Porosity Determination via Contrast Enhanced Micro CT Scanning and Digital Core Analysis: A Case Study of X Field

摘要

There are a number of additional challenges in the development of high CO2 content gas fields. To meet the requirements of the Kyoto Protocol and Paris Agreement,an efficient means to deal with the produced CO2 such as re-injection into the reservoir for sequestration is required. With the intention of developing such high CO2 gas fields,PETRONAS has identified a trial candidate(X field)offshore Sarawak Malaysia,which is a carbonate gas field with 70% CO2 content and good potential to re-inject the produced CO2 into the field’s aquifer zone. To study the feasibility of CO2 reinjection,PETRONAS R&D team are studying the effects of re-injected CO2 on the mineralogical and petrophysical properties of the reservoir and decided to incorporate Digital Core Analysis(DCA)into the case study. Although porosity determination and other petrophysical property characterisation using micro-CT images has been widely used for a number of years,there is still discussion about its accuracy and reliability. Based on previous internal studies,porosity determination via digital core analysis can be limited by the quality and resolution of micro-CT images collected and thus the capability of the image analysis software. This case study investigates accuracy and reliability of the use of contrast enhanced imaging practices and the use of the helical micro CT for porosity determination via Digital Core Analysis(DCA). PETRONAS adopted and optimized a contrast enhanced imaging methodology for use on 1-inch core plugs during scanning via a helical micro-CT and applied this as a case study to X field with the help of a technology partner to evaluated digital core analysis. In the same year,a commercially available image analysis software was launched,with such a DCA workflow in mind. Using this optimized methodology and the newly launched imaging software,the porosity values from DCA of the 1-inch core plugs show good correlation to the values from Routine Core Analysis(RCA)done on the same samples,with less than 1.5 porosity unit difference. In this case study,PETRONAS managed to compare the porosity obtained from DCA directly with porosity measured by RCA. This methodology will be used for porosity determination for wells or other regions of interest where limited samples or different sample sizes are not suitable for RCA.