A computer simulation model, Facies-3D, designed to model the sedimentary processes for carbonates and siliciclastics, has been developed. The Facies-3D carbonate model simulates three-dimensional carbonate facies based on water depth and current velocity in conjunction with estimated paleotopography. It also simulates porosity changes in meteoric diagenetic settings. Input data to the simulations include parameters that define sedimentary facies, basement topography, sea level change, and original current velocity and direction. Output data include sedimentary facies, thickness, and porosity for each grid.

Two simulation case studies were conducted using a depositional and diagenetic model for the Pleistocene Ryukyu Group in Irabu Island of the southern Ryukyus, southwest Japan, and another model of carbonate reservoirs of the upper Miocene Kais Formation in the Walio oil field of Irian Jaya, Indonesia. The Ryukyu Group in Irabu Island consists of two major lithofacies: (1) the coral limestone facies of a shallow shelf setting, predominant in the eastern part of the island, and (2) the rhodolith limestone facies of a deeper shelf setting, predominant in the western part. Enhancement of porosity was observed beneath subaerial exposure surfaces. The Kais reefal carbonate reservoirs in the eastern Walio field were divided into seven shallowing-upward cycles, which were correlated with sequence boundaries of a third-order or a higher order cycle. The cycles consist of the fore-reef facies in the eastern edge of the area and the back-reef facies in the central and western parts. The Kais reservoirs were affected by meteoric diagenesis.

In the simulation case studies of these two depositional models, the Facies-3D carbonate model provided a close approximation to the distribution of the sediments in relation to water depth, current velocity in conjunction with paleotopography, and degree of meteoric diagenesis in relation to paleotopography and sea level change. The Facies-3D carbonate model demonstrates the potential for application as a test tool of a geologic model in a reservoir characterization in oil and gas fields.