Empirical Relation Between Carbonate Porosity and Thermal Maturity: An Approach to Regional Porosity Prediction

Data indicate that porosity loss in subsurface carbonate rocks can be empirically represented by the power function, θ = a (TTI)b, where θ is regional porosity, TTI is Lopatin’s time-temperature index of thermal maturity, the exponent, b, equals approximately -0.372, and the multiplier, a, is constant for a given data population but varies by an order of magnitude overall. Implications include the following. The decrease of carbonate porosity by burial diagenesis is a maturation process depending exponentially on temperature and linearly on time.The exponent, b, is essentially independent of the rock matrix, and may reflect rate-limiting processes of diffusive transport.The multiplying coefficient, a, incorporates the net effect on porosity of all depositional and diagenetic parameters. Within constraints, carbonate-porosity prediction appears possible on a regional measurement scale as a function of thermal maturity. Estimation of carbonate porosity at the time of hydrocarbon generation, migration, or trapping also appears possible.