3D GEO-CELLULAR RESERVOIR MODELLING TO EVALUATE RESERVOIR PROPERTIES OF THE PALEOCENE AND CRETACEOUS FORMATIONS OF ZAMZAMA BLOCK, KIRTHAR FOLD BELT, PAKISTAN

Abstract

This study has been carried out at the Zamzama Gas field, which is located at Kirthar Foredeep, Southern Indus Basin, Pakistan. In the Zamzama field, primary reservoir is the Pab Formation of Cretaceous age which is a fluvio-deltaic sandstone of about 220-meter thick overlain by a secondary 50-meter thinner reservoir section of Palaeocene Khadro Formation. Khadro Formation is heterogeneous reservoir compared to Pab Formation and represents the deposits of few supra-tidal mud-flats having poor to fair quality sands and tidal channels having fair to good quality sands. Static model was built to evaluate the remaining potential of above mentioned Palaeocene and Cretaceous clastic reservoirs. 3D Geocellular model was built by using DSG Earth modelling (EM) software of Halliburton (version EP 10.4). Total 11 wells (Zamzama-1 to Zamzama-9, Zamzama- North-1 and Zamzama East-1) data which includes Formation tops, well logs, core analysis reports, production data and 3D seismic cube were used for static modelling. Structural interpretation for Khadro, Pab and Fort-munro formations were carried out. Structural framework was built by using all the same interpreted horizons and faults. Zamzama structure is elongated, north south, thrust bounded anticline with no surface expression. It is bounded to the east by a major thrust separating the main hanging wall from a smaller footwall structure. Petrophysical properties were estimated for each well which were further used for facies and petrophysical modelling. Four lithofacies (limestone, sandstone, shaly sand, and shale) were defined for Paleocene and three lithofacies (sandstone, shaly sand, and shale) were defined for Cretaceous reservoirs. Then well log, core and lithofacies data were incorporated in the model by using Sequential Indicator Simulation (SIS). Tight limestone at the top interval of Khadro Formation is acting as a seal for Khadro Sands in the model. Porosity and permeability were distributed in the model by constraining them with lithofacies. Saturation height modelling was carried out for water saturation distribution above free water level (FWL) from well log and core data. 2 TCF gas initially in-place (GIIP) has been estimated (recoverable ~1.8 TCF with 90% recovery factor) by using 3D Geocellular model in post processing module of the EM software. The cumulative production data confirms that 1.7 TCF gas has been produced from the field however ~0.1 TCF are the remaining gas reserves