High Pressures While Oil Drilling In Greece

HIGH FORMATION PRESSURES WHILE DRILLING, WESTERN GREECE A. Mavromatidis, Petroleum Development Oman LLC , Muscat, Sultanate of Oman, V. C. Kelessidis, Technical University of Crete, Polytechnic City, Chania, Greece, D. Monopolis, Technical University of Crete

–

Introduction

–

General geological setting

–

High pressures in Deep exploration wells (EW-1 & Sidetrack of EW1)

–

Discussion of Causes

–

Conclusion and Recommendations

GREECE Regional setting - subthrust plays

N

ALBANIA

(> 670mmboe)

ITALY

EW

Demetra Prospect 220mmbbls

Potenza

Cerro Falcone

N

B ari

Tempa Rossa

Monte Alpi

Ioannina

Igo umenitsa

S. Apennines trend > 800mmbbls

Ioannina Plateau Trend > 400mmbbl (on block)

GREECE 0

100km

0

100km

Western Greece

EW-1

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

BC)

commented

Drilling activity since 1940s Oil seeps Gas field What else?

Stratigraphy and Petroleum Geology Reservoir, Seal, Source

S

1 to 4 km maybe 8 km

R

SR

SR

S

IONIAN ZONE

SR

RESERVOIR:

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

THIS WAY UP!

Regional Seismic Lines EW-1 Location Top Quaternary Top Carbonates Posidonia Formation Top Evaporites Base Evaporites Top Reservoir

20 km

Tectonic Scenarios 20 km

(a )

20 km

(a )

Model 1

Model 2 20 km

(b )

20 km

(b )

(b )

Legend

(b )

20 km c la s tic s c a rb o n a te s e v a p o r it e s

Legend 20 km

(b )

20 km

(c )

unknown lithology c la s tic s c a rb o n a te s e v a p o r it e s unknown lithology

Legend c la s tic s c a rb o n a te s e v a p o r it e s

(c )

20 km

Reference Point

Reference Point

2000

4000

4000

Flysch?; carbonates ; or both

Permo-Triassic ?

2000

Permo-Triassic ?

WELL PROGNOSIS AND HYDROCARBON GEOLOGY

Well Location

High Pressures Pressure (psi) 0

0

1,000

3,000

5,000

9,000

7,000

11,000

13,000

Hydrostatic Gradient:0.453 psi/ft Overburden Gradient: 1.04 psi/ft 1,000

Top evaporites 2,000

10 ppg

13 ppg 14 ppg

16 ppg

3,000

Kick at 3,566 m in EW-1S

4,000

5,000

Kick at 3,966 m in EW-1

15,000

DEMETRA - Pressure - speculation about pressure profile in the evaporites

Evaporite interval –

17.5 ppg (2.1gr/cm3)Kick @ 3966m

–

sidetrack

–

17.9 ppg (2.1g/cm3) or 10k to 11k psi)Kick @ 3566m

Evaporite interval is overpressured from about 2100m: - hole size - resistivity/density Only see it when have porosity/permeability Potential for pressured ‘cells’ to give even higher pressure

? CANNOT PREDICT PRESSURE!

What is the mechanism?

Where is the base evaporites?

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?

●

Young & Lepley (2005); Swarbrick et al. (2002) Undercompaction ? Young Sediments, Clay-sand lithology

●

Fluid expansion ?

Thermal effects, clay diagenesis, HC maturation

Tectonic Activity ?

Cross along faults, overthrust, compressional loading

Change of lithology? Base of evaporites?

Lithology and pressures Drilling exponent (Dxc) Depth

Lithology Lithology

0

10.00

Different geology - only few metres distant

Mudstone, clay or shale Limestone

T Q/P Fl

1.00

0.10 1500

Top evaporites

Dolomite

- halite

2000

Overpressure starting?

Anhydrite

Shift due to change of bit to PDC bit ?

Halite 2500

Wide scatter but following ‘normal’ trend Prepared to encounter OP at around 3900m onwards

Chert

Qualifiers

1000

Carbonaceous

3000

Calcite Siliceous

Shift for new pdc bit? Dxc of EW-1S

Bitomenous Dolomitic

Normal compaction line 1.02 kg/lt mudweight equivalent

But kick at 3566mWide scatter but following 3500

10 2000

20

30

40

50

60

Kick at formation pressure 17.3 ppg

Sidetrack offset from original hole (in metres) (Lateral exaggeration x20)

(b)

Kick off point 2833 m Kick in EW-1S at 3566 m

4000

0

0

1000

‘normal’ trend

Kick at formation - drilled no problem pressure 16.5 ppg

in original hole 3000

5000

Pressure (psi) 7000

9000

11000

13000

3000 1000

Overburden Gradient: 1.04 psi/ft

Hydrostatic Gradient:0.453 psi/ft

Kick at EW-1 3966 m

4000

Top evaporites 2000

(a)

Kick at 3,566 m in EW-1S

3000

4000

Kick at 3,966 m in EW-1

High Pressures Not Close to Change of Lithology, still in Evaporites Dolomitic lenses have been ‘pressurized’ due to flysch overpressure EW-1

EW-1S

Smectite to illite Faults

Gypsum – anhydrite

Intra-evaporite overpressure due to earlier isolation of carbonate lenses/rafts within anhydrite while they were at greater depths

EW-1

EW-1S

High Pressures Close to Change of Lithology Overpressured fluid accumulations usually encountered Faults immediately underneath the evaporites (Zilberman et al., 2001). Stringers. Overpressures in the stringers occur as a result of intra-stringer charge. Unfortunately stringers are difficult to be seen in seismic images. EW-1

EW-1S

(b)

Hydrocarbon generation. However, no hydrocarbons in both wells. But if close to the base of the Legend evaporites, then gas can exert such pressures to the overlying evaporites. Mudstone, clay or shale

ReachedLimestone the detachment level -> overpressured sediments beneath the impermeable Dolomite 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 in 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 evaporitic strata in the Ionian Zone. More studies are important for the Ionian Zone and generally 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 because, while there are some 25 oil and gas fields in Albania, only one discovery has been made so far in western Greece, that at west Katakolon, in offshore Peloponnesos region. 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!

Let’s give it a go, let’s unravel the myth and show Herodotus

that the mystery liquid he reported BC fulfils part of the presen needs