Panggabean_reservoir Rock Potential Of The Paleozoic-mesozoic Sandstone Of The Southern Flank Of The Central Range, Iri.pdf

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PROCB@DINGS INDONESIAN PETROLEUM ASSOCIATION Fifteenth Annual Convention, October 1986

RESERVOIR ROCK POTENTIAL OF THE PALEOZOIC-MESOZOIC SANDSTONE OF THE SOUTHERN FLANK OF THE CENTRAL RANGE, IRIAN JAYA H. Panggabean* A. Sufni Hakim* ABSTRACT The southern flank of the Central Range, Irian Jaya is formed by over 5000 m of platform sediments, overlying the northern margin of Australian Continental Crust. Thick, predominantly arenaceous and argillaceous rocks of Paleozoic to Mesozoic age are overlain by approximately 2000 m of the Tertiary New Guinea Limestone Group. The sequences have been exposed by uplift early in the orogeny that formed the Central Range. A petrographic study and a scanning electron microscope (SEM) investigation were carried out on some selected outcrop samples of Paleozoic to Mesozoic sandstones. The study revealed diagenetic features which may affect reservoir rock potential. The use of the SEM also enabled a study of the geometry of primary and secondary porosity of the sandstones. Most sandstones of the Paleozoic Aiduna Formation are characterized by well developed quartz overgrowths, and the pore spaces have been filled by authigenic silica cement during the diagenetic regime stage. Micro-intergranular pore textures are identified as the result of cement dissolution. Authigenic cements, particularly carbonates, were developed within the sandstones of the Mesozoic Tipuma Formation and Kembelangan Group without extensive quartz overgrowths. Nevertheless, secondary intergranular and intracement pore textures appear to be common. It is suggested that several sandstone horizons in the Mesozoic sequences possibly are good reservoir rocks. INTRODUCTION The area of investigation is situated in the southern fall of the western end of the Central Range which includes part of the Waghete-Omba 1:250,000 geological sheet areas, Irian Jaya (Fig.1). The first geological work on the area was undertaken by the Nederlandsche Nieuw Guinea Petroleum Maatschappij N.V. (NNGPM). The area comprises the Arafura Platform to the south and foreland belt complex to the north. The foreland fold belt is believed to be closely similar in style to the Papua Fold Belt (Jenkins, 1974), to the east in Papua New Guinea. Observable outcrops which occur in a narrow belt approximately 40 km wide, provide the major part of the geological data. The Arafura Platform covers all of the Arafura Sea. The platform comprises flat-laying Middle Jurassic to Cainozoic sediments on a block-faulted basement of Palaeozoic to

* Geological Research and Development Centre, Bandung

Triassic sediments (Pigram and Panggabean, 1983). With exception of the Salawati and Bintuni Basins, in the Birds Head and Birds Neck, no oil has been proven in Irian Jaya. Most of hydrocarbon indications known to NNGPM geologists are seepages from the Tertiary limestone and from the Mesozoic Kembelangan Group in the Kembelangan area. Recent geological mapping encountered an asphalt-like seepage south of Paniai Lake (Panggabean, 1981). Potential reservoirs within clastic horizons of the Mesozoic formations, such as the Tipuma Formation, were identified by Foreman et al. (1972). Pigram and Panggabean (1983) considered that some sandstones of the Mesozoic Kembelangan Group (Woniwogi and Ekmai Formations) appear to have reservoir potential. This paper attempts to assess the characteristics and diagenetic features of the Palaeozoic to Mesozoic sandstones which may affect porosity and permeability in potential reservoir rocks. This study uses petrographic and Scanning Electron Microscopy (SEM) analyses. The data were obtained from outcrop samples collected during regional geological mapping by the Geological Research and Development Centre of Indonesia and the Australian Bureau of Mineral Resources (BMR) in 1980. GEOLOGICAL SETTING The geology of the study areahas been described by Visser and Hermes (1962) resulting from the geological'work of NNGPM. The Irian Jaya Geological Mapping Project (IJGMP), a collaborative project staffed jointly by GRDC and BMR carried out systematic 1:250,000 scale geological mapping of the area in 1980. Stratigraphy The distribution of stratigraphic units is shown in Fig. 2. Outcrops are limited to the northern onshore part of the study area; the southern part is covered by swamp and the Arafura Sea. Total thickness of sediments exposed is approximately 10,000 m comprising a typical platform sequence of Palaeozoic and Mesozoic clastic sediments which is overlain by Tertiary limestone and young Cainozoic clastic deposits. The succession of stratigraphic units of the area is shown in Figs. 3 and 5. Palaeozoic Sediments The Modio Dolomite is the oldest unit cropping out in

the area. It consists of well bedded dolostone and dolomitic limestone with chert and pyrite nodules in places; shale, siltstone and calcareous quartz sandstone occur near the top. The age of the formation lies within range from the Silurian to Early or Middle Devonian, based on the general aspects of poorly preserved conodont fauna (Pigram and Panggabean, 1983;Pieters et al., 1983). The Modio Dolomite is probably unconformably overlain by the Early to Late Permian Aiduna Formation, consisting of well bedded felspathic and micaceous fine to coarse-grained lithic sandstone interbedded with carbonaceous shale. and siltstone, minor fossiliferous biocalcarenite and polymict conglomerate. Coal seams up to 1.5 m occur although most are less than 30 cm thick. Cross-bedding, load casts and ripple laminations are common. The Sormation was probably deposited in a paralic to very shallow marine environment; it has a maximum thickness of 2000 meters in the southern flank area. Mesozoic Sediments The oldest unit of the Mesozoic sediments is the Triassic to Early Jurassic Tipuma Formation which lies conformably on the Aiduna Formation. The Tipuma Formation was first recognized as a disti~ctiveunit in the western part of the Central Range by Lehner et al. (1955). The formation consists of maroon, green, grey to white feldspathic or tuffaceous lithic sandstone, minor red to grey micrite, arkose and polymict conglomerate, volcanoclastic sandstone and tuff. The main sedimentary structures in this unit are ripple marks and crossbedding. No fossils are known from the formation. The Tipuma Formation was described by Pigrarn and Panggabean (1983) as a terrestrial, fluviatile facies because of the strong red colour of the sediment and lack of fossils. The maximum thickness of the unit is 300 m. Overlying this formation is the Kembelangan Group subdivided by Pigram and Panggabean (1983) into four units : Kopai Formation, Woniwogi Formation, Piniya Mudstone and Ekmai Formation. The Kembelangan Group rests conformably on the Tipuma Formation. The basal unit of the Kembelangan Group is the Middle to Late Jurassic Kopai Formation, consisting predominantly of glauconitic quartz sandstone interbedded with siltstone and calcareous mudstone and with minor micaceous sandstone, "greensand", conglomerate, calcarenite and calcilutite. Sedimentary structures include small scale crossbedding, cone-incone structures, bioturbation and burrows and ripple laminations. Ammonites, belemnites, pelecypods and gastropods have been collected from this formation. The formation was probably deposited across a shallow marine shelf 'duririg a major transgression. The maximum thickness of the Kopai Formation is 300 meters. The Kopai Formation is conformably overlain by the Late Jurassic t o Early Cretaceous Woniwogi Formatior, comprising well bedded to massive glauconitic orthoquartzite (micaceous in part), with minor siltstone and thinly bedded black calcareous mudstone near the top. The formation contains a few fossils including Hibolithes sp. and Belemnopsis sp. The maximum thickness of the Woniwogi Formation is 200 meters; it was probably deposited in a

beach and near-shore inner shelf environment. This formation is ,conformably overlain by the Late Cretaceous Piniya Mudstone consisting of grey to black micaceous mudstone, glauconitic mudstone, minor muddy glauconitic quartz sandstone and muddy siltstone. Some fossils comprising ammoetes, Inoceramus sp, echinoderms and arenaceous foraminifera were collected from the formation. The Piniya Mudstone was probably deposited on a shallow shelf during a marine transgression. The maximum thickness of the formation is 800 meters. The uppermost unit of the Kembelangan Group is the Late Cretaceous Ekmai Formation which rest conformably on the Piniya Mudstone. The formation consists predominantly of massive to thickly bedded glauconitic quartz sandstone, minor carbonaceous sandstone, siltstone and mudstone. A thin interbedded shale is locally green or red. It contains a few belemnite guards and Inoceramus fragments. The sediments were probably deposited in an inner shallow shelf environment; the maximum thickness of the formation is 400 meters. Cainozoic sediments The Cainozoic sediments include the New Guinea Limestone Group (Waripi Formation and Yawee Limestone), and the Buru Formation. The lowermost unit of the New Guinea Limestone Group is the Late Cretaceous to Palaeocene Waripi Formation which is a distinctive well bedded basal unit comprising sandy calcarenite, oolite. limestone, biocalcarenite, calcareous quartz sandstone and siltstone with minor marl and calcilutite. The maximum thickness of the formation is 700 meters. The Eocene to Middle Miocene Yawee Limestone consists of well bedded to massive calcarenite, biocalcarenite, micrite, biomicrite and calcirudite with minor chalk, oolitic calcarenite and sandy calcarenite. Sandy shale and calcareous sandstone are present in places. The Yawee Limestone is a platform-facies limestone deposited in a shallow shelf environment. It conformably lies on the Waripi Formation and its maximum thickness is approximately 1200 meters. The Late Miocene to Pliocene Bum Formation conformably overlies the Yawee Limestone. The formation consists of grey to brown micaceous mudstone, calcareous mudstone, lithic sandstone and limestone, sandy shale and minor polyrnict conglomerate. Very low rank coal seams up to 1.OO m thick also occur in the upper part. Mollusc fragments and foraminifera are common. The Bum Formation was probably deposited in environments ranging from shallow open marine through paralic to open marine flood-plain. The maximum thickness is approximately 2500 meters. TECTONICS AND STRUCTURAL GEOLOGY Tectonics Irian Jaya is part of the northern margin of the Australian continent which is now considered to be an active collision margin. Pigram and Panggabean (1981 and 1984) suggested that the Late Palaeozoic to Mesozoic sequence forming the southern half of the Irian Jaya is related to

The Arafura Platform is predominantly unaffected by the tectonic stage of a rift-drift sequence. Pigram et al. (1982) have assumed that no&western Irian Jaya was Tertiary tectonic events. It consists of flat-laying to very a microcontinent rifted from .Gondwana (Australia) in the gently folded Middle Mesozoic to Cainozoic sediments early Mesozoic and later reunited with the Australian con- lying on a block faulted basement of Palaeozoic to Early tinent by a Late Cainozoic continent-microcontinent Mesozoic sediments. The only known subsurface structure collision. Recent workers @ow and Sukarnto, 1984a; on the Arafura Platform is the Uta Anticline which was 19841, and Dow et al., 1985) argue that Birds Head has first identified by Vinke (1958). The structure appears to always been in its present position relative to the Australian be an asymmetric southeast-facing anticline bounded by continent, representing a large remnant of mostly undefor- trusts on either flank. med continental crust that protrudes into the Pacific Plate. The foreland fold belt is an east-west trending zone In the southern flank of the Central Range region, the approximately 40 km wide. Over 30 fold structures in this pfebreakup stage is represented by the shallow marine to zone from enechelon doubly plunging asymmetrical and paralic sediments of the Siluro-Devonian Modio I d o m i t e box anticlines and poorly developed synclines. The strucand Permian Aiduna Formations. Rifting began at the Per- tures of the foreland fold belt in the southern flank are mian-Triassic boundary producing the characteristic block remarkably similar in structural style to those in the southfaulted basin topography. Thus the beginning of the ern Papua Fold Belt described by the Australian Petrobreakup stage is estimated between the Aiduna and Tipuma leum Company Proprietary Ltd (1961) and Jenkins (1974). Formations, at the end of Permian and beginning of early The cross section shown in Fig. 3, and of the geological Triassic time. During the breakup stage, terrestrial to locally maps (Fig. 2 and Fig. 4) show that the folding expressed marine red beds with minor acid volcanics (Tfpuma Forma- at surface is considered to result from decollement along tion) were deposited in Triassic and Early Jurassic times. several incompetent levels (e.g. shale W s of the Aiduna Subsequently, the start of the post-breakup stage is marked Formation, Piniya Mudstone and mudstone beds of the by a marine transgression which is interpreted as middle Buru Formation). This decollement is possibly associated Jurassic in age. The Kembelangan Group was deposited with moderately dipping tectonic ramps along the detached during the post-breakup phase. By the end of the Jurassic allochthonous sheets, which ride up to form folds in which the northern margin of the Australian continent faced the geometry changes as the displacement increases. a newly formed open ocean connected to the Proto-Pacific The lack of marked unconfomities throughout mdst of Ocean. This ocean was separated from the older oceans of the stratigraphic column, and the involvement of Pliocene New Tethys in the northwest and Panthalasa in the sediments (Buru Formation) in the folding show that most northeast by a screen of continents or microcontinents of the deformation occured during a single orogenic phase detached from Gondwana. at about the end of Pliocene times. However, the initiation A platform carbonate regime began in the Late Creta- of decollement in the southern flank area probably accurred ceous and by Eocene time an extensive carbonate plat- after the deposition of the middle Miocene basal Buru Forform was established. Carbonate sedimentation ceased by mation. Thus, southward movement of allochtonous sheets the Middle Miocene and fine clastics were deposited. During began in the north in the Late Miocene or early Pliocene the middle or possibly Late Miocene, earth movements times and became progressively younger southWd@o-the commenced over the whole of the Central Range region. exposed southern margin of the foreland fold belt where This orogeny was popularized as the Melanesian Orogeny it is still continuing at present day. In general the present by Dow and Sukarnto (1984a and 1984b) and Dow et al. structure appears to be the result of the Pliocene orogenic (1985) and was produced by convergence between the phase, as in the Papua New Guinea Fold Belt (Australian Pacific and Australian Plates. Dow and Sukarnto (1984a) Petroleum Proprietary Ltd, 1961). recognized two distinct phases of earth movements in the A major east-west trending zone called the Tarera-Aiduorogeny. One was an overthrusting of the continental shelf na Fault was first identified by the NNGPM geologists in sediments to the south, forming the Central Range in the the Omba and western Waghete sheet areas (Visser and HerPliocene time, and the other was a southwards underthrust- mes, 1962). The'zone is bounded by two major faults, the ing and incipient subduction of the Pacific Plate in the northern Tarera Fault and the southern Aiduna Fault north during the Pleistocene. (Fig. 4). The climax of convergence between the Pacific and Like the Sorong Fault Zone in the Birds Head area, the Australian Plates caused intense southwards overthursting Tarera.Aiduna Fault Zone is of considerable importance in of the continental Palaeozoic basement and the overlying plate reconstructions of western Irian Jaya. Visser and Hershelf sediments along the Central Range and its southern mes (1962) and Hamilton (1979) have interpreted the Tareflank. ra-Aiduna Fault Zone as a left-lateral strike slip fault with a displacement ranging from 50 to 200 km. stmcture The southern flank of the Central Range consists of fol- RESERVOIR ROCK POTENTIAL ded and faulted platform sediments. As a result of recent Several potential reservoir rocks in the Palaeozoic-Mesomapping, three main structural provinces have been dis- zoic sequences have been reported by Pigram and Panggatinguished by Pigram and Panggabean (1983). From south bean (1983) and Dow et al. (1985). They include the to north they are Arafura Platform, foreland fold belt Tipuma Formation and Kembelangan Group (Woniwogi and Tarera-Aiduna Fault Zone (Fig. 5). and Ekmai Formations). Foresman et al. (1972) have also

noted that sandstone horizons in the Tipuma Formation and Ekmai Formation of the Kembelangan Group are potential reservoir rocks since they have a good porosity and permeability. No oil or gas has been produced in the southern flank of the Central Range, but oil or gas seepages are known from the Kembelangan Group in the southern part of the Lengguru Fold Belt (the Kembelangan seep) and from the Waripi Formation near Tage Lake, Enarotali. These indications suggest that hydrocarbon bearing rocks may occur in the Palaeozoic-Mesozoic sequences. The study of reservoir rocks here will include petrographic and SEManalyses results with special emphasis on identifying the framework, cement matrix, pore texture and diagenetic features of the sandstones.

Petrography of Sandstones The petrography of nine selexted outcrop samples from various Palaeozoic-Mesozoic formations (Aiduna, Tipuma Formations and Kembelangan Group) were examined in detail. The detrital components are quartz, chert, feldspar and metamorphic and volcanic rock fragments. Accessory minerals are common in several formations. Based on FoWs classification (1980) the main sandstone groups of the Palaeozoic-Mesozoic sequences are quartzarenite, sublitharenite, feldspathic litharenite and glauconite sandstone (Fig. 6).

The only sandstone sample examined from the Palaeozoic Aiduna Formation is sublitharenite. The sublitharenite shows high compaction and tight packing; it is well sorted with relatively uniform sized medium sand grains (average 0.4 mm). The quartz content of the sample rniges from 50 percent to 60 percent of the framework grains. Other rock fragments consists of chert, mica schist and slate, volcanic rock fragments, quartzite and feldspar; opaque minerals, mica and apatite are minor constituents. Approximately 10 percent of the framework consists of silica cement with minor iron oxide and clay minerals. Quartz overgrowths are best-developed (up to 10%)with the original grain shape clearly defined by very thin dustlike clay minerals. Indigeneous overgrowths usually interlock with sutured or sinous contacts. More than 80 percent of the simple quartz grains exhibit slightly undulose extinction while straight extinction quartz grains are the second most abundant constitutent. Semicomposite and composite quartz grains are very rare framework constituents. The porosity and permeability examined in thin section were determined by visual techniques following impregnation of samples with a blue dye. The percentage porosity and estimated permeability in this study is based on Levorsen (1967). The result shows that all original pore spaces of this litharenite sample from the Palaeozoic Aiduna Formation have been filled and lined by authigenic silica and clay cements. However, there is a little secondary intergranular and intra-cement micropore texture due to dissolution of grain, cement and matrix during diagenetic events. In general the micropores do not appear to be connected. The estimated porosity is 5 percent to 10 percent (poor) and permeability probably less than 10 md (poor). Three samples analyzed by thin section from the Meso-

zoic (Triassic-Jurassic) Tipuma Formation are feldspathic litharenite (80CP342A and 80CP522A) and sublitharenite (80CP350A). The samples are medium-grained and have 80 percent to 95 percent framework grains and 5 percent to 20 percent cement and matrix. Framework grains of both feldspathic litharenites consist of quartz, chert and other siliceous rocks, feldspar comprising albitized plagioclase and microcline, volcanic rock fragments, quartzite, and other accessory minerals such as mica, epidote, sphene, chlorite, zircon and opaque minerals. Cement and matrix consists of hematite, silica and clay minerals. Thin hematite coated grains are commonly found in these samples and quartz ovegrowths are present but not prominent. The framework grains of the sublitharenite comprise quartz, chert, feldspar, quartzite and volcanic rock fragments; accessory minerals are epidote, pyrite, magnetite and mica. Simple grains of quartz with straight undulose extinction are prominent in these samples. The quartz grains range in shape from angular to subangular and contain rare vacuoles and microlite inclusions. Contacts between grains are usually tangential and show mostly open packing. Pore spaces of the three Tipurna Formation samples examined have been partially filled by cement and matrix comprising sparry calcite, clay and silica. The pores are predominantly secondary intergranular pore texture types. These pore textures are presumably the result of authigenic dissolution of grain and cement or replacement and shrinkage. Intra-cement pore textures are present, probably as the result of incomplete replacement of dissolution cement. The visual pore spaces in thin sections provide estimated porosity ranging from 10 percent to 15 percent (good) and good permeability (10-100 md). However the porosity of the feldspathic litharenites is poorer than the sublitharenite sample. The sandstones of the Kembelangan Group examined petrographically include the Kopai Formation, Woniwogi Formation and Ekmai Formation (Table 1). The sandstone types of the Kopai Formation are glauconitic sandstone, micaceous sublitharenite and quartzarenite; the Woniwogi Formation is typically a glauconitic sublitharenite and the Ekmai Formation is a quartzarenite (Fig. 6). The framework grains of the glauconite sandstone of the Kopai Formation consists of rounded green glauconite, subangular to rounded quartz clasts and minor mica, chlorite and sphene. Cement consists predominantly of siderite and sparry calcite and minor chlorite partially filling original pore spaces. The micaceous sublitharenite is fine-grained and poorly sorted, and is composed of quartz clasts, feldspar (predominantly plagioclase), chert, muscovite and opaque minerals (probably pyrite and hematite). Organic matter is present as dark brown fine banded material. Cement and matrix comprise occupy 5 percent to 10 percent of the rock, comprising clay minerals, silica and carbonate filling the original pores. The quartzarenite of the Kopai Formation is coarsegrained and poor to moderately sorted. The grain shape ranges from subrounded to well rounded. Almost 90 per-

cent of the framework grains are composed of quartz clasts and the remainder comprise quartzite, siliceous argillite and orthoclase; mica and opaque minerals are rare. The framework grains are cemented by sparry calcite and minor siderite and clay minerals, reducing the original porosity. One sandstone smple from the Woniwogi Formation is medium-grained glauconitic sublitharenite composed of quartz, feldspar, quartzite and igneous fragments, glauconite, mica, sphene, tourmaline and opaque minerals. The shape of the framework grains is mainly subangular. The original pore spaces have been filled by sparry and micritic calcite cement and clay minerals. The quartzarenite of the Ekmai Formation is mediumgrained and moderately sorted. The framework grains are predominantly subrounded and closely packed. Some of the contacts between grains are tangential or sutured. Quartz overgrowths are present but they are not well developed. More than 95 percent of the framework grains consists of quartz, while feldspar, chert and quartzite are minor constituents. The original pores have been partially filled by predominantly authigenic clay, clay, calcite and occasional silica cement. However secondary intergranular pore textures are present providing good porosity and permeability. Approximately 80 percent of quartz clasts in the Kembelangan Group examined exhibit straight to slightly undulose extinction and the remainder show strongly undulose extinction. Generally quartz grains contain a variable number of microlite inclusions but few vacuoles. In summary, the average porosity of the sandstones of the Kembelangan Group ranges from 10 percent to 25 percent. The porosity is predominantly characterized by macropores (more than 200 microns in diameter) of secondary intergranular pore textures, and minor primary intracement pore textures. Apart from pores produced by dissolution of cement and grains during effective burial, they may have been inherited from incomplete cementation or authigenic replacement prior to deposition.

Scanning Electron Microscopy The scanning electron microscope (SEM) is designed to produce a magnified irregular surface. The main advantage of this instrument is the large depth of focus at high magnification which gives considerable perspective to the image. The image of the sample is displayed on a TV screen using various magnifications up to 180,000. The use of the SEM enables the study and identification of the type, geometry and shape of porethroat configuration, pore filling cements, overgrowths and other authigenic minerals. It allows estimation of the porosity and permeability of sedimentary rocks to be made (Mirkin, et al., 1978). Such information is used to assess the diagnetic features of reservoir rocks in the southern flank of the central range, Irian Jaya. Ten selected fresh outcrop samples of the Paleozoic and Mesozoic sandstones from the area have been examined (Table 1). Each sample was mounted on a brass stub. Prior to examination with the SEM, the samples were coated with a conductive metal (gold) in the vacuum evaporative

coater. This is necessary to obtain a clear image (Welton, 1984). The coated sample was placed in the sample chamber, evacuated and then examined with a JEOL JSN35C SEM machine. Photomicrographs of the samples were made using an intergrated camera system at various magnifications (Fig. 7). The Paleozoic Aiduna Formation The three sandstones samples examined from the formation include one quartzarenite and two sublitharenites. In general, they are very compact and tightly packed, characterized by well interlocked framework grains (Figs. 7A and 7C), and under low magnification pore spaces are not clearly defined, Although quartz overgrowths are not clearly recognized in the SEM, in thin section they are seen in almost all samples. Most of the remaining pore spaces have been completely filled by authigenic cements deposited during burial and diagenetic events. The authigenic cements are predominantly silica (Figs. 7D and 7G), kaolinite (Figs. 7B, 7G and 7H) and chlorite (Figs. 7D and 7E). The kaolinite crystals are usually formed as "face to face" and "edge to face" stacks defined by Timur et al. (1971), Keller (1978) and Welton (1984). Most of the chlorite cements show an irregular dense pattern which may due to advanced compaction. The type of pores is predominantly micro intracement (the size of pore is less than 50 microns) and rare secondary reduced intergranular pore textures. The micropores appear disconnected having a maximum diameter of 50 microns. They usually occur between platelets of kaolinite crystals. These pores provide poor porosity (5-10%) and poor permeability (less than 10 md). The Mesozoic Tipuma Formation The two sandstone samples that were examined are feldspathic litharenite and sublitharenite. They are also tightly packed and highly compacted and characterized by partly well interlocked framework grains (Fig. 7F). Authigenic cements comprising kaolinite, silica and minor calcite (Figs. 7G and 7H), have completely filled pore sp?ces probably occurring during burial or the mesodiagenesis regime. The kaolinite usually forms irregular plate crystals. Calcite crystals do not appear to be well developed because they may have been partially dissolved. Micropores within the cements are recogniseable (Fig. 7H) but they are not very abundant; they are partly interconnected and range from one to 10 microns in diameter. The micropores also occur in the chinks of kaolinite plates and mica (Fig. 7G). The pore types are predominantly intracement with minor intergranular. The estimated porosity of the Tipuma Formation ranges from 5% to 15% and permeability (10-20 md) is poor to fair. The Mesozoic Kopai Formation The glauconitic sandstone examined is moderately compacted (Fig. 71) and authigenic cements have completely filled pore spaces. The authigenic cements consists mainly of carbonate (calcite and siderite) and vermicules hnd irre-

gularly shaped kaolinite (Figs. 75 and 7K). Some micas are present as matrix (Fig. 75). Intracement micropores of one to 5 microns in diameter are present but they are not prominent. Thus the porosity of the sample is approximately 10% and the permeability is poor.

The Mesozoic Woniwogi Formation In the sublitharenite of the Woniwogi Formation, pore spaces have been partly f a e d by authigenic kaolinite and calcite (Figs. 7L and 7M). Most of kaolinites are densely packed and have irregular shapes. Intergranular and intracement pore textures are common. The rnicropores have a diameter ranging from 5 to 20 microns. The porosity of the sample is approximately 15% and the permeability is poor to fair, The Mesozoic Ekmai Formation Two samples from the Ekmai Formation that were examined are both quartzarenites. Both have a well preserved primary intergranular pore textures and minor secondary intergranular pore textures (Figs. 7N, 7R and 7s). The macropores are of uniform diameter (range from 200 to 500 microns) and are partially interconnected large pores and open throats. The framework grains are usually subrounded to rounded and their contacts are mostly tangential. Some pore spaces have been fdled by authigenic cements consisting of calcite, dolomite and kaolinite (Figs. 70, 7P and 7Q). Secondary intracement pore textures are also pronounced within the cements. The intracement pore textures within the carbonate cements, consists essentially of smah interconnected open microthroats which have a maximum diameter of 10 microns (Figs. 70, 7P and 7T). According to gieke and Hartman (1973), micropores within calcite crystal faces may be formed by mobile water undersaturated with respect to CaC03 during diagenetic dissolution. The other micropores in authigenic kaolinite cements (Fig. 7Q) appear to be disconnected. Nevertheless, intraplate crystals possibly connect the adjacent microthroats. Conspicuous pore textures in the sandstones examined indicate that they have good porosity and permeabilit y. DISCUSSION The porosity of the sandstones from the Paleozoic and Mesozoic successions in the area was determined in thin section and compared with the SEM analysis. The results are summarized in Table 2. Identification of pore types in the sandstones is important in selecting potential reservoir rocks. A classification of porosity of sandstones is based on the genetic and physical characteristics of pore types. Basically, two main classifications of porosity have been introduced for studying the reservoir rocks; they apply to primary and secondary porosity. The term of primary and secondary used in this study follows the nomenclature outlined by Choquette and Pray (1970), and later modified by Hoholick et al. (1 984). Prbary porosity comprises all pore spaces formed before and during deposition (common only in the Ekmai

Formation), whereas secondary porosity occurs if all primary pore spaces have been filled by cement and later processes or diagenetic events developed new openings (predominantly in the Woniwogi, Kopai, Tipuma, Aiduna Formations and partly in the Ekmai Formation). Thus the secondary porosity includes dissolution of cements and framework grains, and also gaps caused by fracture and shrinkage. On the basis of their position, pore textures are called intergranular when they occur between grains, intragranular when they occui within grains, and intracement when they occur within cements. The genetic types of pore system of secondary porosity have been outlined elsewhere (e .g. Schmidt and McDonald, 1979a, 1979b; Pittman, 1979; Shanmugam, 1985a, 1985b). By definition, diagenesis is the progression of changes from sedimentation to the realm of metamorphism, and the secondary effects of atmospheric weathering (Larsen and Challingar, 1979). Fairbridge (1967) has divided the realm of diagenesis into syndiagenesis (penecontemporaneous), anadiagenesis (during burial and orogeny) and epidiagenesis (post-diastrophic). A similar terminology based on characteristics of porosity has been erected by Choquette and Pray (1970) and Schmidt and McDonald (1979a, 1979b) i.e., oediagenesis (early), mesodiagenesis (middle) and telodiagenesis (late) stages. This later terminology is used in this study and both eodiagenesis and mesodiagenesis have operated in forming pore systems in the Paleozoic and Mesozoic sandstones. The diagenesis in the sandstones examined is characterised by pore filling, compaction, the presence of authigenic cements or minerals and when accompanied by dissolution and replacement, secondary pores form. The presence and occurrence of authigenic cements during the diagenetic regime are shown in Fig. 8. Three samples from the Ekmai, Tipuma and Aiduna Formations in Fig. 9 provide examples of diagenetic history commencing with deposition (initial stage) and early burial (eodiagenesis) through compaction into late or dissolution stage (mesodiagenesis). The reduction of rock volume might occur from eodiagenesis into mesodiagenesis stages due to geostatic pressure and burial. These three samples can be compared to the sample of the Aiduna Formation where quartz overgrowths and silica cements have occured during early to late rnesodiagenesis. In the Woniwogi Formation they are also present but are not well developed until late rnesodiagenesis. The Ekmai Formation indicates that many primary pores are still preserved up to early mesodiagenesis. However, some secondary pores are present which have probably been formed by partial dissolution. In the Tipuma Formation, the diagenesis was mostly normal in creating some intergranular and intracement pores, but they are not significantly abundant. The porosity of the Mesozoic sandstone of the Ekmai Formation appears to have been created during eodiagenesis to early mesodiagenesis. This is characterized by partly well preserved primary pores and some open secondary intracement pores within calcite cements due to mesodiagenesis. In contrast, the secondary porosity in the sandstones of the Woniwogi, Kopai, Tipuma and Aiduna forma-

tions was probaly formed during the mesodiagenesis stage. The pores are usually characterized by dissolution remnants of grains (intergranular) and partial dissolution remnants of cements (intracement). The secondary porosity within the Paleozoic sandstones of the Aiduna Formation, however, is not well developed. This is probably because well developed quartz overgrowths and silica cements fill completely the secondary pore remnants so that the secondary pores cannot be normally formed. The sandstone of the Mesozoic Tipuma Formation contain abundant unstable framework grains which are easy to dissolve and create partial secondary intergranular porosity. Therefore, their porosify is higher than the sandstones of the Paleozoic Aiduna Formation. Four main types of secondary porosity are recognized in the Paleozoic-Mesozoic sandstones. They include intergranular, intracement, fracture and shrinkage pores (Table 2). The primary porosity of intergranular open pores is more prominent in the Ekmai Formation while the secondary intracements are the second most abundant, and secondary intergranular pores are rare, The primary pores may have been inherited from the depositional process or from the eodiagenesis regime. It can be seen that the Ekmai Formation pore-filling cements are not significantly effective although some authigenic kaolinite, calcite cements and silica cements are present. The micropores which are prominent within calcite cements are mostly well developed as the result of dissolution. The porosity of the succession tends to decrease with increasing age. Porosity graphs versus succession profiles show that the porosity path represents a moderate curve as indicated in Fig. 8. This configuration indicates that decreasing porosity from younger to older succession certainly coincides with an increase in the development of diagenetic features. Thus, burial and length of burial time have contributed to changes in porosity and permeability in the Paleozoic-Mesozoic sandstones. In addition, grain size, sorting, shape and packing may control and effect the forming of pore spaces. The curvature of the porosity path can illustrate the porosity gradient, but unfortunately this study does not examine a continuous succession from well samples. Nevertheless, it can be estimated that the porosity gradient in the Paleozoic-Mesozoic formations is about 5 percent per 1000 meters. A number of factors controlling porosity gradient may be temperature (geothermal gradient), pressure, chemical composition of sandstones and pore-fluid chemistry, as has been established by Selley 1978) in the North Sea oil-bearing basin. All of these are considered as activators in the development of diagenesis. In summary, the porosity of the Ekmai and Woniwogi Formations ranges from a minimum of 5 percent to a maximum of 25 percent with a mean value of approximately 15 percent. It reduces to 5 percent to 15 percent (mean of 8 percent) in the Kopai and Tipuma Formations. However, the Tipuma Formation has a better porosity than the Kopai Formation. In the Paleozoic Aiduna-Formation, the porosity is noticeably lower, ranging from 5 percent to 10 percent with a mean value of about 7 percent. Overall, the sandstones of the Mesozoic Ekmai orm mi-

tion may be considered to have relatively good reservoir performance, while the sandstones of the Mesozoic M'oniwogi and Tipuma Formations are categorized as having marginal to favourable reservoir potential. The sandstones of the Paleozoic Aiduna Formation have relatively poor to marginal reservoir characteristics.

CONCLUSIONS 1. The total thickness of sediments exposed in the southern flank of the Central Range is approximately 10,000 meters, consisting of typical platform sediments of Paleozoic and Mesozoic ages which are overlain by Tertiary carbonate platform facies and young Cainozoic clastic deposits. Over thirty east-west trending structures form en echelon doubly plunging asymmetrical and box anticlines and poorly developed synclines, and are called the foreland fold belt. The structures are1 remarkably similar in structural style to those in the southern Papuan Fold Belt. In general, the present structures appear to be the result of the Pliocene-Pleistocene orogenic phase. 2. The main sandstone types examined of Paleozoic-Mesozoic age are quartzarenite, sublitharenite, feldspathic litharenite and glauconite sandstone. The sandstones of the Palaeozoic Aiduna and Mesozoic Tipuma Formations are generally highly compacted and tightly packed, where the contacts between grains are usually well interlocked with predominantly sutured contacts. 3 . Significant primary porosity occurs in the sandstones of the Mesozoic Ekmai Formation, while the secondary porosity is the most abundant in the Mesozoic Woniwogi and Tipuma, Formations and less common in the Kopai Formation and in the Paleozoic Aiduna Formation. The sandstones of the Ekmai and Woniwogi Formations have fair to good porosity and permeabiliv, whik the porosity of sandstones of the Tipuma Formation is fair. The Kopai and the Paleozoic Aiduna Formations have poor to fair porosity. Porosity versus succession indicates that it decreases with increasing age because of an increase in the development of diagenetic features. Thus, length of burial time may have contributed to change the porosity and permeability of the Paleozoic-Mesozoic sandstones. 4. Diagenetic events such as eodiagenesis and mesodiagenesis have promoted early loss of primary porosity and subsequent generation of secondary porosity. During diagenetic events, the presence of authigenic cements of kaolinite , calcite, siderite, dolomite, chlorite, illite and silica and quartz overgrowths are characteristic. S i c a cements and quartz overgrowths are more prominent in the sandstones of the Paleozoic Aiduna Formation. They may have prevented the formation of secondary porosity. Thus towards the base of the succession there is a reduction in secondary porosity that probably reflects both the increase in diagenetic effects with the greater time of burial. 5. The sandstones of the Mesozoic Ekmai Formation can be considered potentially good reservoir rocks and the Woniwogi and Tipuma Formations may be marginally favourable as potential reservoirs. Relatively poor t~

marginal reservoir performance in evident in the sandstones of the Paleozoic Aiduna Formation and the Mesozoic Kopai Formation. Further detailed study on the characteristics of the Paleozoic-Mesozoic sandstones for reservoir potential is recommended in the area, in particular by deep subsurface sampling.

Peter and Mount Simon Sandstones in Illinois Basin", Am. Assoc. Petrol Geol. Bull., v. 68, no. 6, pp. 753764. JENKINS, D.A.L., 1974, "Detachment tectonics in Western Papua New Guinea", Geol. Sdc. of Am. Bull., v. 85, pp. 533-548. KELLER, W.D., 1978, "Classification of kaolinites exampliACKNOWLEDGEMENT fied by their textures in scanning electron micrographs", Caly and Clay Mn., v. 26, no. 1, pp. 1-20. We are grateful to Dr. M. Untung, Director of the Geological Research and Development Centre for his permis- KIEKE, E.M. ANDHARTMAN, D.J., 1973, "Scanning electron microscope application to formation evaluation7', sion to publish this paper. Mr. R. Sukamto, Chief of MapGulf. Coast Assoc. of Geol. Soc. Trans., v. 23, pp. 60ping Division, GRDC, and Mr. N. Ratman, Head of Irian 67. Jaya and Halmahera Section, GRDC, are aknowledged for their direction and encouragement of this study. The help LARSEN, G. AND CHILLINGAR, G.V., 1979, "lntroduction-diagenesis of sediments and rocks", In Larsen, G. of Mr. R. Wikarno, Chief of Geology Division, GRDC and Chillingar, G.V. (eds.), Diagenesis in sediments and who provided access to the SEM machine is gratefully sedimentary rocks, Elsevier, Amsterdam, pp. 1-29. acknowledged. The assistance of Messrs. Soediyono and Wikanda with sample preparation is also acknowledged. We LEHNER, P., VAN DER SIJP, de RIJKE, F., BILLARDIE, J. AND HERMES, J.J., 1955", Geological Survey of the fell indebted to Mr. D.S. Trail and Mr. D.B. Dow, IAGMP, Omba-Aidoena area (south coast)", Nederlandsche Niew respectively for critically reading the manuscript and for Guinee Petroleum Maatschappij Report 26380. (unpuaccess to the samples. Finally, Mrs. Jane Susilarto is ackblished). nowledged for her careful typing of the manuscript. LEVORSEN, A.I., 1967, "Geology of petroleum", W.H. Freeman and Company, San Fransisco, 2nd edn., 724 p. REFERENCE MIRKIN, G.R., OSIPOV, V.I., ROMM, E.S., SOKOLOV, V.N. AND TOLKACHEV, M.D., 1978, "The use of the AUSTRALIAN PETROLEUM COMPANY PROPRIETY scanning electron microscope for the investigation of LTD., 1961, "Geological results of petroleum explorathe properties af porous bodies", In Whalley, W.B. (ed.), tion in western Papua 1937-1961", Jour. Geol. Soc. of Scanning electron microscope in the study of sediments. Aust., v.8, pt. 1, pp. 1-33. Geo. Abstract Limited. Univer. of East Anglia, Norwich, CHOQUETTE, P.W. AND PRAY, L.C., 1979, "Geologic NR471J, England, pp. 13-16. nomenclature and classification of porosity in sedirnentary carbonates", Am. Assoc. Petrol. Geol. Bull., v. 54, PANGGABEAN, H., 1981, "Rembesan aspal di selatan Danau Tage, Irian Jaya", Geosurvey Newsletter, v. 13, no. pp. 207-250. 24, pp. 221-223. DOW, D.B. AND SUKAMTO, R , 1984a, "Western Irian Jaya: The end-product oblique plate convergence in PIETERS, P.E., PIGRAM, C.J., TRAIL, D.S., DOW, D.B., RATMAN, N. AND SUKAMTO, R , 1983, "The stratithe late Tertiary", Tectonophysics, v. 106, no. 1-2, pp. graphy of western Irian Jaya", Bull. Geol. Res. and Dev. 109-139. Centre, No. 8. pp. 14-48. DOW, D.B. AND SUKAMTO, R, 1984b, "Late Tertiary to Quaternary tectonics of Irian Jaya", Episodes, v. 7, no. PIGRAM, C.J. AND PANGGABEAN, H, 1981, "Pre-Tertiary Geology of western Irian Jaya and Miss01 Island: 4, pp. 3-9. Implications for the tectonic development of Estern DOW, D.B., ROBINSON, G.P. AND RATMAN, N., 1985, Indonesia", Prof. Indones. Petrol. Assoc., 10th Ann. "New Hypothesis for formation of Lengguru Foldbeit, Conv., pp. 385-399. Irian Jaya", Indonesia. Am. Assoc. Petrol. Geol. Bull., PIGRAM, C.J. AND PANGGABEAN, H., 1962, "Prelimiv. 69, no. 2, pp. 203-214. nary Geological Map of the Waghete (Yapekopra) QuaFAIRBRIDGE, R.W., 1967, "Phase of diagenesis and authidrangle, Irian Jaya", scale 1:250,000. Geol. Res. and genesis", In Larsen, G. and Chillingar, G.V. (eds.), DiageDev. Centre. nesis in Sediments, Elsevier, Amsterdam, pp. 19-89. FOLK, RL., 1980, "Petrology of sedimentary rocks", Hem- PIGRAM, D.J. AND PANGGABEAN H., 1983, "Geological Data Record Waghete (Yapekopra) 1:250,000 sheet phi% Austin, Texas, 182 p. area, Irian Jaya, Indonesia", Geol. Res. and Dev. Centre, FORESMAN' J. B., PERKINS, E.H., FROIDEVAUX, Open file Rp., 126 p., unpublished. C.M. AND MORRIS, D. A , 1972, "Geologic study of the onshore Arafura Sea contract area, West Irian, Indone- PIGRAM, C.J. AND PANGGABEAN, H., 1984, "Rifting sia", Phillips Petroleum Company, Exploration Project of the northern margin of the Australian Continent and Group, Surface Projects Section Report (unpublished), the origin of some microcontinents in eastern Indone134 p. sia", Tectonophysics, v. 107, pp. 331 -353. HAMILTON, W., 1979, "Tectonics of the Indonesian re- PIGRAM, C.J., ROBINSON, G.P. AND LUMBANTO gion", U.S. Geological h e y Professional Paper 1078, BING, S., 1982, "Late Cainozoic origin for the Bintuni 345 p. Basin and adjacent Lengguru Fold Belt, Irian Jaya", HOHOLICK, J.D., METARKO, T. AND POTTER, P.E., Roc. Indones. Petrol. Assoc., 1l t h Ann. Conv. 1984, "Regional variations of porosity and cement: St. PITTMAN, E.D., 1979, "Porosity, diagenesis and produc-

tive capability of sandstone reservoirs", In Scholle, P.k and Schluger, P.R. (eds.), Aspects of diagnesis. Soc. Econ. Pal. and Min., Spec. .Publ., no. 26, pp. 159-173. SCHMIDT, V. AND McDONALD, D.k, 1979a, "The role of secondary porosity in the course of sandstone diagenesis", In Scholle, P.A. and Schluger, P.R. (eds.), Aspect of diagenesis. Soc. Econ. Pal. and Min., Spec. Publ. no. 26, pp. 175-207. SCHMIDT, V. AND McDONALD, D . k , 1979b, "Texture and recognition of secondary porosity in sandstones", In Scholle, P.A. and Schluger, P.R (eds.), Aspects of diagenesis. Soc. Econ. Pal. Spec. Publ. and Min., no. 26, pp. 209-225. SELLEY, R.C., 1978, "Porosity gradient in the North Sea oil bearing sandstones", Jour. Geol. Soc. Lond., v. 135, pp. 1 19-132. SHANMUGAM, G., 1985a, "Significance of secondary porosity in interpreting sandstone composition", Am. Assoc. Petrol. Geol. Bull., v. 69, no. 3, pp. 378-384. SHANMUGAN, G., 1985, "Types of porosity'in sandstones and their significance in interpreting provenance", In Zuffa, C.G. (ed.), Provenance of Arenite, pp. 115-137. TIMUR A , HEMPKINS, W.B. AND WEINBRANDT, R.M., 1971, "Scanning electron microscope study of pore systems in rocks", Jour. of Geophys. Res., v. 76, no. 20, pp. 4932-4948. VINKE, B., 1958, "Report on the gravity survey of the south coast of Netherlands New Guinea", Nederlandsche Nieuw Guinee Petroleum Maatschappij. Report 29547 (unpublished). VISSER, W.A. AND HERMES, J.J., 1962, "Geological results of the exploration for oil in Netherlands New Guinea". Koninklijk Nederlands Geological Mijnbouwkundug Genootschap Verhandelingen Geologische Series 20. WELTON, J.E., 1984, "SEM Petrology Atlas", The AAPG methods in exploration series no. 4,237 p. EXPLANATION OF FIGURE 7. A. Tightly packed and higly compacted quartzarenite of the Aiduna Formation (Paleozoic); sample no. 80CP357A; quartz (Q) grains are well interlocked, pore spaces have been completely filled by authigenic clay cements; porosity ranges from 5% to 10%;magnification x100. B. As for Fig. 7B, but different field, showing irregular and partly regular face to face stacks of authigenic kaolinite; micropores of less than one micron occur between platelet arrangements of kaolinite crystals; magnification x6000. C. Highly compacted sublitharenite of the Aiduna Formation (Paleozoic), sample No. 80P268A, showing a quartz grain (Q) lines by authigenic clay cements; porosity is approximately 10%;magnification x540. D. As for Fig. 7C, but different field, showing authigenic chlorite (ch) and silica (Si) cements; disconnected intracement micropores of 1-10 microns in diameter are visible; magnification x4000. E. Authigenic chlorite cements within sublitharenite of the Aiduna Formation (Paleozoic); sample No. 80P282A; intracement micropores are rare; porosity is approximately 5% magnification x7800.

F. Tightly packed and highly compacted sublitharenite of the Tipuma Formation (Mesozoic); sample No. 80CP353B; most of the pore spaces have been filled by authigenic clay cements; framework grains consisting of quartz (Q) and feldspar (F) ire well interlocked; porosity ranges from 10% to 1.5%; magnification x150. G. As for Fig. 7F, but different field, showing an authigenic kaolinite vermicule (k), silica cements and mica or muscovite (m); micropores are present in a chink of mica and kaolinite plates; magnifikation x2000. H. Authigenic clay cements consisting of silica (Si), kaolinite (k) calcite (c) and mica (m) partly fill pore spaces of feldspathic litharenite of the Mesozoic Tipuma Formation; sample No. 80CP353C; secondary micropores within cements range from 5 to 10 microns in diameter; magnification x 1500. I. Moderately packed glauconitic sandstone of the Mesozoic Kopai Formation, showing quartz grains (Q); authigenic cements consisting of calcite (c) and kaolinite (k) have partly filled pore spaces; micropores of 10-50 microns in diameter are present; porosity is approximately 10%; magnification x54. J. As for Fig. 71, but different field, showing a quartz clast (Q), authigenic cements of kaolinite vermicule (k) and face to face stacks kaolinite and mica (m); micropores of 1-5 microns in diameter are present within cements; magnification x1800. K. As for Fig. 75, enlargement of the area showing the authigenic kaolite vermicule (k); magnification x7800. L. The sublitharenite sample of the Mesozoic Woniwogi Formation, showing authigenic kaolinite (k) and calcite (c) partly filling pore spaces; mcropores of 5-20 microns in diameter occur within cements; porosity range from 10% to1 5%;magnification x2000. M.As for Fig. 7L, but different field, showing secondary quartz (Q) lined by authigeneic kaolinite (k); calcite cements may be present. N. An open packed fine to medium-grained sublitharenite of the Mesozoic Ekmai Formation, sample No. 80P214A, showing uncompleted pore filling cements; major primary intergranular pore textures, rare secondary intergranular pore textures; macropores range from 100 to 500 microns in diameter; porosity is approximately 20-25%; magnification x54. 0 . As for Fig. 7N, but differennt field, showing autliigenic carbonate cements comprising calcite (c), dolonlite rhombohendra crystals (d), kaolinite (k) and illite (i); some secondary intracement pore textures (p) ranging from 1 to 10 microns in diameter are present; magnification x2000. P. As for Figure 7N, but different field. showing another authigenic cement comprising kaolinite (k), calcite (c) and well-developed dolomite rhombohedra crystals (d), interconnected micropores within cement are clearly defined (p); magnification x2000. Q. As for Fig. 7N, but different field and high magnification (x 10,000), showing face to face stacks of pseudohexagonal plates or booklets of kaolinite and calcite crystal (c); interconnected micropores of 1-5 microns in diameter occur within kaolinite platelets.

R. An open packed quartzarenite of the Mesozoic Ekmai Permation, smgle No. 80P35SCyshowing original pores betwben the framework grains of quartz (Q); interc~mwtedmacropores of 50-200 microns in diameter common; porosity ranges from 20% to 25%; magnificintion x-54.

No.

S. As for Fig. 7Ry high magnification x200; showing subrounded to rounded quartz (Q) grains and pore spaces. T. As for Fig. 7Ry but different field, showing a quartz clast (Q), micropores (p) and authigenic kaolinite (k) partly filling pore spaces; magnification ~4000.

SAMPLE No.

FORMATION Ekmai Formation

Quartzarenite

TYPE OF SANDSTONE

1

80

P355C***

2

80

P357A*

,y

Quartzarenite

3

80

P214A**

y7

Sublitharenite

4

80 HP127B**

,9

Glauconitic Sublitharenite

5

80 CP466A*

Woniwogi Formation

Glauconitic Sublitharenite

6

80 HP106A**

7

80 CP222A*

8

80 CP222D*

y1

Quartzarenite

9

80 CP308A***

yy

Glauconite SandSto~e

yy

Kopai Formation

Sublitharenite Micaceous Sublitharenite

10

80 CP342A*

Tipwna Formation

11

80 CP350A*

yy

Sublitharenite

12

80 CP353B**

yy

Sublitharenite

13

80 CP353C*

yy

Feldspathic litharenite

14

80 CP522A*

yy

Feldspathic litharenite

15

80

P204A*

Aiduna Formation

16

80

P268A**

¶,

Carbonaceous Sublitharenite

17

80

P282A**

9y

Micaceous Sublithamite

18

80 CP357A**

yy

Quartzarenite

* ** ***

Feldspathic litharenite

Sublitharenite

Thin section SEM SEM and thin section

TABLE 1 .SAMPLES OF THE PALEOZOIC-MESOZOIC EXAMINED IN THIN SECTION AND SCANNING ELECTRON MICROSCOPY

AIMRIA

60 P282h 80 CP357A

80 P204A

-

-

M. = Major C Comon SP = Sparse R = Rare A Absent

R

SP

A

A

R

A

A

R

A

A

A

SHRINKAGE

2 Fairbridqe 119671 and Larsen and Chilingar (1979) teminologies

t

- SP

C

C

C

A

FRACTURE

1 Choquette and Pray 119701 and Schmidt and Medonald 11979a, 1979b3 teminolaqies

R

A

80 CP342A 80 CPjSOA 80 CP3539 60 CP353C 80 CP522A

TIPUEIA FCRMATION

A

80 CP222h 80 CP222D 80 CP306A

C

C

KOPAI FGREYiTION

A

R

60 CP46E 80 LPlC6;

'

WONIWOGI FOWI/ITiON

P355C P357A P214A kip1278

80 80 80 80

E W I POWTION

mRE TEXTURE

SECONDARY IBTRA-CEMENT PRIMARY NUMBER INTERGRANULAR INTERGRANULAR /M?.TRiX

FORWITION

R

C

C

YJCM

WROSITY

100

- 200

-

1-50

1

1

- 15

5-10

5

5 .- 10

[

GI,IF$NES)

-

h

A

h

C

PRIMARY

SP

SP

SECOXDRIIY

CIASEIFICATION OF POROSITY -

'

2

.

~issolution,leaching of cement

Anadiagenesis

I

Mesadiagene- Anadiagenesis sis

Foor

j

argir.all;

good

.

Polential Reservoir Rock

Eodiagenesis Syndiagenesisl good Mesodiagene- Anadiagenesie sis

1

REGIME OF DIAGSEIESIS

Dissolution,leaching Mesodiagene- Anadiagenesis shrinkage sis

fracturing

and replacebent

Uncompleted Cement and minor dissolution Of cement

GENETIC CxSES OF PRi?rJLRY hN0 SECONDARY POROSITIES.

TABLE 2 - PORE TEXTURES AND OlAGENETlC FEATURES OF THE SAMPLES E X A M I N E D IN T H I N SECTION AND S.E.M.

R

?.

SP

mCRO

TYPE AND SIZE OF PORE

48

MESOZOIC

QUATERNARY

L E G E N D

(

WAilPl

KO..

FORMATlON

F9RMAT8i3N

WOEIiWOGl

PINlYA MUDSTONE

E K M A I FORMATION

L I M E S T O N E GROUP

UNDIVIDED NEW GblNEA

FORMATION

YAWEE L I M E S T O N E

11 a

I

SYRFICIAL DEPOSITS

{n

I

4 1

(

FIGURE 2

PALEOZOIC

MtSOZOC

FORMATION

DOLOMITE

I R l A N JAYA (Waghete sheet a r e a )

GEOLOGICAL MAP OF SOUTHERN

MOD10

uric-ntarmitr

AIOUNA

-

TIPUMA r o a M * r o N

a

FLAtvK,

I

I

LATE

EARLY

MIDDLE

EARLY

:MIDDLE

-

-

LATE

E

PERMIAN

3

[L

Q

'n

'n

2

0

LZ

W

G

m

I

FIGURE 3.

SILURIAN DEVONIAN

A

-

d

1 DOLOMITE

DEPOSITS

1

I

.

.

.

-

:. * : . o ;

. e. . _ . -. - - _

-.

. .

. . . .F. o.,

,

,--

'4,'. .

-. - .

.

'.o..,o.~.~,:0.',-'~.0..:'.',

SECTION

cal-

-

marine

r i n e

mudstone

-

,

-

Dolostone, d o l o m ~ t ~limestone, c siltstone.

conalornerate. coal seam

le, s i l t s t o n e , b i o c o l c a r e n i t e ,

I

shallaw

? M o r i n e

marine

very

and

F l u v i a t i l e

inner-shelf

Sandstone, carbonaceour sha-1 P o a i

nor r n i c r i t i c l i m e s t o n e

Red,green and grey mudstone, sandstone, conglomerate, m i

conglomerate

arenite , siltstone, ne, colcorenite,greensand

Glouconitic, colcoreous, quartz

us

Glaucanitic, p y r i t i c q u a r t z orenite, s i l t s t o n e , c a l c a r e o

Calcareous, g l o u c o n i t i c m u d - ' S h a l l o w she1 f s t o n e , s i l t s t a n e , f i n e sandmarine stone, m a r l , marly l i m e s t o n e

siltstone

G l a u c o n i t i c , c a l c o r e o u s gu o r t z a r e n i t e , l i t h i c sandstone,

Biocalcarenite,oolitic carenite, sandstone

a

I I

I I

I

-ESIB6 -

?\000m

1200m

1500m

S h e l f M

Calcarenite, biocalcarenite, micrite,biomicrite,colciru dite,chalk,minor s a n d s t o n e

-

2500m

Blue-grey mudstone, sandy shale, sandstane,conglamerate,limestane, l i g n i t e seam

I

,ENVIRONMENT,(METERS)

THICKNESS

I

DEPOSITIONAL MAXIMUM

R~ver,flood p l a ~ n , Grovel, sand, mud, st r t , conglomerate, b r e c c i a , l i g n i t e lake d e b r i s f l o w

DESCRIPTION

ROCK

STRATIGRAPHIC COLUMN O F THE SOUTHERN FLANK, IRIAN JAYA

Q

a

Q

I

LITHOLOGICAL

u I

I

Fm

LIMESTONE

Fm

Frn

Frn

NEW GUINEA

KEMBELANGAN

L I M E S T O N E GROUP

1 MESOZOIC

FIGURE

1 : 250000

CAlNOZOlC

-v = / H

Horizontal s c a l e

PALAEOZOIC

i

1

Imp I

1

1

U N N A M E D B A S E M E N T ROCKS

Unconformlty

MOD10 DOLOMITE

-

AIDUNA

oirconforrnity

TIPUMA

J.L.1

P I N I Y A MUDSTONE

NEW G U I N E A L I M E S T O N E GROUP ( U N D I V I D E D )

WARIPI

YAWEE

BURU

LEGEND

(__(

A

SOUTH

5.

URUMUKA THRUST

CROSS S E C T I O N A - B

B

NORTH AMURA FAULT

THE

IN THE

FORELAND

TO

ALONG

S O U T H E R N F L A N K OF CENTRAL RANGE

FOLD B E L T

SHOW T H E S T R U C T U R E OF T H E

L I N E OF S E C T I O N SHOWN I N FIGURE 4

DIAGRAMMATIC

FAULT

MAWAlPlRI

S

R

FIGURE 7 .

%

D I A G E N E T I C

-c

C

a

Z E

FORMATION

= a E ; r

-0 -uc

o t c

0 c "

p u0 s

-u o ; i

c o m, ,p 9 Z E

-

U

8 0

- a

-0,

L

..

1 0

-u' -=Lg

'

C

I

X

CONSTITUENT

4

~

f!

g

=

:

sO L ag

0

a L o

=

a

3

'

0

C

Y

0

:

o

O

L

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C

0

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0

zou

+

2

1 ;

:a*

)

o

g c P O

r

~

=.-

u

>

m o

o

a#

POROSITY

O

1

( O/o

0

L

LL

10

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I

20

30

I

1

I

/

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..

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WONlWOGl FORMATION

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KOPA I

I

.

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FORMAT ION

I.

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TIPUMA

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FORMATION

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.:* . .... ....

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I..

AIDUNA FOR MATION

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FIGURE. 8

SEQUENTIAL DEVELOPMENT OF DlAGENETlC E V E N T S I N T H E SANDSTONES O F T H E PALEOZOtC M E S O Z O I C SEQUENCES. POROSITY IS ESTIMATED F R O M T H 1 N S E C T I O N A N D S.E.M. EXAMINATION

-

I

I

2. E a r l y b u r i a l s t a g e (early c o m ~ a c i i o n )

I.I n i t i a l s t a g e

Predominantly

z

primary

-

porosity

0 W

c

' I EODIA G E N E S I S 4.Late s t a g e - p o s t b u r i a l (dlssolutlon and replacement stage)

3.Advanced pressure and c o m p o c t l o n s t a g e

-

I(L

4 q

S

Predominaotly poro-

3 Y O

primary

u,

stty, mlnor n w n d a r y porosity

E A R L Y MESODIAGENESIS

I

2.Early buriol stage (early compaction)

I. I n i t i a l s t a g e

W

Z

0

k

Predominantly primary

2 W

ol

porosity

22 E I , -" I-

7

E

-

a I 3

I=

I

E O D I A G E N E S I S

-A

4.Lote stage- post b u r i a l ( d i s s o l u t l o n and r e p l a c e m e n t s t a g e )

3.Advonced p r e s s u r e and compaction stage

4 [L

5u

Quartz

Predominantly

5

secondary

[:-F t l d s p a r

porosity

Volcanic r o c k fragments

M E SOD1 A G E N E S I S

J:.=.I

2.Early burial stage ( e a r l v comaactlon)

I. Initial stage

her t Metoquartzite Mica schist Muscovite Ouartz overgrowths C l a y m a t r i x (allogenlc and auth igenle)

E O D I A G E N E S I S

II 1

a

3 E

a

+

7

3. Advanced pressure a n d ccmpaction (early d i s solution)

4 . L a t e stage-post burial (dissolution and repla cement s t a g e )

-

-

3

2

cement

[Y,V,V ~ e m a t ~ t e

Predominantly secondary porori ty

I

silica

M E SODIAGENESIS

Carbonate

-

Chlorite Parea

F l G U R E 9. T H E RECONSTRUCTION OF D E V E L O P M E N T OF D I A G E N E T I C FEATURES I N T H E , AIDUNA,TIPUMA

AND E K M A l FORMA-

TIONS, SHOWING THE I N I T I A L STAGE UP T O L A T E STAGE OF O I A G E N E S I S .

- ES/86-