The Kashagan oil field is the largest oil field discovered in the last 30 years, located in the northern Caspian Sea off Kazakhstan. It contains estimated reserves of 6.4 to 20 billion barrels of oil. However, production has been delayed due to the huge costs involved, environmental concerns with drilling, and reluctance of the Kazakh government to involve foreign oil companies. The field's geology includes carbonate reservoir rocks from the Devonian to Carboniferous periods overlain by Permian salt domes that serve as traps for the oil and gas accumulations.

1. Kashagan Oil Field
by:-
Akhil Prabhakar Subrat Sundaray
Abhinav Singh Sunita Mohapatra
Ankit Khaitan Tanmay Biswas

2. Figure 1: North
Caspian Region
showing Kashagan
and adjoining oil
fields

3. Introduction
 World’s largest oil field discovered in the past three decades.
 Discovered in July, 2000 its considered to be the largest field of
Kazhakhastan.
 6.4 – 20 billion barrels have been estimated as recoverable.
 The field is situated in the northern part of the Caspian Sea close to the
city of Atyrau, offshore in 10 – 22 feet water.
 The size of the field has been estimated to be a whopping 3,20,000
acres.
 The top of the reservoir is 4.5km below sea level and the oil column
extends for more than one kilometre.
But…

4. No production yet!

5. Reasons for no commercial
production yet…
 The huge money involved.
 Every single 1% of take involves 1.5 – 2 billion dollars for the first 10
billion barrels alone!
 Environmental sensitive drilling involved.
 The reluctance of Kazakhstan government to allow involvement of
foreign oil companies.
 High production cost which is increasing with the subsequent delay in
production.

6. Geology

7. Age of rocks
 Mostly the rocks of the north Caspian sea range from geological
age late Devonian to Pleistocene.
 The hydrocarbon bearing rocks which are mostly carbonates,
(limestone & dolomite) they range from age late Devonian to
carboniferous.
 Seal rocks which are composed of salts, they are of lower Permian
age.
 Other rocks are composed of terrigenous sediments which are from
continental source.

8. Basement
 The basement of the Kashagan is a stable platform where the reef
building activity takes place.
 This is an optimum place for reef building because for reef building
we require-
• A stable platform
• Optimum Temperature
• Optimum salinity conditions
• Clear water so that sunlight can reach the basement.
Reservoir Rock
 The hydrocarbon bearing rocks are mostly carbonates in the form of
limestone and dolomite.
 These are secreted by Corals.
 The reef is about 75km long and 35km across, with a narrow neck
joining two broader platforms (Kashagan East and Kashagan West).

9. Salt Domes
 The reservoir rocks are overlain by saliferous formation of
Kungurian stage of Lower Permian age which forms salt domes
and troughs.
 Its thickness varies correspondingly from 0.5 to 1.0 km.
 This deposit plays the most important role in the formation of oil
pool in the Caspian region due to accumulation of salts which tries
to uplift the overlying deposit and in turn develop open spaces on
both sides of intrusion.
 This place acts as a good trap for oil and gas formation.

10. Upper Sediments
 The Upper Permian – Triassic sediments are represented by
terrigenous and terrigenous-carbonate formations.
 From these sediments some came from the continental area and
some are from the carbonate deposit below.
 Its thickness varies from 1.5 to 2.5 km. A base of Jurassic occurs at a
depth of 2.5 – 3.0 km in the inter-dome troughs and upto 0.2 km at
the arches of salt domes.
 At a number of domes, Jurassic – Cretaceous sediments contain
multilayer fields with small reserves (Verblyuzhja, Ka-myshitovoe
wells).
 The sediments of Cenozoic age are represented by terrigenous
formation of continental genesis. Its thickness is 0.5 – 0.8 km.

11. Structures associated with
Kashagan oil field
 Many structures are found in this oil field such as the dome shaped
structure which is found due to the diapiric intrusion of salts.
 We also find faults developed due to this diapiric intrusion and
tectonic movement but they are not so prominent.
 Hence, this oil field is both structurally and stratigraphically
controlled.

12. Seismic profile of the Kashagan Region.

13. Petroleum System

14. Source Rock
 Paleogeographic conditions of sedimentation and facies
architecture indicate that the principal petroleum source rocks in the
North Caspian basin are basinal black-shale facies
contemporaneous with upper Paleozoic carbonate platform
deposits on the basin margins.
 Total organic carbon (TOC) content varies from as low as 1.3 – 3
percent in Lower Permian basinal facies of the west basin margin to
as high as 10 percent in Lower Permian black shale on flanks of the
Karachaganak reef.
 Although data are few, high TOC and silica contents in basinal
shales of all margins and characteristically high X-ray readings on
gamma logs are typical of the deep-water anoxic black-shale facies.
 This facies contains type II kerogen and is the principal oil source
rock in Paleozoic (and many Mesozoic) basins of the world.

15. Events chart of North Caspian Paleozoic Total Petroleum System

16. Mysterious presence of source
rocks in suprasalt sequence.
 Some investigators believe that oil pools in salt dome-related traps
were generated from these strata.
 Although some source rocks of inferior quality may be present
among Triassic strata, these rocks could have reached maturity only
in some deepest depressions between salt domes and thus are of
only local significance.
 Recent geologic and geochemical data show that suprasalt oils were
generated from subsalt source rocks and migrated upward from
depressions between domes where the salt has been completely or
almost completely with-drawn .

17. Source rocks…(continued)
 Caspian basin, the top of subsalt rocks occurs in the oil window or in
the upper part of the gas window.
 The geothermal gradient in the basin is relatively low apparently
because of the cooling effect of the thick Kungurian salt sequence.
 Geothermal gradients in salt domes and adjacent depressions are
different with the rocks beneath the salt domes being much cooler.
 Qualitatively, it can be stated that maturation in deep parts of the
basin started before deposition of the salt.
 Most oil generated at this stage probably was lost because of the
absence of a regional seal (local seals among mostly carbonate
rocks are uncommon and easily breached).
 This loss of early-generated hydrocarbons is demonstrated by
heavy, paleo-biodegraded oils found in a number of fields at depths
reaching 5.5 km

18. Principal stage of hydrocarbon
generation
 The principal stage of hydrocarbon generation and formation of
fields, especially in marginal, shallower areas of the
basin, probably was in Late Permian–Triassic time when the
Kungurian salt seal was in place and thick orogenic molasse
clastics were deposited.
 Significant hydrocarbon generation in later times could have
occurred only locally in depressions adjacent to growing salt
domes.

19. Reservoir Rocks
 There are mainly two types of reservoir rocks in the North Caspian
Basin; Carbonates and Clastics. Kashagan field consists of
carbonate reservoir in the form of limestone and Dolomites.
 Reservoir properties of carbonate rocks strongly depend on
diagenetic changes, primarily on leaching.
 Vuggy porosity related to leaching is better developed in reef
reservoirs, especially in reef-core carbonates.
 Porosities averaging 10–14 percent are characteristic of reefal
vuggy, porous limestones and dolomites.
 Most of the porosity in this field is related to vugs, whereas the
primary pore space does not exceed 2–3 percent.
 Permeability of carbonates is mainly controlled by fracturing and was
observed to vary widely from a few to hundreds of millidarcies.

20. Seal Rocks
 The Lower Permian ‘Kungurian’ evaporite sequence is the principal
regional seal for subsalt reservoirs of the North Caspian basin.
 It covers the entire basin area except for a narrow zone along the
east and south margins.
 Where the seal is absent, hydrocarbons migrate from subsalt source
rocks vertically into Suprasalt reservoirs.
 Thus the salt formation divides the sedimentary succession into two
well-defined hydrodynamic systems - Subsalt system (over-
pressured and high salinity) and Suprasalt system (hydrostatic
pressure and low salt content)
 Both subsalt and suprasalt systems constitute a single total petro-
leum system (TPS) because they were charged by hydrocarbons
from the same subsalt source rocks; however, the upper system was
designated as a separate assessment unit within the TPS.

21. Traps
 The Lower Permian ‘Kungurian’ evaporite sequence is the principal
regional seal for subsalt reservoirs of the North Caspian basin.
 Various morphological types of reefs are present, but atolls and
pinnacle reefs contain the largest hydrocarbon accumulations.
 Several subsalt fields on the east basin margin are in structural
anticlinal traps.
 However, the discontinuous character of clastic reservoir rocks and
large variability in flows from adjacent wells suggest that
hydrodynamic connection between the wells is poor or absent and
that many of these pools are actually in stratigraphic traps.
 In the suprasalt section, all productive traps are related to salt
tectonics and are morphologically variable. Among them, anticlinal
uplifts with a salt core and traps sealed updip by faults and by walls
of salt domes are the most common types.

22. Geophysics

23. Geophysics
 The field is now moving toward the production phase.
 In order to optimize the planning of the future drilling activity, it is
necessary to better understand the fracture network that is difficult to
see using conventional 3D surface seismic data.
 The effect of fracturing on the seismic velocities, Vp and Vs, in low-
porosity limestones from the Kashagan oil field in Kazakhstan is
investigated.
 Laboratory experiments have shown that sonic velocity of
carbonates is mainly controlled by porosity and pore types

24. Moduli M, K and G are the uniaxial P-wave, bulk, and shear drained-
frame moduli, respectively.
Seismic-wave velocities are decomposed into their frame and pore-space
moduli (Murphy et al., 1993).

25. Geophysics (cont.)
 For investigations, a heuristic model for fractured limestones has
been developed. The approach was to:
• Treat intact and fully fragmented limestone as distinct end-member
rock-fabric elements,
• develop a model for intact limestone,
• develop a model for fully fractured and fragmented limestone,
• combine the intact- and fragmented-limestone rock-fabric elements
using a springs-in-series approach and a simple linear scaling
factor, and
• compare the heuristic model to well-log data.

26. Exponents m and n control the rate that moduli K and G decrease with
increasing porosity.
They incorporate the effects of pore geometry and fabric configuration in
limestones.
The endpoint properties at φ equals 0 and 1 are benchmarks values.
Exponents m and n are set to achieve these benchmarks; they must be varied
together.
For Intact limestone:

27. Incorporating fragmented limestone into the framework

28. Results (Geophysics):
 For any porosity, increasing the ( m,n) values causes P-wave velocity to
decrease. The (m,n) = (2.00,1.88) curve tracks the upper limit of the data
sets. These values are used to model intact limestone and explore the effects
of fracturing.

31.  Figures 4 and 5, respectively, show the effect of fragmented-
limestone moduli ( Kfrag , Gfrag) and fraction ( χfrag) on the P-wave
velocity of saturated intact-limestones.
 For any porosity, decreasing Kfrag= G frag and/or increasing χfrag
causes P-wave velocity to decrease. To model the effects of fluid
saturation, we use Kfrag = Gfrag = 5 GPa and χfrag = 0.1.

32. Figure 6: Effect of fluid modulus ( Kf) on P -wave velocity in a combined
model. The curve colors are gray, black, blue, green, and red for empty
frame, bitumen, brine, oil, and gas, respectively. Gray dots are well-log data from
Kashagan.

33.  Moreover, Figure 6 shows that there is a very small effect of fluid
substitution into intact limestone, especially in the porosity range of
Kashagan-East limestones.
The main important results are:
• Porosity and fluid moduli control the properties of intact limestone
• Fluids have small effects on the velocities of intact limestones (solid
curves)
• Fluids affect fractured limestones much more (dashed curves)
• Brine (blue) and bitumen (black) stiffen fractured limestone
• Oil (green) and gas (red) affect fractured limestone less
The results mentioned above were also confirmed with Finite
Difference Modeling on Kashagan field, looking at the seismic response
on fractures and fluid content.

34.  Hence, the elastic framework of intact limestones is very stiff. With all
else parameters remaining equal, porosity is the only factor that
controls the seismic-wave velocities in intact limestones.
 Seismic responses from fluid substitution in intact limestones are very
small, because the intact-limestone frame is so stiff.
 If the intact limestone becomes fractured, the limestone framework
comes less stiff. Seismic P- and S -wave velocities decrease
accordingly.
 The seismic response from fluid substitution in fractured limestones is
varied. In porous and fractured limestones, the largest seismic
response is at the lowest porosity. This response diminishes as porosity
increases.
 The primary response is a stiffening of the rock frame by fluids, causing
P-wave velocities to increase. This stiffening is greatest for bitumen
and then brine. It is much less important for gas and live oil.

35. Exploration and
Production history

36.  The area covering the Kashagan Contract has changed hands several
times since independence of Kazakhstan.
 Interest in the Caspian Sea first began in 1992 when an exploration
program was begun by the Kazakhstan government. They sought the
interest of over 30 companies to partake in the exploration.
 In 1993 the Kazakhstancaspiishelf (KCS) was formed which consisted
of Eni, BP Group, BP/Statoil, Mobil, Shell and Total, along with the Kazakh
government.
 This consortium lasted 4 years until 1997 when the seismic exploration
of the Caspian Sea was undertaken.
 Upon completion of an initial 2D seismic survey in 1997, KCS became
the Offshore Kazakhstan International Operating Company (OKIOC).

37.  In 1998 Phillips Petroleum and Inpex bought into the consortium. The
consortium changed again slightly when it was decided that one
company was to operate the field instead of the joint operatorship as
agreed before. Eni was named the new Operator in 2001.
 In 2001 BP/Statoil also chose to sell their stake in the project with the
remaining partners buying their share. With Eni as operator, the project
underwent another change in name to Agip Kazakhstan North Caspian
Operating Company (Agip KCO).
 In 2003, BG Group attempted to sell their stake in the project to two
Chinese companies CNOOC and Sinopec. However, the deal did not go
through due to the partners exercising their pre-emption privileges.
 Eventually, the Kazakhstan Government bought half of BG's stake in
the contract with the other half shared out among the five Western
partners in the consortium that had exercised their pre-emption rights. The
sale was worth approximately $1.2 billion.

38.  On 27 August 2007, Kazakhstan government suspended work at the
Kashagan development for at least three months due to environmental
violations.
 On 27 September 2007, Kazakhstan parliament approved the law
enabling Kazakhstan government to alter or cancel contracts with
foreign oil companies if their actions were threatening the national
interests.
 In October 2008, Agip KCO handed a US$31 million letter of intent for
FEED work on phase two to a joint venture of AkerSolutions,
WorleyParsons and CB&I. WorleyParsons and Aker Solutions are
engaged also in the phase one, carrying out engineering services,
fabrication and hook-up.
 The budget for the development of Kashagan oilfield on Kazakhstan's
Caspian Sea shelf in 2010 was reduced by $ 3 billion.

39. THANK YOU