East Java Basin Research Articles

ONSHORE-OFFSHORE FACIES CHANGE OF NGRAYONG SANDSTONE IN MADURA AREAINDONESIA

Ngrayong sandstone composes a siliciclastic reservoir that produces oil for more than a century in North East Java Basin of Indonesia. Clean sand facies makes the best reservoir in western part of the basin, onshore East Java Island. Meanwhile, sand quality decreases eastward to Madura Island. In Madura, rock gradually changes to be more calcareous and shaly, due to the change of depositional environment. In offshore of Madura, the depositional environment is still questionable. This study is aimed to reveal differences between onshore and offshore facies of Ngrayong sandstone in Madura as their distribution is not well known and oil potential of Madura Strait is not well identified. Study methods consisted of geological field work, well correlation, and petrophysical analysis from several well data. The results show that Ngrayong sandstone was deposited during Middle Miocene, composed by interbedding of thickly bedded sandstone and alternating thinly bedded sandstoneshale. The succession is commonly intercalated by mudstone and thinly bedded limestone. At Madura Island, Ngrayong sandstone overlies the Early-Middle Miocene Tawun Formation, which both represent the Megasequence (MS) 3 interval. Due to regional subsidence and transgression during Late Miocene, Ngrayong sandstone and other equivalent rocks were overlain by monotonous mudstone and calcareous sandstone of Wonocolo Formation. The Ngrayong sandstone is evenly distributed in whole surface area of Madura Island and it spreads further 25-50 Km to the south and 100-125 Km to eastern part of offshore Madura Strait. Sandstone distribution is roughly depleted from the gross thickness hundreds of meters in northern part to only few centimeters in southeast part of study area. The facies changes to be more calcareous to the east, while the southward facies is shaly due to a deeper depositional environment. Despite of facies changing into shales or carbonate facies, Ngrayong sandstone potential in offshore Madura Strait needs to be considered as upside potential due to its distribution is wider than initial estimation, and its petrology and petrophysic data support it as a clastic reservoir.

Application of flow zone indicator and Leverett J-function to characterise carbonate reservoir and calculate precise water saturation in the Kujung formation, North East Java Basin

Application of flow zone indicator and Leverett J-function to characterise carbonate reservoir and calculate precise water saturation in the Kujung formation, North East Java Basin

Paleofacies of Eocene Lower Ngimbang Source Rocks in Cepu Area, East Java Basin Based on Biomarkers and Carbon-13 Isotopes

Paleofacies of Eocene Lower Ngimbang Source Rocks in Cepu Area, East Java Basin Based on Biomarkers and Carbon-13 Isotopes

Velocity Model Analysis Based on Integrated Well and Seismic Data of East Java Basin

Time to depth conversion is an important processof seismic interpretationtoidentify hydrocarbonprospectivity. Main objectives of this research are to minimize the risk of error in geometry and time to depth conversion. Since it’s using a large amount of data and had been doing in the large scale of research areas, this research can be classified as a regional scale research. The research was focused on three horizons time interpretation: Top Kujung I, Top Ngimbang and Basement which located in the offshore and onshore areas of east Java basin. These three horizons was selected because they were assumed to be equivalent to the rock formation, which is it has always been the main objective of oil and gas exploration in the East Java Basin. As additional value, there was no previous works on velocity modeling for regional scale using geological parameters in East Java basin. Lithology and interval thickness were identified as geological factors that effected the velocity distribution in East Java Basin. Therefore, a three layer geological model was generated, which was defined by the type of lithology; carbonate (layer 1: Top Kujung I), shale (layer 2: Top Ngimbang) and Basement. A statistical method using three horizons is able to predict the velocity distribution on sparse well data in a regional scale. The average velocity range for Top Kujung I is 400 m/s - 6000 m/s, Top Ngimbang is 500 m/s - 8200 m/s and Basement is 600 m/s - 8000 m/s. Some velocity anomalies found in Madura sub-basin area, caused by geological factor which identified as thick shale deposit and high density values on shale. Result of velocity and depth modeling analysis can be used to define the volume range deterministically and to make geological models to prospect generation in details by geological concept.

Passive Seismic for Hydrocarbon Indicator : Between Expectation and Reality

In between 5 – 10 years, in our country, passive seismic method became more popular to finding hydrocarbon. Low price, nondestructive acquisition and easy to mobilization is the best reason for choose the method. But in the other part, some people are pessimistically to deal with the result. Instrument specification, data condition and processing methods is several points which influence characteristic and interpretation passive seismic result. In 2010 one prospect in East Java Basin has been measurement constist of 112 objective points and several calibration points. Data measurement results indicate a positive response. Furthermore, in 2013 exploration drliing conducted on the prospect. Drill steam test showes 22 MMCFD in objective zone, upper – late oligocene. In 2015, remeasurement taken in objective area and show consistent responses with previous measurement. Passive seismic is unique method, sometimes will have difference results on dry, gas and oil area, in field production and also temporary suspend area with hidrocarbon content.

Identification of Detrital Carbonate in East Cepu High

East Cepu High is a part of horst – graben series which formed by extensional tectonic processes during Paleogene in North East Java Basin. Due to excellent paleogeography position, the carbonate build-up was growth very well and as the main reservoir in East Cepu High. Sea level change have important factor to provide variation of facies in each carbonate buildup, one of emerging facies is detrital carbonate. Detrital carbonate indicated by onlap horizon featured with carbonate build up body. Based on paleogeography, fluctuation of sea level change and sediment source, detrital carbonate formed in leeward area in lowstand or highstand phases. Distinguish between detrital carbonate facies with other facies, advanced seismic processing performed by using continuous wavelet transform (CWT) and seismic inversion. CWT is one method of spectral decomposition used to find the frequency that represent a facies. The result from seismic inversion will support the interpretation for facies distribution. As the result, seismic data which have interval frequency 10 – 45 Hz and Acoustic Impedance (AI) value above 35000 (from cross plot between acoustic impedance and gamma ray) can be interpreted as detrital carbonate. Based on seismic interpretation, detrital carbonate facies distributed along leeward area with geometrical spreading. The lateral facies change from detrital carbonate to shale was identified which causing this facies become potential as hydrocarbon reservoir with stratigraphic trap. Based on the earlier studies, North East Java Basin have a strong hydrocarbon migration to fill the reservoir, therefore the detrital carbonate have high chance to be a new hydrocarbon prospect in this area.

New Prespective Paleogeography of East Java Basin; Implicationrespond to Oil and Gas Eksploration at Kujung Formation Carbonate Reservoar

Paleogeography is one of critical points that always less considered by explorationist in the world. Almost all of the consideration is focused on trapping mechanism. Paleogeography is guidance in understanding both of physical and chemical of rock characteristic which will correlate with its depositional environment. Integration of various geological and geophysical data such as; tectonic, structural geology, stratigraphy, lithology, and biostratigraphy will lead us to a better understanding of rock characteristics. Six paleogeographic interpretations was made consist of; Early Tertiary (P5-56-55 ma), Middle Eocene (P14-41 ma), Late Oiligocene (P22-25.5 ma), Early Miocene (N7-16.5 ma), Middle Miocene (N9-14.5 ma), and Pleistocene (NN19-1.5 ma). That six paleogeographic interpretations are assumed represent the paleogeographic evolution of East Java Basin time after time. In Middle Eocene time, it would be more than hundred possibilities regarding the location where the formation deposited. This would be controlled by the existence of some local structural paleohighs and horsts which oriented NW-SE followed by their own sedimentary transportation path. With assumption that hydrocarbon generation was occurred in 15 Ma and the depth of maturation window lies on about 2,500 m depth. Therefore, the possibility of source rock maturation is high, due to almost of the clastics sediment of Ngimbang deposited into the series of grabens. The Kujung reef types simplified defines and categorize into; 1) Patch Reef 2) Berrier Reef 3) Pinnacle Reef Over Isolated Reef. Kujung Carbonates were deposited in Early Miocene when regional transgression occurred. The depositional environments were dominated by shallow marine littoral-sublittoral. Generally, the reservoir quality of this Kujung Carbonate shows fair to good quality, in range7-32% porosity, and 1-1400 mD permeability (internal SKK Migas data).

Lateral Reservoir Drainage in some Indonesia’s Sedimentary Basins and Its Implication to Hydrodynamic Trapping

DOI: 10.17014/ijog.5.1.65-80Lateral reservoir drainage is a hydrodynamic flow type driven by the difference in overpressure. It can lead to hydrodynamically tilted hydrocarbon water contact, and open an opportunity of finding oil and gas in places where previously are not considered as potential traps. In this paper, some examples of the presence of hydrodynamic traps in Indonesia’s sedimentary basin are discussed. Tilted hydrocarbon water contacts are present in some fields in the Lower Kutai Basin, and our interpretation is that regional lateral reservoir drainage is present in this basin and is responsible for the tilted contacts. It is also interpreted that lateral reservoir drainage leading to tilted hydrocarbon water contacts may be present at the Arun Field - North Sumatra Basin, Vorwata Field - Bintuni Basin, and BD Field - offshore East Java Basin. As most Indonesia’s sedimentary basins are overpressured, the presence of lateral reservoir drainage driven by overpressure difference in the same stratigraphic unit is very plausible to occur, opening the opportunity for hydrodynamically tilted hydrocarbon water contact to be present.

Paleofacies of Eocene Lower Ngimbang Source Rocks in Cepu Area, East Java Basin based on Biomarkers and Carbon-13 Isotopes

The Eocene Lower Ngimbang carbonaceous shales are geochemically proven hydrocarbon source rocks in the East Java Basin. Sedimentary facies of source rock is important for the source evaluation that can be examined by using biomarkers and carbon-13 isotopes data. Furthermore, paleogeography of the source sedimentation can be reconstructed. The case study was conducted on rock samples of Lower Ngimbang from two exploration wells drilled in Cepu area, East Java Basin, Kujung-1 and Ngimbang-1 wells. The biomarker data include GC and GC-MS data of normal alkanes, isoprenoids, triterpanes, and steranes. Carbon-13 isotope data include saturate and aromatic fractions. Various crossplots of biomarker and carbon-13 isotope data of the Lower Ngimbang source samples from the two wells show that the source facies of Lower Ngimbang shales changed from transitional/deltaic setting at Kujung-1 well location to marginal marine setting at Ngimbang-1 well location. This reveals that the Eocene paleogeography of the Cepu area was composed of land area in the north and marine setting to the south. Biomarkers and carbon-13 isotopes are powerful data for reconstructing paleogeography and paleofacies. In the absence of fossils in some sedimentary facies, these geochemical data are good alternatives.

The Influence of Fault and Stress Contributed On Overpressure Mechanism For Neogen Formation (Mundu, Wonocolo, Ngrayong) East Java Basin, Indonesia

Rembang Madura Kangean Sakala (RMKS) fault zone and W-E structures of Kendeng Zone are the main structural elements in back arc basin, East Java, Indonesia. There are many perspectives about the overpressure zone at the basin. This research focus on the overpressure zone that related with formation and tectonic evolution. The study infer that high overpressure is explained by regional and local mechanisms. The results of analysis of log derived porosities at Karang Mudi-1 (KM-1) well indicate that high overpressure and overpressure was Neogen Formation (Mundu, Wonocolo, Ngrayong). Pore pressure prediction at KM-1 exerted Eaton’s method. There are two overpressure zones at depth 2.680 – 4.900 fTVD (B Zone) and 5.600 – 8.400 fTVD (D Zone). High overpressure D Zone are regionally caused by flexural structure (anticline and fracture) from transpression setting (West – East RMKS). High overpressure in KM-1 is transpression setting early which the overpressure follow the pop-up boundary. Area of high overpressure always related with fault thrust. Static mechanism is possible in the present day interplate stress field. Present the maximum horizontal stress was NEE – SWW. Local mechanisms occurs illitization at D zone from depth 6.800 – 8.400 fTVD. D Zone is unloading mechanism (illitization and lateral transfer open fracture).

Facies Development of Carbonate Rock and System Tract Influence Based on Fullbore Formation Microimager (FMI) and Well Log Analysis on Carbonate Reservoir Tuban Formation, North East Java Basin

The North East Java Basin is known to be one of the basins that consist of Miocene carbonate rocks, like the reef carbonate of Tuban Formation. It has the potential hydrocarbons that can be explored. Therefore, the FMI log analysis is very important to identify carbonate rocks of Tuban Formation to know facies and characteristics of that carbonate rocks. The method used descriptive and analysis process of FMI and Gamma Ray log to determine facies of the carbonate rock and the system tract. Based on the result of FMI log analysis, there are variations lithofasies include mudstone, wackestone, packstone, grainstone, floatstone, rudstone and claystone. A collection of rock associations can interpret the reef facies. It involves back reef facies, reef core facies, and fore reef facies. The changes of lithofasies and reef facies are caused by sea level fluctuations and subsidence resulting in the system tract. The system tracts generated in the research area include transgressive and highstand system tract.

Can Payment forEnvironmental Services Promote Socioeconomic Development in Indonesia? An Empirical Analysis

In this research paper, I attempt to investigate the impact of Payment for Environmental Services (PES) on the socioeconomic status of local livelihood. The socioeconomic status that I examine is total household expenditure to capture the nutritional well-being of people who live in an area where the PES project is implemented. Not only total household spending, but I also examine the poverty status of each household in the area of PES project. The area of PES project that I analyze are villages in the vicinity of Meru Betiri National Park, East Java and Segara Basin, Lombok. I use Indonesian Social Economy National Surveys (SUSENAS) by Central Bureau of Statistics Republic of Indonesia (BPS), before and following the implementation of two PES implementation projects to examine the effect of PES in each location and both locations combined. To discuss the impact of PES, I use Difference-in-Difference method and also incorporate Propensity Score Matching to have a better result. I find that statistically, PES project has little significant impact on the socioeconomic status of local livelihood. However, if I look at the magnitude of the coefficient of the effect, the evidence show that PES has affected local livelihood positively. Furthermore, the effect of PES project differs between each location. Keywords: Environmental Services, Socioeconomics, Propensity Score Matching JEL Classification: O13, P28, R11

ANALISIS MEKANISME TERJADINYA TEKANAN-LUAP DAN PREDIKSI TEKANAN PORI PADA LAPANGAN BD, CEKUNGAN JAWA TIMUR

The East Java Basin is one of the sedimentary basins with proven petroleum system and very prospective as an exploration target. However, drilling in this basin is a risky operation because of the presence of overpressure, which is shown by kick and lost during exploration wells drilling in BD Field as an example. Drilling problems and drilling risks can be reduced by doing overpressure study, including overpressure generating mechanism, pore pressure prediction, and estimation top of overpressure. The temperature in this field can reach 80°C at the depth around 1500 m SSTVD. However, the Dutta-Katahara crossplot does not indicate any diagenesis of smectite to illite. It is also confimed by XRD data in one of the well, which shown domination of kaolinitic clay mineral. Based on the vitrinite reflectance data, there is no transformation of kerogene to hydrocarbon in this field. The burial history plot shows rapid sedimentation with the rate of 1723 m/million years. Based on those criterias, the main overpressure generating mechanism is interpreted to be loading mechanism. High sedimentation rate is related to the peak inversion in Plio-Pleistocene time, providing abundant of sediment supply into the basin. Pore pressure in this field can be estimated by using sonic data with Eaton’s method. Both direct and indirect pressure measurements, combine with drilling data are used to support this estimation. Based on well data, top of overpressure in this field is located at the depth around 1500-1600 m SSTVD. The top of overpressure is located within Lidah Formation.

Study of gamma spectrometry laboratory measurement in various sediment and vulcanic rocks

Gamma-ray spectroscopy is the quantitative study of the energy spectra of gamma-ray sources. This method is powerful to characterize some minerals, especially to differentiate rocks which contains among Potassium, Uranium, dan Thorium. Rock contains radioactive material which produce gamma rays in various energies and intensities. When these emissions are detected and analyzed with a spectroscopy system, a gamma-ray energy spectrum can be used as indicator for mineral content of rock. Some sediment and vulcanic rock have been collected from East Java Basin. Samples are ranging from Andesite vulcanics, Tuff, Shale, various vulcanic clay and Alluvial clay. We present some unique characteristics of gamma spectrometry in various sedimentar and vulcanic rocks of East Java Basins. Details contents of gamma ray spectra give enrichments to characterize sample of sediment and vulcanic in East Java. Weathered vulcanic clay has lower counting rate of gamma ray than alluvial deltaic clay counting rate. Therefore, gamma spectrometrometry can be used as tool for characterizing the enviroment of clay whether vulcanic or alluvial-deltaic. This phenomena indicates that gamma ray spectrometry can be as tool for characterizing the clay whether it tends to Smectite or Illite

Source rock formation evaluation using TOC & Ro log model based on well-log data procesing: study case of Ngimbang formation, North East Java basin

Ngimbang Formation is known as one major source of hydrocarbon supply in the North Eastern Java Basin. Aged Mid-Eocene, Ngimbang is dominated by sedimentary clastic rocks mostly shale, shaly sandstone, and thick layers of limestone (CD Limestone), with thin layers of coal. Although, laboratory analyses show the Ngimbang Formation to be a relatively rich source-rocks, such data are typically too limited to regionally quantify the distribution of organic matter. To adequately sample the formation both horizontally and vertically on a basin–wide scale, large number of costly and time consuming laboratory analyses would be required. Such analyses are prone to errors from a number of sources, and core data are frequently not available at key locations. In this paper, the authors established four TOC (Total Organic Carbon Content) logging calculation models; Passey, Schmoker-Hester, Meyer-Nederloff, and Decker/Density Model by considering the geology of Ngimbang. Well data along with its available core data was used to determine the most suitable model to be applied in the well AFA-1, as well as to compare the accuracy of these TOC model values. The result shows good correlation using Decker (TOC) Model and Mallick-Raju (Ro- Vitrinite Reflectance) Model. Two source rocks potential zones were detected by these log models.

Assessing the possibility of Enhanced Geothermal System in western Indonesia

Enhanced Geothermal System (EGS) is one of geothermal system where abnormally hot masses of low permeability rocks are found at depth. Most of EGS are related to thick and deep sedimentary basin with plutons. EGS focused on drilling at hot crystalline rock and create fractured reservoirs. Indonesia has a complex tectonic setting. There were more than 86 basins in Indonesia. Most of sedimentary basins in Indonesia were tectonically stressed. Moreover, the tectonic setting which is generally a part of the Active Continental Margin also allows the formation of plutons that can be act as hot dry rock. Several hot springs or other geothermal manifestation were found in several areas within the basin and its surrounding area. This study compares structural controls and models in different tectonic setting of main basin in Western Indonesia to get the most suitable potential reservoir for EGS. The characteristic of the South Sumatra Basin, North Sumatra Basin, East Java Basin and Tarakan Basin were evaluated and compared based on its geology and geophysics characteristic. As the result, South Sumatra Basin is the first rank for EGS suitability in Western Indonesia.

A review on paleoenvironment suitability for hominid fossils and other early vertebrate faunas: a case from Pucangan and Kabuh Formations, Central and East Java, Indonesia

Abstract The northern part of the East Java Basin has become a focus of research by earth scientists, among others, because of the existence of hominid fossils and remains of other vertebrate taxa within the Quaternary sedimentary sequence. Fossil-bearing layers are found in the Kendeng Zone, mostly within the well-known Pucangan and Kabuh Formations, which are distributed from Central to East Java. However, not all formations contain vertebrate fossils as well as hominid elements. It is important to consider what factors may have influenced the concentration of vertebrate fossils in those formations. In this study, we describe sedimentary facies at three key field locations: Sangiran, Ngawi, and Mojokerto. Our study indicates that vertebrate remains and hominid fossils mainly accumulated in continental sediments associated with lacustrine and fluvial systems. In this regard, Sangiran and Ngawi B offer the greatest prospect for yielding hominid remains, owing to their unique paleoenvironmental and paleogeographical settings as a highland during the Early–Middle Pleistocene period. Certain parts of the Kabuh Formation in the Mojokerto region also hold high potential, especially those displaying evidence of continental deposition.

DEPOSITIONAL MODEL OF NGRAYONG FORMATION IN MADURA AREA, NORTH EAST JAVA BASIN, INDONESIA

The early Middle Miocene Ngrayong Formation, an important reservoir of North East Java Basin, is well exposed in the central anticlinal part of Madura Island. The purpose of current study is to classify the depositional environments of the study area based on the characteristics and geometry of sedimentary facies. In the Madura island, the thicker clastics and deeper carbonates of Ngimbang Formation and Kujung Formation of Late Oligocene-Early Miocene deposited in the northeast-southwest asymmetrical half grabens. After the deposition of Kujung Formation, the basin morphology developed nearly eastwest trending shelf edge and the deposition of Tuban Formation began. The fine grained complex of Tuban Formation was followed by the Ngrayong Sandstones deposition. The depositional model of Ngrayong Formation is being producing of wide variety of depositional environments. Large scale cross-bedded sandstones and bioturbated massive sandstones with thin to medium bedded argillaceous limestone that outcrop in the northern part of the study area are deposited in costal environment. The heterolithic sandstone with planar and trough cross-lamination, fine grained sandstone with interlaminated structure and bioclastic carbonate exposed in the central part of the study area are deposited in upper shallow marine area. Dark grey siltstones and mudstones deposited in lower shallow marine area are well exposed in southern part of the study area. In conclusion, Ngrayong Formation in Madura area is developed in three depositional units which are coastal, upper shallow marine and lower shallow marine.

Kondisi Paelosalinitas pada Miosen Akhir–Pleistosen di Cekungan Jawa Timur Utara, Indonesia, Berdasarkan Perubahan Populasi Nanoplankton

Abstract Quantitative biostratigraphy analysis by observing Sphenolithus abies and Helicosphaera carteri could predict paleosalinity changes at a sedimentary basin diachronically. Hyposaline conditions can be investigated from the abundance changes of Helicosphaera carteri and Calcidiscus leptoporus counts. Along this line, the increasing number of Sphenolithus abies demonstrates particular states of normal saline. Paleosalinity changes in the North East Java Basin, from Late Miocene to Pleistocene were identified from the top of Wonocolo Formation to bottom of Ledok Formation. Paleosalinity along this episode was interpreted as hyposaline condition. While at the top of Ledok Formation to Mundu Formation; paleosalinity had changed to normal saline. Furthermore, environmental conditions return to hyposaline when Selorejo Formation sediment was deposited. And during the deposition of Lidah Formation, deposition environment had returned to the normal saline.

Indonesian Fieldwide Application of Intelligent-Well Technology - A Case History

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 21063, ’Indonesian Operator's First Fieldwide Application of Intelligent-Well Technology - A Case History,’ by Kim Sam Youl, and Harkomoyo, SPE, Kodeco Energy Company and Doug Finley, SPE, Halliburton, prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed. A fieldwide application of intelligent-well-completion technology was used in Indonesia to commingle “free energy” from an overlying gas cap to support production from underlying oil reservoirs that typically have a high water cut. Previously, wells in this offshore field were developed with conventional gas lift completions that used gas supplied from outside the platform. The application of an “auto-gas-lift” (AGL) concept, an intelligent-well technology, eliminated the capital equipment associated with conventional gas lift completions along with the conventional downhole gas lift equipment. Introduction The KE-38 field is in the East Java basin, approximately 30 miles off the northern coast of Madura Island, Indonesia (Fig. 1). Water depth averages approximately 190 ft in this block. The oil columns are between 60 and 300 ft thick, with a 500-ft-thick gas cap (on average) and an underlying water zone. True vertical depth of the gas/oil contact is 4,500 to 5,000 ft subsea. Porosity of the oil rim ranges from 18 to 26%, and permeability ranges from 20 to 100 md. The reservoir is normally pressured, and productivity ranges from 5 to 20 bbl/(psi-D). Maximum bottomhole pressure and temperature are 2,200 psi and 195°F, respectively. The oil is a slightly waxy, 35°API crude. Given that the reservoir fluid is nearly saturated, initial production from the wells was with natural flow. However, because the flowline pressure is high (approximately 900 psi), these wells would require artificial lift during the initial stage of operation to begin flow and maintain the gas/liquid ratio to optimize the produced-oil rate. Conventional gas lift completions have a setting-depth limitation relating to the gas lift mandrel. The maximum setting angle is less than 60°. However, an AGL interval-control valve (ICV) is capable of being set in any trajectory angle and can be set at the deepest point in the wellbore to optimize oil production. The AGL completion enables altering the flow characteristics of a zone without mechanical intervention.