Reservoir system quality prediction

The economic success of any prospect ultimately depends on reservoir system performance. The reservoir system controls two critical economic elements of a prospect: (1) the rate and (2) the amount of hydrocarbons recovered. In geologic terms, pore type and pore–fluid interaction are the most important elements determining reservoir system performance.The interrelationship of reservoir porosity, permeability, thickness, and lateral distribution determines reservoir system quality. Although quality prediction is most effective with large amounts of superior data, useful predictions can still be made from very limited data. This section discusses methods for predicting the quality of sandstone and carbonate reservoir systems.

Sandstones vs. carbonates

Sandstones and carbonates are the dominant reservoir rocks. Although quite similar, they are different. The table below compares variables affecting reservoir system quality for sandstones vs. carbonates.

Variable	Sandstones	Carbonates
Sediment composition	High variability (depending on provenance and depositional environment)	Low variability [variations of CaCO3 and MgCa(CO3 )2 ]
Cement mineralogy	Quartz, calcite, dolomite, clay, and anhydrite, etc.	Aragonite, high- and low-Mg calcite, dolomite
Original pore geometry	Intergranular	Intergranular predominates, but intragranular is important
Ultimate pore geometry	Intergranular = intercrystalline > moldic	Intergranular = intercrystalline = moldic > microporosity
Uniformity of pore size, shape, and distribution	Fairly uniform within a facies	Ranges from fairly uniform to extremely heterogeneous, even within a facies
Influence of diagenesis	Minor to major	Usually major

See also

• Predicting sandstone porosity and permeability
• Predicting carbonate porosity and permeability
• Pore systems
• Water saturation
• Pore-fluid interaction

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