Novel Application of Micro-CT and Interpretive Geological Analysis to Assess Asphaltene Deposition by CO2 Injection
A. Emadi Ltd, R. Khabibullin, I. Patey Ltd, Z. Abu Grin, M. Grivet and K. Elgridi Ltd
Event name: IOR 2017 - 19th European Symposium on Improved Oil Recovery
Session: Miscible/Immiscible Gas Injection
Publication date: 24 April 2017
Info: Extended abstract, PDF ( 1.64Mb )
Price: € 20
The asphaltene related issues are known to cause operational problems during well drilling, completion and production life of oil reservoirs. In many cases, this has a significant impact on the development of marginal fields due to the cost associated with inhibition and/or remediation treatment. Therefore, the understanding of asphaltene properties and deposition potential is an important consideration in the reservoir development and design of the EOR/IOR processes. This paper introduces a new approach that tries to enhance our understanding of asphaltene deposition by adding petrography analysis and Micro-CT studies to conventional PVT type asphaltene analysis and coreflood tests. The application of this approach for a CO2 injection process is presented as a case study which shows how the addition of interpretive geological analysis can assist our understanding of asphaltene deposition and the mitigation solutions. The main objective of this study was to investigate asphaltene deposition and permeability impairment during CO2/Hydrocarbon flow in the reservoir rock. Asphaltene onset pressure (AOP) and CO2 titration tests were performed using SDS and filtration techniques to characterize asphaltene phase behaviour. Based on the results of the characterization tests, coreflood tests were designed and carried out using reservoir oil and CO2 with CO2 injection ratios increasing from 0.25 to 1.00. Effective permeability measurements were undertaken before and after test to determine the level of permeability alteration due to asphaltene deposition and fluid rock interactions. Comparison of the permeability data before and after the tests shows average permeability reductions of 31% and 13% for two samples with initial permeability of 23.42 and 251.80 mD, respectively. The inverse relationship between permeability loss and original permeability is believed to be due to the smaller size of pore throats in the low permeability sample which boost effect of damaging mechanisms on the permeability. The interpretive geological analysis (micro-CT, thin section analysis and dry SEM) showed the permeability loss can be attributed to (1) Fluid-Fluid interactions between CO2 and reservoir oil which results in deposition of asphaltene and, (2) Rock-Fluid interactions between CO2 and reservoir rock which results in clay fines redistribution and removal. The results show that the effect of asphaltene deposition in porosity change is significantly higher than the effect of clay fine redistribution. The micro-CT analysis also show asphaltene deposition takes place soon after mixing between crude oil and CO2.