Introduction to sequence stratigraphy and its application to reservoir geology

Transcription

1 Introduction to sequence stratigraphy and its application to reservoir geology Massimo Zecchin Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS

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3 Historical development

4 Definitions Systems tracts are interpreted based on stratal stacking patterns, position within the sequence, and types of bounding surfaces, and are assigned particular positions along an inferred curve of base level changes at the shoreline (Catuneanu, 2002).

5 Key concepts Relative sea-level: sea level relative to an immaginary reference horizon called datum (Posamentier et al., 1988; Catuneanu, 2002). Base level: a surface of equilibrium between erosion and deposition (Cross, 1991). It is usually below sea level due to the scour of waves and currents. It corresponds to the fluvial graded Profile in continental settings. Accommodation (space): the space available for the accumulation of sediment (Jervey, 1988). It can be created or destroyed by variations in base level.

6 Relative sea level

7 Relative sea-level rise

8 Relative sea-level fall

9 Relative sea-level changes

10 Base level

11 Interplay between base level changes and sediment supply Transgression: the landward migration of the shoreline It occurs when the rate of accommodation creation outpaces the sedimentation rate at the shoreline - Landward facies shift - Deepening of the shallow-marine area - Retrogradational stacking pattern Regression: the seaward migration of the shoreline It occurs when the sedimentation rate outpaces the rate of accommodation creation at the shoreline (normal regression) or during base level fall (forced regression) - Seaward facies shift - Shallowing of the shallow-marine area - Progradational stacking pattern

12 Accommodation and sediment supply

13 Model-independent vs. model-dependent aspects

14 Stratal terminations (model-independent)

15 Genetic types of deposits (model-independent)

16 Normal and forced regressive deposits

17 Sequence stratigraphic surfaces

18 Subaerial unconformity (SU) - The SU develops during base level fall - It is subjected to river incision and pedogenesis - It progressively extends basinwards during the forced regression of the shoreline - It has a marine correlative conformity (CC) connected to its basinward termination SU CC

19 Subaerial unconformity (SU) Lower Cretaceous Axel Heiberg Island Mid Pleistocene Crotone Pliocene to Holocene - Gulf of Mexico

20 Basal surface of forced regression (BSFR) and regressive surface of marine erosion (RSME) - The BSFR marks the base of all marine deposits accumulated during the forced regression of the shoreline. It corresponds to the paleo-seafloor at the onset of forced regression - The RSME is cut by waves in the shoreface during the forced regression of the shoreline, and marks the base of forced regressive shorefaces. It easily reworks the BSFR in proximal settings. Its formation depends on wave energy, slope, and subsidence RSME BSFR Cretaceous Blackhawk Fm., Utah RSME

21 Basal surface of forced regression (BSFR) Pliocene to Holocene - Gulf of Mexico BSFR

22 Maximum regressive surface (MRS) or transgressive surface (TS) - The MRS marks the boundary bentween prograding (regressive) and subsequent retrograding (transgressive) deposits - It is formed when the increasing rates of accommodation creation start to outpace the sedimentation rates. Early and Middle Triassic Ellesmere Island MRS

23 Maximum regressive surface (MRS) or transgressive surface (TS) Pliocene to Holocene - Gulf of Mexico

24 Ravinement surface (RS) - The RS is a diachronous erosional surface cut by waves (WRS) or tidal currents (TRS) in the shoreface and coastal settings during transgression - It is associated to transgressive lags or condensed bioclastic deposits - It climbs toward the basin margin - Its formation depends on wave energy, slope and rates of relative sea-level rise and sediment supply Upper Cretaceous Panther Tongue Member, Star Point Fm., Utah RS

25 Ravinement surface (RS) RS Late Pleistocene Crotone

26 Ravinement surface (RS) Off Crotone Zecchin et al. (2011) Amendolara bank Zecchin et al. (2011)

27 Maximum flooding surface (MFS) - The MFS marks the end of the shoreline transgression - It separates retrograding (transgressive) strata below from prograding (regressive) strata above - It is formed when the sedimentation rates start to outpace the rates of creation of accommodation - It is a downlap surface (in seismics) Jurassic Axel Heiberg Is. - It is commonly associated with a condensed section MFS

28 Maximum flooding surface (MFS) Pliocene to Holocene - Gulf of Mexico

29 Systems tracts

30 Falling stage or forced regressive or early lowstand systems tract

31 Lowstand or late lowstand Systems tract

32 Transgressive systems tract

33 Healing phase wedge Late Pleistocene Gulf of Mexico

34 Highstand systems tract

35 Systems tracts at the Shelf edge

36 Deep-water sequence

37 Deep-water sequence TST HST LST L-FSST E-FSST

38 The Zinga Sandstone (lower Pliocene, Crotone) From Catuneanu & Zecchin (2013)

39 The Capo Colonna terrace (Late Pleistocene, Crotone) From Zecchin et al. (2009)

40 The Holocene sequence of Venice From Zecchin et al. (2009)

41 Upper Pleistocene shelf From Lobo & Ridente (2013) Gulf of Lions Bengal shelf Brazilian shelf

42 Systems tracts in the Gulf of Mexico Pliocene to Holocene - Gulf of Mexico LST TST FSST FSST HST BSFR Modified from Catuneanu (2006)

43 Lower Cretaceous of West Siberian Basin From Abreu et al. (2010) Sequence Stratigraphy of Clastic Systems The ExxonMobil Methodology. SEPM Con. Sed. Pal. 9

44 Pelotas Basin (southern Brazil) Four sequences from Aptian to Present 10 km APD = HST+FSST R = TST PA = LST From Abreu et al. (2010) - ExxonMobil

45 Wheeler diagram

46 Sequence stratigraphic models Mitchum et al. (1977) Posamentier et al. (1988) Van Wagoner et al. (1988) Hunt & Tucker (1992) Galloway (1989) Johnson & Murphy (1984)

47 Depositional sequence of Posamentier & Allen, 1999

48 Depositional sequence of Hunt & Tucker, 1992 and Helland-Hansen & Gjelberg, 1994

49 T-R and genetic sequences

50 Sequence hierarchy Ma First order 50+ Second order 3-50 Third order Fourth order Fifth order Sixth order From Vail et al. (1991)

51 Application to reservoir geology: HST Fluvial Sediment budget: good (aggrading systems) Reservoir: fair (channel fill, crevasse splays) Poor source, fair seal (overbank fines) Coastal Sediment budget: good (deltas and strandplains) Reservoir: good (shoreline sands) Source and seal: poor Shallow-water Sediment budget: good (shoreface and shelf facies) Reservoir: good (shoreface sands) Source and seal: fair (shelf fines) Deep-water Sediment budget: poor Reservoir: poor Source and seal: good (pelagic facies)

52 Application to reservoir geology: FSST Fluvial Sediment budget: poor Reservoir: poor Source and seal: poor Coastal Sediment budget: fair (offlapping deltas, downstepping beaches) Reservoir: fair (detached shoreline sands) Source and seal: poor Shallow-water Sediment budget: fair (shoreface and shelf facies) Reservoir: fair (shoreface sands) Source and seal: fair (shelf fines) Deep-water Sediment budget: good (debris flows and high-density turbidity flows) Reservoir: good (turbidites) Source and seal: fair ( overbank pelagics)

53 Application to reservoir geology: LST Fluvial Sediment budget: good (amalgamated channel fills) Reservoir: good (channel fills) Source and seal: poor Shallow-water Sediment budget: good (shoreface and shelf facies) Reservoir: good (shoreface sands) Source and seal: fair (shelf fines) Coastal Sediment budget: good (shelf/shelfedge deltas, strandplains) Reservoir: good (shoreline sands) Source and seal: poor Deep-water Sediment budget: fair (low-density turbidity flows) Reservoir: good (turbidites) Source and seal: fair ( overbank pelagics)

54 Application to reservoir geology: TST Fluvial Sediment budget: good (aggrading systems) Reservoir: fair (channel fills, crevasse splays) Poor source, fair seal (overbank fines) Shallow-water Sediment budget: fair (onlapping shoreface and shelf facies) Reservoir: fair (shelf sands, basal healingphase wedges) Source and seal: good (shelf fines) Coastal Sediment budget: good (estuaries, deltas, backstepping beaches) Reservoir: good (estuarine, deltaic and beach sands) Poor source, fair seal (central estuary facies) Deep-water Sediment budget: fair (low-density turbidity flows and debris flows) Reservoir: fair (turbidites) Source and seal: good (pelagic facies)

55 Continuity of reservoirs in continental settings Good reservoir continuity Isolated reservoirs Potential source rock Isolated reservoirs Good reservoir continuity

56 Potential continental to coastal reservoirs Paleocene of Colombia

57 Continental to shallow-marine reservoirs Potential reservoirs Sealing deposits

58 Continental to shallow-marine reservoirs

59 Deep-water reservoirs TST HST LST L-FSST E-FSST

60 Deep-water reservoirs Pliocene to Holocene - Gulf of Mexico BSFR

61 Final remarks - Sequence stratigraphy represents a powerful tool for the study of sedimentary successions, allowing the recognition of the relationship between stratal architecture and changes of base level and sediment supply. - The linkage between sequence stratigraphy and eustasy is an outdated concept. Modern sequence stratigraphy refers to relative sea-level (base level) changes of various frequency and amplitude, which depend on the interplay of eustasy and tectonics. - Sequence stratigraphic analysis should be conducted on the basis of descriptive, model independent criteria, by the recognition of genetic units and surfaces typified by diagnostic physical attributes. The application of the preferred or the most appropriate model may follow. - The application of sequence stratigraphy ranges from research in academia to hydrocarbon industry. The sequence-stratigraphic method is the modern sedimentologic and stratigraphic approach for the identification of stratigraphic traps by predicting facies distribution and stratal architecture within the basin fill.

62 Thanks for your attention!