Petroleum Prospectivity of EP 127 and EP 128 Georgina Basin Northern Territory, Australia. Executive Summary

Transcription

1 Petroleum Prospectivity of EP 127 and EP 128 Georgina Basin Northern Territory, Australia Executive Summary Isis Petroleum Consultants Pty Ltd December 2009 Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 1

2 Table of Contents 1. Introduction 2. Source 3. Reservoir 4. Plays 5. Gravity and Magnetics 6. Conclusions 7. Recommendations Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 2

3 1. Introduction Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 3

4 Introduction Isis Petroleum Consultants conducted a desktop review of the prospectivity of EPs 127 & 128 in the Southern Georgina Basin, Northern Territory. This document forms an Executive Summary of the work carried out. The review incorporated all available open file data, papers and references The study identified three (3) working petroleum systems and several play types across the permit areas Structures are inferred to exist from interpretation of coarse gravity and magnetic data Several reservoirs have been identified within the blocks Reservoir quality and continuity are considered the key risks for exploration of EPs 127 & 128 Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 4

5 Location and Shows Map Heavy oil staining Heavy oil staining EP 128 Oil saturated interval Bitumen bleed Oil extracted from plug EP 127 Tr bitumen Bitumen Oil staining Oil staining and bitumen Source: Boreham & Ambrose, 2007 Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 5

6 2. Source Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 6

7 Charge: Oil Stains and Bitumen in cores Boreham & Ambrose, 2007 Cambrian core photos from the Georgina Basin a) Strong oil stain from Owen-2, m, Thorntonia Limestone b) Oil stain/solid bitumen in vuggy porosity from Elkedra-2, 283.9m, Hagen Member c) Weak oil stain from Elkedra-2, 353.5m, Hagen Member Elkedra-2 Owen-2 Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 7

8 Charge: Source Characterisation Boreham and Ambrose (2007) typed oil stains and identified three oil families; Thorntonia, Arthur Creek and Hagen Formations These source rocks were deposited in anoxic bottom waters that extended into the photic zone within platformal to deeper water slope settings The Georgina Basin oil families are the result of the Middle Late Cambrian global oceanic anoxic event and the worldwide deposition of organic-rich source rocks (Boreham and Ambrose, 2004) Possible Middle Proterozoic source units in deeply buried half grabens form a potential gas source Source: Boreham & Ambrose, 2007 Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 8

9 Charge: Maturity Ambrose et al (2001) Lower Arthur Creek Formation Source Rock Distribution and Maturity Source: Ambrose et al, 2001 Rich Middle Cambrian marine source rocks of the Lower Arthur Creek Formation were mature for oil in the Toko Syncline in the Middle Ordovician and are in the gas generation zone present day (Jackson, 1982) The deeper parts of the Dulcie Syncline are also likely to be gas-saturated present day In the Elkedra region, residual oil extracts from dolostones indicate maturity in the middle of the oil window, Rc %, on the basis of aromatic hydrocarbon maturity ratios (Volk et al., 2007) Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 9

10 Charge: Timing and Migration Burial history modelling indicates multiple phases of oil generation and expulsion with the earliest phase beginning during the Ordovician, which has subsequently been degraded to bitumen A later phase currently exists as a relatively non-degraded crude of aromatic intermediate composition (Karajas, 1994) Expulsion of the latest phase of hydrocarbons was possibly in the Cretaceous or Paleogene (Radke, 2009) Oil types are generally found within the intraformational reservoirs suggesting short range migration (Radke, 2009) The identification of multiple petroleum systems in the southern region of the basin, together with relatively short migration distances from source to trap, improve prospectivity of this region (Boreham and Ambrose, 2007) Post charge erosion of much of the southern Georgina Basin, initiated during the Alice Springs Orogeny, has resulted in reservoirs now occurring at shallow depths of 300-1,000m with an increased risk of oil alteration during this protracted time period Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 10

11 3. Reservoir Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 11

12 Potential Reservoirs Both sandstone and carbonate reservoir targets Sandstone reservoirs from Early Cambrian to Devonian Sandstone reservoirs incorporate shoreline and channel plays Carbonate reservoirs from Early Cambrian to Ordovician Carbonate reservoirs comprise shoals, debris flows, karstic facies, tempestites and fractured carbonates Source: Volk et al, 2004 Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 12

13 Key Reservoir Targets Thorntonian Limestone: The basal dolostone unit underlies the source rock unit and is best developed over palaeohighs and in shoreward settings. Better reservoir developments contain dolomitised grainstones with intercrystalline, vuggy, and locally extensive fracture porosity. Effective permeabilities range up to 1,055 md in gross potential reservoir of 17m Steamboat Sandstone: The Steamboat Sandstone is a near shoreline calcareous/ siliciclastic sandstone, interbedded with oolitic carbonate rocks The unit is extensive and it is usually approximately 70 m thick in the southern portion of the basin and reservoir quality decreases from the Ross-1/Owen-2 area with Ø = 5 17%, K = 0 20 md; into the basin at Todd-1 Ø = 5 10%, K = 0 5 md Chabalowie Fm: The basal Hagen Member is an extensive nearshore regressive blanket in the western part of the depocentre. Net reservoir thickness ranges between 3 and 18 m, porosities between 6.9 and 14.6%, with permeabilities between 2 and 3,400 md. Overlying this reservoir are tight anhydritic argillaceous carbonates (Karajas, 1994) Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 13

14 Key Reservoir Targets Eurowie Sandstone: The Eurowie Sandstone Member in Elkedra-7A is m ( m) thick it is a fine- to medium grained, porous sandstone with a dolomitic matrix in part, dolomite with chert nodules, algal laminate, dolarenite, claystone, siltstone and intraformational breccia Kelly Creek Formation: In the Toko Syncline, a thick and relatively homogeneous potential dolostone reservoir exists within the Early Ordovician Kelly Creek Formation and it is characterised by high intercrystalline porosity and permeability (Radke and Duff, 1980). Fracture porosity and that associated with hydrothermal dolomite are additional secondary/diagenetic plays in an otherwise tight carbonate sequence (Radke, 2009) Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 14

15 4. Plays Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 15

16 Play Types and Objectives 9 1. Red Heart Dolostone 2. Thorntonia Limestone structural play, dip and fault closures; also pinchout play Upper Arthur Creek Formation shoal play 4. Upper Arthur Creek Formation middle ramp debris flow, tempestite facies Steamboat Sandstone shoreline channel plays 6. Hagen Member shoreline play 7. Chabalowe Fm in structural traps 8. Eurowie Sandstone Member Source:Volk et al, Early Ordovician Kelly Creek fractured carbonates in structural traps Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 16

17 Play Types: Dunster et al (2007) The most prospective areas encapsulate a combination of: Early formed structures / highs Proximity to depocentres with early oil maturity Shale acting as a fault detachment surface and / or a hydrocarbon source / seal The presence of structures associated with early Ordovician faults A general lack of deformation and new faulting during the later phases of the Alice Springs Orogeny A suitable reservoir at a drillable depth Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 17

18 5. Gravity and Magnetics Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 18

19 Bouguer Gravity Unfiltered Data Gravity data downloaded from the Geoscience Australia web-site on approx 800 m x 800 m grid The deeper sedimentary troughs lie in the Dulcie Syncline & Toko Syncline correlate with gravity lows Positive and negative gravity anomalies exist within basement rocks caused by variations in rock type from granites to metamorphics EP 128 EP 127 Dulcie Syncline Basement Toko Dulcie Syncline Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 19

20 Residual Bouguer Gravity Gravity Unfiltered Residual Gravity A residual gravity map was made by subtracting the filtered gravity on a 20 x 20 km spatial filter from the original gravity values Resulting residual anomalies may originate from basement density variations or from thickness or density variations within sediments above basement Calibration with seismic and wells and/or gravity modelling is required to validate potential sedimentary anomalies Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 20

21 Residual Gravity and Structures Residual gravity anomalies displayed on the surface geology (Volk et al, 2004) Anomalies which lie partly or wholly within outcropping basement or Proterozoic rocks have been omitted Anomalies in some cases may be related to sedimentary structures The anomalies may be caused by basement density variations Calibration with seismic and wells and/or gravity modelling is required to determine their likely origin The anomalies are future focus areas with the potential to trap hydrocarbons Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 21

22 Residual Gravity Anomalies: Calibration Arthur Creek Fm Basement Brown residual gravity anomalies show some correlation with sedimentary structures on seismic lines Gravity modelling is required to further check the validity of the correlation Higher resolution gravity data has been requested from NT Department of Minerals & Energy and should be used for the additional work Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 22

23 Regional Magnetics and Geology Regional Total Magnetic Intensity ( TMI ) contours downloaded from the GA website Presence of outcropping to shallow Basement partly correlates with areas of smaller wavelength magnetic values Analysis of magnetic Basement depth within the area would be difficult but it may provide more information on potential sedimentary structures Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 23

24 6. Conclusions Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 24

25 Conclusions There is good evidence of a working petroleum system in the southern area of the Georgina Basin in the area of permits EP 127 & 128 Oil shows of poor to fair quality have been recorded in a large number of wells Oil and gas generation has occurred Source is therefore a relatively low risk in the study area The critical factor in evaluating the Georgina Basin is the definition and evaluation of effective reservoirs in the Cambrian section The vertical and areal distribution of the potential reservoirs and reservoir quality is currently poorly understood Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 25

26 Conclusions Seismic data is very sparse and is located almost entirely in the western end of the permits Gravity and magnetic data is available at semi-regional scale over the study area The interpretation of structures from gravity and magnetic data has proven to be difficult because of the strong variations in the properties of basement rocks, which varies from granitic to metamorphic The primary reservoir target Cambrian section comprises carbonates and sandstones and the contrast in density between these sediments and Basement is expected to be small in specific areas Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 26

27 7. Recommendations Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 27

28 Recommendations It is recommended that a thorough study be made of cuttings and cores in wells and using electric logs to understand the potential reservoirs in the permits Reservoir quality is likely to be enhanced by fracturing and for this reason it is recommended that a detailed study be made of Landsat data to determine areas where fractures might be better developed It is recommended that a detailed analysis be undertaken of the higher resolution gravity and magnetic data with the objective of potentially identifying structures, including calibrating to seismic data when it is received It is recommended that work be undertaken using combined gravity and magnetic data sets to define the depth to magnetic basement and the presence of structures Executive Summary: Petroleum Prospectivity EP 127 & EP 128, Georgina Basin 28