Application of Digital Core Analysis (DCA) and Pore Network Modeling(PNM) based on 3D Micro-CT Images for an EOR project in a mature oil field in East Malaysia.
Authors: Bt W Mohd Zainudin W. Nur Safawati , Md Zain Zahidah , Riepe Lutz 
Published: March 2015

For the planning of an EOR project in a major mature oil field in East Malaysia, an extensive Routine and Special Core Analysis (RCA/SCAL) programme has been performed on unconsolidated clastic reservoir rocks. In view of the limited availability of homogeneous core plugs of suitable size for core flooding experiments and for "conventional" SCAL laboratory investigations, a complementary analysis of petrophysical properties was performed based on the acquisition of high resolution 3D Micro-CT (MCT) images, that are used to identify homogeneous sub regions of plugs, and to exclude zones that were damaged during coring. From these regions of undisturbed zones, reliable static reservoir parameters are derived by application of Pore Network Modeling (PNM) techniques.

In addition to the generation of "static" parameters (e.g. porosity, permeability, grain size and pore size distributions), PNM simulations of primary drainage and imbibition, and the resulting pc and Krel curves were undertaken.

The 3D MCT images were complemented by Fluorescense Microscopy and Field Emission Scanning Electron Microscopy (FESEM) investigations to visualise at a higher resolution possible effects of wettability changes due to cleaning, restoration and flushing of the cores. Variation of the residual oil phase distribution (ROS) due to wettability changes during the cleaning and core handling processes were observed.

In view of the planned immiscible Water Alternating Gas (iWAG) process to increase the recovery, water injectivity tests and formation damage (FD) studies were performed in the lab. Potential causes for formation damage (e.g. changes in pore morphology or blocking of pore throats due to fines migration) were visualised by comparing registrations of MCTs at different stages of the flooding and FD experiments.

The application of 3D MCTs and PNM proved to be a unique new option to visualise and understand the sensitivities during the handling of cores, and to quantify potential effects of the experimental procedures on the multiphase flow in conventional flooding experiments. As such the Digital Core Analysis and PNM technology is a very quick and robust complementary alternative for the optimised investigation of EOR options, especially in cases where conventional laboratory investigations are limited due to time constraints or due to the status of the core material and resulting potential experimental artefacts.

Introduction

As part of an extensive core study for a re-development of the EOR programme of a mature oil field in East Malaysia, the "conventional" core analysis program was complemented by acquiring 3D images and applying "Digital Core Analysis" (DCA) /Pore Network Modeling (PNM) methods at different scales with the following main objectives:Visualise the status and monitor potential changes of pore morphology, fluid distributions and wettability during the handling and execution of lab experiments on unconsolidated/friable rock samples.Evaluate and model the impact of sample heterogeneity and wettability changes on petrophysical properties, with special attention to primary drainage and imbibition effects.Provide petrophysical properties for individual distinct rock types at pore scale for heterogeneous or irregular shaped samples that are not suitable or available for RCA/SCAL and flooding experiments.