Using thomeer hyperboles for rocktyping in a tight carbonate reservoir

Rocktyping is a crucial part of static and dynamic reservoir modelling. By grouping together rocks with the same characteristics, models construction is both simplified and improved. Several types of rocktyping techniques exist, focusing on different aspects such as petrophysical properties like porosity and permeability, or sedimentary facies. This paper presents a simple petrophysical rocktyping methodology based on pore size distributions instead or their resulting properties, by using Thomeer hyperboles and multivariate clustering techniques. A set of sixty four Mercury Injection Capillary Pressure curves from a Middle East tight carbonate reservoir were modelled with Thomeer hyperboles and grouped using Kmedoids clustering. The number of groups in which to divide the sample was experimented upon by grouping the samples into several numbers of groups and its effects on the saturation model resolution were assessed by the means of the covariance between the original and the grouped dataset. The result of this comparison showed that the ideal number of rocktypes is seven, allowing a good reproduction of saturations in the original dataset and still maintaining a low number of rocktypes which favours dynamic simulation models. The comparison of the grouped data with the petrophysical properties showed that different pore size distributions can yield similar porosity and permeability values, reinforcing the importance of grouping rocks based on pore systems instead of their resulting properties. This method also assists in determining the most relevant samples to define the rocktypes.