More than 60% of the world’s oil and 40% of the world’s gas reserves are held in carbonate reservoirs. In the Middle East, 75% of their total oil reserves are made up of carbonate reservoirs – 62% of the world’s total.
For this reason, in the Middle East has had a quandary on its hands on how to recover oil from many of its abundant supply of carbonate reservoirs. Unlike conventional reservoirs, carbonate rocks tend to be multi-faceted and “heterogeneous at every level”.
It is this composite and fractured nature which makes normal oil recovery incredibly difficult, with no two reservoirs ever being identical, and therefore individual methods of tackling the reservoir are required.
“Carbonates rocks are formed locally by the deposition of minute marine organisms, coral and algae, together with the precipitation of calcium carbonate in shallow, warm water. Their complexity means that no two reservoirs are identical, and so they cannot be tackled in the same way. These dynamics result in a higher level of unpredictability and risk,” explains Mohammed Badri, managing director, SDCR.
“Carbonates present recovery problems due to their highly complex internal structure. Allowing carbonates to produce more efficiently requires significant research, experimentation and testing at all levels.
“Also, some fractured carbonates are prone to water breakthrough and early gas making oil harder to produce. To better mitigate these potential risks, the industry is eager to learn more about their structure and consequently how to model and simulate them more effectively.”
Established in 2001 and inaugurated in March 2006, the Schlumberger Dhahran Centre for Carbonate Research (SDCR) was opened in order to develop new cost-effective technologies for greater hydrocarbon recovery from carbonate reservoirs.
Built in Dhahran Techno-Valley, Saudi Arabia, the complex works closely with the Schlumberger Abu Dhabi Regional Technology Centre, as well as King Fahd University of Petroleum and Minerals, and other universities across the Middle East.
Schlumberger proudly boasts of the centre being the first R&D facility solely dedicated to carbonate research, whilst drawing upon complementary work currently being conducted at other Schlumberger R&D centers located in Boston, USA; Cambridge, UK; Stavanger, Norway; and Moscow, Russia.
“The decision to locate SDCR in Dhahran was based upon recognition of Saudi Arabia’s growing leadership in oil production to meet global energy demand; the desire to bring scientists closer to many of the world’s major reservoirs; and the wish to be close to a center of academic excellence. Additionally, SDCR has close proximity to producing carbonate reservoirs,” says Badri.
Tackling the problem
The potential is enormous for those wishing to enhance recovery from carbonate reservoirs, and with depleting reserves around the world and increasingly hard to reach oil and gas reservoirs, the attractiveness of carbonate reserves increases.
“In recent years the demand for energy has surged, which means that the petroleum industry will have to increase production significantly from all types of reservoirs. It is clear that the relative importance of carbonate reservoirs compared with other types of reservoirs will increase dramatically during the first half of the twenty-first century,” says Badri.
“And as the value of the carbonate market rises, new creative approaches and technologies will be required to ensure the maximum benefits are met.”
At present, the SDCR is working with the Schlumberger Abu Dhabi Regional Technology Centre (RTC) to apply fracture Cluster Mapping (FCM) workflow to giant carbonate reservoirs in the region.
The FCM workflow was introduced by Schlumberger in order to improve fracture characterisation and the modelling of carbonate reservoirs, integrating Q-Technology services, borehole measurements and Petel seismic-to-simulation software.
“Modelling fracture systems has always been and still is a challenge for geoscientists in the oil industry. The FCM workflow helps to make better decisions for the location of injectors and producers, plan well trajectories, improve production predictions and form realistic Discrete Fracture Network (DFN) models,” says Badri.
“It makes a clear distinction between diffuse fractures that can be modelled using geo-statistical techniques, and fracture corridor ‘highways’ that must be detected and placed in the reservoir model at their exact field location.”
Fracture cluster maps can then be used in conjunction with technology to allow drillers to steer wells to the most favourable targets within the Reservoir.
