| dc.description.abstract | Carbonate reservoirs are a major source of oil and gas produced across the world. Carbonate reservoirs are distinct from sandstone reservoirs in terms of deposition and characteristics. Sandstones are formed by deposition of sediments which were transported by weathering agents. The deposition of these sediments along with organic matter for millions of years formed hydrocarbons in sandstones. The porosity and permeability of the sandstones are mostly a function of the overburden of the sediment layers. Carbonate rocks are formed by deposition of carbonate particles from seawater. The organic matter in the sea is also deposited along with the carbonates. The porosity of carbonate rocks is affected by the overburden of the sediments and diagenetic processes taking place after deposition. This lends a unique character to carbonate rocks with a very heterogeneous porosity and permeability at the micro-scale and macro-scale.
This unique structure of carbonate rocks may not be amenable to simple scale models or conventional steady state permeability assessment methods. Therefore, a transient simulation based methodology was developed and implemented on a pore network extracted from a carbonate micro-CT scan image to compute permeability and additional transport properties.
This methodology was validated on a synthetic sandstone pore network model. The transient method based on the Well Test Derivative (WTD) analysis showed good agreement with the conventional method .The transient method based on Depth of Investigation (DOI) showed good agreement with the results from the conventional method for the synthetic sandstone pore network with varying degrees of heterogeneity.
The transient method based on the Well Test Derivative analysis showed good agreement with the conventional method for the carbonate pore network. However, the transient method based on DOI for the carbonate pore network, which was a dual porosity framework, infers permeability values which are quite high when compared with the steady state permeability or Well Test Derivative (WTD) permeability values. The carbonate pore network contains many high permeability and low Diffusive Time of Flight (DTOF) paths. These paths have a low combined cross-sectional area when compared to the total cross-sectional area of the whole carbonate pore network. The DOI analysis method captures the permeability of these paths which results in these high permeability values. | en |
