Kujung Formation Research Articles

Identification of Shale Layer in Offshore Field of North East Java Basin for Non-Conventional Oil and Gas Exploration

<p>Non-conventional hydrocarbon exploration is one way to develop shale potential to increase oil and gas reserves in Indonesia. Shale is a rock that is rich in organic material and is a target for non-conventional exploration, because it functions as a source and reservoir rock with a large shale volume and low permeability. Isopach maps can represent the thickness of shale layers and have the potential to become non-conventional exploration targets located in thick shale layers. Based on this background, this research will identify shale layers in the offshore fields of the North East Java Basin for non-conventional oil and gas exploration. The methods used are well logging and seismic methods. This research focuses on determining the location of shale layer depocenters based on isopach maps as a first step in localizing areas that will be targeted for the development of non-conventional hydrocarbon exploration. This research uses 29 2D seismic lines and 2 well data, namely NP-1 and NP-2 wells and the research target is the Kujung Formation and Ngimbang Formation in the offshore area of the North East Java Basin. The results obtained from the isopach map show that the depocenter location of the Kujung Formation is in the northwest direction with a shale thickness of 600-800 meters, while the Ngimbang Formation is in the east direction with a shale thickness of 1000-1300 meters. From the depocenter location, it can be seen that this location has a wealth of organic material so it has the potential to become a source rock and reservoir.</p>

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.

Petrophysical Analysis and Acoustic Impedance Inversion to Determine the Storage Target of Carbon Dioxide in Gundih Block, Central Java

A pilot project of Carbon Capture and Storage in Indonesia is being prepared in the Gundih field, Central Java. This project acquired Kujung formation as their target area. However, an alternative to that formation is being investigated with Kujung formation's data as a benchmark to determine the total capacity of storage in Gundih Block. To determine the other carbon dioxide storage target, several tests are needed, one of which is petrophysical analysis. The results of this analysis are porosity, permeability, and thickness of a reservoir. After determining the porosity cut off from the Well data, we use the acoustic impedance inversion approach to assess the spread of the reservoir laterally. In this paper, we estimated that the porosity ranges from 7-12% with an average permeability of 10 mD. After examining the lateral distribution of the reservoir through the inversion, we can roughly estimate the distribution of good porosity reservoir. With the same method and logs derived from Kujung formation, we estimate that the upside potential from Ngrayong formation has an average porosity of 30% and average permeability of 16 mD. which are good enough to become an area of interest. With these results, we conclude that determining the area of interest from other target formation through petrophysical analysis and acoustic impedance inversion is sufficient to determine reservoir areas in a formation, though further injection feasibility studies are needed to determine the feasibility of injection of CO2 in Ngrayong Formation.

Oligocene Palynological Zonation Scheme From East Java Sea

Systematic biostratigraphic analyses have been undertaken on the Oligocene clastic and carbonate Kujung Formation from the East Java Sea, North of Madura. The succession has been examined mainly using cutting samples in two wells, using a combination of foraminiferal, nannofossil and palynological analyses at regular spacing. Nannofossil analysis indicates that the Late Oligocene to basal Early Miocene succession is more or less complete, with zones NP24, NP25 and NN1 are all being well developed. In addition, the Early Oligocene is indentified by larger foraminifera indicating the Tc/ Td Letter Stage. Because the traditional palynological zonation of Morley (1978) does not work well in this area, the succession has been divided into broad assemblage zones, which appear to be controlled mainly by climate. These zones are OL-1, OL-2, OL-3, OL-4 and OL-5. Zone OL-1 is based essentially on the absence of seasonal climate and riparian elements, whilst zone OL-2 is characterized by the regular occurrence of seasonal climate elements, especially of Malvacipollis diversus. Zone OL-3 is indicated by common to abundant Dacrydium and Casuarina pollen, with a strong acme of dinoflagellate cysts dominated by Operculodinium spp. and Spiniferites spp., whereas zone OL-4 is marked by abundant Dacrydium and regular Casuarina pollen, but low representation of riparian elements. Finally, the youngest zone is OL-5 which is characterized by reduced Dacrydium and Casuarina pollen, and increased riparian elements. The above palynological zonation suggests climate change, which closely parallels the climate succession from West Java Sea (but with changes less pronounced). Therefore, this study provides a well dated Oligocene palynological zonation which can be applied across Java.

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.

Carbonate-shelf evolution during the Oligocene to early Miocene: insights from shelf architecture, lithofacies, and depositional models of the Kujung Formation, offshore East Java, Indonesia

ABSTRACTOligocene–Miocene carbonates are prolific hydrocarbon reservoirs in Southeast Asia. Extensive subsurface data for this stratigraphic section has become available through exploration and production activities. A carbonate shelf in the study area showed an evolution in shelf architecture and lithofacies during this period. Despite the economic importance, complexity, and data availability, there have been few published studies on a comprehensive description and interpretation of carbonate-shelf evolution in the region.We utilized data from nineteen wells and 1,300 km2 of 3D seismic data from offshore East Java to study the Oligocene–Miocene Kujung Formation. An average of 700 m stratigraphic sections from this formation were analyzed. This interval spans 13.5 million years (My) from the Rupelian, Chattian, through Aquitanian constrained by numerical ages from 87Sr/86Sr. The Kujung Formation is subdivided into the Rupelian–Chattian mixed-siliciclastic–carbonate shelf (MSCS) and the Aquitanian carbonate-buildups shelf (CBS) based on shelf architecture and lithofacies. The boundary between the MSCS and CBS is interpreted to be near the Oligocene–Miocene boundary at 23 Ma. Accumulation rates in the CBS are up to three times greater than that of the MSCS. We propose new depositional models for the Kujung Formation, which was used to discuss the dominant controls on shelf evolution.This study suggests that although climate played a role in dictating environmental conditions during the Oligocene–Miocene, the dominant factors controlling carbonate-shelf evolution in the study area appear to have been antecedent topography, routing of siliciclastic sediment, and patterns of sea-level fluctuation.

Depositional and diagenetic history of limestones and dolostones of the Oligo‐Miocene Kujung Formation in the Northeast Java Basin, Indonesia

AbstractLithological and geochemical features of platformal carbonates record the signatures of the global climates and the regional environmental settings and also reconstruct the diagenetic history and porosity evolution, which are essential to evaluate the potential of hydrocarbon reservoirs. This study investigates the platformal carbonates of the Oligo‐Miocene Krunji Formation of North East Java Basin, which are potentially significant hydrocarbon reservoirs. The carbonate sequence in a 283 m thick section at Kranji in East Java is subdivided into three lithological units: limestone unit 1, dolostone unit 2, and limestone unit 3, in ascending order. The strontium‐isotope ratios of well‐preserved calcite samples indicate the depositional period from Chattian (late Oligocene) to Burdigalian (early Miocene), which is consistent with ages of the foraminifer assemblages. Unit 1 consists of low‐porosity limestone, in which two horizons of subaerial exposure are recognized by the occurrence of red‐colored matrix and lower δ13C values. Unit 2 consists of dolomitic rock and exhibits coarse‐grained calcitic grains and cross‐stratified structure. Considering that this unit has been subject to dolomitization, the sediment of unit 2 was initially permeable and was likely deposited in a shoal setting. The overlying unit 3 of Aquitanian–Burdigalian age is characterized by a highly granular texture. High porosity and uniformly low δ13C and δ18O values indicate that Unit 3 was subjected to more intense meteoric diagenesis than the Chattian unit 1. This was likely a consequence of the Antarctic ice‐sheet expansion during the Oligocene/Miocene transition, which amplified sea level change. The unit 2 dolomite has high δ13C and δ18O values and a high 87Sr/86Sr ratio which resulted from the reflux of seawater into permeable the sediment body in middle‐late Miocene (Burdigalian Tortonian) following the deposition of unit 3. The porosity and permeability of the Kujung Formation were initially controlled by sedimentological processes, but largely modified by later diagenetic processes.

Seismic characteristics and strontium isotope ages of the Middle Miocene Ngrayong Formation in the Madura Strait Basin: Implications for the paleogeographic reconstruction of East Java

East Java, on the southeastern margin of the Sundaland Shelf, is an ideal and pilot location to study paleogeographic changes due to the interactions of the Eurasian and the Indian-Australia plates. Many studies have been conducted; however, some issues remain poorly understood, such as the initial compression stage and associated paleogeography of East Java. Here, we report newly acquired high-resolution seismic data and drilling wells in the area of the Madura Strait. We systematically reconstruct a three-dimensional model on the paleogeography of East Java in the Middle Miocene in combination with others’ results. Different depositional environments and characteristics of the related lithofacies observed on both sides of the Middle Miocene volcanic arc imply that weak subaerial and subaqueous volcanism existed in East Java. The extensive Ngrayong fining in the southward clastic sequences, located north of the mentioned volcanic arc, were deposited in a bathyal marine environment, which showed an oversteepening slope and basinal characteristics with outer neritic to bathyal facies within the present-day Kendeng Zone and Madura Strait area. This differs from the northern region of the present-day Rembang-Madura Inversion Zone and the northern offshore region of East Java, which were deposited in a transitional and neritic marine environment. We identified two new turbidite fans showing opposite source directions based on 3D seismic data within the Madura Strait area. Four controlling factors contributed to the formation of the Ngrayong turbidite fans, including the paleotopography of the underlying Kujung Formation, short-term intense regional tectonic events, high rates of sediment supply and occasional volcanic activity.

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

Acoustic Impedance Inversion To Identify Oligo-Miocene Carbonate Facies As Reservoir At Kangean Offshore Area

Model based inversion was applied to inversion process of 2D seismic data in Kangean Offshore Area. Integration acoustic impedance from wells and seismic data was expected showing physical property, facies separation and reservoir quality of carbonate rock, particularly in Kangean Offshore Area. Quantitative and qualitative analysis has been conducted on the inversion results to characterize the carbonate reservoir part of Kujung and correlate it to depositional facies type. Main target exploration in Kangean Offshore Area is Kujung Formation (Oligo-Miocene Carbonate). The type of reservoir in this area generate from reef growing on the platform. Carbonate rock is a reservoir which has various type and scale of porosity. Facies determination is required to to predict reservoir quality, because each facies has its own porosity value. Acoustic impedance is used to identify and characterize Kujung carbonate facies, also could be used to predict the distribution of porosity. Low acoustic impedance correlated with packstone facies that has acoustic impedance value below 7400 gr/cc*m/s. In other situation, high acoustic impedance characterized by wackestone facies above 7400 gr/cc*m/s. The interpretation result indicated that Kujung carbonate rock dominated by packstone facies in the upper part of build-up and it has ideal porosity for hydrocarbon reservoir.

Origin and age of carbonate clasts from the Lusi eruption, Java, Indonesia

Deep stratigraphic constrains below the Indonesian Lusi mud eruption are currently lacking due to the absence of deep wells and good quality seismic data. A collection of carbonate clasts has been sampled from the Lusi site, active since its birth in 2006. These specimens are part of a large variety of lithotypes erupted from the main crater. The carbonates analysed comprise scleractinian coral and bivalve shell fragments, probably shallow-water in origin, and clasts consisting of planktonic foraminifera-bearing mudstone, from pelagic deposits. Selected rocks were analysed using planktonic foraminifera and 87Sr/86Sr dating with the aim to constrain their age and to improve the understanding of the, so far unknown, sequence of limestone deposits inferred at this site.Based on biostratigraphy using planktonic foraminifera, one group of samples reveal to belong to the Planktonic Foraminifera Zone M5b, with an age comprised between 16.29 and 15.10 Ma (Miocene, Latest Burdighalian to Langhian). The Sr isotope-based ages of clasts analysed for 87Sr/86Sr cover a larger time window spanning from Pliocene (Zanclean and Piacenzian), Miocene (Messinian) down to Eocene (Priabonian). The Pliocene and Messinian ages are unreasonably young from what is known of the local geology and one sample provided an 87Sr/86Sr age that is ∼8 My younger compared to that obtained from the planktonic foraminifera assemblage occurring in that sample. The discrepancy suggests that this and the other unduly young samples have possibly been contaminated by geological materials with radiogenic Sr isotope composition. The minimum age of 37.18 Ma obtained by 87Sr/86Sr from a well-preserved oyster shell indicates that some of the clasts can be attributed to the deep seated Ngimbang Formation.The dating has been combined with the interpretation of seismic profiles to investigate the stratigraphy of inferred carbonates below Lusi and the PRG-1 well located some kilometres to the north east. PRG-1 borehole data are also integrated and discussed in this study.The obtained results reveal multiple implications: a) the Tuban and Kujung Formations are overlapping at Lusi site; b) the Lusi feeder conduit brecciated and mobilized to the surface carbonate lithologies buried as deep as possibly ∼3.8 km as well as even older and deeper seated lithotypes from the Ngimbang Formation; c) since the deeper carbonate samples erupted in 2006 belong to the typically not overpressured Kujung Formation, an additional overpressure generated from deeper units (Ngimbang Formation) would be required to force these fragments to surface.

Genesis and evolution of the Watukosek fault system in the Lusi area (East Java)

Detailed analysis of two-dimensional seismic lines acquired in the NE Java basin has been performed to unravel the subsurface geology of the region around the Lusi mud eruption. This work revealed the existence of a system consisting of a complex set of faults, here called the Watukosek fault system, forming triangular deformation zones converging at the top of the early Miocene Carbonates. This system continues downwards with vertical individual fault segments, often bordering the steep margins of the carbonate platforms. The analysis of data includes the interpretation of seismic lines, regional structural data inferred from basement gravity maps and present-day main direction of stress. Results suggest that a possible rotation of stress direction from N40E-S40W to N-S occurred during the post-Miocene history of the Java back arc tectonic evolution. The Watukosek fault system was first generated as a tensional lineament during the E-W sinistral transpressive strain, which involved the basement. In this phase, synthetic and antithetic Riedel faults formed, the former controlling the NW-SE orientation of the structural highs represented by Oligo-Miocene carbonate platforms. As a consequence of the rotation of the main principal stress direction to a N-S direction, the Watukosek fault and similar parallel lineaments became sinistral Riedel shears, developing intense triangular deformation zones. Based on the stratigraphic position of gentle anticlinal deformations with axis corresponding to the N40E-S40W oriented triangular deformation zones, the transpressive strain linked to the N-S main stress compression occurred likely in the Late Pliocene-Early Pleistocene.The detailed examination of a) stratigraphy at the wells BJP-1 and Porong-1 as well as b) the seismo-stratigraphic architecture of the entire succession in the study area, allowed a new subsurface interpretation and revision of the stratigraphic units below Lusi. The thick Early Miocene Tuban Formation is found sandwiched between the coheval Upper Kalibeng Formation and the Early Miocene Carbonate of the Kujung Formation, which in turn overlain the older Ngimbang Formation.

Carbonate facies and reservoir quality of the Kujung Formation in Kangean Island, East Java, Indonesia

Carbonate facies and reservoir quality of the Kujung Formation in Kangean Island, East Java, Indonesia

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.

Fluid transport properties and estimation of overpressure at the Lusi mud volcano, East Java Basin (Tanikawa et al., 2010)

1. IntroductionThe Lusi mud volcano in Sidoarjo, East Java, started to erupt onMay 29th 2006 and has displaced 13,000 families. Controversysurrounds whether the mud volcano was caused by drilling of theBanjar Panji 1 gas exploration well (Davies et al., 2007; Manga, 2007;Davies et al., 2008; Tingay et al., 2008) or due to the Yogyakartaearthquake that occurredat 05:54 amon the27th May2006(Mazziniet al., 2007; Sawolo et al., 2009). Constraining (a) pore pressure insedimentary strata prior to drilling; (b) changes in pore pressure thatoccurred due to drilling the Banjar Panji 1 well and the earthquake,and; (c) potential routes for fluid to the surface are critical forresolving this debate. These areas are tackled in the recent paper byTanikawaetal.(2010),whomodelporepressuredevelopmentduringburial of sedimentary strata at the site of the eruption and measurethe permeability and porosity of outcrop samples of formations ofequivalent age and lithology as those penetrated by the well. Fromthis analysis, they conclude that overpressure developed withinspecific successions, in particular the Upper Kalibeng clays and a deepcarbonate formation. They go on to argue that the overpressure madethe clay-rich unit susceptible to liquefaction as a result of cyclicdeformation duringtheYogyakartaearthquake,and thatthisinitiatedthe mud volcano. In this discussion we begin by summarising themain conclusions made by Tanikawa et al. (2010) and then considerthe validity of their most important conclusion that Lusi is a naturaldisaster. Lastly, we reiterate the compelling evidence (Davies et al.,2008;Tingayetal.,2008)thatLusiisman-madeandwascausedbyanunderground blowout at the Banjar Panji 1 well.2. Main conclusions of Tanikawa et al. (2010)The main conclusions of the Tanikawa et al. (2010) paper werethat overpressure developed within the bluish grey clay, termed theUpper Kalibeng Formation Unit 2, and therefore, these strata wereundercompacted and susceptible to remobilisation. They consideredthe deeper carbonates (termed the Upper Kujung Formation) as themost likely source of fluids. (Note: earlier papers on Lusi (e.g. Davieset al., 2007; Mazzini et al., 2007) referred to the carbonates as theKujung Formation however, strontium isotope ratios from themindicate they are 16–18 Ma (Kusumastuti et al., 2002), and thus arenottheOligioceneKujungFormation, butrathershouldbetermedthePrupuh or Tuban Formations (Tingay, 2010) and are thus termed thePrupuh Formation for the remainder of this discussion.) The authorshypothesized that the elevated pressure within the Upper KalibengFormation Unit 2, made the sediment more susceptible to the smallamplitude static or dynamic stresses caused by the Yogyakartaearthquake, so that small changes in pressure were sufficient toinduce liquefaction. The rapid influx of gas and liquid from the deepcarbonates flowed through pre-existing pathways formed by naturalhydraulic fractures, and this explains the continuous mud eruption atLusi. In summary, Tanikawa et al. (2010) hypothesize that pore fluidpressure changes caused by the Yogyakarta earthquake causedliquefaction of undercompacted shales and fluid flow occurredthrough natural fractures.3. DiscussionThe paper provides key new information on the hydrodynamics ofLusi, and we indeed agree with several important points made by theauthors. For instance data from Banjar Panji 1 corroborates themodelling by Tanikawa et al. (2010) that the Upper Kalibeng Unit 2 isa fine grained lithology that is overpressured and undercompacted.We also agree that the most likely source of fluid is the deepcarbonates. Furthermore, we agree with the model results suggestingthat significant overpressures exist in and below the PrupahFormation carbonates. Very high magnitude overpressures wereobserved in the same section in the Porong 1 well, 6 km away fromLusi.Although we are in agreement in these areas, there are severalconclusions on how the mud volcano was triggered which are at oddswith our published research (Davieset al., 2007; Manga, 2007; Davieset al., 2008; Tingay et al., 2008) and given the scale of thishumanitarian disaster it is important that these are challenged. Themost important of these, is their reasoning that the Yogyakartaearthquake triggered the eruption rather than drilling of the BanjarPanji 1 well. Tanikawa et al. (2010) propose that stress fluctuationsinduced by the M6.3 Yogyakarta earthquake (2 days prior to theeruption) caused the mud in the Upper Kalibeng Unit 2 to losestrength and liquefy (their abstract and section 7.1). Others have also

PEMBUATAN PETA STRUKTUR-KEDALAMAN SHELF-EDGE FORMASI KUJUNG, LAUT JAWA TIMUR

Construction of Depth-Structure Shelf-edge Map for Case Study of Kujung Formation, East Java Sea. In general, reflection seismic method has capability to represent sub-surface in time domain. Seismic cross-section that depicts the formation of sub-surface usually use time domain in the format of TWT (Two Way Times). This due to in the process of seismic data acquisition, seismic wave propagates in down-going and up-going manner so that the obtained results from data processing are in the format of TWT seismic vs. shot points. This paper will describe the construction of depth-structure map for case study of Kujung Formation, East Java Sea, as exploration activities of oil companies in Indonesia. Manual data is peaked from seismic cross section and crossed with Vrms data of 3 wells in exploration location. TWT Shelf-edge map of Kujung Formation is divided into 2 parts and the results is crossed with velocitystructure map using Geoframe software CPS-3 so that depth-structure of shelf-edge of Kujung Formation, East Java Sea, is obtained. One of the objectives of this map construction is to get more real visualization of sub surface by using depth domain approach and as sustainable exploration activities of oil companies in Indonesia.

Fluid transport properties and estimation of overpressure at the Lusi mud volcano, East Java Basin

Generation and maintenance of overpressure can prevent sediments from compaction and weaken sedimentary rocks in deep basins. Excess fluid pressure is one of the key factors to explain the disastrous mud eruption that took place in Sidoarjo, East Java, on 29 May 2006, though the mechanism by which it developed is not well known. We measured permeability and specific storage at a confining pressure of 100 MPa in outcrop samples from the East Java Basin. Both permeability and specific storage in our samples showed large stratigraphic variations. The mudstone of the Upper Kalibeng Formation that is thought to be the source of mud at Lusi had the lowest permeability of our samples at around 10 − 19 –10 − 20 m 2, and the permeability of the Upper Kujung Formation limestone was 10 − 16 m 2, which is two orders of magnitude larger than that of the Lower Kujung Formation limestone. In addition, the permeability and porosity of cemented sedimentary rocks showed low sensitivity to effective pressure. From numerical basin analysis of the Lusi site together with laboratory data, we evaluated the evolution of pore pressure and porosity histories and their present distributions. Our results show that high overpressure was generated below the mudstone of the Upper Kalibeng Formation and almost reached lithostatic levels. The modeled fluid pressure variation is consistent with the observed data. The long-lived overpressure at depth is mainly caused by the existence of thick low-permeability sediments and a high sedimentation rate. Undercompaction of the Upper Kalibeng Formation because of overpressurization may have caused the mud to lose strength and cause liquefaction (and hydrofracturing) as a result of small stress fluctuations induced by the Yogyakarta earthquake, which may have ended up causing the mud eruption.