Regional Evaluation of SourceRock Quality in Azerbaijanfrom the Geochemistry ofOrganic-rich Rocks inMud-volcano EjectaGary H. IsaksenExxonMobil Exploration Co.,Houston, Texas, U.S.A.

Adil AliyevGeological Institute of Azerbaijan,Baku, Azerbaijan

Scott A. BarbozaExxonMobil Upstream Research Company,Houston, Texas, U.S.A.

David PulsExxonMobil Exploration Co.,Houston, Texas, U.S.A.

Ibrahim GuliyevGeological Institute of Azerbaijan,Baku, Azerbaijan

ABSTRACT

Rock ejecta brought to the surface by mud volcanoes offer a unique op-portunity to characterize sedimentary units both within and beyond con-ventional drilling depths. Present among ejecta from mud volcanoes in

the South Caspian Basin are the organic-rich rocks of the Oligocene–MioceneMaikop Formation, the primary source rocks for oil and gas in the region. Theserocks have total organic carbon contents as much as 7% wt. and hydrogen in-dices as much as 500 mg hydrocarbons/g organic carbon. They are dominated bymarine, algal-amorphous organic matter accumulated under dysoxic to anoxicconditions. When integrated, the rock analyses can aid in the reconstruction ofpaleodepositional environments and paleogeography of source rock intervalsand, thus, help high-grade oil and gas exploration targets.

Chapter 10Isaksen, G. H., A. Aliyev, S. A. Barboza, D. Puls, and I. Guliyev, 2007,

Regional evaluation of source rock quality in Azerbaijan from thegeochemistry of organic-rich rocks in mud-volcano ejecta, in P. O.Yilmaz and G. H. Isaksen, editors, Oil and gas of the Greater Caspian area:AAPG Studies in Geology 55, p. 51–64.

51

Copyright n2007 by The American Association of Petroleum Geologists.

DOI:10.1306/1205839St551436

INTRODUCTION

The South Caspian Basin (SCB) is a prolific oil and

gas province. As a result of its very thick sedimen-

tary package (as much as 25 km [15 mi]), rapid sedi-

mentation rate (10–12 km [6–7.5 mi] of sediment

fill deposited in the last 6 m.y.), and likely Jurassic

oceanic crust, the basin is relatively cool (Devlin et al.,

1999). Geothermal gradients range from 208C/km in

the Kura depression to 158C/km in the SCB proper.

Consequently, source rocks for oil remain imma-

ture for oil generation down to approximately 6 km

(3.6 mi). The rapid burial and compressional tectonic

regime has resulted in the formation of numerous

mud volcanoes, which are common in the Gobustan

area of eastern Azerbaijan and throughout vast re-

gions of the SCB.

Study Objectives

Lithoclasts brought to the surface by eruptingmud

volcanoes offer a unique opportunity to characterize

the sedimentary section, which is generally too deep

to be sampled by conventional drilling. Although

lithoclasts from numerous sedimentary sections are

brought to the surface as ejecta, we have focused our

study on the organic-rich rocks. Many of the mud

volcanoes in the Gobustan area of Azerbaijan are

rooted within the Oligocene–Miocene section of the

organic-rich Maikop Formation. When placed in the

context of petroleum explo-

ration, the rock ejecta should

enable us to reconstruct the

paleodepositional environ-

ments fromwhich the ejecta

originated, assess the source

rock potential of organic-rich

rocks, and assess the thermal-

maturity levels of sedimenta-

ry units located deeper than

conventional drill depths.

Geological Setting

The SCB, located within

the Alpine–Himalayan oro-

genic belt, extends fromwest-

ern onshore Turkmenistan

throughouttheSouthCaspian

Sea, including the Apsheron–

Balkhan uplift, and north-

westward into the Kura de-

pression of Azerbaijan and

Georgia (Narimanov, 1993).

The Kura depression lies between the eastern parts of

the Greater and Lesser Caucasus fold belts (Figure 1).

The area that evolved into the SCB experienced

a major increase in accommodation and sediment

fill from the latest Miocene to the present day. The

cause of this is found in the regional tectonic his-

tory, as the collision of India and Arabia into the

Eurasian plate resulted in the formation of the Zagros

and Himalayan terrains, respectively. During the Ju-

rassic, the areas can be classified as a marginal basin

that underwent extension behind a volcanic arch

that extended east–west along the northern margin

of the TethysOcean (Zonenshain and LePichon, 1986).

Geophysical studies of the deep crustal structure sug-

gest that the basin is underlain by oceanic or proto-

oceanic crust from the paleo-Tethyan Ocean (Reza-

nov andChamo, 1969; Berberian, 1983; Priestley et al.,

1994). Subduction has occurred since the middle Mio-

cene (evidenced by folds along the Apsheron Arch),

with the Jurassic oceanic crust and sedimentary cover

moving beneath the Turan–Scythian margin of Eur-

asia. Following a period of tectonic quiescence, reacti-

vation occurred during the late Pliocene–Quarternary.

Accommodation space was rapidly filled in with 10–

20 km (6–12 mi) of sediments caused by uplift and

erosion of hinterland areas (Caucasus and Himalaya

orogens and Russian platform) and drained by three

rivers: the Volga from the north, the Uzboy and Amu

Darya from the east, and the Kura from the west

FIGURE 1. Tectonic setting of the South Caspian Basin.

52 / Isaksen et al.

(Devlin et al., 1999). In general terms, theMesozoic

and Cenozoic sections comprise 20–25 km (12–

15 mi) of sediment, with an 8–12-km (5–7.5-mi)-

thick Neogene section, a 5–8-km (3.1–5-mi)-thick

Pliocene section, and a 2-km (1.2-mi)-thick Quater-

nary section.

Geopressure

Large volumes of the Azeri subsurface are over-

pressured. Overviews of mechanisms for generating

overpressure in sedimentary basins include Osborne

and Swarbrick (1997) and Kopf (2002). Gretener and

Bloch (1992) define two broad geological conditions

for the formation of overpressuring: (1) compaction

disequilibrium, in which there is unrestricted lateral

flow and restricted vertical flow; and (2) sealed com-

partments, in which there are restrictions to both

lateral and vertical flow. In more detail, the various

causes of overpressuring are

� rapid sedimentation rates where the escape of

pore waters cannot keep pace with burial� tectonic forces, especially incompressional regimes� thermal expansion of any type of pore fluid� volumetric expansion of formation waters relat-

ed to the transition of montmorillonite to illite� volumetric expansion of kerogen associated with

the generation of oil and gas� volumetric expansion caused by thermal break-

down (cracking) of heavier hydrocarbons to form

light hydrocarbons.

The high pressures in the

SCB area are considered to

be primarily caused by com-

paction disequilibrium be-

cause of relatively high sedi-

mentation rates during the

late Tertiary, gas generation

from both kerogen catagen-

esis and metagenesis, and

gas generation from thermal

cracking of generated oil.

Gaarenstroom et al. (1993)

noted that thermal cracking of as little as 1% of the

oil volume in closed systems can account for pres-

sures sufficient to increase the pore pressure from

hydrostatic to above lithostatic. A significant amount

of oil cracking has occurred within the Maikop and

deeper sections, where temperatures are high enough

for in-situ oil cracking given a thermal gradient of

208C/km.

GEOLOGY OF MUDVOLCANOES

Occurrence, Origin, and Characteristics

Mud volcanoes are ubiquitous both on- and off-

shore Azerbaijan, a region that is host to nearly 30%

of the world’s known mud volcanoes. These features

are typically associated with compressional tectonic

regimes and/or rapid sedimentation rates where

the mud extrusion (Figures 2, 3) is related to the pres-

sure release of overpressured,mobile shales. Themain

mud volcanoes on- and offshoreAzerbaijan are shown

by Figure 4. This data set is naturally biased toward

onshore occurrences, but recent sea-floormappinghas

revealednumerous, very largemud-volcano structures

offshore with the appearance of seamounts.

Kuklakova andLebedev (1996) recognize two classes

of mud volcanoes in this basin. The most wide-

spread class is related to faults on brachy-anticlinal

and diapiric folds where the vent penetrates the

fold and at the crest to form a debris cone. Thesemud

volcanoes occur in the Apsheron–Balkhan zone of

highs, the Baku archipelago, the Abikh and Shatskiy

FIGURE 2. Example of surfaceexpression of one of themany mud volcanoes west ofBaku. The truck-wheel mark-ings in the foreground serveas a scale. Photo: G. H. Isaksen.

Evaluation of Source Rock Quality in Azerbaijan from Mud-volcano Ejecta / 53

zones of highs, and in the basins onshore central zone.

Mud volcanoes of the second type are represented as

stocks or dikes. Their surface expression is typically as

small cones, and they occur in limited numbers on

highs as well as depressions. A typicalmud volcano of

the second type is Gryaznyy.

The two fundamental causes of diapir and diatreme

formation are (1) density inversion and (2) hydrostatic

pressure. These can operate independently. The basic

premise for the density inversion process is a buoy-

ancy contrast within the sedimentary column. Such

buoyancy may be primary (e.g., sediment densities)

or secondary (e.g., fluid influx). The supply of fluids,

especially gases, and their volumetric expansion un-

der decreasing pressures, provides a strong buoyancy

force for vertical flow. Flows are typically triggered by

mechanical failure of the overburden rock because of

high pressures, as well as earthquakes. Bagirov et al.

(1996a, b), in a study with observational data from

533 earthquakes and 220 mud volcanoes throughout

the past 160 yr, noted a correlation between earth-

quake activity and mud-volcano activity, suggesting

that many mud volcanoes erupt between 0 and 5 yr

prior to earthquakes. The periodicity of flow and, thus,

eruptions is mainly related to three factors: compres-

sional tectonics, an increase in pressure caused by

the ongoing generation of gas, and the mechanical

compaction associatedwith

each eruption. In their study

of mud volcanoes in accre-

tionary wedges in the Timor

area of Eastern Indonesia,

Barberet al. (1986)envisioned

the shales becoming over-

pressured as a result of over-

thrusting. Excess pressure is

releasedalongverticalwrench

faults, which cut through

the overthrust units; over-

pressured shales, containing

blocks of consolidated units,

rise along the fault zones as

shale diapirs (intrusivemech-

anism); and escaping water,

oil, and gas construct mud

volcanoes at the surface (ex-

trusive). McManus and Tate (1986) considered the

main driving mechanism to be connate waters flash-

ing into superheated steam, which is then forced

upward as hot mud.

Our seismic and structural analysis studies have

shown that most of the structures in the SCB are

large buckle folds overlying a regional ductile detach-

ment zone at depth (Devlin et al., 1999). In this in-

terpretation, upper Miocene to Holocene sediments

behaved in a relatively rigid fashion, deforming as

folds by bedding-parallel flexural slip. The detach-

ment surface is thought to be within the Maikop

shales presently at 10–12-km (6–7.5-mi) depth. At

these depths, the Maikop shales are overpressured

because of a combination of factors described earlier,

including hydrocarbon generation and thermal crack-

ing, and undercompaction as a result of the high

sedimentation rates. This is in agreement with the

findings of Hedberg (1974). Given a highly overpres-

sured gas at the upper Miocene and lower Pliocene

level, fracture-induced vertical-migration pathways

are developed that either feed into more porous sedi-

mentary units or develop further along preexisting

fault zones. It is not until the gas comes in contact

with significant volumes of formation waters and un-

consolidated sediments that it takes the form of a

mud-dominated system, which reaches the surface

FIGURE 3. The Toraguy mudvolcano in the Shamakha-Gobustan district. Photo cour-tesy of A. Aliyev, GeologicalInstitute of Azerbaijan.

54 / Isaksen et al.

as a mud flow or mud eruption with significant vol-

umes of gas released. Thus, it ismore correct to refer to

the subsurface expression of ‘‘mud volcanoes’’ as gas-

dominated diatremes. We have adopted the distinc-

tions made by Brown (1990); i.e., mud diapirs are de-

fined by a single-phase viscous flow, whereas mud

diatremes have polyphase flow of water and/or gas

causing fluidization. Geoscientists at the Geological

Institute of Azerbaijan (GIA) have estimated that ap-

proximately 500 m3 (17,600 ft3) of gas is released dur-

ing the eruption of onshore mud volcanoes in Go-

bustan. Eruptions from some of the offshore mud

volcanoes are known to release orders of magnitude

larger volumes of gas. Naturally, such violent erup-

tions in the offshore areas are severe hazards for ship-

ping and drilling operations. Dadashev et al. (1992)

described onshore mud volcanoes that sent 50-m

(164-ft)-wide columns of flames more than 200 m

(660 ft) into the air. A physical model for the mech-

anism of eruption and gas ignition was proposed by

Ivanov and Guliev (1988). In their model, ascending

gas, traveling at twice the speed of sound, will com-

press when it encounters physical restrictions along

the vertical-migration pathway. Such rapid compres-

sion cancause gas toheat adiabatically and self-ignite.

Indeed, more than 1000 yr ago, the Caspian region

was known as ‘‘the land of eternal fires’’ because of

burning oil and gas seeps andmud-volcano eruptions,

and these pillars of fire were worshipped by the Zoro-

astrians (Yergin, 1991). DuringWorldWar II, German

pilots relied on these burning sites as navigational

aids. Today, several places exist where gas is burn-

ing as it flows from outcropping sedimentary units

(Figure 5). Ejecta found within the surface mud flows

are known to have originated from all sedimentary

units along the stem of the gas diatreme, both from

its deeper, predominantly gaseous state and its shall-

ower mud and gas state.

FIGURE 4. The main onshore and nearshore mud volcanoes in Azerbaijan. The different circles denote no oil, an oil film,or larger amounts of oil found near the volcano.

Evaluation of Source Rock Quality in Azerbaijan from Mud-volcano Ejecta / 55

Rates of mud flow at the surface of mud volca-

noes varies greatly, from a continuing flux of mud

andwater at rates of 2–5 cm/yr (0.8–2 in./yr) formud

volcanoes on theBarbadosRidge (Langseth et al., 1988)

to infrequent, but violent, eruptions of 38,000 km/yr

(23,600 mi/yr) (Kopf, 2002). Measurements and es-

timates made by Bagirov et al. (1996a) on onshore

Azerbaijan mud volcanoes showed that the released

gas volumes could be described by an exponential

distribution with an average value of 590� 106m3/yr

(20.8 � 109 ft3/yr). Guliev et al. (1992) reported an an-

nual flux of 20 Azeri mud volcanoes of 1.3–731 m3/yr

(46–25,800 ft3/yr) with an average of 89.5 m3/yr

(3160.6 ft3/yr). In their study of the Mediterranean

Ridge, Kopf and Behrmann (2000) estimated flow

rates of 60–300 km/yr (37–186 mi/yr) (approxi-

mately 1 km/day [0.6 mi/day]) for conduit widths of

2–3 m (6.6–9.8 ft).

High pressures and violent eruptions of gas, fluid,

or mud are known to rip lithified clasts from the in-

truded strata. Geological and geochemical analyses

of such lithified ejecta provide important informa-

tion about subsurface conditions. Schulz et al. (1997)

acquired thermal-maturitydataonejecta samples from

the Napoli mud volcano to infer the likely mobiliza-

tion depth, whereas Robertson et al. (1996) studied

the likely origin of the ejecta. Chemical character-

ization of the oil- and gas-generative capability of

organic-rich ejecta was done by Akhmanov (1996) in

his study of the Mediterranean Ridge.

Cronin et al. (1997) recoveredOligocene–Miocene-

age clasts as much as 1 m (3.3 ft) in size from sea-floor

mudvolcanoesontheeastern

Mediterranean Ridge, where

deep-towedvideo footage over

one of the volcanoes showed

clasts up to several meters

across within the crater area.

In some cases, temporary

blockage of gas-dominated

diatremes can cause the host rock near the vertical

stock to mechanically fail and form clasts once the

obstruction is removed.

RESULTS AND DISCUSSION

Source Rocks: Insights from Outcrops

TheMaikop Series constitutes a diverse assemblage

of lithofacies. During the early to middle Oligocene,

the SCB experienced a major restriction in marine cir-

culation, the consequence of which was the develop-

ment of anoxic bottom waters and enhanced preser-

vationofmarine, planktonicorganicmatter.A cessation

of input of coarser clastics to the basin is evidenced by

the predominance of clay-silt-size clastics, fine-scale

(millimeter to centimeter) lamination of the shales,

development of calcareous lithologies, and, based on

the preservation of organic matter, an inferred oxic-

anoxic boundary in the water column. In her study

of outcrop samples along the Belya River in the west-

ern Pre-Caucasus, Saint-Germes (1998) reported car-

bonate contents as much as 25% in the Oligocene–

Miocene (lowerMaikop) section and a rapid decrease,

to less than 5%, into the middle Miocene (younger

Maikop) shales. Interbeddedmarls are, however, found

sporadically throughmost of the early to middle Mai-

kop section. In contrast, the upper Maikop is char-

acteristically devoid of calcareous units.

Thermally immature outcrops of the lower Maikop

along the Kura depression have total organic carbon

(TOC) contents upward to 4wt.% and hydrogen index

(HI) values as much as 350 mg hydrocarbons (HC)/g

FIGURE 5. More than 1000 yrago, the Caspian region wasknown as ‘‘the land of eternalfires’’ because of burning oiland gas seeps andmud-volcanoeruptions. Today, severalplaces exist where natural gasis burning as it flows from out-cropping sedimentary units.Photo: G. H. Isaksen.

56 / Isaksen et al.

organic carbon (C). Outcrops near Angicharan repre-

sent more proximal facies deposited near the north-

western margin of the Kura depression. The richest

samples are dominated by algal and algal-amorphous

organic matter. These typically occur as 10–30-cm

(4–12-in.)-thick light-gray to dark-gray claystones al-

ternating with fine-grained sandstones. The paleo-

depositional environment is interpreted as a marine

shelf, where the accumulation of clays and plank-

tonic algae was periodically interrupted by transport

of sand into the basin. Proximity to shoreline is indi-

cated by the presence of herbaceous and woody or-

ganic matter. More distal facies outcrop near the vil-

lage of Perekyushkyul approximately 20 km (12 mi)

west of Baku (Figure 6). Here, the lowerMaikop is pres-

ent as a more uniform succession of clays with only

minor influx of coarser grain sizes. Total organic car-

bon contents and HIs range from 1 to 3% and 150

to 400 mg HC/g organic C, respectively.

The middle Maikop outcrops near Perekyushkyul

contain organic-rich claystones with TOC contents of

11%andHIs asmuch as 600mgHC/g organicC. These

are present as discrete, very dark claystones with a bed-

set thicknessof1m(3.3 ft) andcontainapredominance

of algal organicmatter. As expected, themost algal-rich

kerogens are observed within units associated with in-

ferred maximum flooding surfaces in the transgressive

systems tract of a sequence-stratigraphic classification.

Oil and Gas Generation and Migration

The rapid sediment fill and relatively cool ther-

mal structure of the basin has also influenced the

timing of oil and gas generation from theMaikop and

diatomaceous source rocks. Because the predominant

oil-prone constituent in the Maikop kerogen is ma-

rine algal organic matter, the kinetics of oil and gas

generation follow, as expected, thoseof classical type II

kerogens from other basins (e.g., Paris basin, North

Sea). This is true for a heating rate of 18C/m.y. How-

ever, the heating rate in the SCB has been much higher,

near 168C/m.y. during the Pliocene–Pleistocene and

as much as 188C/m.y. during the last 20,000 yr. Tem-

perature measurements from wells in the Kura basin

and SCB show gradients of 20 and 14–168C/km, re-

spectively. Peak oil generation occurs near 1508C, andonset and termination of oil generation would occur

near 110 and 1758C, respectively.In our study area, the basal Maikop is interpreted

to be near depths of 13–14 km (8.07–8.69 mi) and

temperatures of 195–2108C. Under such high tem-

peratures, there is both late-stage conversion of ker-

ogen to gas, as well as thermal cracking of free oil to

gas. If pressure-relief sites are poorly developed, large

overpressured compartments will develop, especially

as thermal cracking of only 1% of oil volume in a

closed systems can account for pressures sufficient to

increase the pore pressure from hydrostatic to above

FIGURE 6. A total of 52 separate, lithified rock fragments were collected from most of the mud-volcano and outcroplocations shown here.

Evaluation of Source Rock Quality in Azerbaijan from Mud-volcano Ejecta / 57

lithostatic (Gaarenstroom et al., 1993). In areas where

crude oil was able to accumulate, includingmigration

pathways in the mudrocks and siltstones, the in-situ

thermal cracking of oil will leave pores linedwith pyro-

bitumen, which could block pore throats and im-

pedemigration. Secondarily, high pressures are caused

by undercompaction because of the inefficient re-

lease of pore waters during burial. This is associated

with thermal expansion of water, which further aids

in fluid migration in the subsurface. Barker (1972)

and Magara (1974) presented the relations between

specific water volume (i.e., water expansion) and in-

creasing burial depth for different geothermal gra-

dients. For example, with a geothermal gradient of

158C/km, the specific volumeof water would increase

from 1.0 cm3/g (0.061 in.3/g) at surface conditions to

1.05 cm3/g (0.064 in.3/g) at 10 km (6 mi).

Taken together, these processes cause a significant

degree of overpressure in the Maikop, and the basal

Maikop in particular. Undercompacted mudrocks

will be fluidized and try to reequilibrate. The process

of reequilibration causes vertical pressure relief and

development of gas diatremes. Such conduits can serve

as important migration pathways for oil and gas.

MUD-VOLCANO EJECTA

Because the main focus of this study was the

source rock potential of the ejecta, sampling was nat-

urally biased toward the fine-grained rocks (mudstones,

shales, and siltstones) thought, from initial visual

descriptions, to be organically enriched. A total of

52 separate, lithified rock fragments were collected

from 14 mud volcanoes and 3 outcrop locations

(Figure 6). The samples are listed in Table 1, along

with a visual description, age estimate, and the spe-

cific mud volcanoes from which the samples were

derived. We chose our sampling sites to obtain the

best possible regional understanding of subsurface

rock properties.

Evaluation of Data Integrity

Tabulated data fromRock-Eval pyrolysis (Bordenave

et al., 1993) should always be interpreted together

with the corresponding pyrograms. This enables

1) the evaluation of the validity of Tmax, produc-

tion index (S1/[S1 + S2]), and hydrogen index

(HI; mg HC/g organic C) data

2) a check on the presence of bitumen (free hydro-

carbons typically having stained the rock being

analyzed)

Within our sample set of 52 rock samples, 11 sam-

ples have only a minor or no development of an

S2 peak (representing pyrolyzable kerogen). For these

samples (S2 less than 0.15 mg/g), the reported Tmax

value is erroneous, and the production index (PI) and

HI values are questionable (Table 2). Other samples

contain free bitumen, observed as a shoulder, or sec-

ondpeak, in the S2 peak.Whenpresent, suchbitumen

elutes early in the S2 peak as less energy is required

to thermally degrade bitumen relative to kerogen.

Samples with bitumen are marked by an asterisk in

Table 2. The remaining data in Table 2 are considered

reliable.

Prior to any evaluation of organic richness, organic

matter quality, and molecular characterization, one

must ascertain if the rock sample has been stained

by in-migrating hydrocarbons (i.e., hydrocarbons

generated from a different source unit). The degree

of staining can be determined from the PI of the

Rock-Eval pyrolysis technique (Bordenave et al., 1993).

Samples with a PI greater than 0.2 are likely stained by

in-migrated hydrocarbons. Within our sample set,

consisting of 52 samples, 30 samples have a PI greater

than0.2, and 10have a so-called ‘‘bitumen shoulder’’

developed on the S2 peak of the Rock-Eval pyrograms.

Of these 30 samples, 20 samples (67%) have TOC

values less than 1%; implying that any staining is of

such a small magnitude that it has not affected the

overall assessment of the rocks’ organic richness

(TOC) or organic matter quality (HI).

Organic Richness and Quality

All samples were analyzed for their TOC content

and by Rock-Eval pyrolysis (Table 2) to establish or-

ganicmatter quality (HI) and thermalmaturity (Tmax).

Total organic carbon contents range upward to 12.4%

wt., and HI values range to 588 mg HC/g organic C.

Maikop and upper Miocene mud-ejecta samples are

oil prone and can be classified as type II kerogens.

Most upper Maikop and some Maikop mud-ejecta

samples haveHI values less than 200mgHC/g organic

C and are, accordingly, classified as type III kerogens.

Sarmatianmud-ejecta samples are also oil prone, with

HI values from 400 to 600mgHC/g organic C, where-

as Chokra-age mud ejecta have more of a type III

kerogen.

Organic-matter Quality and Maturity

All samples collected as ejecta from the mud vol-

canoes and screened according to the S2 peak devel-

opment criteria discussed earlier, have Tmax values

less than 4408C (Table 2). Tmax values about 4358C

58 / Isaksen et al.

Table 1. Lithofacies and estimated ages for rock clasts derived from mud volcanoes.

Number Volcano’s Name SampleNumber

Type Age Microfauna Complex

1 Bozdag-Gyuzdeg 0 Shale Upper Miocene(Sarmatian)

Not found

2 3 Sandstone Upper Miocene(Sarmatian)

Elphidium regina, Elphidium macellum

3 5 Shale Upper Miocene(Sarmatian)

Porosononion subgranosus

4 8 Shale Maikop Globigerina officinalis, Globigerina bulloides

5 Akhtarma-Karadag 9 Shale Upper Maikop Not found

6 10 Shale Upper Maikop Not found

7 11 Shale Upper Maikop Not found

8 13 Shale Upper Maikop Caucasina sp.

9 Touragai 16 Shale Maikop Subbotina officinalis, Nonion sp.

10 18 Shale Eocene Discorbis rotundus, kidneylike radiolaria

11 19 Shale Maikop Subbotina officinalis, Nonion sp.

12 20 Shale Upper Miocene Elphidium macellum, Nonion sp.

13 25 Shale Paleogene Kidneylike radiolaria

14 26 Shale Miocene Not found

15 27 Shale Maikop Not found

16 28 Shale Upper Maikop Not found

17 29 Shale Eocene Cibicides lectus vassl, Planulina costata(Hantk.,) Cibicides praeuhgerianus chal.

18 Lokbatan 32a Shale Upper Miocene Not found

19 32c Shale Chokrakian Not found

20 32d Shale Maikop Not found

21 Bakhar 33 Shale Sarmatian Nonion boganowici, Elphidium macellum,Elphidium regina

22 34 Shale Maikop Globigerina officinalis, Florelus boucanus

23 36 Shale Maikop Pieces of Globigerina officinalis, fish remains

24 37 Shale Upper Miocene Elphidium macellum, Nonion sp.

25 Bozdag-Kobi 39 Shale Sarmatian Porosononion subgranosus, Elphidium regina

26 Dashgil 42 Shale Miocene Porosononion martkobi, Elphidium aculeatum,Elphidium marcellum

27 Sarynja 47 Dolomite Maikop

28 Ayaz-Akhtarma 53 Shale Paleogene Abundant kidneylike radiolaria

29 54 Shale Maikop Not found

30 Korturdag 56 Shale Maikop Globigerina officinalis, Globigerinabulloides, Cibedes sp.

31 59 Shale Chokrakian Spiratella andrussovi, Floribus boucanus

32 60 Shale Lower Paleogene Suttalites trumpyi, Subbotina variata,Globoratalia psuedobulloides

33 63 Shale Chokrakian Spiratella andrussovi

34 Bulla Island 68 Shale Not found

35 70 Shale Not found

36 71 Siderite –

37 Big Kyanizdag 74 Dolomite Chokrakian –

38 76 Shale Maikop Nonion nizamiformis, Globigerina sp.

39 77 Shale Sarmatian Porosononion subgranosus, Nionion martkovi,Elphidium regina

40 78 Shale Upper Miocene Not found

41 Nardaran Akhtarma 85a Shale Upper Miocene Not found

42 85c Shale Upper Miocene Not found

Evaluation of Source Rock Quality in Azerbaijan from Mud-volcano Ejecta / 59

Table 2. Analytical results from Rock-Eval pyrolysis and total organic carbon analyses.

SampleNumber

Quantity Tmax* S1** S2*** S33y PIyy PC*yyy TOCb Hydrogen

IndexbbOxygenIndexbbb

GIA-0 100.7 425 3.07 50.04 2.32 0.06 4.42 10.52 476 22

GIA-3 99.4 425 11.83 59.39 2.71 0.17 5.91 10.67 557 25

GIA-5 99.3 430 0.66 13.17 1.55 0.05 1.15 3.12 422 50

GIA-8 96.2 433 0.21 1.19 1.71 0.15 0.11 1.20 99 143

GIA-9 92.2 420 0.21 0.44 0.62 0.33 0.05 0.77 57 81

GIA-10 101.8 435 0.13 0.51* 3.92 0.20 0.05 0.78 65 503

GIA-11 97.9 423 0.18 0.48 0.91 0.27 0.05 0.98 49 93

GIA-13 99.9 440 0.15 0.40 3.68 0.28 0.04 0.67 60 549

GIA-16 99.9 365 0.19 0.08 0.96 0.73 0.02 0.12 67 800

GIA-18 95.6 439 0.29 1.23 1.30 0.19 0.12 1.23 100 106

GIA-19 95.1 432 6.98 11.29 0.83 0.38 1.52 1.92 588 43

GIA-20 95.0 431 1.46 29.13 0.91 0.05 2.54 5.84 499 16

GIA-25 101.8 431 0.23 0.22 0.62 0.52 0.03 0.42 52 148

GIA-26 104.9 432 0.44 1.22* 0.63 0.27 0.13 0.51 239 124

GIA-27 101.8 468 0.16 0.23 3.24 0.42 0.03 3.11 7 104

GIA-28 98.4 439* 1.81 3.29* 0.76 0.35 0.42 1.69 195 45

GIA-29 97.5 444 0.25 0.19 0.68 0.57 0.03 0.44 43 155

GIA-32a 100.6 421 6.33 62.66 2.66 0.09 5.74 11.39 550 23

GIA-32c 95.9 356 0.19 0.04 1.44 0.86 0.01 6.04 1 24

GIA-32d 95.7 412 0.95 5.49 1.34 0.15 0.53 4.11 134 33

GIA-33 92.1 409 0.05 0.14 0.74 0.28 0.01 0.36 39 206

GIA-34 99.7 320 0.16 0.08 0.80 0.67 0.02 0.22 36 364

GIA-36 92.7 301 0.04 0.02 0.48 0.67 0.00 0.08 25 600

GIA-37 95.1 330 0.07 0.04 0.39 0.70 0.00 0.14 29 279

GIA-39 92.3 429 0.28 5.94 0.67 0.05 0.51 2.38 250 28

GIA-42 98.4 386 0.10 0.06 1.03 0.62 0.01 12.39 0 8

GIA-47 100.0 421 0.05 0.12 0.32 0.31 0.01 0.30 40 107

GIA-53 103.6 426 0.30 0.95* 0.50 0.24 0.10 1.14 83 44

GIA-54 100.0 385 0.05 0.24 0.26 0.18 0.02 0.34 71 76

GIA-56 95.2 345 0.06 0.18 0.14 0.25 0.02 0.41 44 34

GIA-59 84.0 411 0.90 5.17 0.60 0.15 0.50 3.60 144 17

GIA-60 93.0 426 0.15 0.87 0.74 0.15 0.08 0.74 118 100

GIA-63 96.4 416 0.44 1.57 0.64 0.22 0.16 2.57 61 25

GIA-68 95.5 388 0.10 0.15 0.69 0.42 0.02 0.31 48 223

GIA-70 102.7 431 0.21 0.55 1.66 0.28 0.06 0.69 80 241

GIA-71 95.2 428 2.25 22.10 0.82 0.09 2.02 7.18 308 11

GIA-74 117.2 434 0.31 2.01 0.62 0.13 0.19 0.90 223 69

GIA-76 95.8 438 0.27 2.32 2.67 0.10 0.21 1.66 140 161

GIA-77 93.1 430 0.26 0.54 0.42 0.32 0.06 1.48 36 28

GIA-78 97.8 424 2.33 8.87* 0.60 0.21 0.93 4.82 184 12

GIA-85a 118.1 426 0.25 0.81* 0.75 0.24 0.08 0.45 180 167

GIA-85c 143.0 432 0.07 0.22 0.34 0.25 0.02 0.29 76 117

AZ98-01 87.5 412 0.41 25.46 1.72 0.02 2.15 7.91 322 22

AZ98-02 96.3 440 1.17 1.13* 1.03 0.51 0.19 0.65 174 158

AZ98-03 101.2 439 0.10 0.14 6.75 0.42 0.02 0.38 37 1776

AZ98-04 98.4 421 0.31 0.93 1.90 0.25 0.10 1.31 71 145

AZ98-05 98.1 418 0.25 0.58 0.87 0.30 0.06 0.95 61 92

AZ98-06 96.9 404 0.46 2.42 1.64 0.16 0.24 2.32 104 71

60 / Isaksen et al.

are considered representative of the onset of oil-

window maturation, i.e., where subsurface tempera-

tures have reached levels of 80–908C. Thus, most

ejecta samples are immature for hydrocarbon gener-

ation. Twoof the four ejecta sampleswithTmax values

of 435–4408Chave bitumen staining as evidenced by

the bitumen shoulder on the S2 peak. This bitumen

may indeed represent the earliest yield product from

amaturing source rock as opposed to in-migrated hy-

drocarbons from a nonassociated source rock.

With a geothermal gradient of 208C/km in the

Kura Valley (data from the Azerbaijan Institute of

DeepOil andGas), we can infer that the early-mature

ejecta samples are derived from about 4 km (2.5 mi)

depth. This applies for samples GIA-18 (Koun/

middle Paleogene) and GIA-76 (Maikop), from the

Osmanbozdag and Boyuk Kamizadag mud volcanoes,

respectively.

Further insight to the organic-matter type and

thermal-maturity level of the samples is obtained from

visual kerogen analyses. Here, the rock’s mineral ma-

trix is dissolved by HCl and HF acids, and the result-

ing kerogen concentrate is viewed under the micro-

scope. The results are tabulated in Table 3. TheMaikop

samples GIA-8, GIA-19, GIA-32d, and upper Miocene

and Sarmatian (GIA-0) have a predominance of ma-

rine, algal-amorphous organic matter. With the ex-

ception of the GIA-19 sample, these are all thermally

immature based on the thermal alteration index

(TAI), which measures the temperature-induced color

change among spores, pollen, etc. (Staplin, 1969). The

GIA-19 sample is a Maikop sample from the Osman-

bozdag mud volcano and is thermally more mature

(TAI 2.0), in agreement with the GIA-18 sample from

the same mud volcano mentioned above.

The upper Maikop (GIA-28 and GIA-51) and up-

per Miocene samples (GIA-32a, GIA-39, and outcrop

AZ98-09) have a predominance of herbaceous (spores

and pollen) organic matter and secondary amounts

of amorphous and woody material. It thus appears,

from this limited sample set, that this area experi-

enced a greater input of terrigenous higher plant

material during the lateMiocene. The Paleogene sam-

ple (GIA AZ98-09) is also dominated by herbaceous

material, with secondary amounts of algal-amorphous

and woody-inertinitic material.

Based on the geochemistry results discussed thus

far, it appears that the Maikop section evolved from

an overall transgressive system during early to middle

Maikop (shorelines moved farther away from our sam-

pling points), followed by a highstand system during

late Maikop and upper Miocene (shorelines and asso-

ciated terrigenous input, closer to our sampling sites).

Sulfur analyses (Table 4) confirmed the assump-

tion that sulfur bound within the organic matter of

SCB source rocks is very low. Organic sulfur contents

are in the range of 0.01–0.03%. Most free sulfur has

bound with iron and formed pyrite. This implies that

the depositional environment during early diagenesis

contained an abundance of active iron sites on clay

mineral that acted to scavenge any free sulfur. Pyritic

sulfur contents range from 0.32 to 2.39%.

Timing of Hydrocarbon Generation

Kinetics analyses were carried out on three sam-

ples (GIA-5, GIA-19, GIA-39, and AZ98-08). These

show a consistency of maximum yields around 49–

53 kcal/mol. Furthermore, the unimodal distribu-

tion suggests uniform composition of reactive organic

Table 2. (cont.).

SampleNumber

Quantity Tmax* S1** S2*** S33y PIyy PC*yyy TOCb Hydrogen

IndexbbOxygenIndexbbb

AZ98-07 101.7 432 0.22 1.97 0.53 0.10 0.18 1.04 189 51

AZ98-08 91.5 423 0.42 16.78 0.67 0.02 1.43 4.46 376 15

AZ98-09 100.7 421 0.38 17.43 0.56 0.02 1.48 2.28 764 25

AZ98-10 92.8 423 0.43 5.74 0.87 0.07 0.51 6.98 82 12

*Tmax = temperature index ( 8C).**S1 = free hydrocarbons (mg HC/g of rock).***S2 = residual hydrocarbon potential (mg HC/g of rock).yS3 = CO2 produced from kerogen pyrolysis (mg CO2/g of rock).yyPI = S1/(S1 + S2 ).yyyPC* = 0.083 (S1 + S2).bTOC = total organic carbon (wt.%).bbHydrogen index = mg HC/g organic carbon.bbbOxygen index = mg CO2/g organic carbon.

Evaluation of Source Rock Quality in Azerbaijan from Mud-volcano Ejecta / 61

matter, i.e., similar type of algal-amorphous and her-

baceous organic matter as indicated by visual kerogen

analyses.

Implications for Oil and Gas Exploration

Rock ejecta correlated to the Oligocene to lower

Miocene Maikop Series are organically rich and con-

tain a predominance of algal-amorphous organic

matter. These rocks constitute the principal oil-prone

source rocks in the sedimentary sections affected by

mud volcanoes. Potential for oil generation is also pres-

ent in the middle–upper Miocene diatomaceous suite,

albeit as a lesser quality source rock than the Maikop.

The low organic-sulfur content (less than 0.03%) is in

agreement with the generation of sweet crudes and

an absence of H2S gas throughout the area.

In our study area, the basal Maikop is interpreted

to be near depths of 13–14 km (8.07–8.69 mi) and

temperatures of 195–2108C. Under such high tem-

peratures, both late-stage conversion of kerogen to

gas and thermal cracking of free oil to gas are present.

Consequently, late charges of gas may displace oil in

certain trap configurations.

CONCLUSIONS

� The mud-ejecta samples are immature to early

mature with respect to hydrocarbon generation.� With a geothermal gradient of 208C/km, the early-

mature ejecta samples are likely derived from

about 4 km (2.5 mi) depth. (This applies for

samples GIA-18 [Koun/middle Paleogene] and

GIA-76 [Maikop], from the Osmanbozdag and

Boyuk Kamizadag mud volcanoes, respectively.)� Organic sulfur contents of the organic matter are

low. Free sulfur present in the depositional envi-

ronment from early sulfate reduction has mostly

Table 3. Summary of organic carbon and visual kerogen data.

SampleNumber

Age TotalOrganicCarbon

OrganicMatterType

Visual Abundance Normalized (%) AlterationStage*

ThermalAlterationIndex**

ALy AMyy Hb Wbb I{

GIA-0 Upper Miocene 10.52 Am(Al); H; – 11 44 44 0 0 1 to 1+ 1.2

GIA-8 Maikop 1.2 Am(Al); –; – 33 67 0 0 0 1+ to 2� 1.5

GIA-19 Maikop 1.92 Am(Al); H{{; – 22 44 33 0 0 2� to 2 2

GIA-28 Upper Maikop 1.69 H; W; Am-1 0 13 50 25 13 3� to 3+ 3.2

GIA-32a Upper Miocene 11.39 Am(Al); H{{; – 22 44 33 0 0 1+ to 2� 1.6

GIA-32d Maikop 4.11 Am(Al); H; – 27 36 36 0 0 1 to 1+ 1.2

GIA-39 Upper Miocene 2.38 H{{; Am(Al); W-I 9 27 45 9 9 2� to 2 2

GIA-59 Chokrakian 3.6 H; Am(Al); W(I) 8 23 46 15 8 2 2.2

AZ98-01 Paleogene 7.91 H; Am(Al); W 9 18 64 9 0 1+ 1.4

AZ98-09 Upper Maikop 2.28 H; Am(Al); W(I) 15 15 46 15 8 1+ to 2� 1.6

*Alteration stage = degree to which kerogen macerals have been thermally altered on a scale from 1 to 3+.**The thermal alteration stage is an equivalent scale from 1 to 3.5 (Staplin, 1969).yAL = algal.yyAM = amorphous.bH = herbaceous.bbW = woody.{I = intertinite.{{ Organic matter types column notation: predominant = 60–100%; secondary = 20–40%; trace = 0–20%.

Table 4. Sulfur analytical data from ejecta andoutcrop samples.*

Sample Total S Sulfate S Pyritic S Organic S

GIA-0 2.63 0.21 2.39 0.03

GIA-5 1.09 0.22 0.86 0.01

GIA-19 0.60 0.13 0.45 0.02

GIA-32a 2.37 1.11 1.24 0.02

GIA-32d 1.89 1.62 0.26 0.01

GIA-39 2.00 0.88 1.11 0.01

GIA-59 3.38 1.36 2.00 0.02

GIA-76 0.56 0.23 2/60 0.02

GIA-78 4.85 2.23 2.60 0.02

AZ98-08 1.09 0.15 0.91 0.03

*Data are reported in percent inorganic matter.

62 / Isaksen et al.

bound with iron to form pyrite. The results are

the generation of sweet crudes and gases.� TheMaikop samples are, for themost part, domi-

nated by algal organic matter. As with theMaikop

outcrops, the lithology andorganicmatter content

of the Maikop can vary significantly from lami-

nated shales to sandstones and marine algal to

herbaceous and terrigenous organic matter.� Based on the geochemistry results, it appears that

the Maikop section evolved from an overall trans-

gressive system during early to middle Maikop

(shorelines moved farther away from our sam-

pling points), followed by a highstand system

during late Maikop and upper Miocene (shore-

lines and associated terrigenous input closer to

our sampling sites).

ACKNOWLEDGMENTS

We thank the Geological Institute of Azerbaijan

and ExxonMobil Exploration Company for permis-

sion to release these data.

We also extend our thanks to William J. Devlin

with ExxonMobil and Ken O. Stanley (deceased) for

helpful insights into the basin history and regional

tectonics and early reviews of the manuscript.

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