exploration & production
carbonate reservoirs EXTRACTING THEIR VALUE
the know-how Series
s s s
Page 04 BACKGROUND // Challenges Concentrated mainly in the Middle East, carbonate reservoirs contain half the worlds hydrocarbon resources. However, their heterogeneity and the acid gases they usually contain pose huge challenges.
Page 06 A WINNING HAND // ToTal seTs The sTandard On the strength of its experience and its commitment to continuous innovation, Total is setting ambitious goals to enhance its mastery of carbonate reservoirs, largely untapped to date.
Page 08 REFERENCES // experTise aT work From the Arabian/Persian Gulf to the glacial horizons of the Arctic Circle, a panorama of key projects where Total is implementing an array of leading-edge technologies.
P. 09 dolphin P. 10 abu al Bukhoosh P. 13 al khalij P. 14 kharyaga and kashagan
Page 16 KNOW-HOW // aT The forefronT of TeChnology From understanding the long history of basin geology to optimizing well productivity, carbonate reservoirs demand the mobilization of experts in every discipline.
P. 17 defining and modeling heterogeneities P. 20 The difficult task of predicting reserves P. 23 optimizing production
Page 26 TOMORROW // new Challenges ahead In the upstream and downstream sectors alike, it is by fully integrating all its fields of expertise that Total unlocks its innovative capabilities and remain in the vanguard of the strategic area of producing carbonate reservoirs.
P. 27 overcoming obstacles to seismic characterization P. 29 enriching conceptual geological models P. 30 improving well performance
EXTRACTING THEIR VALUE
In 2006, Total decided to add carbonate reservoir expertise to the list of specialized know-how required to drive vital future growth in the worlds hydrocarbon production. That decision signalled the launch of a multidisciplinary Research & Development program specifically dedicated to mastering these promising structures. The geologic diversity of limestone and/or dolomitic reservoirs, which are much more complex than their sandstone counterparts, reflects the diversity of the fossilized remains of living organisms that led to their formation. Carbonate reservoirs exhibit extreme heterogeneity. The significant small- and large-scale
variability in their properties, coupled with the often acid fluids they contain, make them challenging targets and to date, they remain under-exploited, despite the fact that they contain half of the worlds hydrocarbon resources. On the strength of expertise already acquired in this area, Total has the determined ambition of being among the industry frontrunners who will forge vital innovations to optimize their value.
The determined ambition to forge vital innovations
Key implications for future growth in oil reserves
The desert of Abu Dhabi, United Arab Emirates.
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Carbonate reservoirs are concentrated primarily in the Middle East but are found on every continent. The fact that they contain approximately 50% of the worlds hydrocarbon resources attests to their importance for the long-term growth of petroleum reserves. And the challenges involved in producing them are proportional to that promise.Because carbonates are composed of the fossilized remains of living organisms and their myriad paleoenvironments, they bear the imprint of this complexity. The extreme variety of the sedimentary deposits and the climatic conditions in which they were formed, as well as the numerous physical-chemical transformations they have undergone over time, together translate into highly heterogeneous geology. For the oil companies seeking to develop them, they entail tremendous challenges: characterizing the reservoirs, understanding fundamental heterogeneities, reducing the uncertainty of reserve estimates and improving productivity and recovery factors.
What is a carbonate reservoir?Carbonate rocks are the fossilized product of biological activity that took place mainly in shallow, warm-water marine environments. They are the result of the build-up of organisms or organic debris of varying size and nature: bacteria; foraminifers; gastropod, lamellibranch and rudist shells, and others (see photos). In other words, carbonate deposits
reflect the evolution, diversity and extension of species over the course of geological time. In addition to the considerable original heterogeneity of these sediments, the numerous transformations that have taken place over thousands of years (diagenesis) have altered the initial properties of the reservoirs. From the chemical standpoint,
carbonate reservoirs are generally characterized by high concentrations of the acid gases hydrogen sulfide (H2S) and carbon dioxide (CO2). Two factors explain the presence of these gases. One is the absence of iron: unlike sandstone reservoirs, in which H2S readily reacts with the ferrous minerals present in the deposits and mineralizes to form pyrite, such
HAlF THE worlds rEsErvEs
BACKGROUND // Challenges
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The Middle East: the crux of the matter
Carbonate reservoirs are highly prevalent in the Middle East, especially in the countries bordering the Arabian/Persian Gulf (Saudi Arabia, Iran, Iraq, United Arab Emirates, Oman, Qatar, Bahrain), where they
account for 80% of the regions oil reserves and 90% of its gas reserves (or 45% of oil and 30% of gas reserves worldwide). The Commonwealth of Independent States (CIS) is the second main carbonated province, with most
of its carbonate reservoirs located in Russia and Kazakhstan. Other carbonate traps are scattered throughout South America, Central America (Mexico), Africa, Europe and Asia.
difficulties for reserve recoveryThe recovery factors currently being achieved in the major carbonate fields are not, by any means, determined by permeability alone, and range from less than 10% to more than 40% on fields of average permeability (10 to 100 mD). Fractures and permeable drains are the fundamental heterogeneities and thus determine the dynamic behavior of the reservoir, but are much more difficult to model. This explains why recovery from this type of reservoir is so difficult to predict and so variable. The diversity of recovery mechanisms and development plans only adds to the difficulty.
What is a carbonate reservoir?mineralization is not possible in carbonate reservoirs, which explains why H2S can easily accumulate there via physical-chemical processes that may also evolve CO2. The other factor is the presence of sulfates in carbonate reservoirs, because they supply the sulfur needed to form H2S either by organic decomposition or by thermo-chemical reactions.
1. Laminar limestone showing traces of rich organic content.
2. Carbonate grains fringed with cement.
3. Ooid with partially dissolved concentric envelope bands.
4. Hole left by a burrowing organism, with calcite and anhydrite fill.
5. Rudist colony (giant mollusks of the Cretaceous).
Ultimate recovery factor versus permeability. (Source: IHS, SPE)
Carbonate fields of various averagepermeabilities and their recovery mechanisms. (Source: IHS, SPE)
Gulf of Aden
Carbonates oil province
Through its involvement as operator or partner in the prolific regions of the Middle East, the Commonwealth of Independent States and the Caspian Sea, in Africa and in Europe, Total has had many opportunities to enhance its expertise in the field of carbonate reservoirs. Its knowledge in this area is already longstanding, drawing notably on the Groups presence in Abu Dhabi since 1939, its development and production of the huge sour gas field at Lacq (France) beginning in the 1950s, and the operation of the Abu Al Bukhoosh (Abu Dhabi) field for more than thirty years to date. Today however, finding economically-viable ways to extract value from carbonate reservoirs has become one of Totals strategic objectives. Due to their complexity, most of these reserves are still untapped. Each carbonate reservoir is unique and poses its own challenges: in addition to being extremely heterogeneous, difficult to characterize, unsuited to the use of many conventional tools to estimate reserves and to interpret fluid dynamics within the reservoir, many plays are complex to drill and produce, and contain acid gas. These are the reasons behind Totals 2006 decision to launch an integrated, multidisciplinary R&D program dedicated to producing carbonate reservoirs, to develop the leading-edge tools and technologies needed to better characterize, model and exploit these promising targets.
A WINNING HAND // ToTal seTs The sTandard
R&D in the heart of the Middle EastAs Totals first Research & Development center in the Middle East, the new Total Research Center-Qatar (TRCQ) houses laboratories dedicated to two major areas of interest related to carbonate reservoirs: geochemistry, notably focusing on heterogeneities in the composition and distribution of sour gases; and optimization of well stimulation processes.
Model of fluid flows, Al