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Asia Petroleum Geoscience Conference and Exhibition (APGCE)
- Conference date: November 28-29, 2022
- Location: Kuala Lumpur, Malaysia
- Published: 28 November 2022
1 - 50 of 132 results
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Carbonate Facies Description for a Large Gas Field, Central Luconia, Sarawak Basin
Authors P. Henglai, K. Poret and A. SallerSummaryRock sample analysis provides crucial information that enable creation of a robust depositional facies model, which is a key input for reservoir modelling and the field development plan. However, the conceptual facies model suggests that facies distribution in the carbonate platform varies in both vertical and lateral directions as a result of the original depositional facies and diagenesis history. Therefore, the current dataset may not be enough to capture this uncertainty, and thus we require more data to gain a clearer understanding of reservoir heterogeneity.
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Permeability Modelling using Rock Fabric Number and Neural Networks in Carbonate Reservoirs
Authors H. Zulkiply, K.H. Ling and K.S. NgSummaryDetermination of permeability is vital in the static and dynamic modelling of reservoirs. Carbonate reservoirs pose a unique challenge due to heterogeneity caused by primary and diagenetic processes. Generalized porosity and permeability relationships were developed by linking permeability and porosity with rock fabric classifications. Applications of Lucia Rock Fabric Number (RFN) method to estimate permeability is possible where specific data is available. It is postulated that spatial distribution of RFN within a field may be estimated based on Neural Networks. By combining well-based RFN classifications and Neural Network Modelling, a 3D profile of permeability and rock fabric can be obtained.
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Quantification of Mid Aptian Net Uplift and Erosion in Lower Congo Basin
Authors S.S. A Aziz, L.K. Yeap, S. Dasgupta, S. Saidi, Z.K. Gulab and R. DasSummaryThe Early to Mid-Aptian marks the cessation of rifting via seafloor spreading. Widespread uplift and erosion accompanied this early drift phase, which was likely caused by flexural rebound, though inversion due to tectonic forces may also have contributed ( Chen et al., 2013 ).
This drift phase uplift and subsequent erosion significantly impacted Aptian petroleum systems (source rocks, reservoirs, and seals; Dore & Jensen, 1996 ). In this study, our objective was to quantify the scale of uplift and erosion to develop a better picture of petroleum system dynamics and risk. Our methodology was to utilize sonic interval transit time of shale intervals in the Gamba and Dentale Formations. In addition, the results derived from sonic interval transit times were corroborated with vitrinite reflectance measurements from another 19 wells. Our analysis identified six (6) anomalous wells in southern Gabon and these were used to estimate net uplift and erosion during the Mid-Aptian.
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Predicting the Distribution and Concentration of H2S in Eastern Central Luconia
By M. ChooSummaryThe distribution of the H2S in sour gas carbonate fields in eastern Central Luconia is geographically influenced, where fields near the deep-rooted WBL generally have higher concentration of H2S likely due to their proximity of accessing the thermal fluid migration with TSR via the WBL fault system. The efficiency of the H2S-generating process relies on the proximity of the sour gas carbonate fields to the source of H2S (sulphate), the energy source and the timing of migration of the H2S into the gas reservoir. It is observed that carbonate fields with a small Hhc/Hstrc ratio have lower concentration of H2S; as opposed to the ones with high Hhc/Hstrc that exhibits higher concentration of H2S levels. This is attributed to the water-scrubbing process of removing the H2S from the sour gas that occurs naturally due to the existence of a large water column beneath the GWC. These observations are used to ascertain the maximum possible H2S concentration of the on-going B14 development; therefore, minimising the potential project and commercial risk of the project. The same observations and learnings can be transferred into the uncertainty assessment of the presence of H2S and estimation of its concentration in future exploration and appraisal wells.
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A Delineation of Multi-Formation Fluid Components Using Cased Hole Logs for Offshore Malaysia Gas-Condensate Reservoir
Authors J. Yii, A. Simanjuntak, S. Shirai and E.C. LimSummaryGas reservoir fluid properties vary during the production phase as the reservoir pressure declines below the dew point. The evaluation of formation saturation across such reservoirs may become more complicated when water saturation increases due to water influx from the aquifer.
Formation saturation analysis using conventional pulsed neutron carbon/oxygen and thermal neutron capture cross section (sigma) logs do not provide a clear sensitivity between gas and condensate. A combination of a multi-detector pulse neutron tool with an improved analysis capability has been the key to unlocking some of the challenges faced by an operator of a gas-condensate field located off the coast of Sarawak, offshore Malaysia.
Pulsed neutron logging was performed for three-phase saturation evaluation as part of a multi-well logging campaign. Production logging was also conducted in a flowing condition in one of the wells to determine the contribution from perforated intervals.
The saturation results will provide a reference to determine if there are changes required to be made on the inputs to calculate the fluid saturations (particularly water saturation, Sw) for the initial condition. This update on the inputs will improve the reservoir dynamic modelling in part with delivering actual production vs modelling.
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The Importance of PVT and Trap Analyses in the Distribution of Hydrocarbons in the Malaysian Basins
Authors F. Zainetti and N.F. Bt Ahmad SharifSummaryThis study suggests that the distribution of oil and gas accumulations of the Malaysian basins is predominately controlled by the saturation pressure regime, which defines the depth range of a dual phase system. Therefore, even though the underlying source rocks are expelling a gas-condensate hydrocarbon mixture – typically in single vapour phase, the interaction between the pressure regime and the trap characteristics still allows the accumulations of liquid pools.
In conclusion, it is important to analyze petroleum systems with a holistic approach. Once charge is established, the focus needs to be shifted to the trap geometry and its physical characteristics in relation to its seal capacity. Analyzing these relationships at a regional to semi-regional scale, would be the most effective analytical modeling method to predict and commercially exploit the remaining material liquid potentials still present in the Malaysian basins.
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CO2 Sequestration in South East Asia: Screening Methodology for Potential Storage Sites in Depleted Gas Fields
Authors N.Z. Mat Razali, L. Hong Shien, E. Intrieri, K. Mei Ching, N. Hashim and A. DimabuyuSummarySite selection is the most crucial, time-consuming, and costly process at the initial stage of a CO2 sequestration project. This paper highlights the regional screening approach and maturation study for Southeast Asia depleted gas fields. Based on the methodology, several fields situated in various basins in the region have been identified as potential candidates for future CO2 storage. Geological boundaries such as faults, stratigraphy, and hydrogeology are ideal cases for site selection characterization. However, in practice, the study area is defined by the authority on the basis of block or concession boundaries and is also limited by data availability.
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Precision Dating and Correlation from the Malay Basin to Sabah Using SEA Depositional Cycles
Authors R. Morley, S.S. Hussein, H.P. Morley, J. Jais and M.R. AripinSummaryObtaining confident age interpretations using a traditional biostratigraphic approach fail in most continental margin successions since most microfossil extinction datums are diachronous due to a combination of facies and carbonate dissolution issues, whereas evolutionary appearances are affected by both facies and caving, and so there is invariable subjectivity in placement of such datums. Sequence biostratigraphy allows confident age interpretations through the identification of transgressive-regressive cycles (SEA cycles) that faithfully capture the sedimentation ‘pulsebeat’ driven by patterns of Antarctic glaciation in the Oligo-Miocene and northern hemisphere glaciations in the Pliocene, even in very deep-water settings. Cycles are ‘fingerprinted’ by age-restricted microfossils in distal facies with correlations relying on sequence boundaries rather than first or last microfossil appearances. Based on the evaluation of 101 biostratigraphic datasets from the Malay and Penyu Basins, offshore Sarawak and offshore Sabah, a total of 46 transgressive-regressive cycles are identified. The SEA cycle succession demonstrates that other sequence biostratigraphic schemes, such as the TA and TB cycle schemes include a mixture of cycles of different rank and are thus less useful for stratigraphy prediction. To undertake sequence biostratigraphic evaluations, biostratigraphers need to become equally familiar with all three biostratigraphic disciplines of micropalaeontology, nannopalaeontology and palynology
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Improvement of FWI with Progressive Transfer Learning
More LessSummaryThe lack of low-frequency data components has been a major obstacle in FWI applications for velocity model building. Many theoretical approaches have been proposed to extrapolate low-frequency components. Progressive transfer learning was proposed to solve the problem by using a deep learning-based approach to predict low-frequency components. In this paper, we demonstrate the effectiveness of the progressive transfer learning workflow by building a practical workflow and applying it to the field data.
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Uncertainties Associated with Quantitative Fault Seal Prediction; Case Studies from Sarawak & Sabah Basins-Malaysia
By M.H. MohamadSummaryQuantitative fault seal predication concept, methodology and related software developed during last 33 years ( Allan 1989 , Knippe et al 1997, Yielding 2002 , Bretan et al, 2003 ) and became a standard technique in hydrocarbon exploration industry for predrill hydrocarbon column height and ultimately volumetric estimation. Rocks which get entrained in the faulting process- aka Shale Gouge Ratio (SGR)- is one of the main sealing mechanisms when sand juxtaposes sand on either side of the fault ( Fristad et al 1997 , Yielding et al 1997 & Yielding 2002 ). To the latter, statistical data from North Sea, Sarawak and Sabah indicate across fault pressure difference and related hydrocarbon column is a function of relative SGR ( Yielding 2002 , Hisham et al 2022 ). Increasing SGR of up to 50% results in bigger hydrocarbon column at the trap. However, overall data for SGR/pressure and/or SGR/hydrocarbon column height suggest a wide range of pressures and hydrocarbon column for the same percentage of SGR. This presentation focusses on how established methods for calculating hydrocarbon column height can benefit from newly acquired knowledge based on the integrated fault seal analysis of several fields in Sarawak and Sabah basins. This study help understanding predrill sealing capacity and hydrocarbon column height prediction.
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Machine Learning for Lithology Percentages Prediction from Cutting Photos: Massive Validation, Results, and Challenges
Authors M. Mezghani and E. TolstayaSummaryDrill cutting samples are valuable data that cover the major part of drilled well compared to the core samples that cover only a limited depth interval. Therefore, accurate and objective cutting description plays major role in decision making while drilling, in the reservoir characterization studies, and in modeling workflows. We developed an Artificial Intelligence workflow to automatically predict cutting lithology percentages using cutting photos. The workflow can be applied in near-real-time as soon as photos are acquired.
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Turning high Resolution FWI Model into Reflectivity: a Case Study Using Sparse OBN
More LessSummaryFull-waveform inversion (FWI) has been a very valuable tool for deriving accurate and detailed velocity models in various geological settings, especially for sub-salt imaging. By increasing the inversion frequency in FWI, more details and lithology related features start to show up in the inverted velocity model. It contains richer information, other than just providing a velocity model for migration. Migration image is usually considered as normal reflectivity of the sub-surface. A pseudo-reflectivity can be directly derived from the FWI velocity model without going through the migration route. The derived pseudo-reflectivity inherited the full benefits of FWI in terms of illumination compensation and noise reduction, and provides a supplementary volume to the migration image.
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Flat Spots in Carbonates: Rocks, Fluids, or Myth?
More LessSummaryQuestions are raised whether flat spots within carbonates are DHIs. High sensitivity of elastic properties to porosity and mineralogy, and the low sensitivity to fluids combined with high degree of heterogeneity all act to reduce the likelihood of strong and coherent fluid induced flat spots. In some regions of Sarawak Basin, offshore Malaysia apparent flat spots are observed within some carbonates. Where drilled the flat spots occur at or close to the GWC, but there is also a coincidence with changes in porosity and lithology. In some cases, the coincidence of changes in porosity coinciding with changes in fluid have been thought to be linked by diagenetic factors, where porosity is preserved or enhanced especially when CO2 level is high. Given not all flat spots are perfectly flat, question is raised whether these features can be predictive of gas. Recent well drilled into one of these carbonates and through the flat spot found gas but also found that the flat spot was caused by change in lithology and porosity. Further rock physics modeling showed that fluid induced flat spots might be present when the porosity and homogeneity were sufficiently high. Such examples were found on the flank of the carbonate.
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An Erosional Unconformity at the Top of the Nyalau Formation, Central Sarawak: Regional Context and Significance
Authors M. Madon, M.H. Amir Hassan and J. JongSummaryThis paper documents an erosional unconformity at the top of the Nyalau Formation (Oligocene-Early Miocene) exposed in a road-cut near Bintulu in central Sarawak. The outcrop of interest, which we call Outcrop no. 7 (longitude 113.212502°, latitude 3.325615°), is located about 25 km to the northeast of Bintulu between Tg. Kidurong and the Similajau Industrial Park. The main exposure is a 100 m-long road cut on the eastern side of the Bintulu-Miri road. It exposes sandstones of the Nyalau Formation overlain by mudstone in a channel-like feature with an erosional base. The erosional surface is irregular, and has a concave-upward surface, which is interpreted as representing a major regional unconformity.
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Crustal Structure and Evolution of the Bunguran Trough: New insights from Gravity and Seismic Data
More LessSummaryThe Bunguran Trough is an enigmatic 15 km-deep basin that straddles the Sarawak shelf-slope region, offshore Malaysia. The trough is the deepest part of the Cenozoic Sarawak Basin, comparable to the Baram Delta depocentre on the opposite (eastern) side of Central Luconia carbonate province. Despite the enormous sediment thickness, there is no gravity or bathymetric expression. A simple bouguer slab correction applied to the free-air gravity anomaly does not explain the presence of such a thick sediment-filled trough. Although its presence is known for a long time, its origin is not well understood. In this paper, we present some new insights into the nature and origin of the Bunguran Trough based on analysis of gravity and seismic data across the Sarawak Shelf. The results of this analysis have been discussed in detail by Madon & Jong (2022) . This paper only highlights some key points.
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Seisimic and Gravity Evidences of Pre-Tertiary Subcrops Beneath the Malay Basin
Authors S. Anak Suntek, M. Madon and J. JongSummaryThe “basement play” concept in the Malay Basin has been based mainly on hydrocarbon discoveries in pre-Tertiary metasediments at Anding, SW Malay Basin (e.g., Kadir, 2010 ). Hydrocarbons in these fractured “basement” reservoirs are believed to be sourced from overlying Tertiary lacustrine source rocks within the deep half-grabens. This play concept, which drew analogy from the granitic basement play in offshore Vietnam, was the main driver for the “fractured basement” exploration since the mid-1990s. Besides metasediments, other lithologies also occur beneath the Base-Tertiary Unconformity (BTU), reflecting the complex pre-Tertiary geology of the surrounding landmasses. Hence, a better understanding of the pre-Tertiary basement geology is required to explore for hydrocarbons in the pre-Tertiary. To this end, we reviewed the evidence from seismic, well, and gravity data on the nature and distribution of pre-Tertiary rocks beneath the BTU.
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Empirical Detection of Suppressed Vitrinite in Legacy Data: an Example from the Malay Basin
Authors M. Madon, J. Jong and N. Dayang AimiSummarySuppressed vitrinite reflectance (Ro) can have a big impact on exploration decisions if not recognised and corrected for. It is known to occur in the Malay Basin where optically determined Ro values have been compared with equivalent Ro analysed by the FAMM (Fluorescence Alteration of Multiple Macerals) technique. Although “apparent” suppression of Ro may be minimised through strict laboratory protocols, explorationists may have to deal with legacy data (say pre-1995) comprising only optically determined Ro of unknown quality. How then would suppression be detected? In this paper, we examine both Ro and FAMM data in the Malay Basin to see if a general suppression trend can be established and consider its potential implications for exploration.
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A Review of the Structural-Stratigraphic Framework and Petroleum Systems of the Sandakan Basin, offshore East Sabah
More LessSummarySandakan Basin, located offshore East Sabah, is one of the few regions in Malaysia that have yet to produce commercial hydrocarbons despite decades of exploration effort. The exploration history and hydrocarbon occurrences in the area up to year 2000 have been summarised by Leong & Azlina (1999) . A number of sub-commercial discoveries have demonstrated the presence of a generative petroleum system in the offshore Sandakan Basin between the Sandakan and Dent Peninsulas. These occurrences complement the numerous oil and gas seeps commonly associated with mud volcanoes and salt springs, especially on Dent Peninsula (e.g., Leong & Azlina, 1999 ). This paper provides an updated overview of the structural-stratigraphic framework and petroleum systems in the basin.
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Alteration of Mudrocks by CO2
Authors M. Sams and T. JayasangarSummaryAnomalous features observed in seismic data from parts of the Greater Sarawak Basin are believed to be diagenetic fronts associated with the presence of CO2. Measurements from well log data show that the elastic properties of shales and silts behind these diagenetic fronts have been altered through a loss of capillary bound micro-porosity. It is hypothesized that this is due to the action on the clays of carbonic acid, which diffuses along a concentration gradient away from the reservoir rocks, which contain high concentrations of CO2 that have accumulated in traps along with hydrocarbons. The velocity and density data can be corrected based on an empirical model that matches similar changes caused by normal mechanical compaction. The degree and shape of the alteration is sufficient for these effects to be observed on seismic data. The amplitudes and AVO characteristics of the seismic data drastically change due to the alteration thereby making reservoir and fluid prediction significantly more challenging. The alteration might be used as an indirect hydrocarbon indicator as there is a strong correlation within the current data between hydrocarbon presence and shale alteration.
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The Shaping and Demise of the Tusan Beach “Drinking Horse”, Southwest of Miri, Sarawak
Authors M.H. Bin Yussof, J. Jong and F. KesslerSummaryThe Miri-Bekenu coastline is formed by Neogene clastic rock formations that are poorly consolidated. These formation outcrops are shaped by weathering elements of tropical rainfalls, wind and marine erosions, and deformation processes such as tectonic uplift, structural faulting and folding. The geological monuments of the Miri area such as the iconic Tusan Beach “Drinking Horse” cliff structure generally withstand weathering degradation and marine erosion poorly. Further to this, housing projects, road constructions and encroaching new plantations had their share in destructing geological landmarks. In this article, we discuss the case study of the “Drinking Horse” starting from its creation, the impact of weathering elements and coastal erosions, and human interferences that resulted in its ultimate demise. Nonetheless, due to its present-day state of seaward-dipping sedimentary layers prefect for gravity sliding, coupled with pounding erosions, the cliff had inevitably collapsed and any prior preservation effort carried out to protect the structure were seen in vain.
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Seismic Imaging Workflow Optimization and Velocity Model Uncertainty Quantification in Carbonate
Authors M.H. Pua, M.I. Supardy, C. Lee Slind, W.H. Tang, S. Maitra and F.F. BasirSummaryThe velocity Model plays a remarkably important role in seismic processing, especially in seismic imaging, as it directly affects the final data quality. Carbonate fields velocity model building are even more complicated as they are known to be much more complicated in chemistry and physics that leading to high heterogeneity and uncertainty. Often in carbonate fields, other complications also will associate together such as shallow gas in this case study where it increases the complexity and difficulty to obtain the most optimum velocity model for seismic imaging. This accumulation of complications can be resolved mostly through advanced and modern seismic processing techniques however, there will be still some uncertainty remaining in the velocity model building. In this case study, a tailored imaging workflow that includes Q-tomography, Q-APSDM, and FWI has been applied and plays an important role in solving most of the challenges while optimizing the velocity model. The uncertainties that underlie the velocity model produced even with this sensible workflow will still be present and need to be quantified. The quantification of velocity model uncertainty will be through the tomographic inversion process and able to provide velocity standard deviation as an output that reflects velocity model uncertainty.
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Upgrading and Redefining Cycle I GDE of Deepwater Sarawak via Multi-Attributes Analysis of Cycle I Coal
SummaryThis study covered within North Luconia region which warrant a guidance towards Cycle I gross depositional environment (GDE) revision. Previous model of 2020–2021 Cycle I GDE represent separated bodies at Well C-1, Well O-1, Well P-1, Well Q-1 and Well R-1 due to those wells was sitting at paleo high as supported by Bouger anomalies and was affected by marine incursion. In general, coal deposition in Cycle I was associated with lower coastal plain (LCP). However, the coal deposition in the previous model was not extensive and this therefore, raised a possibility that it might be a single coastal body instead. Questionable on the swampy area which only pointing at Central Luconia while at North Luconia province, the coal still can be established as depicted by Well A-1, Well C-1, Well J-1, Well O-1, Well P-1, Well Q-1 and Well R-1.
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Uplifting Vintage 3D Land Seismic Dataset with Modern Processing Workflow: a Case Study from Thailand
Authors N. Wanpiyarat, R. Chakraborty, S.H. Ng and N. PhantaweeSummaryWe present a case study based on the application of modern contemporary signal processing and depth- imaging techniques to vintage data from the Phitsanulok Basin, onshore central Thailand, in which four overlapping vintage 3D land surveys were merged and imaged pre-stack to form a single volume. The vintage data processing was limited to the application of dip-filter-based noise attenuation, pre-stack time imaging and post-stack survey merging, which leads to unresolved geophysical challenges associated with each process. In the reprocessing, a cascaded application of surface-wave and coherent noise attenuation was followed by surface-consistent deconvolution that is robust against surface-inconsistent noise and suitable for stabilizing the amplitude and phase response of the embedded wavelet. 5D matching-pursuit Fourier interpolation technique was utilized for interpolation and regularization in offset-vector tile domain of the sparsely and irregularly sampled data. Anisotropic depth imaging was implemented to reduce the structural uncertainty. Additionally, pre-stack merging of the vintage seismic data facilitated accurate structural imaging in and around the overlap area of the surveys. The improvement attained in the reprocessed seismic images will reduce the risks associated with future development plans, overcoming the limitations of the suboptimal acquisition parameters.
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Understanding Stage IVD-Pink Reservoir through Hard Data-detailing Geoseismic, Integration of Updated PDA and Newly Constructed GDE
SummaryThe distribution trend of Stage IVD Pink is matches with the shelf edge cut in Southeast to Northwest direction which suggesting the entry point is coming from Baram and Champion delta. During syn-kinematic deposition of Stage IVD Pink, the sand transportation tries to find the lower structure as a main pathway towards distal toe-thrust area. The Stage IVD Pink behavior is deposited during syn-kinematic event where the deposition takes place during structuration forming ponded turbidites. Based on well and biostratigraphy analysis at Stage IVD Pink, it is correlatable to NN11/NN10. Seismic facies summary demonstrates 8 seismic facies categories interpreted in the area. The new analysis of Stage IVD Pink PDA covered 22 wells constrained within area of interest and failure analysis is generated based on 9 wells (excluding discovery and unevaluated wells) PDA shows reservoir as the main causes of exploration failure due to previous wells drilled targeting crestal part of toe-thrust area. Pink interval is deposited during syn-kinematic phase, hence thicker sands is believed to be deposited at the flank area and thinning onto the crest. The distribution of Stage IVD-Pink reservoir is limited towards distal toe-thrust as shown by NN11/NN10 zone at well 23-1.
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Chasing the Remaining Hydrocarbon in Carbonate Build-Ups of Central Luconia Field, Offshore Sarawak, Malaysia
Authors Z. Abdul Rahman, J. Baharom, N.F. Zawri and S.S. Ab RahmanSummaryOpen-winged carbonate platform characterised by thin carbonate wings were interpreted to have been deposited in situ as a thin carbonate platform during marine transgressions. 3D seismic data of the Terumbu Luconia covering an area of approximately 13,483 km2 was used in this study. The advancement in the interpretation technology allows extensive number of seismic horizons to be picked and mapped with consistent polarity. Seismic interpretations revealed that the open wings tend to extend for several kilometres away from the buildups along flat-lying surfaces and may have volumes significantly larger than the volumes of their corresponding buildup intervals. Central Luconia province is one of the major producing areas in Sarawak fields with almost 250 fields and 65 tcf recoverable gas discovered to date. However, most of the producing wells targeted to the main long-lived carbonate buildups. The results indicated that there is promising gas potential for NFE exploitation in the allochthonous play within the study area for further evaluation.
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Detached Offshore Bars. Testing a Stratigraphic Play, Offshore Sarawak, Malaysia.
SummaryOffshore bars are an enigmatic and often under-recognized constituent of the shallow marine deposition system. In the Pliocene aged, Cycle VI clastic sedimentary succession located offshore Sarawak Malaysia, offshore bars have been interpreted from sediments previously thought to be lower-to-middle shoreface deposits. The reclassification of these sediments from shoreface to offshore bars yields compelling exploration opportunities as detached bars, encased in shelfal mudstones may constitute stratigraphically isolated traps.
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Unlocking Significant Hydrocarbon Potential with Newly Identified Carbonate Play in North Luconia, Deepwater Sarawak, Offshore Malaysia
SummaryThis abstract presents the recent G&G work which led to identify Carbonate Play in North Luconia province deepwater area of Sarawak, offshore Malaysia. North Luconia, offshore Sarawak is a relatively frontier area for exploration having very sparse well density and presently low exploration activities. The understanding of petroleum system elements in this area is relatively fair to good. In the past most wells drilled in Northern Luconia deep-water, targeted Cycle I and Cycle II Clastic reservoirs. There are few wells drilled to target deep-water turbidites sands in Cycles V–VII. So far, no commercial hydrocarbon accumulation has been encountered, however there are few sub-commercial discoveries made in the region, have proven working petroleum system. Recent interpretation of Seismic 3D PSDM data leads to identification of a potential Pre-Cycle I ( Sequence-A Carbonate Play) in Late Eocene - Early Oligocene age. The integration of other G&G data, i.e., seismic, wells, and Gravity-Magnetic have been made to identify prospects in Sequence-A Carbonate Play in PETRONAS Carigali operated Blocks ND1, ND2 and ND3. Preliminary evaluation of Sequence-A carbonate play indicates evidence of huge hydrocarbon potential in deepwater area of Sarawak, which will certainly rejuvenate exploration activities in this region.
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Revealing the Reservoir Underneath Volcanic Rocks and Folding Structures in the Liaohe Basin
More LessSummaryMultiphase volcanic eruption and fault-related folding form good traps for hydrocarbon reservoirs in Liaohe-basin, China. Exploration activities in the deep Paleozoic section in the region have been limited due to poor subsurface imaging underneath complex overburden. Strong surface-related multiples are present, because of frozen surface conditions and high impedance contrasts between sediment layers and volcanic rocks. These multiples overwhelm weak primary signals in deep section. Meanwhile, drilling history revealed high spatial variation of the velocity in deep target zone due to major faults and volcanic rocks. Such complex overburden poses significant challenges for seismic imaging. Imaging is further complicated by the inadequacy of available data sets, which all have narrow-azimuth coverage and limited offsets. None of these challenges have been fully addressed in the vintage seismic processing. In this study, we first demonstrate the importance of 3D surface-related multiple elimination (SRME) after adaption for the data here, and then present iterative time-lag full-waveform inversion (TLFWI) to derive an accurate high-resolution velocity model that can correct the kinematic distortions due to the complex overburden. With a tailored flow, the Paleozoic section and the major Rongxi reverse fault are clearly revealed in our latest re-imaging, which helps reduce uncertainties for future exploration.
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Advanced Geostatistical Seismic Reservoir Characterization in the Growler Field
Authors A. Mannini, S.J. Yap, D. Cunha, E. Shirley, J. Zhou, A. Mathur, A. Mandong, R. Shaw and J. TingSummaryThe Growler field located in the Cooper–Eromanga Basin, South Australia, is an onshore field producing oil from the middle Birkhead formation of Jurassic age. The main producing area is a low relief four-way dip closed structure consisting of a channel reservoir of 15–20m thickness that has been mapped from the 3D seismic amplitudes and confirmed by the drilled wells. Interpretation of 3D seismic data has revealed relatively lower quality oil reservoir in the form of minor sandstone channels and crevasse-splay deposits. To draw strategy for optimum development of this field and to support further exploration campaign pre-stack seismic inversion has been carried out. An innovative workflow comprising iterative seismic petrophysics, rock physics modelling, preconditioning of seismic data was used to calibrate the seismic AVO response with well data. Deterministic inversion was carried out and litho-facies estimated using Bayesian inference to understand the intricacies of the aforesaid challenges before application of geostatistical inversion to derive highly detailed subsurface model. Joint facies and elastic properties inversion facilitated by geostatistical inversion using Markov Chain Monte Carlo method has resulted in good quality facies results that match wells at several blind locations and conform to the depositional setup of the area.
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Why Subsurface Uncertainties don't have to be Lognormal and other Practices to Avoid
By J. De JagerSummaryThe risks and volumes of oil and gas prospects are in most companies assessed in commercially available probabilistic Risk & Volume tools. Despite a lot of effort is put into this, the exploration community continues to over-predict (on average) the oil and gas volumes of prospects. This is in part due to some misunderstandings that lead to common practices that are best avoided. In this presentation several of these will be discussed: the incorrect assumption that subsurface uncertainties must be lognormal, incorrect truncation of uncertainty distributions at the low end, and the way that uncertainty is often confused for risk. A better understanding and application of these basic aspects of sound Risk & Volume assessments may reduce the risk of over predicting prospect volumes.
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Decomposing Zoeppritz: A Visual Interpretation of AVA
Authors M. Sams and T. KurniawanSummaryFor most people, the Zoeppritz equations are impenetrable and provide a barrier rather than an aid to interpreting seismic amplitudes in terms of key reservoir properties. Even very basic simplifications can be challenging for some. AVA blocky modelling is commonly used to visualise the AVA behaviour of half spaces, but these only provide limit use for the complexity of most geological situations where vertical variations are occurring at many scales. We propose that a deeper understanding of the AVA behaviour of seismic data is better achieved by visualising synthetic AVA gathers based on well log data, which have been decomposed into three terms representing the response to variations in acoustic Impedance, shear modulus and density. The decomposition shows how the AVA is governed by the vertical variations in the elastic properties and the inter-relationships between those elastic properties. These insights will allow the interpreter to more readily make the link back to the geology and the quantitative interpreter set expectations on the reliability of estimates of elastic properties from AVA inversion. Case studies for a soft gas sand and a hard wet sand are provided.
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Defining Reservoir Compartments and Baffles: A Case Study in Deepwater Sabah, Malaysia
Authors J. Jong, M.A. Khamis, S.M. Barker, R.C. Shoup and W.M.Z. W EmbongSummaryOne of the key challenges in deepwater exploration is the prediction of reservoir geometries. Basin floor fans, deepwater channel systems and crevasse splays, ponded turbidites and MTDs are the main depositional geometries that can result in reservoir compartmentalization and baffling in a shale-dominated environment. This study aims to define and understand the various reservoir compartments from a deepwater Sabah case study, applying both structural and stratigraphic approaches over the Kinarut to Pink stratigraphic intervals. The application of sequence-stratigraphic interpretation techniques in conjunction with sedimentary-processes enables geoscientists to unravel the complex deepwater depositional architecture. The integration of multiple G&G data is employed to define the deepwater reservoir setting and possible sand fairways. These methods include structural and sedimentary seismic analysis, seismic attribute studies and spectral decomposition analysis. The interpreted results are then related to regional deformation episodes, with a pre-kinematic phase and a post-kinematic phase observed. Their impact and controls on the sedimentation styles and the resultant variations in reservoir geometries and compartmentalization are then discussed.
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Influence of Frequency and Training Models on Physics-Guided Velocity Model Building
Authors S. Dhanapal, H. Rusmanugroho, M.D.D. Muhammed, J. Sun and J. LiSummaryVelocity model building (VMB) is subsequently used to provide subsurface velocity model for workflows such as seismic imaging and interpretation. As two widely used velocity model building techniques, ray-based tomographic approaches are not very effective in complex geological settings; and Full waveform inversion (FWI) approaches are computationally extensive and sensitive to initial model. The physics-guided deep learning based velocity model building, that involves deterministic, physics-based modelling and data-driven deep learning components, is designed to capture the subsurface salt body shapes and locations, with a small amount of training models. In this work, we further discuss the influence of dominant frequency and training models on the velocity prediction by using H-PGNN method. Our results show that, the higher the dominant frequency, the more accurate the prediction accuracy of the salt body shapes and background information. For more complicated velocity models and real datasets, simple synthetic training models are not capable of capturing the salt body shapes, nor the background information. A more practical synthetic training set with much more smoothed background layered structures is more suitable to predict complicated models.
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A Review of Digital Transformation Initiatives for Real-Time Formation Evaluation
Authors K. Katterbauer, A. Al Shehri and A. YousifSummaryWe present a thorough overview of the state-of-the-art developments of artificial intelligence and automation, including robotics, in the area of formation evaluation, well logging and reservoir monitoring. The 4IR is and will be a key component in the development of new technologies in these domains and more broadly in upstream oil operations. While there are substantial challenges that need to be overcome in the near future, there is also tremendous potential with the availability of an increased number of interconnected sensing devices for real-time monitoring and interventions [ 25 ]. The 4IR trend is clear and unrestrainable also in Formation Evaluation: automation of measurements, interpretation, interventions and decision making, with minimal human intervention; as well as extensive use of artificial intelligence to support data analytics and interpretation in a framework of indirect measurements, complex characterization, data scarcity and ill-posed problems.
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We Think we're in Control, but are we? A Case Study from Offshore Sarawak-East Malaysia
Authors S. Nazari, P.A. Restrepo-Pace, C. Lee and H.'. Ahmad MunifSummaryStructural restoration and structural forward modelling of 2D cross sections presented here are used to provide structural validation and insights into the kinematic evolution of a hydrocarbon field offshore Sarawak. Structural restoration is the primary workflow used for interpretation validation. Structural forward modelling, on the other hand, provides holistic kinematic review as it constrains deeper fault shape trends. During cross section balancing fault throw, horizon cutoffs and seismic character across faults is checked. The datasets are loaded in two different structural platforms, applying similar methodology in order to investigate how their algorithms operate in an effort to establish more efficient ways to conduct routine modelling. Software A & Software B perform restoration primarily using the block restoration, vertical slip and flexural slip as the parameters. Reference horizon is used and faults slips are removed in order to restore interpreted surfaces and seismic ( Nunns, 1991 ). Due to the uncertainty of deeper fault geometry (poor imaging), structural modelling is used to constraint fault shape. We have now conducted restoration for interpreted seismic sections and forward modelling for fault trend trajectory for Sarawak offshore. Thus, comparison between the restoration results and forward modelling using two different software to narrow down the uncertainty.
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Seismic Characterization of Carbonate Flank Deposits Delineating Upside Potential : A Case Study in Central Luconia
Authors H. Ismail, R.S. Djumeno, A.H. Abd Latiff and N.A. AzmanSummaryCarbonate Flank deposits considered as one of the emerging hydrocarbons play within the proven plays in Central Luconia Sarawak. The potential of hydrocarbon occurrences within this play has been proven by one of the producing fields. Seismic characterization and mapping techniques utilizing multi attributes extractions and well data analysis will aid in delineating the Flank deposits features and connectivity. Detail seismic evaluation of the untapped resources within the carbonate flank deposits is expected to provide good input to assist volume estimation within Central Luconia aimed for hydrocarbon monetization and future resource addition.
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Empirical Anisotropy Correction in Deviated Well Logs from the Malay Basin.
Authors S. Ronghe, A. Locke, S. Teng, S. Chee Chuan and A. ChuangSummaryShales in the Malay Basin are anisotropic. Well log measurements of p-velocity and s-velocity are affected by shale anisotropy, especially in deviated wells. Anisotropic measurements create inconsistency within the data set and impact results and interpretation. In this paper we present a novel, empirical technique to correct for anisotropic effects in velocity logs, referenced to a rock physics model.
Data comprised 22 wells from the Malay Basin including 15 with varying angles of deviation (up to 70°). The wells were spread across an area of approx 2,000 sq km, covered by seismic angle stacks. The project involved absolute seismic simultaneous inversion followed by lithology and fluid interpretation, calibrated to a statistical rock physics model.
Velocity logs from deviated wells were corrected for anisotropy. The correction involved adjusting low frequency trends of the logs to the trends from vertical wells for non-reservoir lithologies. The correction was applied proportional to the magnitude of well deviation - as the angle of deviation increased, rock physics trends from vertical wells carried greater weight.
Anisotropy corrections improved the consistency of elastic logs across wells and enabled their tighter integration with seismic for reservoir characterisation in deriving predictions of lithology and fluid distributions.
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Pore Pressure and Drilling Experience: A Deepwater Well Case Study in the Gulf of Mexico
Authors H.Y. Sau, B.C. Ong, F. Wijnands, N.N.H. C Soh, M.S. Masnan, F.A. Ismail, J. Sagahon and M.R. Paul TingaySummaryThis is a case study of the predrill pore pressure estimation and post-drill pore pressure analysis of Well X in the Gulf of Mexico. Well X is a deepwater wild cat well in the Gulf of Mexico with very sparse offset well data. The objective of Well X is to test the hydrocarbon presence in the Miocene aged deepwater stacked channels/lobes in an NW-SE trending toe thrust anticline with a reverse fault in the core and edge of the structure at a depth of ∼ 3600 m TVDDF. Conventional 1D pore pressure prediction methods have limitations and high uncertainty in structurally complex deepwater frontier exploration areas. Pore pressure predictions rely mainly on seismic interval velocities and a velocity-pore pressure transform, particularly in areas with limited offset wells. With an excellent geological understanding, pore pressure analysts integrate all the geological inputs into a robust predrill pore pressure model for the well design and planning. Nevertheless, all pore pressure models have uncertainties, and a key goal of pre-drill pore pressure prediction is to appropriately capture these uncertainties to enable safe well design.
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Unleashing Potential Stratigraphic Play via High Resolution Strata-Slicing Approach in North Malay Basin, Offshore Peninsular Malaysia
SummaryIdentifying new opportunities in the Malay Basin is challenging as heavy exploration activity has taken place with more than 700 wells drilled since 1969. Nonetheless, Yet-to-Find (YTF) estimation in 2021 indicates around 3 Bboe of remaining potential are awaiting to be explored. This paper describes the utilisation of specialised seismic interpretation technology in combination with high resolution strata-slicing, as an alternative approach in identifying exploration potential within North Malay Basin. The geological nature of the NMB reservoirs comprising lower coastal plain channelised system, provides an ideal geological setting to test this application. More than 400 horizon strata slices were generated from the top of basement to the seabed using merged 3D seismic data obtained from Relative Geological Time (RGT) model using PaleoScan™ software. The strata slices are then used for amplitude attributes extraction and spectral decomposition analysis, in combination to interpret the geomorphological features and define it’s associated geobodies where approximately 250 prospects were identified. One of the largest prospects yield a gas-initially-in-place (GIIP) of up to 2 Tscf. These findings are dominantly represented by fluvial channels within Groups F to I, which provided a new insight in a relatively mature basin.
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Enhancing Interwell Saturation Mapping via an Innovative Quantum Machine Learning Framework
Authors K. Katterbauer and A. Al ShehriSummaryUtilizing a quantum machine learning method for mapping interwell saturation based on well logs and electromagnetic tomography provides a data-driven approach to deep diagnostics of the reservoir, honoring both geology as well as reservoir dynamics. The 4IR framework has exhibited a strong estimation quality of the water saturation profile for a realistic reservoir box model via training the network with well-log data in the near-wellbore zone.
This new approach can be readily supplemented with new data to improve the accuracy of the predicted saturation maps. The 4IR framework is flexible enough to be adapted to different geological structures and petrophysical relationships and the results from this reservoir box model study exhibited great potential in a broader application of the technique for interwell saturation mapping.
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Delineating Prograding Deposit of Syn-Rift Play of North Malay Basin via Seismic Attributes and Wheeler Transformation
SummaryThis study was carried out in the Late Oligocene to Early Miocene interval of the North Malay Basin offshore Peninsular Malaysia. This paper demonstrates an integrated interpretation of geological information from seismic mapping, attributes analysis and seismic sequence stratigraphy via wheeler transformation in assessing the prograding deposit within the top synrift of the area. The result of this study shows that alternative methodologies from semi-automated interpretation and Relative Geological Time (RGT) model to the application of Wheeler Transform are able to enhance the definition and delineation of prograding sequence within the top synrift of North Malay Basin. The combined approaches of refined interpretation of the seismic supplemented by generation of instantaneous phase and thinning attribute from RGT, have successfully mapped the strata termination plus its associated thinning and thickening patterns. Together with other attributes, the clinoform outline within the interval were greatly enhanced which helps in extracting potential prospect. The overall results indicate a series of interesting stratigraphic/seismic geomorphological features representing the potential prospects (prograding sandy deposit?) that could add to the Yet-To-Find (YTF) resources candidates.
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Ultra-Shallow Water OBN offshore Sarawak - High-Resolution Model Building to Image Shallow Gas and Complex Geology
Authors A. Verba, W.L. Cheah, J.W.L. Ming, S.W. Cheok, S. Chen, S.B.A. Rahman, T.W. Hoong and A.I. YusofSummaryOil and gas fields offshore Sarawak in the Malaysian basin present a number of challenges for seismic imaging due to the shallow-water environment and uncertainties in seismic reservoir definition and reservoir characterization. These are mainly due to a complex overburden, including heavy faulted zones and shallow gas accumulations. Legacy seismic images show poor fault delineation and a lack of continuity of events beneath the shallow gas, due to the limits of both the acquisition and imaging technologies previously available.
An ocean-bottom node (OBN) survey was conducted in the offshore Sarawak area due to the low-frequency, full-azimuth, and ultra-long offset information the OBN data would provide. These benefits can be used to improve illumination of the main target reservoir. When combined with contemporary signal processing and depth imaging technology, it can reveal the geological structures and provide reliable amplitude especially beneath the shallow gas body for reservoir characterization.
This paper focuses on the earth model building and describes the combination of full-waveform inversion (FWI), common-image-point (CIP) tomography and Q tomography workflows to build detailed and accurate velocity and Q models to improve the seismic imaging, capture overburden heterogeneity, and uncover the structures masked by the gas body above the target area.
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Management and Mitigation of CO2 Emissions During Marine Seismic Surveys
Authors A. Long, M. Christiansen and C. JamesSummaryTo take urgent action to combat climate change and its impacts, we have committed to reduce relative CO2 emissions (t CO2 per CMP km) by 50% compared to 2011 within 2030. DataOps optimization of vessel and survey management has been applied to four Titan-class Ramform seismic vessels since 2020 and allows realtime tracking of fuel consumption, CO2 emissions and many vessel performance metrics. Guided by the digital platform used to measure and manage the vessel operations, the two focus areas for attention are elements of survey design and drag reduction initiatives. Tools are being developed to translate modelled dynamic loads and drag of specific acquisition configurations into modelled fuel consumption versus vessel speed. The ‘equivalent CO2 budget’ should be predictable for a survey as a function of different key acquisition parameters, at least qualitatively in terms of comparative configurations.
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Arising Play: Post MMU Clastics with Lupar-Rajang Systems as Reservoir Provenance in West Sarawak
Authors M.I. Mahmood, S.H. So, M.N. Zubir, S.N. Jamil and M.A. AriffSummaryWest Sarawak is located at the western most of Borneo, tucked to the east of Natuna Basin. The region can be divided into three provinces namely West Luconia, Southwest Sarawak and Tatau. Exploration had begun in the 1970s with many gas discoveries in Cycle V clastics and Cycle IV carbonates. Despite all, there are still more to learn about this region’s tectonic and stratigraphy. Cycle VI to VIII has been perceived as having low prospectivity with high uncertainty in reservoir presence. Recent evaluations suggest, thick package of sediments within Cycle VI to VIII have deposited in Bunguran Inboard. Based on the evidence, there is a high possibility for this package to be sandy with Lupar and Rajang as the provenance for this reservoir.
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Trends And Observations On Co2 High Uncertainty To Revitalize West Luconia.
Authors M.I. Mahmood, S.H. So, M.N. Zubir, H. Kahar and M.A. AriffSummaryWest Sarawak is located in between Central Luconia Province and Natuna. The region consists of West Luconia, Southwest Sarawak and Tatau province. Since 1970s, there are approximately 25 exploration wells drilled the region. Considering the areal extent of this region (80000 sq. km), the wells are deemed as sparse, thus making it a frontier region. Even though the drilling success rate at West Sarawak is high, CO2 in the reservoirs appeared to be ranging from 2% to 90%. Consequently, the region is well known as ‘cursed’ by CO2. Recent studies have indicated that West Sarawak tectonic and stratigraphy settings could influence the CO2 occurrence and accumulations. Deep-seated faults could be the conduit to transport CO2 from deep source to the reservoirs. In addition to that, different stratigraphy such as Cycle VI and Lower Cycle V may capture lower CO2 depending on the migration pathways. It was also observed that CO2 Halo diagenetic effect can be associated with the occurrence of CO2, however it has no correlation with the concentration of CO2.
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Deep Seated Faults Reactivation; Insight from Subsidence Analysis, West Luconia-Sarawak Basin-Malaysia
Authors M.L. LEE, S. Sherkati, S.S. Mustahim, S.H. So, M.I. Mahmood and M.N. ZubirSummaryWestern flank of Sarawak basin subdivided into 5 main geological provinces namely Bunguran Trough, West Luconia Rim, SW Luconia, Half Grabens and Sibu. The current exploration target is focusing from Pre-Cycle I to Cycle VIII (late Paleogene-Neogene). Play targets ranging from marine clastic, carbonate, terrestrial clastic and basement play. High uncertainty of CO2 concentration in West Luconia is one of the main challenges for hydrocarbon exploration, which linked with deep seated faults reactivation. Deep burial depth and poor seismic imaging prevent understanding the inherited faults reactivation timing and its impact on structuration. The aim of this study is to use subsidence analysis and 2D/3D regional structural restoration to overcome this problematic. Furthermore, paleotopography for different time steps were estimated and sedimentary distribution relation with tectonic evolution discussed. In conclusion, restoration and back striping analysis in west of Sarawak basin show deep seated faults most probably reactivated several times in the past. Deep seated faults reactivation had a major impact on seabed topography and sedimentation accordingly and CO2 migration from mantle. Our study highlighted the area with higher potential for carbonate deposition during Cycle III & IV.
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