GNS Science 1 Fairway Drive Avalon Lower Hutt 5010 PO Box 30368 Lower Hutt 5040 New Zealand T +64-4-570 1444 F +64-4-570 4600 3400 3500 3600 3700 3800 3900 MH2 MH2 Maui-6 MH1 No age diagnostic data No age data No conventional cores Cores available in Kapuni-3. -14 PM3a 3100 3200 3300 3400 Dm-Dh Dw MH1 PM3 3600 3700 3800 3900 4000 4100 MH1 PM3 4650 4700 4750 4800 4850 4900 4950 5000 5050 MH1 Dm-Dh Dw-Dh MH2 MH2 Thin section data from Kapuni-3. -14 Pukeko-1 Maui B-8(P) Kapuni-13 Cardiff-1 Depth (m) Depth (m) Depth (m) Depth (m) GR GR GR GR F/D Age F/D Age F/D Age F/D Age M Zone M Zone M Zone M Zone Setting Setting Setting Setting QEM QEM QEM QEM Core Core Core Core TS TS TS TS MH2/MH1 boundary: Omata Member/D-shale equivalent upper part of MH1 zone (Dm- Dh): K3E Sandstone in Kapuni Field and D-sands in Maui Field Intraformational mudstones and coals lower part of MH1 zone and PMb zone (Dw) Eocene Paleocene 3. Well Correlation Well correlations have been made both perpendicular and parallel to the paleoshoreline using wireline logs constrained by biostratigraphy (e.g., Fig. 2). More detailed correlation is planned following targeted biostratigraphic analyses and full facies interpretations. The top of the Kaimiro Formation is taken as the base of a widely developed marine mudstone (Omata Member/D-shale) of Heretaungan age (Dh), equivalent to the upper MH1 miospore zone. The base of the study interval (Paleocene/Eocene boundary) is taken at the top of the PM3a miospore zone. Figure 2. ENE-WSW oriented cross section through the coastal plain/marginal marine environment from Cardiff-1 to Pukeko-1, approx. parallel to the depositional paleoslope. Biostratigraphic sample depths (F/D, foraminifera/dinoflagellate; M, miospore), cored intervals, thin section (TS) and QEMSCAN (QEM) sample depths are shown. Setting is the broad depositional environment with the key presented in Fig. 1. These data suggest that much of the producing K3E reservoir of the Kapuni Field (estuarine channel facies) may be time-equivalents to the producing D-Sands of the Maui Field (tidal channel facies). wsw ENE Reservoir Quality Prediction for the Kaimiro Formation, Taranaki Basin 1. Introduction and Methods The Early to Middle Eocene Kaimiro Formation represents an attractive reservoir play in Taranaki Basin. Hydrocarbons were discovered in the formation in the late 1960's, and are still being produced from the Maui and Kapuni fields today. However, the formation remains under-explored, partly due to burial depths, which are >4,500 m over much of the Taranaki Peninsula. Preliminary results are presented from a new Kaimiro Formation reservoir study being undertaken at GNS Science. The main objectives are facies interpretation, correlation, petrography and reservoir assessment, ultimately with the aim of developing a better understanding of the controls on reservoir quality, and in order to discriminate regions where the Kaimiro Formation is likely to have the most favourable reservoir properties. The study area extends along the length of the ENE-WSW trending reservoir fairway, and includes many newly released offshore wells (Fig. 1). Open-file biostratigraphic data, core data, and petrographic data has been used. New analyses are planned which will target data gaps and thereby better illustrate reasons for reservoir variability within the formation. References Core Laboratories, Flores, R.M., Higgs, K.E., Strogen, D., Griffin, A., Ilg, B., Arnot, M., King, P.R. and Thrasher, G.P., Strogen, D.P., 2007: 2004: 2012: 1996: 2010: Detailed petrographic evaluation of sidewall core samples from Hector No.1 well. PR report 3806. Coal buildup in tide-influenced coastal plains in the Eocene Kapuni Group, Taranaki Basin, New Zealand.AAPG Studies in Geology, v.51, p.45-70. Reservoirs of the Taranaki Basin, New Zealand. GNS Science Data Series No. 2012/13a. Cretaceous-Cenozoic geology and petroleum systems of the Taranaki Basin, New Zealand. IGNS monograph 13. Updated paleogeography maps for the Taranaki Basin and surrounds. GNS Science Report 2010/53. Acknowledgments This project is supported by public research funding from the Government of New Zealand; we also acknowledge NZ Petroleum and Minerals for funding the PEGI initiative, which has provided a source of petrographic data (Higgs et al., 2012). Authors: Karen Higgs and Ian Raine; Email Contact: [email protected] 6. Summary · · · · · The Early to Middle Eocene Kaimiro Formation is considered to be a good reservoir target along most of the coastal plain to shallow marine reservoir fairway due to 1) common occurrence of fine-, medium- and coarse-grained sandstones, and 2) a consistently quartz-rich, lithic-poor composition. Excellent reservoir properties have been proven in marginal marine channel facies at Maui and Kapuni; slightly poorer reservoir properties occur in coastal plain facies at Toru-1. There is little available data for shallow marine facies, but these deposits are likely to contain some of the best reservoir properties due to: dominant medium grain size with moderate-good sorting; high energy facies with little detrital matrix; good lateral sandbody connectivity; good vertical stacking of sandstone beds (i.e., less heterolithic than sandstones within the coastal/marginal marine environment). Relatively poor reservoir properties occur in the deeply buried parts of the stratigraphy (>4.5 km) due to severe compaction, and relatively abundant quartz cement and illitic clay minerals. Preliminary results indicate that the best reservoir quality is likely to be developed in the high energy facies of marginal to shallow marine environments, where present-day burial depths are < 4 km. 4. Petrography Sandstone grain size and mineralogy has been determined by thin section analysis of core and SWC samples. Most samples are from fluvial or tidal/estuarine channel facies, with a few SWC samples from the shallow marine facies (wells Tui-1, Hector-1, Hochstetter-1). QEMSCAN data is available for some cuttings samples and this allows grain size and mineralogical assessment through uncored parts of the Kaimiro Formation. Grain size data show the Kaimiro Formation to comprise very fine- through to very coarse-grained sandstones (Fig. 3). Fine (upper) through to coarse (lower) sandstones predominate, with overall more coarse-grained facies in the relatively proximal settings (fluvial/estuarine channel facies); these coarser sandstones are generally associated with moderate to poor sorting (Higgs et al., 2012). Medium-grained sandstones predominate in the shallow marine depositional environment, and are often characterised by moderate to good sorting. Point-count data suggest the mineralogy of sandstones is fairly limited, with most samples plotting as feldsarenites or subfeldsarenites (Fig. 4). These results are consistent with QEMSCAN data of cuttings, which illustrate the quartzose nature of the samples, both stratigraphically and geographically (e.g., Fig. 5). The formation is lithic-poor, feldspar is typically minor, and K-feldspar is the dominant feldspar type. Feldspar is particularly scarce at Cardiff-1, which we interpret to be related to the deep burial depth and advanced diagenesis at this wellsite. Clay minerals are variably abundant in the Kaimiro Formation. Detrital clay is common in the relatively fine-grained sandstones (low energy facies), and mica is locally common in tidally influenced facies. Authigenic clay minerals are locally abundant (e.g., at Pukeko-1, Kapuni-13, Cardiff-1). However, the dominant clay differs (Fig. 6), which we interpret to be due to different burial and fluid histories. Other authigenic minerals comprise locally pervasive carbonate cements and generally minor quartz cement; abundant quartz overgrowths have only been identified in deeply buried wells. Figure 4. Ternary diagram showing the quartz- feldspar-lithic composition (Q-F-L) for the Kaimiro Formation based on thin section data. Hector-1 data from Core Laboratories (2007). Figure 3. Histogram summarising the mean grain size for Lower-Middle Eocene sandstones based on thin section petrography and QEMSCAN. Data has been grouped into relatively proximal to relatively distal wells. Background Quartz Fe-infiltrated Muscovite Chlorite Biotite/Phlogopite K-Feldspar Plagioclase Feldspar Illite/Muscovite Glauconite Smectite Kaolinite Pyrite Calcite Ferroan Calcite Dolomite Ferroan Dolomite Fe-Oxides Siderite CaFeCO3/Ankerite Heavy Minerals Porosity Figure 5. QEMSCAN image maps for selected Early to Middle Eocene cuttings showing dominant quartz and subordinate/minor feldspar grains. Lithified sandstones occur over parts of the Taranaki Peninsula where strata are deeply buried. Loose grains are dominant elsewhere and may be indicative of better quality sandstones. Kiwa-1, 3481 m: Loose grains are dominant and may be indicative of poorly consolidated sandstones. Quartz dominant, subordinate feldspar. Tui-1, 3470 m: Loose grains are dominant, mostly quartz, suggesting presence of poorly consolidated, quartzose sandstones. Pukeko-1, 3585 m: Sandstone with quartz and remnant feldspar; abundant kaolinite interpreted as a diagenetic alteration phase related to acidic flux. Te Whatu-2, 3453 m: Common loose and coarse quartz grains; finer lithologies including kaolinite and carbonate cemented sandstones. Kaimiro-1, 4750 m: Common sandstone cuttings suggesting the presence of relatively lithified deposits. Quartz dominant, subordinate feldspar, illitic clay. Cardiff-1, 4845 m: Common sandstone cuttings, predominantly composed of detrital quartz and authigenic illite; rare feldspar due to advanced feldspar reactions. 0 10 20 30 40 vfL vfU fL fU mL mU cL cU vcL Frequency Grain Size (class) 0 20 40 60 80 100 100 80 60 40 20 0 0 20 40 60 80 100 L Q F Maui Field Kapuni Field Cardiff-1 Toru-1 Pukeko-1 Maui-4 Tui-1 Hector-1 Hochstetter-1 Sublitharenite Subfeldsarenite Quartz Arenite Litharenite Feldspathic Litharenite Lithic Feldsarenite Feldsarenite Note the variation in abundance of feldspar Proximal wells Distal wells Clays dominated by illite Clays dominated by kaolinite Illite/muscovite Depths are present-day, along-hole (AH). Plots are in stratigraphic order with the left-hand plot representing the shallowest sample. Fe-muscovite/biotite Chlorite Kaolinite Smectite Glauconite / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / Hochstetter-1 c. 3 km Kiwa-1 3.2-3.6 km Pukeko-1 3.5-3.7 km Rahi-1 3.1-3.3 km Toru-1 3.8-3.9 km Kapuni-13 3.7-3.9 km Cardiff-1 c. 4.8 km Kaimiro-1 4.5-4.8 km Maui-2 c. 3.3 km Tui-1 3.4-3.5 km Maui-7 c. 3.1 km Maui B-8(P) c. 3.4 km Te Whatu-2 c. 3.4 km Maui-4 2.2-2.3 km Max extent of Early to Middle Eocene shoreface Min extent of Early to Middle Eocene shoreface N Max extent of deposition or preservation of the Kaimiro Formation. From Strogen (2010). Figure 6. Pie charts showing clay mineral composition based on QEMSCAN, plotted by sample and well. Clays include kaolinite, illite/mica, chlorite, smectite, glauconite. Note locally dominant kaolinite (Pukeko-1, Te Whatu-2, Maui-4) interpreted as a diagenetic alteration of feldspar and other unstable minerals during circulation of acidic fluids. Illite is dominant in deeply buried wells (Cardiff-1, Kaimiro-1). Clay mineralogy in wells from the shallow marine environment (Hochstetter-1, Kiwa-1, Tui-1; <4 km depth) is generally comparable (illite/kaolinite co-dominant). Note variable chlorite and glauconite, generally more common in marine-influenced settings. 5. Reservoir Quality Conventional core analysis data are used here as a proxy for reservoir quality. Most data is from the Maui and Kapuni fields (Fig. 7A, 7B), which display similar ranges of porosity- permeability and illustrate the locally excellent reservoir properties of marginal marine channel sandstones. Variability in reservoir properties is largely due to facies heterogeneities. The cored sections at Toru-1 and Cardiff-1 do not contain the same excellent quality sandstones as seen at Maui/Kapuni (>1D permeability; Fig.7C); slightly poorer quality at Toru-1 could be related to the relatively proximal sedimentary environment, whilst poor reservoir quality at Cardiff-1 is a result of deep burial, advanced compaction and diagenesis (quartz/illite cements). Conventional core analysis data from the shoreface environment is limited to a few rotary SWC (Hector-1, Taranui- 1). However, these data suggest that excellent quality sandstones do occur in the shallow marine facies (Fig. 7D). Figure 7. Measured helium porosity versus air permeability for all conventional core and rotary SWC samples, Kaimiro Formation, Taranaki Basin; data from well completion reports. 0.01 0.1 1 10 100 1000 10000 0 5 10 15 20 25 30 35 Horizontal Permeability (mD) Measured Porosity (%) Hector-1 Taranui-1 0.01 0.1 1 10 100 1000 10000 0 5 10 15 20 25 30 35 Horizontal Permeability (mD) Measured Porosity (%) Toru-1 Cardiff-1 0.01 0.1 1 10 100 1000 10000 0 5 10 15 20 25 30 35 Horizontal Permeability (mD) Measured Porosity (%) Kapuni-1 Kapuni-14 Kapuni-3 0.01 0.1 1 10 100 1000 10000 0 5 10 15 20 25 30 35 Horizontal Permeability (mD) Measured Porosity (%) Maui A-1(G) Maui-7 Maui B-P(8) A) B) C) D) Figure 1. Paleogeographic maps showing study well locations, the ENE-WSW trending shoreline belt, and overall transgression from the Early to Middle Eocene (Dw to Dh). Maps are modified from Strogen (2010). 2. Core Facies and Paleogeography Conventional cores have been cut through the Kaimiro Formation in the Maui and Kapuni fields (D-Sands/K3E reservoir respectively), with short cores also at Cardiff-1 and Toru-1 (Fig. 1). Cored lithologies are vertically heterolithic, composed primarily of sandstone, siltstone, mudstone and, less commonly, coal (King & Thrasher, 1996; Flores, 2004). They represent a range of coastal plain and marginal marine facies, with fluvial and tidal/estuarine channels as the prime reservoir facies. Conventional cores are not available for the more seaward, shallow marine depositional environment. / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / Kapuni-3 Kapuni-8 Taranui-1 Kupe South-4 Fresne-1 ? ? ? North Tasman-1 peneplain Hochstetter-1 Kiwa-1 Hector-1 Pukeko-1 Rahi-1 Toru-1 Kupe South-4 Kapuni-13 Kapuni-14 Cardiff-1 Te Kiri-1 Kaimiro-1 Inglewood-1 Maui-1 Maui-2 Maui-5 Maui-3 Maui-6 Tieke-1 Tui-1 Kiwi-1 West Cape-1 Amokura-1 Pateke-2 Kopuwai-1 Maui-7 Maui B-8(P) Moki-1 Maui-4 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / peneplain Hochstetter-1 Kiwa-1 Hector-1 Pukeko-1 Rahi-1 Toru-1 Kupe South-4 Kapuni-13 Kapuni-3 Kapuni-14 Kapuni-8 Cardiff-1 Stratford-1 Te Kiri-1 New Plymouth-2 Kaimiro-1 Inglewood-1 Maui-1 Maui-2 Maui-5 Maui-3 Maui-6 Tieke-1 Tui-1 Kiwi-1 West Cape-1 Amokura-1 Pateke-2 Kopuwai-1 Taranui-1 Maui-7 Maui B-8(P) Te Whatu-2 Moki-1 Maui-4 Fresne-1 ? ? ? North Tasman-1 Dw-Dm (c. 54 Ma) Dm-Dh (c. 49 Ma) Shelf Shoreface Marginal marine Coastal plain Fan (from seismic) Study well Other well with Early-Middle Eocene Other well, no Early-Middle Eocene Maui Field N Kapuni Field 50 km