Northeast Java Research Articles

The Miocene/Pliocene Boundary In The North East Java Basin, Indonesia

As a part of the LEMIGAS Research Programme on Neogene Epoch Boundaries in the Indonesian Tertiary Basins, in 1981 fiscal year is selected North East Java Basin as an object for research. In this paper we will stress our work on the Miocene/ Pliocene Boundary of the basin based on planktonic Foraminifera. More recently a lot of paleontologists have been working on the Miocene/Pliocene Boundary problem. Bandy (1963) used the first appearance of Sphaeroidinella dihescens as a boundary in the Phillipine, whereas boundary based on the initial apppearance of Globoratalia margaritae. carried out an examination of samples from the Trubi Marl of the Zanclean Sicily and came to the conclusion approximately with middle N18 of this zonal scheme. Bolli ( 1966, revision in 19/0 ) put this stage In 1969, Blow Berggren (1973) proposed the limit of this stage boundary based on the last occurrence of Globoquadrina dehiscens. Kaneps (1974) based on this observation on planktonic Foraminifera of the DSDP cores from the Eastern Equatorial Pacific Ocean came to the conclusion that the Miocene/Pliocene Boundary lies at the base of Globoratalia tumida zone. The base of this zone was placed at the horizon of the initial appearance of Globoratalia tumida while the upper boundary was placed at the horizon of reversal in coiling direction of Pulleniatina primalis from left below to right above. Pringgoprawiro and Baharuddin (1979) on the other hand proposed the initial appearance of Sphaeroidinella immatura as a boundary between these two periods. The purpose of this paper is to study the ranges of some selected important species, and to detect how far these species can be used as a tool for Miocene/Pliocene Boundary in the North East Java Basin. No radiometric age dating has been done in the area.

UTILIZATION OF REMOTELY SENSED DATA TO GEOTHERMAL, OIL AND GAS DEVELOPMENT

Some of LEMIGAS experiences in the utilization of remotely sensed data will be briefly discussed, these are : Jambi Sub Basin and North East Java Basin for Preliminary and advanced oil and gas exploration respectively. Dieng field for geothermal exploration, and Balikpapan offshore for sea water quality assessment. It is hoped, through this information, better understanding of the operational aspects and appreciation of the subject can be achieved.

Penerapan Metode K-Means Dalam Mengelompokkan Persebaran Lahan Kritis Di Indonesia Berdasarkan Provinsi

The study aims to group the distribution of critical land in Indonesia by province. To solve this problem, researchers applied the K-Means Algorithm method. Where the source of research data is collected based on documents - documents of Information on The Extent and Dissemination of Critical Land By Province produced by the Central Statistics Agency (BPS). The data used in the study was data from 2011, 2013 and 2018 consisting of 34 provinces. Data will be processed by clustering in 2 clusters, namely clusters of high critical land distribution rates and clusters of low critical land distribution rates. The high cluster amounted to 4 data, namely the provinces of North Sumatra, Jambi, East Java, and Central Kalimantan. With the conduct of research can contribute in improving the performance of Balai Pengelolaan Daerah Aliran Sungai dan Hutan Lindung (BPDASHL) on the process of fixing and tackling critical land in the provinces in Indonesia.

EOCENE-OLIGOCENE CLIMATE BASED ON PALYNOLOGICAL RECORDS

This study is a part of the investigation on Tertiary paleoclimate conducted by LEMIGAS Stratigraphy Group. The paleoclimate reconstruction covers most area of western Indonesia including South Sumatra Basin, Sunda-Asri Basin, Northeast Java Basin South Kalimantan and Northeast Java Basin, West Natuna and South Sulawesi (Figure 1). This paper is aimed to figure out the regional paleoclimate of western Indonesia which occurred during Eocene-Oligocene. In fact, the knowledge of paleoclimate is useful to define sea level changes which are believed to have relationship with stratigraphy and sedimentology of these areas. The paleoclimate interpretation can be approached using different tools such as biostratigraphy and geochemistry. In this study, paleoclimate is interpretated based on biostratigraphy (microfossil evidences) including palynomorph and foraminifer. Palynomorphs were mainly applied on the non-marine to transitional sections, whilst foraminifers were used in interpreting shallow to deep marine sediments. In fact, most interpretations rely on palynological evidences as these simply provide suitable data for paleoclimate analysis. In case of both microfossils appear in the same section, the paleoclimate interpretation based on palynomorph can be placed in a certain stratigraphic level which is defined based on the occurrence of the age-restricted foraminifer. The paleoclimate interpretation of certain strati- graphic level is based on the compilation of palynological and foraminiferal data deriving from different areas. This method is used to obtain representative picture of paleoclimate which occurs in the selected stratigraphic range of the western Indonesia

Oligocene Palynology Of On-Shore West Java

Compared to its counterpart in the off-shore area (including Northwest Java and Northeast Java), the Oligocene sediment of on-shore West Java provides low pollen assemblages. In addition, superwet elements of Dacrydium and Casuarina commonly occurred in off-shore area are less represented in the on-shore area. However, it is believed that the study area still experienced wet climate condition as proved by common occurrence of rattan pollen Dicolpopollis spp. indicating a thick growth of swamp forest under moist climate. Unlike its counterpart in the off-shore North West Java, the studied sediment rarely yields lacustrine elements suggesting the disappearance of lake deposit. The Oligocene sediment of on-shore West Java is defi ned by the regular appearance of Oligocene marker of pollen Meyeripollis naharkotensis. The last occurrence of this pollen marks the top Oligocene age. In fact, the appearance of pollen M. Naharkotensis is obviously used to separate Oligocene age from Miocene age in the off-shore area. Moreover, marine micropaleontology analysis on foraminifers and calcareous nannoplankton confi rms this age. The studied sediment was deposited in the transition to shallow marine environment as indicated by rare occurrence of marine microfossils. The common brackish pollen of Zonocostites ramonae (Rizophora) and Spinizonocolpites echinatus (Nypa) indicates mangrove/ back-mangrove environment. Moreover, the domination of shallow water benthonic over the planktonic forms suggests shallow marine setting.

APPLICATION OF OLEANANE AND STERANE INDEX FOR BIOSTRATIGRAPHIC AGE DETERMINATION: EXAMPLES FROM KANGEAN OILS, NORTHEAST JAVA BASIN

Northeast Java Basin is known as mature Cenozoic basin, yet this understanding override possibility ofsediment older than Cenozoic. This thoughthas brought current exploration strategy of this basin concerningwithin only Cenozoic sediments. Therefore, it is believed that the source rock in this basin was also derivedfrom Cenozoic sediments, especially the Ngimbang Formation, which was formed during Late Eoceneto Early Oligocene in the stage of Early Synrift. On the other hand, the occurrence of Alisporites sp haspointed Cretaceous sediments is a potential source rock. However, it is still debatable due to the presence ofAlisporites similis in Serawak Basin of Malaysia, which is present until Paleocene. Three crude oils from theKangean oil fi eldNortheast Java Basin, namely NEJB-748, NEJB-749 and NEJB-750have been investigatedusing gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS).Kangean oils areclassifi ed as mixed oil with organic matter originated from marine and terrestrial deposited under oxidizingand reducing conditions. Moreover, Kangean oils show very low oleanane and steraneindexthat may leadus to the conclusion that the oils were originated from Cretaceous source rock.

The Determination of Kesongo Mud Volcano System Zone Using Seismic Interval Velocity at Potential Overpressure in The Tawun Formation, “F” Field, NE Java Basin

The Mud Volcano System (SMV) is an interesting topic, especially the relatively shallow oil and gas basin in North East Java. The Tawun Formation is an alternating layer of claystone that is quite thick. It has been confirmed in several oil and gas fields as a potential layer of a mud volcano system, specifically the Kesongo Mud Volcano System. The existence of this system is a challenge to further exploration; therefore, zoning is essential. The data used in this research were interval velocity cubes which were re-picked in each of the two bin sizes (2x25m) as the primary data. The well and velocity data were performed to determine the deviation from the Normal Compaction Trend (NCT). Furthermore, the seismic interval was confirmed with drilling data such as mud log and mud weight. The value of preliminary pore pressure was also derived from interval velocity using Eaton Equation which is confirmed by mud weight data. The Zoning of the Mud Volcano System was carried out via a depth slice at 3D seismic intervals. The results showed that the Tawun Formation has a Mud Volcano System prone zone at a depth of 204 m and decreases in geometry as the depth increases. Meanwhile, the OP-1 zone was the safest zone for exploration, followed by OP-2 but requires passage through the Kesongo Mud Volcano System zone of 1000 m thickness.

Textural Characteristics and Depositional Environment of Ngrayong Sandstone (Middle Miocene) from Rembang Area, Northeast Java, Indonesia

Granulometric analysis of Ngrayong sandstone samples from Rembang area of NE Java (Indonesia) has been carried out to examine the textural characteristics and elucidate depositional environment. The result data from the grain size analysis indicates that the Ngrayong sediments are classified as sand or muddy sands. They are very fine- to medium-grained (phi values: 1.67 to 3.35), moderately- to well-sorted (standard deviation: 0.19 to 0.57), strongly fine-skewed to strongly coarse-skewed (skewness values: 4.82 to −5.97), and very platykurtic to very leptokurtic (kurtosis values: 0.36 to 2.41). Sandstone samples show unimodal grain size distribution. The sediments are interpreted to be transported in all three modes-traction, saltation and suspension, however, suspension and rolling are the major processes during transportation. Discriminant functions indicate diversity in the depositional environment for the sandstones. However, shallow marine is regarded as the dominant depositional environment. The preponderance of fine-grained sediments and lack of coarse sands suggest low to moderate energy conditions during deposition of Ngrayong sediments.

Sandstone Provenance Study in Wonosegoro, Boyolali Regency, Central Java

Wonosegoro is part of western Kendeng Zone, the depocenter of North East Java Basin that is mainly filled with thick pelagic and volcaniclastic sediments. Sandstones lithofacies is presence within the research area and may act as a useful tool to reach the aim of this research, which is to determine the provenance. The research has conducted field observation, petrographic analysis on seven thin sections of sandstones from the field, and bathymetry interpretation from benthic foraminifera. Overall, the sandstones are predominantly composed of lithic components (72.73%-88.05%) and significant matrix (25%-50%), thus classified as lithic greywacke. The combination of quartz-feldspar-lithic (QFL) and the heavy minerals composition suggest that the sandstone provenance in research area is a product of Oligo-Miocene volcanic of southern mountain range.

Quaternary nannoplankton in the Northeast Java Basin

In Indonesia, nannofosils are commonly used for age estimation on Miocene marine sediment, but they are rarely performed on Quaternary sediment. This paper introduces two nannofossil biozones, Martini (1971) and Backman et al. (2012) and the comparison between the two biozones. An uninterrupted interval of marine sediments was described and picked for quantitative nannoplankton analysis. The samples were taken from Ledok Formation to Lidah Formation in Pati Region, Northeast Java Basin. The samples were prepared by quick smear slides method and and analyzed by quantitative field of view method. Martini (1971) biozone can be used to subdivide the Late Miocene–Pleistocene sediments into 5 biozones, but Backman et al. (2012) can be used to classify the same sediments into 8 biozones. The biozone subdivision from Backman et al. (2012) is more detailed than that of Martini (1971) because an updated dating and biozone in the three new dating zone data.

Identification of gas hydrate on bottom-simulating reflector characteristics with 2D seismic pre-stack time migration of North Bali Waters

Gas hydrate is a physical compound composed of gas molecules that are formed in a seabed layer characterised by high pressure and low temperature. It is known as one of the alternative non-conventional hydrocarbons besides petroleum and natural gas. One of the identified areas of gas hydrate stability zone is in the North Bali Waters. The North Bali Waters is part of the North East Java Basin, which has oil and gas exploration and production, both conventional and non-conventional. One method of identifying the content of gas hydrates is by looking at the appearance of the Bottom Simulating Reflector (BSR) as shown on the Pre-Stack Time Migrated seismic sections. The detection of gas hydrate zone is determined by the presence of high amplitude, reversed polarity reflection and cross-cut reflection of sedimentary layer. This study aims to determine the existence of a BSR in the waters of North Bali. The procedures for analysing the existence of Bottom Simulating Reflector in this study are pre-processing, processing, and interpretation of 2D marine seismic data. The result shows gas hydrates found with indicated Bottom Simulating Reflector on CDP 35-812 at TWT depth of 1526-1582 ms, characterised by high amplitude-reverse polarity.

RESERVOIR PERFORMANCE ANALYSIS USING MATERIAL BALANCE METHOD IN GAS FIELD

The RF reservoir is a dry gas reservoir located in Northeast java offshore that has been produced since 2018. The RF reservoir has produced 2 wells with cumulative production until December 2019 is 31.83 BSCF. In January 2018 the gas production rate from the two wells was 36 MMSCFD and the reservoir pressure at the beginning of production was 2449.5 psia, peak production occurred in April 2019 with a gas flow rate of 98 MMSCFD but in December 2019 the gas production rate from both wells decreased to 30 MMSCFD with reservoir pressure decreased to 1607.8 psia. Changes in gas flow rate and pressure in the RF reservoir will affect changes in reservoir performance, so it is necessary to analyze reservoir performance to determine reservoir performance in the future with the material balance method. Based on the results the initial gas in place (IGIP) is 80.08 BSCF. The drive mechanism worked on the RF reservoir until December 2019 was a depletion drive with a recovery factor up to 88% and a current recovery factor (CRF) is 40%. The remaining gas reserves in December 2019 is 39 BSCF and the reservoir will be made a production prediction until December 2032. Based on production predictions of the four scenarios, scenario 2 was chosen as the best scenario to develop the RF reservoir with a cumulative production is 66.1 BSCF and a recovery factor of 82.6%.

Facies modelling of Ngimbang Clastics interval of Ngimbang formation with the integration of rock physics analysis and simultaneous inversion, North East Java Basin

Facies modelling of Ngimbang Clastics interval of Ngimbang formation with the integration of rock physics analysis and simultaneous inversion, North East Java Basin

The hidden sedimentary basin underneath the Quaternary volcanic unit in Bogor and Kendeng area

The Java Island is an active volcanic arc that experiences several volcanism episodes, which gradually changes from South to North from the Late Oligocene to Pleistocene, following the subduction of the Australian plates underneath the Eurasian plates. During the Eocene, the southern and northern part of Java was connected as one passive margin system with the sediment supply mainly comes from Sundaland in the north. The compressional tectonics creates a flexural margin and a deep depression in the central axis of Java Island and acts as an ultimate deep-sea depocenter in the Neogene period. In contrast to the neighboring Northwest and Northeast Java Basins in the Northern edges of Java Island, the basin configuration in the East-West trending depression in median ranges of Java (from Bogor to Kendeng Troughs) are visually undetected by seismic due to the immense Quaternary volcanic eruption covers.Five focused window areas are selected for this study. A total of 1,893 Km sections, 584 rock samples, 1569 gravity and magnetic data, and 29 geochemical samples (rocks, oil, and gas samples) were acquired during the study. Geological fieldwork was focused on the stratigraphic unit composition and the observable features of deformation products from the outcrops. Due to the Paleogene deposit exposure scarcity in the Central-East Java area, the rock samples were also collected from the mud volcano ejected materials in the Sangiran Dome.The distinct subsurface configuration differences between Bogor and Kendeng Troughs are mainly in the tectonic basement involvement and the effect of the shortening on the formerly rift basin. Both Bogor and Kendeng Troughs are active petroleum systems that generate type II /III Kerogen typical of reduction zone organic material derived from transition to the shallow marine environment. The result suggests that these basins are secular from the neighboring basins with a native petroleum system specific to the palaeogeographical condition during the Paleogene to Neogene periods where the North Java systems (e.g., Northwest and Northeast Java Basin) was characterized by oxidized terrigenous type III Kerogen.

Crustal thickness estimation in Indonesia using receiver function method

The existence of seismic wave velocity difference in the Earth crust and mantle creates the possibility to use earthquake data for estimating the crustal thickness utilizing the Ps conversion phase in the boundary. The radial component signal was deconvolved from the vertical component in the frequency domain to estimate receiver function for Indonesia region. We implemented the water level deconvolution techniques with a Gaussian filter of 2.5 Hz to eliminate the high frequency noise in the receiver function. The H-k stacking technique was performed to all receiver functions from each event to predict the crustal thickness and the Vp/Vs ratio below the stations. We analyzed ten azimuthally distributed teleseismic earthquakes recorded by 108 stations of BMKG. The result shows that the crustal thickness in Indonesia varies from 20 to 39.9 km. The western part of Sumatera, northern part of Sulawesi Island, and North Maluku region show generally thinner crust with value about 20 to 25 km. The North Sumatera, Central Java, and East Java show a considerably thicker crust of up to 36 km. Furthermore, our result also reveals a difference of crustal thickness about 5 km with the previous studies.

Elastic Property Modeling, Extended Elastic Impedance (EEI) and Curve-Pseudo Elastic Impedance (CPEI) Inversion for Pore Type Analysis and Hydrocarbon Distribution in Carbonate Reservoir, Kujung I Formation, “Humaira” Field, North East Java Basin

The complexity of the pore shape in carbonate rocks causes the need for a special strategy to characterize carbonate reservoir. The more information used, the more accurate the reservoir characterization will be. Pore type analysis is the important study because it relates to the fluid flow properties. The elastic property modeling show a good match to the actual data. The results of the well log and petrophysical data analysis show that the gas zone is located at the upper side of Kujung I Formation. Based on rock physics modeling result, the possible pore type developing in the Kujung I Formation is reference pore with the dominance of the aspect ratio value of about 0.17-0.19. The carbonate layer containing hydrocarbons is characterized by low Lamda-Rho, Lamda/Mu values and a low Poisson ratio. Porous carbonate layer, characterized by a low Mu-Rho value. The slice results show that the gaseous area is located on the anticline. The zone that has good porosity indicated by low Mu-Rho. In the IN-3 well there are no hydrocarbons, this analysis is in accordance with the geological condition of the IN-3 well which is in a low area on the time structure map. The inversion results show a good match between CPEI against water saturation log and CPEI against porosity log.

The testing of Qp and QsQp equation in Kujung I Formation, East Java, Indonesia

Hydrocarbon-bearing reservoir shows attenuation on seismic section, but the use of attenuation in hydrocarbon exploration is less popular than other attributes. This is due to the sophisticated and advanced technology required to measure attenuation. Meanwhile, some studies were designed to estimate attenuation by formulating rock quality factor equations from a wire-line log, although others run on sandstone samples. Therefore, this study aims to estimate rock quality factors in carbonate rock of Kujung Formation using three different methods, discriminate hydrocarbon-bearing reservoir, and identifying the impact of carbonate facies. The results showed the P-wave quality factor method is sensitive to discriminate high gas saturation on facies A. Meanwhile, the QsQp ratio is sensitive to discriminate shale and carbonate. The SQp and SQs methods are sensitive to discriminate hydrocarbon-bearing reservoirs and less affected by carbonate facies. The novelty of this is to estimate the rock quality factor from various methods and identify the impact of facies in hydrocarbon identification, especially for carbonate reservoirs in Northeast Java Basin. Therefore, a new understanding of facies impact on rock quality factor contributes to choosing the best methods in discriminating pore-filling fluid identification.

Total Organic Carbon (TOC) Value Prediction in Source Rock Potential at North East Java Basin, Indonesia

This research aims to determine the potential of the source rock in the Kujung and Cepu Formations in the North East Java Basin, using Total Organic Carbon (TOC). TOC is calculated using the Passey method. The Passey method is used by overlaying the sonic log and the resistivity log and determining the baseline to get the separation of Δlog resistivity, which is then used to predict the TOC log by including the LOM (Level of Organic Maturity) variable obtained from the data of vitrinite reflectance. After the TOC log value is obtained, a correlation is made with the TOC core value. The prediction result of TOC log in a PM-1 well is 2.16%, which means it has excellent quality. The prediction of TOC log in a PM-2 well is worth 2.68%, which means it has excellent quality. The correlation value between the TOC log and the TOC core of the PM-1 well is 0.67, which means the correlation is strong. In PM-2 well, the correlation between the TOC log and TOC core is 0.92, which means that the correlation is robust.

Seismic wave attenuation in carbonate rock and its implication to hydrocarbon-bearing reservoir identification, East Java, Indonesia

The heterogeneity of carbonate rock properties triggers propagated seismic wave to get some attenuations. This mechanism allows that attenuation can be applied in hydrocarbon exploration to identify lithology, porosity, fluid content and fracture identification. Unfortunately, to measure the degree of attenuation, the sophisticated tools and advanced processing technology are required. Thus, some methods were formulated to estimate attenuation. This study is aimed to estimate and compare attenuation from wireline log interpretation by using four different methods. The study is also supported by a series of exploration wells penetrating Kujung I Formation in northwestern edge of North East Java Basin, Indonesia. The result shows that only Qs from Zhang et al method is overestimate. P-wave quality factor of Klimentos and Zhang methods and scaled quality factor (SQp and SQs) method are sensitive to identify hydrocarbon. Furthermore, lithofacies also affects estimated rock quality factor. The novelty of study is to estimate and compare the attenuation from different method and review its result and application in hydrocarbon identification, especially for carbonate reservoir in North East Java basin, Indonesia. So that, a new understanding of attenuation characteristic in carbonate reservoir contributes to discriminate pore fluid identification in hydrocarbon exploration.

Ntegration of Petrophysical Analysis and Elastic Log Properties as an Input to Optimize the Development Wells Target in Unique Globigerina Limestone Gas Reservoir in Madura Strait

The Madura Strait PSC is located in the southern part of North East Java Basin with biogenic gas from Globigerina limestone Pliocene Mundu and Selorejo sequence as main target. At early stage of field development,understanding and knowledge about petrophysical and elastic properties of reservoir rock quality is required and very important. The petrophysical analysis provide properties such as clay volume, porosity, permeability, water saturation and mineral volume to separate reservoir and non-reservoir zone. The elastic rock properties such as acoustic impedance (AI), shear impedance (SI), velocity ratio (Vp/Vs), and Poisson’s ratio (σ) were generated to identify clay zone, gas and non-gas also focused to distinguish reservoir rock quality inside gas zone as an effective reservoir characterization. This research is done by utilize core data, quad combo logs from eleven wells and shear velocity from eight wells. The purpose of this research is to optimize development well target in Globigerina limestone gas reservoir, which have good to best reservoir rock quality shown with high porosity and permeability,low clay volume and water saturation. Results from this research indicate that lime mud matrix have significant impact in the reservoir rock quality. Meanwhile, gas saturation can affect the elastic properties due to this high gas saturation can decrease compressional velocity (Vp) value. Finally, the integration of petrophysical result and combination of elastic properties implementation can help in distinguishing the best reservoir rock quality, which contains gas that should be penetrated by the development wells