First EAGE Workshop on Evaluation and Drilling of Carbonate Reservoirs
More than 60% of the world’s oil and 40% of the world’s gas reserves are held in carbonate reservoirs. Carbonates accumulate predominately through the in situ growth and destruction of organisms, with transportation over relatively short distances. The nature of carbonate deposition, along with evolutionary changes in biota and primary mineralogy, results in the development of facies that can exhibit highly varying properties. Diagenetic processes (e.g., cementation, compaction, dolomitisation, dissolution) can cause considerable changes in textures resulting in complex reservoir porosities, permeabilities and flow mechanisms within small sections of the reservoir.
The complexity of sedimentological and diagenetic processes and resulting heterogeneities has historically made carbonate reservoirs difficult to characterize. The resulting complex stratigraphical architecture of carbonate sequences provides complex challenges for drilling, geosteering, completing, stimulating and producing carbonate reservoirs. Carbonate characterization is becoming ever more important as the industry moves from the recovery of easy oil to more intense use of tertiary recovery (Improved Oil Recovery/Enhanced Oil Recovery) mechanisms. A detailed understanding of the geological processes that define the nature of carbonate reservoirs is the key to identifying the uncertainties and challenges associated with the drilling and evaluation of these reservoirs.