In the petroleum system, one of the key requirements is the presence of a high quality reservoir rock, this rock can either be siliciclastic (i.e. sandstone) or carbonate (i.e. limestone or dolomite).

The quality of a reservoir can be defined with reference to two main rock properties:

• Porosity - this is defined as the volume within rock that can contain fluids or gases (percentage of pore volume or void space). Porosity can be depositional (primary porosity, such as void space between mineral grains that were not compacted together completely) or can develop during subsequent burial and diagenesis (secondary porosity, preferential dissolution of mineral grains or fossils from sandstones). Effective porosity is the interconnected pore volume in a rock that contributes to fluid or gas flow in a reservoir, excluding physically isolated pores. Total porosity is the total pore volume in the rock irrespective of whether or not it contributes to fluid or gas flow.
  
• Permeability - this is defined as the ability of a rock to allow the flow of fluids or gases through it, typically measured in millidarcies. Formations that transmit fluids readily (e.g. sandstones) are described as permeable and typically have significant numbers of large, well-connected pores. Impermeable formations (e.g. shales and siltstones) are typically finer grained or have a variable grain size, with smaller, fewer, or less interconnected pores.

By analysing reservoir (or potential reservoir) porosity and permeability from rock samples, in conjunction with other direct measurements of rock properties (such as petrographic data, geochemical/isotopic data, fluid inclusion data), SRK Petroleum staff are able to determine for a particular formation or geographic location:

• Key controls on reservoir quality - for example, diagenetic processes (mineral precipitation/dissolution), burial processes (e.g. compaction) or depositional mineralogy (e.g. quartz arenite versus volcaniclastic sediment).
  
• Relative timing of the occurence of these controls.

The addition of in-direct measures of rock properties such as wireline log and seismic data allows prediction of reservoir quality to be made over a wider geographic area, through data inversion and correlation with physical measurements.

SRK specialises in the following aspects of reservoir characterisation and quality assessment:

• Siliciclastic and carbonate reservoir analysis and description
• Design and execution of sampling and analysis programs
• Petrology and quantification of diagenetic effects
• Fluid inclusion analysis
• Isotopic analysis
• Integration of micro and macro scale data

Contact SRK for further details of our range of Reservoir Services for exploration.