition of successive depo-facies belts, a truncated Gaussian-with-trend (TGT) scheme is used. This provides the framework to propagate the lithofacies within the depo-facies, powered by exploration data analysis and a truncated Gaussian simulation (TGS) scheme. The TGS has the added advantage of using the underlying probability field to model the transition between varying facies rather than governing the process simply by global fractions. This provides a robust framework to propagate facies/porosity, and the porosity model is used next to create a permeability and initial water saturation model based on the core-calibrated function for each lithofacies.

The proposed method provides an integrated way of facies modeling where core-driven facies association is uniquely captured, characterized, and represented in dynamic simulation with functions calibrated to it.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013