Abstract The process of diagenesis can be defined for HD-reservoirs as porosity constructive or porosity destructive. Most reservoirs have been “metamorphosed” to some extent, especially carbonates, and this process develops reservoir heterogeneity. Constructive diagenesis primarily involves dissolution of grains, matrix and/or cements in sandstones and carbonates. Replacement of limestone by dolomite is usually a constructive process. Porosity destruction is primarily the result of cementation, usually in the form of quartz overgrowths in sandstones or calcite and dolomite cements in carbonates. Neither of these processes are considered uniform and often add to reservoir heterogeneity caused during deposition. Karstrfication is pan of the larger process of pore fluid diagenesis as shown on the chart. Karst can be defined as a diagenetic process in a carbonate which involves turbulent flow through 5mm or greater vugs by hydronorma) or hydrothermal waters. Karst processes are both constructive and destructive. The anatomy of karst can be described based on the relative position of the water table. The opposing figure shows the standard profile of karst and it is divided into the above the water table vadose zone and the below the water table phreatic zone. The water table is seldom static so the oscillation zone is described for that area, which is between vadose and phreatic. A study of stratigraphic discontinuities is a requirement to understanding karst processes. A so called “strong” unconformity does not necessarily indicate the setting for good karst development. It takes a general understanding of tectonic history, eustatic sea-level changes and lime gap