Abstract Many ancient carbonate build-ups are impacted by meteoric diagenetic processes, including karstification. However, very little is known about the acoustic properties and seismic expression of karstified reservoirs. This paper investigates potential seismic expressions of karstified build-ups by means of synthetic seismic modelling. The overall stratigraphic architecture and physical properties of rock are derived from published examples of SE Asian carbonate build-ups. Various karst systems, corresponding to distinct stages of karstification of varying intensity, have been superimposed to the background facies-related acoustic model. Three-dimensional synthetic seismic cubes have been computed from the karst-bearing acoustic model and by testing various wavelet frequencies. The proposed approach allowed several types of palaeokarst to be reproduced, from dendritic karst and flank-margin caves to cave networks, in amplitude sections. However, geometrical seismic attributes, like coherency, cannot be accurately reproduced with modelling based on the available literature. In addition, the exploration of this synthetic seismic data shows that non-stratiform diagenetic bodies (i.e. leached carbonate wedges in a mixing zone) appear as stratiform even in very-high-resolution seismic. Thus, their detection and characterization require advanced techniques or prior knowledge, such as borehole data.

Abstract The stochastic stratigraphic well correlation method considers the stratigraphic correlation of well data as a set of possible models to sample and manage uncertainty in subsurface studies. This method was applied to the Malampaya buildup (a well documented offshore gas field located NW of the Palawan Island, Philippines), aged upper Eocene to lower Miocene. Previous studies highlight that rock petrophysical properties are mainly controlled by diagenesis. Correlation rules are thus developed in order to adapt the stochastic stratigraphic well correlation method to the study of diagenetic units. These rules are based on wireline log shape and diagenetic units types. Four stratigraphic correlation models are generated using the proposed correlation method: a deterministic one corresponding to the most probable model considering only well data and three stochastic ones. These correlation models are bound with geostatistical methods to build static reservoir models. Synthetic seismic profiles are computed from facies models conditioned to acoustic impedance models. It leads to comparable seismic amplitude images, highlighting the importance of considering several well correlation models for one given seismic survey. Stochastic stratigraphic correlations are shown to have a first-order impact on reservoir unit characterization, rock volumes and fluid flow response on the reservoir model.