Evolving Technologies and Opportunities in Carbonate Systems

Charles Kerans, Senior Research Scientist and Senior Technical Advisor

ABSTRACT
Carbonate reservoirs are famous for their prolific reserves and infamous for their complexity and unpredictable behavior. Yet it is precisely this combination of vast promise and challenging technical frontiers that ensures that carbonate hydrocarbon reservoirs will form the cornerstone of global energy supply for the next half-century. The vast resource still remaining in giant carbonate oil fields in the Middle East, the Caspian region, the Cretaceous of Latin America, the Atlantic and Caribbean provides substantial motivation for a renewed focused R&D effort in carbonate exploration and exploitation similar to the spirit that thrived during the Shell golden years of the 1960’s.

The basis for our modern understanding of carbonates has evolved very rapidly, almost entirely within the last half-century. Spurred by carbonate discoveries in the Permian Basin and Middle East, a combination of industry, academic, and U.S. Geological Survey workers in the mid–late 50’s initiated modern depositional environment studies and petrographic studies that provided the springboard for modern carbonate geology. Central to this effort in the mid 50’s to mid-60’s was Shell’s Bellaire/Coral Gables group. This group formed a focused integrated research effort on all aspects of modern and ancient carbonate depositional environments, diagenetic systems, and their application to solving stratigraphic elements of carbonate systems. Much of our fundamental understanding of carbonate exploration and exploitation models can be traced back to this central effort. The 70’s saw studies focus ever inward, with reservoir-scale facies models, diagenesis and petrography gaining importance. The 80’s saw an explosion in the application of trace element and isotope geochemical techniques for documenting the processes and hydrologies of carbonate diagenetic systems with the goal of developing an element of predictability to this field analogous to that achieved in the 60’s for carbonate depositional systems. Before this diagenetic research reached fruition, Exxon’s concepts of sequence stratigraphy exploded onto the carbonate scene in the mid-80’s. The last 15 years has seen rapid development of refined sequence models at both exploration and development scales, a key achievement being the major improvements in our ability to generate 3-D reservoir models and to interpret carbonate stratal patterns.

Will the next 50 years of technological development in carbonate systems compare favorably with the last half-century? The target of more than 50% of the world’s remaining hydrocarbons should be sufficient incentive. Seismic imaging capabilities that have revolutionized sedimentologic analysis in clastic systems have not transferred rapidly to carbonates. This task is made difficult by the lack of lithology contrast and ambiguous amplitude/impedance signature of a wide range of tight and permeable carbonates. The winner in this challenge will need a more sophisticated multivariate analysis that includes geology in addition to derivatives of amplitude, but the reward will be huge. Enormous predictive potential also looms in the revisitation of the abandoned avenue of carbonate diagenesis as seen through sequence stratigraphic eyes integrated with sophisticated geochemical flow simulations. With models like the Shell Bellaire group’s, advances of the last half-century, and a target of half the world’s remaining resource, the scene is set for another exciting 50 years.