Plumbing the Depths of the Pelican Field

Transcription

1 Plumbing the Depths of the Pelican Field Thurza Frenz Pelican

2 Talk Objectives To discuss the development of the northern area of the Pelican Field, in particular: The relationship between reservoir quality, facies and depth and how this impacted the most recent well placement in the northern area The early performance of the PUP22S1/PUW23S1 producer/injector pair and some interesting observations about how these wells interact May 18 th 2016 DEVEX 2

3 The Pelican Field: Introduction Location: East Shetland Basin, NNS Discovered: 1975 (211/26-4) Type: Subsea oil development tied back to the Cormorant Alpha Platform STOIIPs and Recovery: TOTAL: 486 MMstb Recovery to date: 74 MMstb (15 % RF) PELICAN MAIN: 369 MMstb Recovery to date: 71 MMstb (19 % RF) PELICAN NORTH: 116 MMstb Recovery to date: 3.31 MMstb (3 % RF) Depth: 10,500-12,300 ft TVDSS Contact: OWC not penetrated, estimated at 12,300 ft DEVEX 3

4 The Pelican Field: Introduction Location: East Shetland Basin, NNS Discovered: 1975 (211/26-4) Type: Subsea oil development tied back to the Cormorant Alpha Platform STOIIPs and Recovery: TOTAL: 486 MMstb Recovery to date: 74 MMstb (15 % RF) PELICAN MAIN: 369 MMstb Recovery to date: 71 MMstb (19 % RF) PELICAN NORTH: 116 MMstb Recovery to date: 3.31 MMstb (3 % RF) Depth: 10,500-12,300 ft TVDSS Contact: OWC not penetrated, estimated at 12,300 ft DEVEX 4

5 Broom Lower Brent Rannoch Etive Lower Ness Upper Brent Upper Ness The Pelican Field: Reservoir in a Typical Well Middle Jurassic Brent Group 211/26a-12RE ZONE GR TVDSS PHIE PERM Field average: 350 ft thick Crestal erosion of Tarbert and Upper Ness Well shows reduction of reservoir quality with depth Results in top-heavy distribution of permeability throughout the Brent Best quality reservoir in Upper Ness sands Leads to water cycling through Upper Ness interval - potential bypass of Lower Brent reserves 65 % of field STOIIP is within Lower Brent May 18 th 2016

6 Pelican North Appraisal wells CA23S1 & CA23S2 drilled into head area of the Pelican Field in 1998 Found 350 ft thick Brent interval Significantly less sand in Upper and Lower Ness Etive - tight, low resistivity sands Broom - water bearing CA23S2 perforated but failed to produce due to low Productivity Index In 2013 TAQA drilled first successful producer into the North - PUP22S1 DEVEX

7 Broom Rannoch Lower Brent Etive Lower Ness Upper Brent Upper Ness Pelican North Appraisal wells CA23S1 & CA23S2 drilled into head area of the Pelican Field in 1998 CA23S1 ZONE GR TVDSS PHIE PERM Found 350 ft thick Brent interval Significantly less sand in Upper and Lower Ness Etive - tight, low resistivity sands Broom - water bearing CA23S2 perforated but failed to produce due to low Productivity Index In 2013 TAQA drilled first successful producer into the North - PUP22S1 DEVEX 7

8 Pelican North Appraisal wells CA23S1 & CA23S2 drilled into head area of the Pelican Field in 1998 Found 350 ft thick Brent interval Significantly less sand in Upper and Lower Ness Etive - tight, low resistivity sands Broom - water bearing CA23S2 perforated but failed to produce due to low Productivity Index In 2013 TAQA drilled first successful producer into the North - PUP22S1 DEVEX

9 Broom Rannoch Lower Brent Etive L. Ness Upper Brent Upper Ness Pelican North: PUP22S1 Well Results Encountered 350 ft thick Brent sequence at 11,350 ft TVDSS ZONE PUP22S1 GR TVDSS PHIE PERM Excellent reservoir properties in both Upper and Lower Ness intervals Significant drop-off in permeability below Lower Ness Reservoir more similar to flank NW Hutton Field than Pelican Main - presence of Etive Interfluve DEVEX 9

10 Pelican North: PUP22S1 Well Results Significant erosion of the Etive took place prior to Lower Ness deposition Erosion created an irregular incised valley topography onto which the Lower Ness was deposited Thick Etive encountered at PUP22S1 is located in an interfluve position where less erosion took place than the main field and nearby NW Hutton DEVEX Adapted from Marriott, 2015

11 Broom Rannoch Lower Brent Etive L. Ness Upper Brent Upper Ness Pelican North: PUP22S1 Well Results Encountered 350 ft thick Brent sequence at 11,350 ft TVDSS ZONE PUP22S1 GR TVDSS PHIE PERM Excellent reservoir properties in both Upper and Lower Ness intervals Significant drop-off in permeability below Lower Ness Reservoir more similar to flank NW Hutton Field than Pelican Main - presence of Etive Interfluve Pressure tests showed northern area to be at virgin pressure Produced 3.31 MMstb since August 2013 (to February 2015) Injector needed to maximise recovery and maintain pressures for future drilling DEVEX 11

12 The Significance of Facies Reservoir quality is severely affected by depth PUP22S1 results prompted re-look at reservoir degradation with depth Upper Ness Fluvial Channels Use of analogue data from NW Hutton Field was key Core data from both fields reassessed Etive Shoreface Sandstones Key link found between facies (grain size) and reservoir quality May 18 th 2016 DEVEX 12 Adapted from Marriott & Besley, 2015

13 PUP22S1 Facies & Depth Coarse grained fluvial channels retain best reservoir properties at depth Found exclusively within Ness interval Net reservoir preserved at depths in excess of 12,500 ft TVDSS Etive Shoreface Sandstones Finer grained facies such as mudstones and lower shoreface show the most degradation with depth Become non-net below a depth of 11,800 ft TVDSS Primarily affects permeability but slight degradation of porosity also seen Upper Ness Fluvial Channels May 18 th 2016 DEVEX 13 Adapted from Marriott & Besley, 2015

14 Depth (TVDSS ft) PUW23S1 The Pelican Field: Well Depth Comparison May 18 th 2016 DEVEX Cored Wells

15 PUW23S1: Key Risks & Uncertainties Facies Presence and quantity of good quality fluvial channel facies Presence of Etive Interfluve Connectivity Sealing/ baffling faults between injector and producer Pressure Potentially large pressure differential across Mid Ness Shale due to production at PUP22S1 leading to drillability issues DEVEX 15

16 PUW23S1: Pre-Drill Pore Pressure Prediction Pre drill estimates of depletion ~ 4400 psi in Upper Ness with virgin pressure in Lower Brent units PUW23S1 PPFG Prognosis No safe mud window Mud Weight > Fracture Gradient in Upper Ness Borehole strengthening material used Estimated additional strength of 400 psi No losses during drilling of reservoir section 4000 psi depletion measured in Upper Ness DEVEX

17 PUW23S1: Pre-Drill Pore Pressure Prediction Pre drill estimates of depletion ~ 4400 psi in Upper Ness with virgin pressure in Lower Brent units PUW23S1 PPFG Prognosis No safe mud window Mud Weight > Fracture Gradient in Upper Ness Borehole strengthening material used Estimated additional strength of 400 psi No losses during drilling of reservoir section Addition of Wellbore Strengthening Material 4000 psi depletion measured in Upper Ness DEVEX

18 Broom Rannoch Lower Brent Etive L. Ness Upper Brent Upper Ness PUW23S1: Results Encountered top reservoir at 11,797 ft TVDSS ZONE PUW23S1 GR TVDSS PHIE PERM Top heavy reservoir quality distribution Good quality Upper and Lower Ness interval with good permeabilities Poor quality Lower Brent similar to that seen at PUP22S1 Etive Interfluve encountered as at PUP22S1 May 18 th 2016 DEVEX 18

19 Broom Rannoch Lower Brent Etive L. Ness Upper Ness PUW23S1: Results Electro-facies show some good quality Fluvial Channel facies (yellow) within the Upper Ness ZONE PUW23S1 GR TVDSS PHIE PERM Pressures taken throughout the Upper Ness show depletion of 4,000 psi - consistent with predicted pressures Shows good communication with PUP22S1 producer Unable to get pressures throughout Lower Brent due to very low mobility May 18 th 2016 DEVEX 19

20 PUW23S1 PUW23S1: Results Facies, in particular grain size, plays a significant role in preserving reservoir quality at depth Etive Shoreface Sandstones Coarse grained fluvial channels preserve much better permeabilities than the finer grained sands at the same depth Fluvial channels approx. 60 md Finer grained sands approx. 2 md Upper Ness Fluvial Channels May 18 th 2016 Adapted from Marriott & Besley, 2015

21 PUW23S1: Early Injection Performance 13 psi/day BHP increase 3.0 MMbbls STOIIP PUP22S1 & PUW23S1 Pressures 3.0 psi/day BHP increase 40 MMbbls STOIIP Fractured injection of >10,000 bpd Oil benefit >1,000 bopd Unexplained drop in PUP22S1 BHP Sep/2015 Dec/2015 April/2015 Very rapid response between PUW23S1 and PUP22S1 Water breakthrough after 3 months Oil rates stabilised above previous declining trend Pelican Field Oil Production May 18 th 2016

22 Observations Depositional facies plays an important role in preserving reservoir quality at depth: Diagenesis strongly influenced by original grain size Coarse grained fluvial channel facies retain good reservoir quality below 12,500 ft Increased confidence and opportunities available to Pelican development at depth North of Pelican still challenged due to structure and distance from manifold Coarse grained fluvial channel facies presence far less certain than main field Assessment of reservoir drilling risks was robust and use of wellbore strengthening material allowed drilling risk to be mitigated Injectivity shows excellent connection between producer/injector pair with uplift in production justifying injector well May 18 th 2016 DEVEX 22

23 Acknowledgements Derek Littlejohn Andrew Bostock May 18 th 2016 DEVEX 23

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25 SANDFACE INJECTION PRESSURE SANDFACE INJECTION PRESSURE PUW23S1: Injection Related Hydraulic Fracturing Hydraulic fracturing took longer than expected based on experience from PUW12S3 injector: Investigation underway to compare injection and understand differences: Wellbore strengthening material increasing near field stresses Well angle, length and orientation in relation to stress field orientation and injection water cooling Uncertainty in rock properties in relation to elastic and thermal properties Sand exposure and distribution relating to restriction of fracture growth vertically PUW23S1 Injection - Temperature and Pressure Effects on Fracture Breakdown Pressure Expected scenario PUW23S1 Injection - Temperature and Pressure Effects on Fracture Breakdown Pressure Possible problematic case Top Heather Top Heather Heather Caprock Top Brent Heather Caprock Top Brent Upper Ness Sands Upper Ness Sands

26 Relationship of diagenetic style to depositional environment Besley, 2015

27 Upper Ness - Grain Size & Diagenesis The Upper Ness high energy fluvial channel sandstones are typically medium grained and well sorted with little detrital clay Blue stain = porosity The pore system is open Feldspar has suffered grain dissolution but fluid flushing is thought to have prevented the formation of, or removed, diagenetic kaolinite 1000 μm Quartz overgrowths form rigid bridges between grains that help resist compaction Feldspar grain dissolution pore 200 μm Marriott, 2015

28 Etive- Grain Size & Diagenesis The Etive shoreface sandstones are finer grained with locally abundant detrital clay matrix and smaller pore throats The pore system is closed Feldspar grain dissolution results in diagenetic kaolinite blocking pores 1000 μm Illitisation of kaolinite and detrital clays Quartz overgrowth development is inhibited where detrital clay matrix coats the grains. Where present this tends to occlude pore throats rather than preserving an open pore system Detrital & authigenic clays block pores 200 μm Marriott, 2015