North East Java Basin Research Articles

GEOLOGICAL INTERPRETATION OF NORTH MADURA OFFSHORE SEDIMENTARY BASIN BASED ON GRAVITY DATA ANALYSIS

The area of north Madura offshore is one of the sedimentary basins within the North East Java Basin which has interesting paleogeographical developments. These developments are the result of various sedimentation processes and changes in the depositional environments. The purpose of this study is to identify subsurface geological structures, delineate sedimentary sub-basins, and estimate sediment thickness. For that, we do spectrum analysis, optimum upward continuation filtering, spectral decomposition analysis, 2D forward modeling and 3D inversion of gravity data. The results of the spectral analysis show that the average thickness of sedimentary rocks in the study area is around 3.788 km. From the gravity data analysis, 10 sedimentary sub-basins were delineated, indicating structural patterns of basement high, grabens, and faults. 2D and 3D modeling revealed four layers of stratigraphy, in order from youngest to oldest are Tertiary-Neogene sedimentary rocks with a density value of 2.1 gr/cc, the Tertiary-Neogene sedimentary rocks with a density of 2.3 gr/cc, the Tertiary - Paleogene sedimentary rocks with a density of 2.45 gr/cc, and the basement layer identified as volcanic igneous rock with a density of 2.67 gr/cc.

Oil volumetric calculations of Kujung Formation in the North East Java Basin based on 3D static modelling using geostatistical approach and additional control variable

Carbonate rock is known as the leading oil and gas reservoir such as Kujung Formation in the North East Java Basin which has been proven to produce fossil energy since 2002. The extended time of oil and gas production needs to be reconsidered by investigating reservoir conditions. The 3D static modelling is constructed by integrating seismic, well log, and geological data using the geostatistical approach to delineate the petrophysical properties which can represent the reservoir heterogeneity. Oil and gas volumetric are calculated by two different techniques. First, the Sequential Gaussian Simulation (SGS) algorithm is used to distribute petrophysical properties, in particular porosity and water saturation with seismic and well log as controlling data. Similar to SGS algorithm, the other method involves AI Cube in co-kriging operation as a secondary variable for generating the porosity ratio. The oil and gas volume estimation using 3D static modelling has been done by integrating co-kriging operation and SGS algorithm establishes higher volumetric value than calculation merely involve SGS algorithm. The higher volumetric value from the combination method is more reliable due to the calculation having various variables that influence the result. The outcome of this research is perchance to beused as field development reference.

Sedimentation Rate During Miocene to Pleistocene Related with Nannofossil Biostratigraphy, in Banyuurip, Kedewan, Rembang Zone, East Java Basin, Indonesia

The researched area is located in Rembang Zone, North East Java Basin. The Rembang Zone is one of the largest basins in Indonesia. In this area, there are many oil wells that today are still actively producing. The research concerning the content of microfossils in marine sedimentary outcrops is needed to determine the rate of sedimentation in a basin. The method is basically based on the result of stratigraphic measurements of two sections with a distance of 2,743.7 m. Sedimentation rate is the average thickness ratio to the average time interval. The sections have a good outcrop and a continuous stratigraphic sequence from Miocene (Wonocolo, Ledok, and Mundu Formations) to Pleistocene (Lidah Formation). Samples taken in the section consisted of fourty-one samples of marls and shales. The results of the analysis show eighteen genera with fifty-seven species of nannoplankton. While the resulting biostratigraphic zone can be arranged into eleven zones consisted of two partial, one range and eight interval zones. The development of sedimentation rate (RoS) of studied area consists of ten periods, those are (1) CNM15 Zone/ Late Miocene of Ledok Formation at a depth of 427.8 - 322.4 m, and has a sedimentation rate (RoS) of 11.46 cm/ ky, (2) CNM16-CNM20 Zone/Late Miocene to Early Pliocene, Ledok Formation at a depth of 322.4 - 279.3 m and has a RoS of 1.54 cm/ky, (3) Mundu Formation is CNPL2 Zone/Early Pliocene at a depth of 279.3 - 223 m and has a RoS of 5.41 cm/ky, (4) CNPL3 (Early Pliocene) Zone at a depth of 223 - 148.4 m and has a RoS of 33.91 cm/ky, (5) CNPL4 Zone (Middle Pliocene) at a depth of 148.4 - 82.7 m and has a RoS of 5.09 cm/ky. (6) Zone of CNPL5 (Middle-Late Pliocene) at a depth of 82.70 - 53.1 m and has a RoS of 21.14 cm/ky, (7) CNPL6 Zone/Late Pliocene at a depth of 53.1 - 52.0 m and has a RoS of 0.24 cm/ky, 8). CNPL7 Zone/Late Pliocene to Early Pleistocene at a depth of 52.0 - 33.8 m and has a RoS 8.27 cm/ky, (9). CNPL8 Zone (Early Pleistocene) at a depth of 33.8 - 26.4 m and has a RoS of 1.14 cm/ky, (10) CNPL9 Zone? (Early Pleistocene) at a depth of 26.4 - 12.5 m and has a RoS of 1.7 cm/ky. The relatively faster sedimentation rate of the CNPL3 is due to the faster subsidence and maximum sediment supply. During the development of sedimentation rate, there are two unconformities, namely (1) after the CNM20 Zone resulting in a sedimentation interval during CNPL1 and (2) after CNPL6 (Late Pliocene). Keywords: sedimentation rate, biostratigraphy, Rembang Zone, Banyuurip

Analysis of Unconventional Oil and Gas Reservoirs using Well Logging, Geochemical and Seismic Data

Since conventional oil and gas is under a depletion phase, unconventional oil, and gas have become prime candidates for current and future oil and gas production. Based on this, investment and research have increased significantly related to unconventional oil and gas exploitation, especially in the North East Java Basin, one of the sedimentary basins producing oil and gas. The research was conducted in the form of well-logging, geochemical, and seismic data analysis to determine the quality and quantity of oil and gas reservoirs. The thickness and TOC value of the reservoir were determined using well-logging data using the Passey method, resulting in a thickness ranging from 900-954 ft and an average TOC value of 3.87 Wt% in the Kujung III Formation. Based on geochemical data analysis, the reservoir has type II kerogen with an immature-early mature maturity level (Ro and Tmax). Meanwhile, based on seismic data, the reservoir thickens to the northwest, ranging from 500-600 m. Unconventional oil and gas reservoirs in the research area have the potential to be developed because they meet several criteria, such as being rich in organic material and thick, even though the maturity level is still in the immature phase. It is estimated that deeper areas will produce different levels of maturity as pressure and temperature increase.

Surface Geology Analysis on the Relationship between Fault Creep and Overpressure in Grobogan, Central Java, Indonesia

The Grobogan Regency is a significant location for oil and gas exploration due to its proximity to active oil and gas fields. Geologically, this area is intersected by the Kendeng thrust fault and exhibits several surface manifestations of mud volcanoes near the fault. However, there have been limited studies examining the activity of the Kendeng thrust fault and its relationship to overpressure and earthquakes, which could affect oil and gas exploration and natural disaster mitigation in the region. This paper focuses on utilizing surface geological mapping data and Interferometric Synthetic Aperture Radar (InSAR) data to analyze the relationship between fault creep and overpressure manifestations in Grobogan, Central Java. While continuous research on fault creep has been conducted since the 1960s on the San Andreas fault in the United States, there has been a lack of continuous research on onshore fault creep in the Northeast Java Basin or Kendeng Basin, particularly in the Grobogan area. This region, known for its abundance of active mud volcano manifestations, is predominantly characterized by marl and clay lithology. It represents a warm basin environment that is prone to overpressure and ideal for fault creep occurrences.To investigate further, fluid, gas, and mud samples were collected from the mud volcanoes, along with rock samples from the surrounding area, for comprehensive laboratory analysis. The integration of these sample analyses aimed to determine the correlation between the activity of the Kendeng thrust fault creep and the subsurface overpressure conditions. While this study observed several indications of creeping in the vicinity of InSAR anomalies, the exact location of the creeping fault plane could not be definitively determined. The Kendeng thrust fault exhibits the three main factors necessary for initiating fault creeping. The fault segment’s extremely slow creeping may be linked to the activity of the mud volcanoes, as indicated by the results of fluid, gas, and rock sample analysis. The findings of this research hold potential for informing the development of oil and gas fields, as well as enhancing the mitigation of natural disasters associated with oil and gas exploration and earthquakes in the region.

Trace Fossils Of The Selorejo Formation, Rembang Zone, North East Java Basin, Indonesia

The Rembang Zone of the North East Java Basin is a zone that develops as a petroleum system and is one of the areas with Indonesia’s largest oil reserves. One of the lithologies in the Rembang Zone is a sedimentary rock carbonated as a marker of marine sediments. The outcrop is continuous and rich in trace fossils, especially in the Ledok and Selorejo Formations. The existence of trace fossil outcrops is crucial for the learning process of earth science, biology, and other sciences, but recently these outcrops have been closed and have become damaged. Their numbers are decreasing due to community mining activities, so unique research on trace fossils in the Rembang Zone must be done immediately. This research aims to discover the variation of trace fossils found in the Selorejo Formation. The methods used are field mapping, measured stratigraphic measurements, rock sampling, and laboratory analysis (sedimentology, petrography, and paleontology). The research shows trace fossils in Planolites, Helminthopsis, Thalassinoides, Conichnus, Chondrites, Macaronichnus, Bergauria, Ophiomorpha, Skolithos, Terebellina, Palaeophycus, and Asterosoma.

The implementation of well logging method, geochemical analysis, and seismic method to determine source rock potentials at field “X”, Northeast Java Basin

East Java is an area with the potential to produce oil and gas. Oil and gas are hydrocarbon mix produced from the subsurface, sourced from matured organic materials, and migrated to be drilled to be produced into oil and gas. The methods to explore oil and gas are well logging and seismic methods. Combining both methods can obtain vertical and horizontal subsurface information. The study was performed by analyzing secondary data processing results of wells, seismic data, and ko chemistry data. Geochemical data were used to analyze source rock potentials in the study area. Source rock is rock containing organic materials to produce hydrocarbons. Therefore, this study aimed to determine source rock potentials. Using the three methods, it concludes that Field “X” as the study site in the northeast Java, can produce hydrocarbons on the northwest region of the study area because the source rock zone at Field “X” has a 3.87% TOC with type II kerogen. Although the source rock is immature, it can produce oil and gas.

Source Rock Characterization of the Eocene-Miocene, Central Deep, North East Java Basin

This study was conducted to obtain the characteristics of the source rock through organic geochemical analysis in Central Deep, NE Java Basin, in the field off the north coast of Madura. Three samples of Cassiopeia-1, Pollen-1, and Alpha-1 wells were analyzed using organic geochemical methods including Total Organic Carbon analysis, Maturity using vitrinite reflectance, Tmax, and Production Index data, and then analysis of the kerogen type, isoprenoid, sterane, and carbon isotope. Based on those data, an analysis was carried out to determine the origin of the material and the depositional environment. The rock samples in the three wells showed characteristics in TOC, maturity, kerogen type and source of organic material have a similarity. The source rock characteristics have a medium to a good category as source rock and tend to generate gas and a little oil from kerogen types II and III. This source rock is included in the category of immature to mature, deposited in delta until terrestrial depositional environment and contains sources terrestrial and marine organic material.Keywords: Madura, North East Java Basin, organic geochemical, source rock.

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.

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

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.

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.

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.

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.