High Formation PressuresWhile Drilling, Western Greece

A. Mavromatidis, Petroleum Development Oman LLC , Muscat,Sultanate of Oman,

Angelos.Mavromatidis@pdo.co.om V.C. Kelessidis, Technical University of Crete,

Chania, Greece, kelesidi@mred.tuc.gr D. Monopolis, Technical University of Crete

AAPG Energy Conference & Exhibition1

AAPG Energy Conference & ExhibitionAthens, Nov. 18-21, 2007

Presentation Summary

Introduction• Introduction

• General geological settingGeneral geological setting

• High pressure in Deep exploration wells (EW-1 & Sidetrack of EW-1)

Di i f• Discussion of causes

• Conclusion and recommendation• Conclusion and recommendation

2

GREECE, Regional setting - subthrust playsplays

B ariITALY

N

Demetra Prospect

ALBANIA N(> 670mmboe)

EWTempa Rossa

Monte Alpi

Cerro FalconePotenza

Demetra Prospect220mmbbls

Ioannina

Igoumenitsa

EW

30 100km

S. Apennines trend> 800mmbbls

0 100km

GREECEIoannina Plateau Trend> 400mmbbl (on block)

Western Greece

EW-1

The myth is here:Herodotus (484-425 BC) Herodotus (484 425 BC) commented on oil seeps

Drilling activity since 1940s

Oil seepsOil seeps

Gas field

What else?

4

Stratigraphy and Petroleum Geology

5

RESERVOIR: Ionian Carbonates Reservoir Section, Fractured Calci-turbidites and Debris flows.Fractured Calci turbidites and Debris flows.

6

Regional Seismic Lines

7

Tectonic Scenarios

( ) 20 km

Legend

clastics(a) 20 km clastics

carbonates

evaporites

unknown lithology

Model 1 Model 2Reference Point

8(b) 20 kmc) 20 km

Well prognosis and hydrocarbon geology

2000 2000

4000Flysch?; b t

4000

carbonates ; or both

9

Well Location

10

Lithology and pressuresDepth

Lithology

0

LithologyMudstone, clay or shale

LimestoneDifferent geology

T Q/P Fl 0 Limestone

Dolomite

Anhydrite

Halite

only few metres distanthalite

1000

Chert

QualifiersCarbonaceousCalciteSiliceous Prepared to encounter

2000Sidetrack offset from original hole (in metres)

(Lateral exaggeration x20)

10 20 30 40 50 60

BitomenousDolomitic

Prepared to encounter OP at around 3900m onwards(Lateral exaggeration x20)

Kick off point2833 m

Kick in EW-1Sat 3566 m

onwards

But kick at 3566m, 3000

Kick at EW-13966 m

drilled with no problem in original hole

114000

3966 m

(a)

How? Causes of High Pressures

Anomalously high pressure kick was totally unexpected No change in cuttings (anhydrite with dolomite interbeds)

What is the pressure mechanism?p

Young & Lepley (2005); Swarbrick et al (2002)Young & Lepley (2005); Swarbrick et al. (2002)Undercompaction ? Young Sediments, Clay-sand lithologyFluid expansion ? Thermal effects clay diagenesisFluid expansion ? Thermal effects, clay diagenesis,

HC maturationTectonic Activity ? Cross along faults overthrustTectonic Activity ? Cross along faults, overthrust,

compressional loadingChange of lithology? Base of evaporites?

12

g gy p

High pressures not close to change of lithology still in evaporiteslithology, still in evaporites

Dolomitic lenses have been E W -1have been ‘pressurized’ due to flysch

E W -1 Sdue to flysch overpressureSmectite to

F a u lts

Gypsum–anhydrite

illite

Gypsum anhydrite

Intra-evaporite overpressure due to earlier isolation of carbonate lenses/rafts within anhydrite

hil th t t d th13

while they were at greater depths

High pressures close to change of lithology

Overpressured fluid accumulations usually encountered immediately underneath theevaporites (Zilberman et al., 2001).

Stringers. Overpressures in the stringers occur as a result of intra-stringercharge. Unfortunately stringers are difficult to be seen in seismic images.

E W -1

E W 1 SE W -1 S

Hydrocarbon generation. No hydrocarbons in both wells. But if close to the base of theevaporites, then gas can exert such pressures to the overlying evaporites.

14

Reached the detachment level -> overpressured sediments beneath theimpermeable evaporites characterized by extreme fluid overpressuring. Fluids ?water and/or gas.

Conclusions and recommendations

Despite all pre-drilling preparations, unexpected high pressures can be encountered.Proper post-drilling analysis could allow for assessment of causes of overpressure and better preparation for future drilling activity. Use of advanced drilling technology and the better formulation of drilling fluids, capable of operating with minimal problems under these harsh conditions.The availability of better detection pore pressure mechanisms, like ability to see ahead of bit. No well has ever penetrated the whole Triassic

15

evaporitic strata in the Ionian Zone.

Conclusions and recommendations

More studies are important for the Ionian Zone andgenerally for western Greece, such as the pre-Apulian Zone, which has similar lithology to the Ionian Zone, and the Gavrovo Zone. These studies must trace the deep evaporitic strata and target areas where the evaporites will be fully penetrated.Drilling in western Greece should continue

there are some 25 oil and gas fields in Albania,only one discovery has been made so far in westernonly one discovery has been made so far in western Greece (west Katakolon)

This is highly significant as it proves the existence of a

16

This is highly significant as it proves the existence of a viable play and its continuation throughout western Greece

Holy Triad: Source Rock, Reservoir, Seal

The ‘cursed’ evaporites maybe a bless!L ’ i i l ’ l h h Let’s give it a go, let’s unravel the myth

and show Herodotus

that the mystery that the mystery

liquid he reported BC fulfils

part of the present energy

17

part of the present energy

needs