Central Luconia Province Research Articles

Subsurface Geosciences Learning in Virtual Reality: A Case Study in Central Luconia Province, Malaysia

The recent proliferation of Extended Reality (XR) applications in geoscience education and research has opened new avenues for the enhanced visualization and analysis of the Earth’s geodata. This study specifically explores the benefits for teaching when supplementing industry standard software packages, such as Paleoscan, Petrel, and JewelSuite, with 3D visualization in XR. The teaching focuses on but is not limited to an understanding of subsurface seismic and well data. During this study, the undergraduate Petroleum Geoscience students transitioned from 2D computer screen visualizations to immersive XR tools. The dataset selected for teaching focuses on the subsurface carbonate EX field in the South China Sea. The EX-field in Central Luconia is located 100–300 km from Sarawak’s coastline in water depths of 60–140 m. It includes a post-stacked time- 3D seismic cube linked to wells, allowing students to work with seismic data, adjust scales, and conduct preliminary seismic analysis. The findings revealed a significant improvement in respondents’ skills in comprehending and analysing seismic and core data, enhancing the overall learning experience in Petroleum Geoscience. This paper also examines the students’ feedback on their learning experiences during virtual subsurface visualization throughout their university degree in geoscience. For evaluating learning success, we used an approach that merges quantitative and qualitative data, The students’ perceptions were assessed through anonymous quantitative surveys and questions. The analysis of student responses emphasizes the valuable learning experience offered by 3D virtual environments designed for realistic first-person navigation and freedom of movement, like a real field experience. The results highlight the potential of virtual subsurface visualization for imparting essential skills to geosciences.

Effective application of geological process modeling for unravelling carbonate build-up complexity: A case study from the EX-Carbonate build-up in central Luconia Province, Malaysia

In the dynamic field of carbonate reservoir Exploration, the need for specialized models is vital, assisting as a key tool to facilitate interdisciplinary collaboration and enhance strategies for predicting reservoir behavior. This study examines the use of geological process (GPM), a standard tool to simulate forward stratigraphic modelling, particularly focusing on the Central Luconia Province in the South China Sea. Central Luconia Province stands out for its extensive carbonate build-ups and is recognized as a prolific hydrocarbon reservoir. Forward Stratigraphic Modelling (FSM) leads to a paradigmatic change in geological modeling. Unlike geostatistical models controlled by geometrical parameters, FSM relies on mathematical representations of the physical rules determining erosion, transport, and sedimentation in carbonate growth. This tool, supported by various researchers, has proven its ability in quantitative sedimentary system analysis across diverse temporal and spatial scales. This study located in EX Field showcases the ability of stratigraphic forward modeling in replicating sedimentary complexities and resulting stratigraphic architecture of the EX isolated carbonate platform. The methodology links parameters from existing literature with multiscale data. Additionally, carbonate production laws, contingent on water depth, play a pivotal role in the meticulous modeling process. This work illustrates the efficacy of geological process modelling as a transformative approach for unraveling the complexities of carbonate systems, particularly in regions with prolific hydrocarbon reservoirs like Central Luconia. The incorporation of literature-derived parameters and multiscale data serves as evidence of the model's ability to offer nuanced understandings of the dynamic evolution of carbonate platforms, thereby advancing our understanding of reservoir prediction and future management strategies.

Deep structural controls on the distribution of carbonate reservoirs and overburden heterogeneity in Central Luconia province, offshore Borneo revealed by 3D anisotropic inversion of regional controlled-source electromagnetic and magnetotelluric profile data

Understanding the deep structural controls on reservoir distribution and overburden heterogeneity is important for near-field exploration and green-field development of the Miocene to Holocene carbonate buildups in Central Luconia province in offshore northwest Borneo, Malaysia. Data from 59 stations along an approximately 180 km long controlled-source electromagnetic (CSEM) and magnetotelluric (MT) survey line with three segments recorded using different CSEM transmitter-towing directions were available. We applied three-dimensional (3D) anisotropic resistivity inversion with cross-gradient constraint and verified the resulting models using resistivity logs from nearby wells and the acoustic basement interpreted from seismic data. Our anisotropic resistivity models reveal a fragmented carbonate-rich zone atop a segmented basement comprising electrically resistive horsts coinciding with the northerly Mega-platform, Central and Southern Field Highs, separated by steep conductive zones coinciding with the West, East, and Southeast Troughs previously interpreted from seismic data. The structural highs correlate with the spatial distribution of the known carbonate buildups implying a genetic link. The carbonate bodies are overlain and underlain by persistent layers (C2 and C3) of low resistivity and high anisotropy, which we interpret as indicating compressional deformation or detachment zones. Overburden layer C2 (whose base coincides with the top of a key sedimentary package, Cycle V in seismic data) is thinnest over the East Trough and is discontinuous at the eastern margin of the West Trough, which are locations where drilled wells did not find hydrocarbons implying that the seal rocks are inefficient or breached at those localities. We used these observations to refine the existing seismic-based interpretation of carbonate play-types along our transect indicating how 3D joint CSEM-MT imaging can potentially contribute to derisking or optimizing future exploration and/or development work in this province.

Seismic stratigraphy of Late Pleistocene incised valleys and adjacent environments, eastern Central Luconia Province, offshore north‐west Borneo

AbstractIncised valleys are commonly investigated based on outcrop, modern setting and seismic data, which are often limited by data availability, especially for broad (ca >100 km wide) shelf settings. Consequently, few have described complete depositional systems of the incised valleys, especially those linked to their corresponding modern rivers in a source‐to‐sink framework to determine comprehensive controlling factors. This study documents Late Quaternary incised valleys and their characteristics in the Balingian – Central Luconia shelf based on regionally‐extensive three‐dimensional seismic data, two‐dimensional high‐resolution seismic data and boreholes. The three‐dimensional seismic data show that the main Tatau incised valley and tributary Suai incised valley fed the Tatau–Suai shelf‐edge delta. The Tatau incised valley is interpreted as the main incised valley based on its broader width, thicker infill, two‐tier stratigraphic architecture and its larger drainage basin area compared to the tributary Suai incised valley. The Tatau incised valley shifted its direction towards an active tectonic lineament (West Baram Line) and bypassed sediments to the deep‐water via a series of upper slope channels. The Tatau incised valley system comprises the following elements: (i) an upstream segment characterized by rivers dissecting an uplifted hinterland comprising Neogene sedimentary rocks, humid‐tropical vegetation, monsoonal climate, extremely high river discharge and sediment supply; (ii) a midstream segment comprising an emergent, vegetated (tropical rainforest to mangroves) and relatively narrow (ca 150 to 200 km wide) shelf, which was characterized by basinward‐increasing, tectonically‐driven accommodation space, valley incision and deposition; (iii) a downstream segment with increasing tidal‐influence where the Tatau and its tributary valley merged; and (iv) a short (15 to 20 km), narrow (10 to 15 km), tectonically‐controlled shelf‐edge delta and channelized upper slope. This study demonstrates the value of documenting an incised valley system in the context of its broader source‐to‐sink setting, which may provide a useful analogue for ancient incised valleys in comparable geological settings.

INTEGRATED ANALYSIS FOR ASSESSMENT OF DEEPER HYDROCARBON PLAY POTENTIAL IN REBAB-1, CENTRAL LUCONIA PROVINCE, SARAWAK

The basin history, thermal maturity, and hydrocarbon entrapments of Rebab-1 Well in Central Luconia have been relooked through the study of seismic, well log, and geochemical data to find new hydrocarbon potential in the deeper section of the well. The quality of source rocks in this area was based on assumptions, and hydrocarbon exploitation only occurs on shallow hydrocarbon plays making the potential for deeper plays difficult to ascertain. This study was conducted based on two 2D seismic lines, integrated with well lithological and stratigraphy data and geochemical data such as total organic carbon, pyrolysis, and vitrinite reflectance. Integration of these data was used to determine the deeper hydrocarbon play of Rebab-1 in Central Luconia Province. The seismic data were interpreted using Petrel software with validation from the report. Cross-plots from bulk geochemical analysis data were interpreted for the source rock's organic richness, kerogen quality, hydrocarbon-generating potentials, and thermal maturation levels. The results of seismic interpretations showed that extensional and compressional tectonics shaped the field of Rebab-1, with structures mainly trending to the NW-SE and NE-SW directions. Geochemical analysis showed that the total organic carbon content (TOC) of the samples analysed ranges between 0.06 and 2.98 wt.% indicating fair to very good source rocks producing mainly type II and mixed type II-III kerogen as the dominant kerogen. These types can generate mainly gas and mixed oil and gas accumulations upon attaining thermal maturation level. Also, Rebab-1 shows fair to very good hydrocarbon-generating potentials. The vitrinite reflectance (Ro) and Tmax results showed that the analysed samples are generally plotted in the immature, mature, and post-mature stages of oil generation but still within the gas generation window. Overall, source rocks from Rebab-1 can be said to have attained maturity at the youngest during depositions of Cycle III to older than that, and faulting and folding serves as hydrocarbon trap systems, indicative of potential in having deeper hydrocarbon plays in Rebab-1 well.

Case Study: Oil Production Optimized With Autonomous Inflow Control Devices Offshore Malaysia

_ Advanced well completions have proven to be an effective method of moderating gas breakthrough while producing a thin oil rim when placed in a heterogenous, carbonate reservoir. In addition, several studies have proven that the application of autonomous inflow control devices (AICDs) acts as a type of insurance policy against geological and dynamic reservoir uncertainties to reduce the risk and variation in the expected oil production profiles. During 2019 and 2020, Sarawak Shell Berhad conducted development campaigns in the central Luconia province in a thin oil rim carbonate reservoir offshore Sarawak, Malaysia. The horizontal, approximately 6,000-ft development wells were expected to intersect with different geological layers with varying rock properties, resulting in an uneven reservoir influx toward the wellbore. Oil production from these wells was expected to suffer severely from early gas and water breakthrough. To produce the oil rim without the risk of early gas production, global production optimization specialist, Tendeka, incorporated FloSure AICDs in the lower completion design at the reservoir interface along the horizontal section of the wells. As an active flow control device, the technology delivers a variable flow restriction in response to the properties of the fluid entering the wellbore and the rate of flow passing through it to help manage gas coning/cusping risks. The fluid is then lifted to surface with natural in-situ gas lift built into the upper completion. A three-phase development was planned for the field, and to date, two phases have been completed. New-Generation ICD The first AICD completion was installed in Norway in 2008 and widely implemented in the Troll field in 2013 with very encouraging results (SPE 159634). However, its use is relatively new to both the Asia Pacific region and this type of application. Similar to a standard ICD which balances the influx of reservoir fluids, the FloSure AICD will delay the production of unwanted effluents prior to their breakthrough (proactive solution). However, once a breakthrough occurs, the device restricts the production of unwanted effluents with lower viscosity, such as gas (in light oil applications) and both gas and water in viscous oil production (reactive solution) (OTC 30403, OTC 30363, SPE 193718). The device delivers a variable flow restriction in response to the properties of the fluid and the rate of flow passing through it. Flow enters the device through the nozzle in the top plate of the body. This impacts the disk and spreads radially through the gap between the disk and the top plate, then turns around the top plate and is discharged through several outlet ports in the body (Fig. 1). The overall geometry of the device is critical to its ability to balance these forces effectively and create the desired fluid-dependent pressure drop. Field A employed 7.5-mm AICD valves to match the performance of the devices to the potential well flow rate. The oil, water, and gas viscosities are 0.40 cP, 0.27 cP, and 0.018 cP, respectively, at downhole flow conditions.

Integrated Carbonate Rock Type Prediction Using Self-Organizing Maps in E11 Field, Central Luconia Province, Malaysia

Reducing uncertainty in 3D carbonate rock type distribution is a critical factor that profoundly impacts field development for hydrocarbon or carbon capture and storage (CCS) projects. Miocene carbonate reservoirs in the Central Luconia offshore region are economically important global gas reservoirs. The nature of these carbonate rocks can be visually distinct in the core and the multiscale reservoir heterogeneity might vary in scale from the 100-m scale to the sub-millimeter scale. This work presents a series of steps workflow to obtain spatial information about the organization scheme of carbonate rock types, and capture the most important petrophysical and sedimentary controls on rock property distribution in the E11 field, a carbonate buildup, located in Central Luconia Province, offshore Malaysia. The spatial data were generated from a supervised neural Kohonen algorithm. The rock types predicted with this workflow were propagated using IPSOM probabilized self-organizing maps SOM. This tool is used for classifying multivariate data samples according to “patterns” or multivariate responses. The workflow includes several steps: A Step 1—Core data description, B Step 2—Thin section description, C Step 3—Well log interpretation, and D Step 4—IPSOM probabilized self-organizing maps for facies prediction SOM. The depth plots of the predicted rock type showed close correspondence to the core-based rock types in terms of the stratigraphic organization of tight and reservoir layers, proportions, and juxtaposition. This result is sufficient to merit the application of the rock type logs into a future porosity model of the E11 field, and to understand the lateral and vertical distribution of tight and reservoir rock types of distribution. The results can be used to build a future realistic digital twin of the subsurface, and in digital geological modeling.

Compaction history based on porosity, pressure and temperature relation in Central Luconia province, offshore Sarawak

This study investigates the role of porosity in relation to temperature and pressure within Miocene-Pliocene sediments in Central Luconia province. The main objective is to understand the effect on porosity loss within Miocene-Pliocene sediments as part of the compaction of the sediments through time. The methodology involves seismic interpretation of 2D seismic lines and analysis of four wells over the central complex in Central Luconia province. Thick sedimentation was found within the clastic sediments of Cycle VI, indicating major clastic influx from the deltas and onshore of Sarawak during Pliocene. These clastic sediments had become a major source of weight in the offshore basin, inducing compaction within the older formations. Porosity distributions based on the wells showed that Cycle VI had the highest porosity in LH1 well with 33.77% porosity, while porosity within Cycle IV & V limestone showed an average porosity of 22% in all wells. Porosities within Cycle III and Cycle II were observed to be average of 16%. The porosity within the reservoir rock was reduced as the depth increased. This porosity reduction was relatively due to the compaction of the sediments, linked with the changes of pressure and temperature indicated by several evidences found in each well. Overpressure zone affects irregularity of porosity reduction with depth, whereas high temperature promotes diagenetic reaction that causes sudden porosity loss. Nevertheless, a sudden increase in porosity was also observed at the top of Cycle IV & V limestone due to a major drop in the sea level during the Early Late Miocene, which had encouraged the karstification process, inducing secondary porosity. This study has proved that compaction within Miocene-Pliocene sediments is not only related to the loss in porosity, but it involves changes in pressure and temperature regime of sediments and is highly dependent on the natural changes of sea level.

Reducing the risk of low saturation gas using controlled-source electromagnetic (CSEM) in K-Field, Central Luconia: a forward modeling case study

The application of controlled-source electromagnetic (CSEM) in hydrocarbon exploration significantly facilitates the detection of economic hydrocarbon. The method captures anomalies through the resistivity contrast between the overburdens and hydrocarbon-bearing lithologies. In most cases, the resistivity contrast is only prominent when there is sufficient hydrocarbon saturation. K-Field is situated on the continental shelf of Sarawak Basin, a sub-mature area for oil and gas in the Central Luconia province. Despite the low saturation of the gas in the Cycle VI sand, the seismic data shows a strong amplitude in the shallow section. Therefore, this study is conducted to assess the change of resistivity and CSEM response to the gas saturation and thickness variations of thin-gas sand in the K-Field. 3D resistivity models and three exploration wells are provided and two main methods are implemented in this study comprising the resistivity and CSEM forward modelings. The resistivity modeling is conducted using the Indonesia water saturation equation for different gas saturation scenarios and subsequently, the modeled resistivity is inputted in 1D and 2.5D CSEM forward modeling. The modeled CSEM response analysis is done by normalizing the modeled CSEM amplitude to the background or also known as normalized amplitude response (NAR). In gas saturation variation, the modeled resistivity showed an insignificant resistivity increase from 0.45Ωm to 0.55Ωm from wet case to 5% of gas and strongly increases to 35Ωm at 90% of gas saturation. The 1D CSEM NAR shows a very weak response of less than a 3% increase for 5% of gas and up to 230% increase for 90% of gas. In gas thickness variation, the CSEM NAR is weak and less than a 15% cutoff for all the tested thicknesses for 5% and 45% of in-situ gas. At 70% of gas, 25m is the minimum detected gas thickness with a 17.5% response increase, and at 90% of gas, the response is already strong at a minimum 5m thickness with a 35% increase. The modeled 2D CSEM responses also show that only 70% and 90% of gas sand layers in the K-field were delineated distinctively by the inline receivers with a 40% and 200% response increase respectively.

Application of Spectral Decomposition Technique to Delineate the Evolution of Karst on Carbonate Platforms of Central Luconia, Offshore Sarawak, Malaysia

Karstification in carbonate platforms of the Miocene age in Central Luconia province, offshore Sarawak, Malaysia, has been discussed since the onset of exploration and initial discoveries in the region, with over 200 mapped platforms to date. An extensive drilling program over the last decade confirmed the existence of karst during the drilling process where issues such as total loss circulation and bit drops were common. Karst in Central Luconia has been proposed by several authors; however, detailed quantitative description of the observed features have not yet been conducted. This study involves systematic mapping of loss circulation depths, chalkified/rubble/vuggy zones described from cores, and vugs of >2 mm in size and moldic porosity observed on thin sections of the Jintan platform. These data supplement the interpretation of karst from multiple 3D seismic attributes. Seismic interpretation of the Jintan and M1 platforms revealed an extensive dendritic pattern which is on average 70–100 m deep and 3–5 km long, and circular geobodies of 1 km in width that exist on the upper part of the platform. Spectral decomposition, also known as time-frequency analysis, was used to enhance the interpretation of karst features on seismics within a specific wavelength. In this study, a comparison of three spectral decomposition methods applied on the 3D seismic cube of the Jintan and M1 platforms was undertaken to determine the method which allowed for better delineation of the karst features. The results show that the short-time Fourier transform (STFT) method using frequencies of 46, 54, and 60 Hz delineated most of the karst features compared to the continuous wavelet transform (CWT) Morlet and CWT Ricker wavelet methods. This paper aims to discuss the dimensions, evolution and geometry of the karst features quantitatively on three selected karst horizons named “K1”, “K2”, “K3”. Interpretation revealed that the dendritic karst features were found to be most prominent on the K2 horizon which lies below a conspicuous change of the external geomorphology of the platform. Backstepping of the platform margin by 12 km is observed in both platforms. Quantitative seismic interpretation shows that the karst observed in M1 platform is approximately 70–100 m deep, and the dendritic features are around 1–2 km in length and approximately 500 m wide; whereas, in the Jintan platform the dendritic features observed are up to 5 km in length with several 1 km wide circular/sinkhole features. More than 20 dendritic features orientated SE and NS were mapped mainly in the transitional area as well as the center of both platforms. The nature of the karst morphology in Central Luconia remains controversial; however, it is proposed to be of mixing zone karst origin.

Shallow vs. Deep Subsurface Structures of Central Luconia Province, Offshore Malaysia Reveal by Aeromagnetic, Airborne Gravity and Seismic Data

Across the Luconia continental shelf, the nature and structures of the crust are lacking geological understanding and precise characterization. Newly acquired, aeromagnetic, and airborne gravity data were used to assess deep and shallow sub-surface signals within the Central Luconia Province, off the coast of Sarawak, offshore Malaysia. Regional aeromagnetic anomalies appear to primarily reflect deep crustal features while depth (Z) tensors of airborne gravity anomalies evidence shallow subsurface structures. Strike directions of the interpreted structural trend on aeromagnetic and airborne gravity anomalies maps are measured and plotted into rose diagrams to distinguish the structural orientations for all datasets. Signature patterns extracted from the depth profiles were correlated with parallel seismic lines and nearest exploration wells and coincide well with the top of carbonate for Cycle IV/V and structures seen within the Cycle I and II sediments. The orientation of faults/lineaments at shallower depth is dominated by a NW-SE orientation, similar with the faults extracted from two recently published structural maps. Deeper subsurface sections yielded E-W to NWW-SEE dominant directions which were never presented in the published literature. The E-W oriented anomalies are postulated to represent the remnants of the accretion between the Luconia crustal block and southern boundary of the Palawan block. The NW-SE trend follows the same direction as prominent faults in the region. The insight into shallow and deep subsurface structures in Central Luconia Province imaged through airborne gravity and aeromagnetic data should provide guidelines and complementary information for regional structural studies for this area, particularly in combination with detailed seismic interpretation. Further evaluation on the response of Air-FTG® gravity and aeromagnetic could lead to the zonation of potential basement highs and hydrocarbon prospects in this area.

STRUCTURAL MODEL & SEDIMENTOLOGY ANALYSIS OF THE EX CARBONATE FIELD, CENTRAL LUCONIA PROVINCE, SARAWAK

Central Luconia Province displays various structures in different parts of the basin attributed to extensional, strike-slip, and wrench tectonics. This affected the growth of the EX carbonate platform, the heterogeneity of carbonate facies, and lithological properties variations in the EX field. Such complexities restrict the understanding of the structures and sediments and may lead to well placement problems during a development stage. This research aims to study the carbonate growth of the EX field in accordance with the structural deformation and to analyse the field’s sedimentology. Detailed research of the structures in the EX carbonate platform was done using seismic interpretation to determine the nature of the relationship between faults and carbonate formation. Concurrently, a comprehensive sedimentary analysis was conducted using core and thin section studies to interpret facies characterization and depositional environment. The spectral decomposition attribute was used to study the seismic response of the lithologies in this field by demonstrating the anomalies of the carbonate platform using frequencies ranging from 328 Hz to 356 Hz. This research contributed to the interpretation of individual faults and the generation of a conceptual growth and structural model based on a seismic, attribute, and structural interpretation. The anomalies were used to identify the EX carbonate body and features such as the rim of the build-up through the spectral decomposition attribute. The sedimentary analysis from the EX-4 well also improved facies distribution and depositional environment, ranging from a deeper lagoon to a reef environment. This research can be used as an input for further correlation studies of the Central Luconia basin at a regional scale.
 Keywords: carbonate platforms, tectonics, spectral decomposition, carbonate core

Bayesian facies inversion on a partially dolomitized isolated carbonate platform: A case study from Central Luconia Province, Malaysia

We have developed a case study of geophysical reservoir characterization in which we use elastic inversion and probabilistic prediction to estimate nine carbonate lithofacies and the associated porosity distribution. The study focuses on an isolated carbonate platform of middle Miocene age, offshore Sarawak in Malaysia that has been partly dolomitized — a process that increased the porosity and permeability of the prolific gas reservoir. The nine lithofacies are defined from one reference core and include a range of lithologies and pore types, covering limestone and dolomitized limestone, each with vuggy varieties, as well as sucrosic and crystalline dolomites with intercrystalline porosity, and argillaceous limestones and shales. To predict the lithofacies and porosity from geophysical data, we adopt a probabilistic algorithm that uses Bayesian theory with an analytical solution for conditional means and covariances of posterior probabilities, assuming a Gaussian mixture model. The inversion is a two-step process, first solving for P- and S-wave velocities and density from two partial seismic stacks. Subsequently, the lithofacies and porosity are predicted from the elastic parameters in the borehole and across a 2D inline. The final result is a model that consists of the pointwise posterior distributions of the facies and porosity at each location where seismic data are available. The facies posterior distribution represents the facies proportions estimated from seismic data, whereas the porosity distribution represents the probability density function at each location. These distributions provide the most likely model and its associated uncertainty for geologic interpretations of lithofacies associated with distinct stages of carbonate platform growth.

Assessing controls on isolated carbonate platform development in Central Luconia, NW Borneo, from a regional 3D seismic facies and geomorphology investigation

Abstract The Central Luconia province in the South China Sea, offshore Sarawak, features extensive development of Middle to Late Miocene isolated carbonate platforms. This study presents a regional seismic architecture – seismic facies review of platform flank geometries and off-platform depositional styles, with the goals of understanding their patterns and exploring the controlling processes. The information on flank steepness and predominant shedding direction is contextualized with respect to extrinsic and intrinsic factors of carbonate platform growth, including tectonics, eustatic sea-level fluctuations, hydrodynamics and regional palaeogeography. Results reveal that flank geometries are consistent throughout the Middle to Late Miocene. In the north of the province eastern flanks are dominantly aggradational, steep and sediment-starved escarpments, whereas western flanks show more progradation and are accretionary in nature. Discrepancies from this pattern are observed among closely spaced platforms. The eastern-aggrading flanks are interpreted to have been highly influenced by monsoonal wind-driven currents. Further south in the province tidal currents, antecedent topography and syn-depositional tectonics were more important controls on platform architectural development. This study of regional processes and geomorphic products provides a basis for enhanced conceptual facies models and reservoir quality predictions.

Unravelling an abandoned giant in Central Luconia Province, offshore Sarawak, Malaysia — Success story of Lang Lebah

In 1994, two exploration wells were drilled consecutively to explore for gas prospectivity in Lang Lebah, a Miocene carbonate buildup in the geologic province of Central Luconia located in the Sarawak Basin in Malaysia. High overpressure and operational problems prevented both wells from fully evaluating the target. Postdrill analysis concluded that Lang Lebah has limited potential due to poor reservoir quality, small gas column, and challenging drilling conditions. For these reasons, it was left dormant for 25 years. In 2016, new 3D broadband seismic acquisition and megamerge reprocessing of 3D seismic data sets followed by an integrated application of multidisciplinary workflows successfully derisked key petroleum system elements of the Lang Lebah structure, yielding a more optimistic view of its potential. A new well was justified at Lang Lebah and resulted in one of the major gas discoveries of 2019.

What matters for flow and recovery in carbonate gas reservoirs: Insights from the mature Central Luconia Province, offshore Sarawak, Malaysia

Miocene carbonate reservoirs in Central Luconia, offshore Sarawak, Malaysia, have been delivering gas for over 30 yr. In this paper, learnings from that period of production are used to understand the key drivers affecting flow during production and recovery optimization in existing fields as well as development decisions for new discoveries. The large data set, generated over more than 40 yr, was analyzed in a consistent manner through a holistic database, constrained by a stratigraphic framework, to allow reservoir units to be compared like-for-like (“integrated knowledge base” [IKB] concept). Carbonate reservoir heterogeneities impacting flow are grouped into “horizontal–heterogeneities”—argillaceous flooding layers and exposure-related karst—and “vertical–heterogeneities”—large-scale architectural elements, found especially along platform margins. Both types of heterogeneities control water ingress during production and influence the recovery mechanism. Argillaceous flooding layers can act as baffles, holding back water rise during production, or can form pressure compartments. Long-lived, fault-bounded reef margins, carbonate shoals, islands, and karsts can be vertical conduits for aquifer inflow. Platform shape and architecture impact column height and hence recovery efficiency. Additional drivers impacting recovery were found to be gas-column height, aquifer size and permeability, pressure connection to neighboring fields, and field development concepts. All drivers identified impact decisions throughout the field life, e.g., well count and design, intervention capabilities, evaluation and mitigation of early-water breakthrough, reservoir management, selecting enhanced recovery methods, and abandonment pressure. The IKB allowed to derive “big rules” on what matters for flow, which were used to decide on development strategies for greenfields in Central Luconia. The presented outcomes can be extrapolated to comparable carbonate systems, whereas the IKB approach can be adapted and applied to other mature basins and reservoir types where equally vast and historic data sets are awaiting to be used in the current era of digitalization.

Seismic architecture of a Miocene isolated carbonate platform and associated off-platform strata (Central Luconia Province, offshore Malaysia)

Abstract Rather than being homogeneous and isotropic, many isolated carbonate platforms in the geologic record include internal heterogeneity and complex geometric relations with off-platform strata on their flanks. To better understand stratal architecture of a Miocene isolated platform (Central Luconia, offshore Malaysia), this study integrates core, log and seismic data, revealing stratal terminations and geometries that define several seismic stratigraphic units. A thick in the basal seismic unit, the initial deposits of the carbonate buildup, is 4–5 km across. This thick includes abrupt thinning to the west and east, with onlap onto its flanks, but continues outside of the survey area to the north and south. Above a mappable surface, a less extensive (2 × 5 km) seismic unit represents a backstepped isolated platform (Platform Stage 1). Across a pronounced normal fault on the east/southeast margin of the platform occur marked isochron and seismic character changes, with thicker carbonates on the downthrown (western) block. The northern and western margins are not faulted. A third seismic unit, representing a smaller, elongate ( The most marked stratigraphic theme within the isolated platform is the successive backsteps, but the pattern is complicated by interactions with the basinal strata. Superposition and cross-cutting relations document that isolated platform-sourced flanking beds (”wings”) interfinger with basinal clinoforms (”wedges”), as defined by geometries on the margins and flanks of platform stages. The platform evolution also was influenced markedly by syndepositional structural activity, although structural trends changed from the initial buildup to later platform stages. The results, and comparison with other isolated platforms, demonstrate the complex controls on carbonate platform growth and interactions with basinal siliciclastics.

Reservoir characteristics of carbonates build-ups in southern Central Luconia Province: A study based on different scales

Reservoir characteristics of carbonates build-ups in southern Central Luconia Province: A study based on different scales

Imaging of karsts on buried carbonate platform in Central Luconia Province, Malaysia

Imaging of carbonate rocks in the subsurface through seismic method is always challenging due to its heterogeneity and fast velocity compared to the other rock types. Existence of karsts features on the carbonate rocks make it more complicated to interpret the reflectors. Utilization of modern interpretation software such as PETREL and GeoTeric® to image the karsts morphology make it possible to model the karst network within the buried carbonate platform used in this study. Using combination of different seismic attributes such as Variance, Conformance, Continuity, Amplitude, Frequency and Edge attributes, we are able to image the karsts features that are available in the proven gas-field in Central Luconia Province, Malaysia. The mentioned attributes are excellent in visualize and image the stratigraphic features based on the difference in their acoustic impedance as well as structural features, which include karst. 2D & 3D Karst Models were developed to give a better understanding on the characteristics of the identified karsts. From the models, it is found that the karsts are concentrated in the top part of the carbonate reservoir (epikarst) and the middle layer with some of them becomes extensive and create karst networks, either laterally or vertically. Most of the vertical network karst are related to the existence of faults that displaced all the horizons in the carbonate platform.

Integrated Approach for Overpressure Prediction in an HP/HT Well Offshore Malaysia

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18909, “An Integrated Approach for Overpressure Prediction in a Wildcat High-Pressure, High-Temperature (HP/HT) Exploration Well Offshore Sarawak, Malaysia,” by Avirup Chatterjee, Amitava Ghosh, and Sanjeev Bordoloi, Baker Hughes, and Anifadora Bt. Mustapha, Petronas, prepared for the 2016 International Petroleum Technology Conference, Bangkok, Thailand, 14–16 November. The paper has not been peer reviewed. Copyright 2016 International Petroleum Technology Conference. Reproduced by permission. Pore-pressure prediction plays an important role in well planning as exploration targets shift to deeper, overpressured reservoirs. Pressure-related problems in such zones are mainly associated with narrow operating windows, resulting in severe well-control incidents, sometimes even leading to early abandonment. Uncertainties in prediction models arise from input data, assumptions used in the work flow, and the complexity of the geological or structural conditions. It is important to analyze these uncertainties and develop an understanding of them before drilling. Introduction Central Luconia is a geological province of the Sarawak Basin characterized by extensive development of Miocene to Holocene carbonate buildups. The buildups reveal complex seismic geomorphologies, facies, and structural setting. There have been several discoveries in the shallow-water (approximately 90-m depth) area of central Luconia province offshore Sarawak. A predrill pore-pressure- and fracture-gradient-prediction study was initiated for a planned high-pressure/high-temperature (HP/HT) well with three offset wells (Offsets 1, 2, and 3) drilled in the vicinity of the study area. The objective of the study was to help in well design to reach desired deeper target reservoirs. The prospect is situated in a structure characterized by a northwest/southeast normal fault. It was formed on the foot wall block for the shallow (post-carbonate clastic) reservoirs and crossing the fault to the hanging wall block to hit the main targets in deeper (precarbonate clastic) cycles. The lithology for the shallow cycles is interbedded fine-grained siliciclastic shale and sand with limestone streaks. The deeper cycles consist of predominantly sandstones with interbedded shales. Two offset wells (Offsets 2 and 3) penetrated a thick carbonate sequence, and the other offset well (Offset 1) encountered a thick sand/shale sequence with interbedded carbonate stringers, which is similar to the prognosed-well result. Therefore, in the predrill modeling, there was only one relevant offset well (Offset 1) available in the study area that penetrated similar lithostratigraphic units. Well Issues A detailed analysis of all the drilling problems encountered in the offset wells was catalogued. This was achieved by reviewing the daily drilling reports, final well reports, and mud-logging reports and documenting all the events on a daily basis. Overall, all the offset wells analyzed during the study indicated several drilling issues related to pore pressure, including internal blowout with violent gas flow from the bell nipple, influxes, gas-cut mud, high gases, connection gases, pumps-off gas, and cavings. In addition, wells showed significant challenging drilling conditions such as equivalent static- and circulating-density contrast because of high temperature, wellbore breathing caused by a narrow mud window, and several hole-stability issues such as tight hole, lost circulation, and stuck pipe, eventually leading to multiple sidetracks.