Sunda Basin Research Articles

LOW RESISTIVITY PAY DEVELOPMENT: CASE STUDY OF TALANGAKAR FORMATION ASRI BASIN, OFFSHORE SOUTHEAST SUMATRA, INDONESIA

Southeast Sumatra is a prolific oil and gas block located offshore in the Java Sea, 90 km north of Jakarta Bay. This area covers two major basins, namely Sunda Basin and Asri Basin. The initial development of the area focused on faulted and high closures and high-resistivity reservoirs. Further analysis shows that there are special low-resistivity reservoirs in Widuri Area, especially in the Aryani field. This paper will discuss the low resistivity pay zone reservoirs and fluid containment of the intervals. The paper will also include further assesment this undeveloped interval to increase oil production, considering the upside potential of the reservoirs using current geological, geophysical, and reservoir engineering approaches. Additionally, it will describe the operational challenges faced during the production period. The low-resistivity pay zone, a hydrocarbon-bearing reservoir in the Aryani field of the Widuri area, was identified using gas readings in the daily drilling reports, complemented with mud logging data. The Basal Sand interval, which drapes above the basement, was the site of the first producing well of Basal Sand, Aryani AC-X, preceded by a hydraulic fracturing job. Lambda-mu-rho inversion was implemented to delineate this reservoir. To recognize the potency in those wells, data reconfirmation was conducted between the elan summary, sidewall core, and cutting data. Aryani AC-X has successfully drained oil using a submersible pump, with an initial production of 408 bopd and cumulative production of 240 MBO.

Rock Wettability Characteristics Of Some Indonesian Limestones Case Study: Baturaja Formation

Rock wettability plays a very important role in affecting various rock physical properties such as relative permeability and capillary pressure. Common practice at present is that carbonate rocks are assumed to be preferentially oil wet in nature. This assumption may prove fatal since the need of true knowledge over the real wettability for one’s carbonate reservoir is often neglected, and wettability aspect in reservoir modeling is in turn based on assumption. To prove over reliability of the assumption a study is carried out using information from 350 core samples taken from Baturaja Formation. The choice for the Baturaja limestone is basically based on the fact that it is a mature productive rock formation and its extensive spread into three of the most productive sedimentary basin in Indonesia, Northwest Java Basin, South Sumatra Basin, and Sunda Basin. The study proves that the assumption of the generally oil wet limestone does not apply for Baturaja limestone. The Baturaja limestone tend to exhibit, quantitatively, equality in their tendency towards oil wettability and water wettability and leave some proportion to neutral or mix wettability as well. However, when a more detailed comparison is made results show that qualitatively the limestone are indeed more inclined to oil wettability than water wettability even though this finding is insufficient to support a conclusion that the Baturaja limestone are specifically oil wet. Other finding from comparison with past studies also shows that limestone may behave in the way sandstones do. Both limestone and sandstones may vary in the same way and no assumption over their preferential wettability is justified without direct measurements. Wettability alteration as the result of hot core cleaning following the widely accepted standard procedure is also strongly indicated. It is therefore concluded that the practice has to be abandoned for a better and reliable laboratory testing results.

Remaining Reserves Drainage Optimization Using Infill Drilling Based on Subsurface Study Field

The XY Field is an oil field in the Sunda Basin which was developed since 1981 and has been produced in the Baturaja carbonate layer and Talang Akar sandstone layer. Decreasing the amount of oil production in the reservoir can have a detrimental impact on the company so it is necessary to analyze the remaining reserves of the reservoir. The calculation used to evaluate the remaining reserves use the Volumetric, Material Balance and Decline Curve methods. From the three methods, the results that are close to the reserve of the XY field reservoir are 14 MMSTB. OOIP is obtained from the volumetric method and material balance which is divided into P10, P50 and P90. The reserve OOIP for P10 is 110.8 MMSTB and P90 is 60.34 MMSTB, with the last cumulative production in December 2019 being 9.3 MMSTB, where the economic limit of the field is 46 bbl. / day and the contract will be expired in 2038. From the results of the subsurface analysis, the four infill wells are candidates for infill wells because they have hydrocarbon potential. Then in terms of economics this development scenario is feasible to be developed with NPV reaching 9,140 MUSD, the ROR reaching 41% for PSC and 60% for Gross Split, and increases field recovery factor (RF) up to 56%.

Seismic Expression of Paleogene Talangakar Formation - Asri & Sunda Basins, Java Sea, Indonesia

The Asri and Sunda Basin are located offshore Southeast Sumatra under the SE Sumatera Production Sharing Contract (PSC). Currently, Pertamina Hulu Energi OSES operates in the Asri and Sunda Basins, known as Southeast Sumatra (SES) Block. As one of Indonesian prime oil and gas producing area in the past 50 years, these basins have produced cumulatively more than 1,500 MMBOE with an average of 90,000 BOPD. Both Asri and Sunda Basins are part of a series of Cenozoic half grabens developed on the Asian continental margin, that have occupied a retro arc setting since early Neogene times.Hydrocarbon exploration activities in the offshore southeastern Sumatra began with a signed agreement of Contract Sharing between IIAPCO (Independent Indonesian American Petroleum Company) and Pertamina on 6 September 1968.The contract area included the offshore areas east of Sumatra and south of Bangka - Belitung Islands, covering an area of 124,000 km2. After the final relinquishment in 2008, the current PSC boundary covers an area of 5,851 km2.This paper presents the results of integrated petroleum geosciences framework, its implications for Oligo-Miocene reservoirs and hydrocarbon prospectivity of the basins using near field exploration approaches. A four-fold division comprising rift initiation, rift climax, immediate post rift and late-post rift stages of basin evolution characterize the basin filling. Seismic expression of these kinematic units gives an idea about the linkage of their deposition with different stages of rift evolution. The present study has also identified a new potential play concept in Oligo -Miocene reservoirs.

The depositional characteristics and distribution law of shallow-water delta during late rifting stage: a case study on the upper Oilgocene in the Sunda Basin, Indonesia

The depositional characteristics and distribution law of shallow-water delta during late rifting stage: a case study on the upper Oilgocene in the Sunda Basin, Indonesia

Classification and application of flow units in carbonate reservoirs

In the carbonate oil field offshore of Sumatra block in Sunda basin, RQI (Rock Quality Index) and FZI (Flow Zone Index) have proved to be effective method of dividing the flow units. The method utilizes the porosity and permeability of the core rock samples to divide the flow units of the K oil field carbonate reservoirs. The field consists of six flow units, and they represent different flow characteristics. The results show that each flow unit has a specific relationship of porosity and permeability and a specific capillary pressure curve (J function); this feature is related to the rock pore structure and pore size. In the application, the flow unit model is built by a stochastic modeling method, and the permeability model and the oil saturation model are built under the control of the flow unit model.

Oligocene palynological succession from the East Java Sea

Abstract Rich palynomorph assemblages have been obtained through a marine Oligocene succession from the East Java Sea (Indonesia) and provide the first instance of an independently dated Oligocene succession from SE Asia that has yielded a good quality palynological record. The succession has been independently dated by nannofossils and foraminifera. The palynomorph succession suggests climatic control on Oligocene vegetation, on which basis a regionally applicable zonation is proposed. The Early Oligocene is characterized by common rain forest elements, suggesting an everwet, rain forest climate. The early part of the Late Oligocene contains much reduced rain forest elements with grass pollen, indicating a more seasonal climate, whereas for the latest Late Oligocene, rain forest elements return in abundance, suggesting a superwet rain forest climate. This palynological succession is similar to that from the Sunda Basin in the West Java Sea, allowing the Sunda Basin succession to be dated by correlation. The study also extends the stratigraphic range of Dacrydium and Casuarina , two plant taxa previously thought to have dispersed from the Australian Plate into SE Asia at the time of the collision with Sunda, to well before the time of collision. A different means of dispersal for these taxa is proposed.

ABSTRACT: Re-development of structural-stratigraphic traps in the Wanda Area, Sunda Basin, Southeast Sumatra, Indonesia

ABSTRACT: Re-development of structural-stratigraphic traps in the Wanda Area, Sunda Basin, Southeast Sumatra, Indonesia

ABSTRACT: 'Classic clastics' - has high-tech. 3D improved imaging of stratigraphic traps found with 'traditional' techniques? Yvonne 'B' Field, Sunda Basin, Java Sea

ABSTRACT: 'Classic clastics' - has high-tech. 3D improved imaging of stratigraphic traps found with 'traditional' techniques? Yvonne 'B' Field, Sunda Basin, Java Sea

Meridian-parallel faults and Tertiary basins of Sundaland

The pre-Tertiary core of Sundaland contains numerous North-South striking regional faults in addition to, but fewer major faults in Northwest and other directions (Fig. 1). One N-S regional fault extends from the Thailand-China border via the Gulf of Thailand and Peninsular Malaysia into Central Sumatra is the longest at -2,000 km (abbreviated as TBB for Thai-Bentong-Bengkalis). Two other long faults are the Vietnam Shear off the east coast of Indochina and another N-S fault in the gulf parallel to TBB. The other regional faults range in length between 200 km and 700 km. In the Malay Peninsula, the TBB coincides with the Raub-Bentong suture that existed since the Middle Triassic. Faults within the suture shows overprinting of normal faulting (down to east), upon dextral slip that in tum post-dated sinistral slip. N-S faults in the peninsula are considered the oldest set and date from the Jurassic or earlier. The TBB segment in Sumatra is the Bengkalis trough on which dextral slip had continued to affect Miocene strata. Similarly, N-S regional faults in the Tertiary basins of North Sumatra, Central Sumatra, South Sumatra, Sunda basin complex, Arjuna basin, Central Thailand basin complex, Mekong, Nam Con Son, Malay and Penyu basins deformed strata as young as early Late Miocene. These regional faults show mainly dextral slip except the Peusangan (North Sumatra) and the northerly trending faults in Terengganu (Peninsular Malaysia). Left-lateral slip implies that the Terengganu faults are lag structures in the general extrusion of SE Asian crustal slabs towards SE and S. The sinistral slip on the Peusangan fault is attributed to spreading of the Andaman Sea basin since about 11 Ma ago. The geological history suggests that by the Middle Triassic, Sundaland had combined into a single microplate. Some of the meridian-parallel faults, such as the TBB probably have existed since that time. Other N­ S faults may be younger, but perhaps most developed in the Mesozoic and a number ofthese structures became reactivated in the Cenozoic. It seems probable that lateral slip directions were different at different times, but that the latest tectonic displacement sense had been dextral. The origin of most of the N-S regional faults is problematic. The Vietnam Shear may be attributed to the opening of the South China Sea basin from Oligocene to about mid-Miocene. The TBB is a mid-Triassic suture between continental blocks. Those N-S faults traversing Cenozoic sediments are probably reactivated pre­ Tertiary structures. The widespread distribution of these faults in Sundaland may mean that the entire region participated as a single unit in large-scale translations or rotations that have been suggested by paleomagnetic studies. Or, was Earth's rotation responsible for the formation of regional N-S faults in Sundaland? The regional meridian-parallel faults of Sundaland have functioned as (1) originators/initiators of Tertiary basins such as the Mekong and Nam Con Son, as (2) determinants of basin location (Central Thailand and the Gulf of Thailand; sub-basins: Balam-Pematang troughs, Bengkalis trough, Benakat gully, Asri, Seribu, Arjuna, and relatively small basement depressions in the Malacca Strait), and as (3) modifiers of basin geometry (Peusangan fault in the North Sumatra basin; the large dextral offsets off old series in the Malay basin). N-S faults across fold crests of the Malay basin are non-tectonic and formed by tightening of the folds in a persistent compressive stress regime.

Distribution of naphthalenes in crude oils from the Java Sea: Source and maturation effects

Amounts and distributions of C1-C3 naphthalenes and cadalene were determined by capillary gas chromatography in sixty crude oil samples from the Java Sea, southeast Asia and in a sample of Talang Akar (Oligocene) resinite supposed to be a major contributor of hydrocarbons to oils in that area. Maturity of the oils was assessed by the Methylphenanthrene Index (MPI-1). Source effects discovered by scatterplots were scrutinized by Principal Component Analysis (PCA).Based on empirical relationships with C27-C29 steranes (measured by gas chromatography-mass spectrometry), dimethylnaphthalenes in oils from the Ardjuna and Jatibarang (sub-)basins are mainly derived from terrestrial sources. Transition to a marine depositional environment in the Sunda basin, as indicated by a decrease in C29 sterane relative abundance from 70 to 30%, results in a decrease of total dimethylnaphthalene (DMN) concentrations from 20 to less than 3 mg/g oil. This is due, mainly, to a decrease in the concentration of the dominant 1,6-DMN. Thus, terrestrial Ardjuna or Jatibarang oils rich in 1,6-DMN (2–15 mg/g oil) are readily discriminated from marine Sunda oils (0.2–2 mg 1,6-DMN/g oil). Resinite of the Talang Akar type (1.4 mg 1,6-DMN/g total organic matter [TOM]) appears to be a significant contributor of 1,6-DMN to oils in the Ardjuna basin.Terrestrial affinities are inferred also for cadalene from concentration levels that are higher in terrestrial oils (1–3 mg/g oil) and Talang Akar resinite (6 mg/g TOM) than in the marine oils (0.1–1 mg/g oil). Ardjuna basin oils have the highest concentrations of cadalene, hence supporting resinite of the Talang Akar type as a possible source. However, 1,6-DMN and cadalene are likely to be derived from different terrestrial organic matter sources, because they load on different factors in PCA.Maturity levels of the oils in the range of 0.6–0.9% calculated vitrinite reflectance (Rcb), as inferred from the Trimethylnaphthalene Ratio (TNR-2), are in reasonably good agreement with MPI-1 measurements and geological constraints, e.g., highest maturities detected near the depocentre of the Ardjuna basin. The TNR-2 parameter hence proved useful for maturity assessment of Java Sea oils.

Some examples and possible explanations for oil generation from coals and coaly sequences

Abstract Coals and associated shales are important oil source rocks in certain deltaic environments, in which selective processes of degradation or reworking increase the content of hydrogen-rich kerogen. The formation of hydrogen-rich kerogen in a deltaic setting is either by preferential concentration of plant cuticles and spores after reworking of delta top freshwater peats, or, by accumulation of delta margin peats under saline conditions. In each case the source rocks and derived oils may be expected to show distinctive indicators of the depositional environment in the associated alkane content, sulphur content, biomarker and carbon isotope signatures. Coals in the Oligo-Miocene Talang Akar Formation of South Sumatra and Northwest Java Basins contain perhydrous vitrinite and are the source of isotopically relatively light waxy oils which contain biomarkers derived from tree resins. Waxy oils are also produced in the Sunda Basin, between Sumatra and Java but in this case the upper (coaly) part of the Talang Akar Formation is immature and the oils are derived from algal kerogen in the older, lacustrine Banuwati Formation shales; these oils are distinguished by low contents of land plant biomarkers and by a markedly heavier carbon isotopic signature. In the Western Desert of Egypt, coals of the mostly marine Jurassic Khatatba Formation have sourced oils with a relatively heavy isotopic signature. It is proposed that the isotopically heavy character of the coals and oils is due to a combination of microbial contribution, and raised salinity (and sulphate) levels due to marine influence. In northern England, Namurian (Pendleian) marine shales are generally distal turbidites derived from pro-delta sediments but mostly without oil source potential. Rich oil source rocks occur as basinal shales at the extreme margins of or interdigitating with the turbidites or as condensed sequences on structural highs. They contain kerogen derived by reworking of peats of a deltaic-coastal plain environment, and may be correlated with many of the oil shows and produced oils of the area. The examples demonstrate that the recognition of source rock facies aids exploration by guiding the prediction of the location and potential of oil-prone facies, but that this is only possible if all facets of oil and source rock geochemistry are integrated with a knowledge of sedimentary processes.

Plate tectonics and the development of sedimentary basins of the dextral regime in western Southeast Asia

The western part of Southeast Asia is comprised of three tectonic plates: the Southeast Asia Plate, the Burma Plate, and the Australia-India Plate. The present regime of oblique subduction and partial coupling of the combined Australia-India Plate to the Southeast Asian part of the Eurasia Plate was initiated in the Middle Eocene. Resulting dextral shear interacting with the inertia of the largely continental plate were the driving forces of basin genesis and development, setting in train a sequence of temporally and spatially variable tectonic events, diminishing in intensity away from the active plate boundary. The effects can be identified in the east from the Malay Basin to Central Thailand. A Late Eocene to Oligocene rifting phase formed rift troughs in central Sumatra, later spreading north to the Mergui Basin and south to the Sunda Basin. The Sunda Volcanic Arc was initiated. As subduction proceeded, deformation spread out from the vicinity of the plate boundary. In the Oligocene, dextral shear, substantially along preexisting faults and consequential extensional faulting initiated the Thailand basins and the Malay Basin. Subsidence and extension continued until late Middle Miocene time, possibly with some thermal relaxation. In the Late Oligocene to Early Miocene, the back arc basins close to the plate boundary began to subside, extending out from the initial rift troughs during a quiescent interval transition between the rifting and later wrenching phases. Subsidence may have been the result of the withdrawal of heat from the asthenosphere beneath the basins by the cold subducted slab. As the Sunda arc-forearc developed by accretion and magmatism, partial coupling in the plate boundary region was enhanced and transpressional deformation commenced in the Sumatra basins in the Middle Miocene. This Sea defining the northern part of the Burma Plate. South of the Andaman Sea, deformation persisted in a broad zone along the margin of the Southeast Asia Plate. Dextral wrenching in the late Middle Miocene phase affected much of the eastern region, extending south into the Natuna Basin. Deformation diminished markedly at the end of the Middle Miocene with the inception of the Burma Plate. Transpressional tectonics continued through Late Miocene and Pliocene time in Sumatra, in a broad zone as an ill defined southern extension of the Burma Plate. The continuing movement resulted in the uplift of the Barisan Mountains and the deformation of the onshore Sumatra basins. The Sumatra forearc was transferred to the Burma Plate with the establishment of the dextral Sumatra Fault probably in the Pliocene.

Sunda Basin--Important New Indonesian Oil Province: ABSTRACT

The Sunda basin is one of the Tertiary ideogeosynclines bordering the stable Sundaland. Twenty-one prospects have been drilled since offshore exploration started in late 1968 with oil and/or gas being discovered in 52% of these ventures. A north-south horst and graben framework on a rugged Late Cretaceous surface governed erosion, deposition, and tectonic growth throughout the Tertiary in all but the northeastern extremities of the basin. Volcanic and fluvial rocks constitute initial sedimentary deposits. Quantity of sediment influx was primarily responsible for differential sinking of graben blocks during early basin development and resulted in thick deltaic deposits during early Miocene. Downwarp of the backdeep continued with sea invasion through island passages in the geanticline on the south. High tectonic blocks prevented segments of the basin from being invaded during early basin development. With continued denudation and downwarp, Miocene transgression expanded over the Sunda basin. Local high areas persisted, but transgression continued dominant. As basin segments filled, a nearby flat depositional surface developed. Slight lowering of sea level resulted in regional regression, followed by major transgression in post mid-Miocene time. Late in this second transgressive period, most disconnected ideogeosynclines became one regional geosyncline surrounding the Sundaland. Final regional regression occurred in late Miocene, culminating in complete emergence during Pleistocene. Worldwide melting of Pleistocene ice caused a resubmergence of the basin to present marine conditions. Production has been established in principal intervals producing in Sumatra. Major new pays have been established in Oligocene volcanic tuffs and in Oligocene (?)-Miocene sandstones of the Talang Akar. Possible commercial shows have been found in Miocene Batu Radja transgressive limestone and in weathered basement rocks. Major oil production is indicated from Air Benakat sandstone bodies. Gas production has been established in the Parigi Limestone. End_of_Article - Last_Page 367------------