--> Integrated Scratch Test And Sedimentological Analyses For Carbonate Reservoir Characterization In Offshore Sarawak, Malaysia

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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Integrated Scratch Test And Sedimentological Analyses For Carbonate Reservoir Characterization In Offshore Sarawak, Malaysia

Abstract

There are several options for CO2 geological sequestration such as (1) storage in depleted oil and gas reservoirs, (2) storage in producing fields (Re-injection, EOR & etc.), (3) storage in dry structure & penetrated aquifers and (4) CO2 storage and use for enhanced coalbed methane recovery in uneconomic coal beds. Options 1 to 3 are the most likely to further strategize CO2 sequestration program in Malaysia, whereby one of the factor that contribute to final storage decisions is subsurface potential risks evaluation. This includes geological and geophysical analysis on containment, seal analysis and estimation of CO2 storage capacity. Among the challenges faced for green field and depleted field are lack of data for further containment evaluation. This paper will highlight a case study of early assessment of reservoir characteristic for depleted and green field whereby data integration is the main key to fully evaluate potential of CO2 containment. Two fields with different field background were identified from Sarawak basin as potential storage sites. Field A is a green field, Miocene carbonate build-up with high CO2 percentage in situ (~ up to 70% filled up CO2) and meanwhile Field B is a dry carbonate structure and it is non- economical to develop. Both fields were identify with one of the strategy of CO2 injection is to store in the aquifer zone. Therefore, further reservoir quality assessment need to be conducted to ensure the feasibility of injection in this area. Scratch test analysis were conducted for both fields whereby for field A, the test was conducted for 215 meter length of cores included for main reservoir and aquifer section. Meanwhile, for field B, scratch test analysis were conducted for 20 meter of cores in carbonate reservoir only. As heterogeneity in Sarawak carbonate build –up are common, hence, the scratch test analysis were conducted to determine relative rock strength whereby by utilization of available logs data which helps to develop correlation and derived petrophysical scratch properties such as porosity and permeability. At the same time, the powder form from core scratch test were taken for advanced mineralogical analyses. It resulted in clustering and facies identification from scratch test results which has been further validate with mineralogical data (XRD,SEM) and as well as through cores observation and descriptions.

The results shows variation in the rock strength whereby it can be as low as 4-5 MPa and as high as 140 MPa for both Field A and B. The strength profile from sonic logs and scratch test analysis are comparable for both fields and fairly matched (for Field A) with unconfined compressive strength (UCS) from single stage triaxial testing in laboratory. Meanwhile, the scratch test powder analysis indicate dolomitization zone with higher rock strength (62- 70MPa). The results has been further utilize to determine reservoir properties relationship with rock strength and enhance data prediction for fields with limited well data.