Modeling Carbonate Diagenesis for Reservoir Quality Prediction: Predicting Cementation and Compaction as Functions of Mud Content Using Petrographic Data From a Carbonate Reservoir in a Giant Oil Field

Abstract

This study presents a mathematical model of carbonate rock porosity and its evolution through deposition, cementation and compaction. The model uses calibration data from a carbonate reservoir in a giant oil field obtained by quantitative analysis of petrographic images, and relates porosity and cement to mud content of the carbonate rocks. We developed mathematical relations of mud content, amount of cement and porosity using petrographic data from 635 samples in 15 wells. We consider three steps in the formation of carbonate rocks, initial depositional porosity, cementation, and compaction. Petrographic observations show that the cements within the limestones are predominantly marine phreatic and meteoric phreatic. Late burial cement is not commonly observed in the reservoir. Thus we assume in our model that cementation precedes compaction and porosity is subject to decrease by the volume of cement, and then decrease by compaction. The primary variable in our model is mud content. We calculate the initial depositional porosity from mud content using an empirical relation calibrated from literature data where porosities of modern carbonate sediments with varying amount of mud content are reported. The amount of cementation is from point counting data of the reservoir samples. The porosity after cementation is then subject to compaction. We define a compaction factor which represents the fraction of the final interparticle porosity to the interparticle porosity before compaction. We found that the compaction factor is negatively related to mud content, and positively related to the amount of cement, indicating that early cement may act to create a rigid framework preserving interparticle porosity and protecting the rock from later compaction.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017