Diplog and openhole log data has been used to predict reservoir rock type and permeability distribution within a heterogeneous Thamama Group reservoir from a field in the UAE. Porosities within the reservoir are fairly constant, but permeabilities vary by several orders of magnitude for a given porosity, reflecting variations in primary depositional facies and to a lesser extent diagenesis. The reservoir is characterised by common thin vuggy bioclastic-rich facies that form high permeability streaks and tight cemented intervals that are below the resolution of standard openhole logs. The higher resolution of the diplog tool allows the distribution of these thin units to be established.
The diplog data has been processed using the same techniques applied to modern image logs and a series of false colour pseudo-images generated. A diplog facies scheme was established based on the diplog pseudo-images, diplog microresistivity curve response, microresistivity curve activity, and openhole log response, which were calibrated using core. The diplog facies are grouped into a series of diplog rock types (DRT) based on their petrophysical properties and open hole log characteristics. These DRT can be directly related to core-based petrophysically defined reservoir rock types. Each DRT is assigned a permeability range based on statistical analysis of cored wells and then used to provide an estimate of permeability distribution and heterogeneity within uncored wells. Comparison of the diplog rock types with conventional core analysis and miniperm results from a series of ‘blind’ tests indicates that there is a good relationship between DRT and permeability, which shows a broad agreement with the detailed rock typing undertaken on core.
This study demonstrates the value of revisiting old data, and that where diplog data is calibrated with core data, meaningful geological interpretations can be made and provide a valuable input to reservoir characterisation in heterogeneous reservoirs.