1 - Late charge problems in the K5 area

Late Charge problems in the K5 area

1

Bernard GeissTEP Nederland, 5th June 2008TNO/EBN Workshop Utrecht

2 - Late charge problems in the K5 area

Agenda

Regional context

K5-13 results and Post Mortem

Structural Setting K4-K5 area

Conclusions

3 - Late charge problems in the K5 area

SW NE

Top ChalkBase ChalkTop SaltTop RotliegendesHercynian UnconformityTop Westphalian A

Chalk

Salt

5 km

Chalk

Salt

Stratigraphic Column and HC Play in core area

D2

R

HU

E

D1

C2

R

HU

E

D1

C2

TWA

D4

DT

K5-2

4 - Late charge problems in the K5 area

K5-1

K5-12

K5-2

K5-5

K5-6

K5-4

K5-3

K5-7

K5-8

K5-9

K5-11

K4-8

K5-13

K6-8

K6-1

K6-6

K6-5

K6-4K6-2

K6-3

K6-7

K6-9

K3-2

K5-F2 K6-11

K6-10

100%1111K6

100%1212K5

50%12K3

100%22K2

Exploration wells and success rate

10 km

5 - Late charge problems in the K5 area

Westphalian B Coal Measures

K2-2K2-1 K5-11E17-1E17-2E16-1

Miocene Unconf.

Top Chalk

Top SaltBase Chalk

Top RotliegendesHU

Top Westph. A

Top Westph. B

NE SW

T

W

T

1 -

3 -GDT GDT

K5-13

WUT

Regional seismic line

K5bK5-13

K2

E16/17

K5-11

6 - Late charge problems in the K5 area

Random tie line K5bTop ChalkBase ChalkTop SaltTop RotliegendesHUTop Westphalian A

K5-13K5-12K1-5NW ESE

RHU

Top Salt

Fairly similar context with K5-12

m

Top West A

7 - Late charge problems in the K5 area

Well correlation flattened at MFS2K5-12 K5-13

RSWC

Pressure tests

10 m

Sand box concept confirmed

Seq. 212.3 m

39m Seq. 3-3856 mss

-3841 mss

-3834 mss

Seq. 1

Additional sands not predicted

8 - Late charge problems in the K5 area

Seismic Interpretation: K5b Top Westphalian B Depth Structure

Outline of erosion at HU

Westphalian ABC

S N

HU

K5-13K5-12

9 - Late charge problems in the K5 area

Fluvial to aeolian depositional processes: Back stepping of LS system (F16-3) The main NE-SW wrench trend possibly

constrains fluvial sediment supply K6 Block located within the main fluvial belt

axe with an impact on the reservoir properties

L7-2K4-9

K5-12 K1-5

K4-12

L4-2

K5-9

L1.7

F16-3

E-18

K4-K5 : Aeolian dominated, Sand box conceptStrong impact of HU geometry

West.D

West. Upper CWest. Lower CWest. B

West. A

Stephanian

K6-10

Regional Depositional environment sketch - confirmed

Sand deposits on Westphalian B subcrop

K5-13

N

10 - Late charge problems in the K5 area

K5-13: What did go wrong?

Intra Westph. B coalbed

Base Chalk

Top Salt

Zechstein CarbonatesTop Rotliegend

Hercynian Unconformity

2.5 km

K5-13

K5-13

Top Rotliegend Depth Structure Map

SENW

Reservoir

Juxtaposition?

Low saturations of gas in fluid inclusions

11 - Late charge problems in the K5 area

The dilemma to explain the failure of K5-13 Leakage ? Gas found in fluid inclusion but only low

saturations More sands drilled. Sand juxtaposition

across faults still unlikely but possible If such a juxtaposition is present then

the spill point is below the well. However no attic gas found.

Leakage through faults very unlikely as the surrounding formations are supposed to be highly sealing: Silverpit shales laterally and vertically, Zechstein evaporites as ultimate vertical seal.

Lack of HC Charge ? Gas in fluid inclusions where has it

gone? Never observed in K4-K5 area Westphalian SR within the K5-13 horst

block not mature enough to expellsufficient amounts of gas

Presence of N45 oriented faults, separating kitchen area from K5-13 panel

Shales

Evaporites

Reservoir

What is so peculiar about these N45 oriented faults?

12 - Late charge problems in the K5 area

Fault pattern K4/K5 area on NW-SE gradient map

K5-13

Gradient at Top Rotliegendes

13 - Late charge problems in the K5 area

K4-K5 Structural Pattern at Top RotliegendesBlack = Normal faultsRed = Inverted faultsWhite = Transfer Faults

N40

N150

Close-up areaTop Rotliegendes Depth Structure and Dip

14 - Late charge problems in the K5 area

K4-K5 Close-Up Structural Pattern at Top Rotliegendes

N40

N150

K4-A4

K4-7

K5-A2

K5-A4

K5-A1

K8-12

K5-4

K5-10

K4-A3 Black = Normal faultsRed = Inverted faultsWhite = Transfer Faults

Top Rotliegendes Depth Structure and Dip

Xline 1875

15 - Late charge problems in the K5 area

Subtle Transfer faults on Xline 1875

K5-A1

K5-A2

K5-A4

2.5 km (1:4)

K8-12

K5-4

200 m

NW SE

Hercynian Unconformity

Top Salt

Top Rotliegend

Near Top Westphalian B

K5-A1 K5-A4K5-A2 K5-4

Faults with hardly any throw within the Rotliegendes

Reservoirjuxtapositioning

16 - Late charge problems in the K5 area

K5A Pressure History on Well correlationK5K5--A4A4 K5K5--44K5K5--A1 (ex. K5A1 (ex. K5--3)3)K5K5--A2A2

HU

Seq. 6

Seq. 3-4

Seq. 6

Seq. 3-4

1999 236 bar 198 bar 401 bar2006 126 bar 96 bar 221 bar

1988 409 bar 409 bar Not yet drilled 409 barBHP Lower Slochteren Reservoir Sequences 3-4

1994 Production start-up K5-A1 & A2 Not yet drilled 409 bar

K5-A1

K5-A2

K5-A4

K5-4

Transfer Fault Transfer Fault

17 - Late charge problems in the K5 area

Small scale: Graben alike structures along transfer faults

The observed vertical throws are little but may be underestimated as they are often resembling conjugate fault systems.

When evaluating juxtaposition and SGR, we are constantly hurdling against the lack of vertical resolution. Therefore deterministic evaluations are uncertain.

Further uncertainties are the horizontal throw and fault cementation

More throw

18 - Late charge problems in the K5 area

Large scale: Separation of K5-13 from kitchen by

~ 10 km

K5-13

N

Producing Areas (sketched) andno expulsion from SR expected

Kitchen Areas

Kitchen Areas

19 - Late charge problems in the K5 area

NW-SE Striking Normal and Inverted Faults

Top ChalkBase ChalkTop SaltTop RotliegendesHUTop Westphalian BTop Westphalian A

2.5 km

500 m

SWNE

K5-12

Strong throws on the NW-SE (N120-150) faults no reservoir juxtapositionDecoupling between Pre- and Post salt. Salt cored buckle folds above Rotliegend Highs

20 - Late charge problems in the K5 area

Top Rotliegendes Depth MapBase Chalk Depth MapTop Chalk Depth Map

Late Cretaceous to Tertiary Inversion

Late Cretaceous Tertiary inversion axis around N45

21 - Late charge problems in the K5 area

Present day maximum horizontal stress oriented N135

The N135 direction of the present day maximum stress is also confirmed by borehole induced fracturing.

The N45 transfer faults are therefore very likely to be closed

Total data

22 - Late charge problems in the K5 area

Leveille et al. 1997Sealing N40 trending faults

SGR predicts clay smear is not sealing

Leveille argues for cementation, on the basis of cemented fractures from cores

23 - Late charge problems in the K5 area

Conclusions

Confirmation of the geological model for sand deposits above Westphalian B subcrop (Sand box concept)

Fluid inclusions can not conclude on the reason of the failure

Migration from northern kitchen may be deflected by closed N45 faults

These transfer faults have hardly any vertical throw but may form significant barriers to fluid flow. This is not fully understood today

Beware of certainties even in a mature area

24 - Late charge problems in the K5 area

3D View of K5b area

K5-13

The N45 faults appear as distinct corridors on this view. They are not just a thin lineament but a graben system probably composed of helicoidal en echelon faults.

25 - Late charge problems in the K5 area

Throw variation along fault