Sabah Basin Research Articles

Enhancing machine learning-based seismic facies classification through attribute selection: application to 3D seismic data from the Malay and Sabah Basins, offshore Malaysia

Over the past few years, the use of machine learning has gained considerable momentum in many industries, including exploration seismic. While supervised machine learning is increasingly being used in seismic data analysis, some obstacles hinder its widespread application. Seismic facies classification—a crucial aspect in this field—particularly faces challenges such as the selection of appropriate input attributes. Plethora of seismic attributes have been created over the years, and new ones are still coming out. Yet, several have been deemed redundant or geologically meaningless. In the context of machine learning, it is crucial to avoid these redundant and irrelevant attributes as they can result in overfitting, building unnecessary complex models, and prolonging computational time. The current study incorporates an attribute selection approach to seismic facies classification and evaluates the importance of several available seismic attributes. Two datasets from the AN Field and the Dangerous Grounds region offshore Malaysia were utilized. Several attribute selection techniques were evaluated, with most of them yielding perfect attribute subsets for the AN dataset. However, only the wrapper and embedded methods could produce optimal subsets for the more complex Dangerous Grounds dataset. In both datasets, distinguishing the targeted seismic facies was mainly dependent on amplitude, spectral, and gray-level co-occurrence matrix attributes. Furthermore, spectral magnitude components played a significant role in classifying the facies of the Dangerous Grounds broadband data. The study demonstrated the importance of attribute selection, established a workflow, and identified significant attributes that could enhance seismic facies classification in Malaysian basins and similar geologic settings.

Organic geochemical and petrological investigations of the upper miocene bongaya formation in the pitas, onshore sabah basin, and its relevance for hydrocarbon potential

The Upper Miocene Bongaya Formation coal, carbonaceous shale, and shale sediments were collected to investigate their origin, types, and maturity. The main objectives of this study were to verify and update previous claim of possible hydrocarbon showings and to gain new insights about the petroleum potential using different geochemical analysis approach. The primary methodology used in this study is the pyrolysis technique and coupled with petrographic analysis. The bulk geochemistry results revealed that the Bongaya sediments serve as favorable source rock, with the total organic carbon (TOC) content ranging from 0.90 to 63.10 wt% by weight, indicating fair to excellent organic richness. The coal samples exhibited the highest TOC values, followed by carbonaceous shale samples, while shale and coal laminated with sandstone samples displayed fair TOC amounts. Most of the Bongaya sediments analyzed in this study exhibited hydrogen index (HI) values of less than 200 mg HC/g TOC, indicating Type III organic matter, which signifies a significant influence of terrestrial organic matter. However, three coals displayed comparatively higher pyrolysis HI values, corroborated by Pyrolysis gas-chromatography (Py-GC) results and maceral types, indicating a mixture of Type II/III kerogen. This suggests that the Bongaya Formation sediment has the potential to generate gas with minor oil. Maceral analysis also revealed that most of the coal samples contained a high content of resinite maceral, which explains the waxy composition of the oil. The organic matter in the analyzed Bongaya sediments was found to be immature for petroleum generation, as evidenced by low huminite reflectance data (lower than 0.50% VR) and Tmax values between 372 and 432 °C. Consequently, the kerogen in the studied onshore Bongaya sediments has yet to enter the hydrocarbon cracking (catagenesis) phase before expelling petroleum. Therefore, it is essential to consider the offshore equivalent Bongaya sediments, which may be laterally extended offshore and buried at deeper depths to attain optimal maturity for hydrocarbon generation.

The Impact of Clay Minerals on the Porosity Distribution of Clastic Reservoirs: A Case Study from the Labuan Island, Malaysia

Clay mineral content and diagenetic processes are vital factors that affect reservoir quality, especially in tight clastic reservoirs, which are crucial for industrial and scientific purposes. The presence of clay minerals poses one of the most significant challenges in evaluating sandstone reservoirs’ quality. Even though wireline logs may provide a good indication of the reservoir quality, there have been cases where they have failed. This work focuses on the clay minerals’ impact on the porosity and permeability of a clastic reservoir. Typical outcrops from Labuan Island, Brunei–Sabah Basin, were chosen as a case study to investigate the petrophysical and petrographic parameters together with clay mineralogy profiling. The effects of the clays on the petrophysical parameters of the sandstone reservoir were evaluated through air permeability, spectral gamma ray measurements, a petrographic thin section analysis, a visual porosity estimation, and a grain size analysis. Field and petrographic studies revealed that Belait and Temburong formations contain massive, interbedded, laminated, and cross-bedded sandstones. Using an image analysis of the thin sections, porosity values ranged from 7.3% to 23.5%, with different macro and micro porosity distributions. According to the spectral gamma-ray investigation and air permeability, permeability reduction is strongly associated with clay minerals. The microporosity and permeability of the analyzed samples showed a unique pattern influenced by the grain size distribution. It was found that the textures dominated by mud grain size had a more significant impact on the air permeability and visual porosity, with coefficient of determination values of 0.83 and 0.70, respectively. The Belait Formation displayed a higher porosity and permeability compared to the Temburong Formation. This research provides new insight into the potential reservoir of Stage IV (the Belait Formation offshore equivalent) compared to Stage II (the Temburong Formation offshore equivalent).

E&P Notes (March 2022)

E&P Notes (March 2022)

Source rock pyrolysis and bulk kinetic modelling of Miocene sedimentary sequences in southeastern Sabah, Malaysia: The variability of thermal maturity to oil-gas producing kerogen

The study reports a new organic geochemical evaluation for a petroleum source rock in the Southeastern (SE) Sabah basin. The analyses focus on Kalabakan, Tanjong, and Kapilit Formation deposited in the deltaic-shallow marine environment stratigraphically from the Early to Late Miocene sequences. The basin sediments are part of the hydrocarbon prolific Tarakan basin, extending from the northernmost of Kalimantan Indonesia to the southeastern Sabah (mainly onshore area). The hydrocarbon generation of Kapilit and Tanjong Formation pinnacles the Total Organic Carbon (TOC) contents that range from 0.62 to 81.97 wt% and 0.97–92.96 wt% respectively. The dominant black shale in Kalabakan Formation has lower TOC content between 0.50 and 1.82 wt%. The results in the Rock-Eval S2 of Kapilit (0.31–351.61 mg HC/g rock) and Tanjong Formation (3.32–239.78 mg HC/g rock) have excellent source rock potential compared to the Kalabakan Formation (0.12–1.19 mg C/g rock) with fair to good source rock potential. All three formations give a wide maturity range of vitrinite reflectance (VRo) and Tmax values, from immature to over-mature stage. Stratigraphically from youngest to oldest Miocene sequences, the Tmax increases with increasing VRo values. The dispersion of organic matter that requires high maturity and overburden of thick upper succession over Kalabakan Formation reflects a higher maturity stage than the Tanjong and Kapilit Formations. Pyrolysis results in Kapilit, Tanjong, and Kalabakan Formation has HI values to varies between 50 and 498 mg HC/g, 157–367 mg HC/g and 14–110 mg HC/g TOC respectively. The binary plot of HI versus Tmax supported by Py-GC pyrolysis marks that the Kapilit source rock is dominated by Type II-III kerogen, potentially generating immature to mature oil and gas prone. Tanjong Formation portrays a mature to late mature stage of Type III kerogen with a minor Type II kerogen capable of producing mixing of oil and gas prone, with mainly gas. The Kalabakan Formation shows a post-mature Type III and IV kerogen that generates gas or barren source rock. In terms of bulk kinetic evaluation, both Kapilit and Tanjong Formation are derived from heterogeneous organic matter. The projected petroleum temperature varies substantially due to the compositional variation. The onset of bulk petroleum generation in the Kapilit and Tanjong Formation occur at 112 °C - 128 °C and 127 °C - 142 °C respectively. The results are consistent with the maturity generated where the Tanjong has higher thermal maturity than Kapilit Formation due to stable aromatic Type III kerogen. Generally, all samples show great variability in thermal maturity and hydrocarbon generation potential, which that be influenced by the tectonism and development of sediments in the basin. The Early Miocene source rock yields post mature gas prone and continues to generate hydrocarbon that consists of mature oil and gas prone from younger source rocks.

Simulating the effect of salinity and kaolinite concentration on low salinity water flooding in sandstone reservoir of Sabah Basin

Low salinity waterflooding (LSWF) is a technique that involves injection of water at low salinity to improve oil recovery of matured oilfields. The primary objective of this study is to determine the effects of LSWF at different salinity in sandstone reservoirs on oil recovery and to simulate the effect of rock hysteresis on oil recovery. Reservoir simulation softwares ECLIPSE 100 and Petrel were utilized to simulate low salinity waterflooding in sandstone reservoir of the Sabah Basin. This study considers salinities from 100 up to 500 ppm (parts per million) at 1100 STB/day and 500 psi bottom-hole pressure. The results revealed that the highest oil recovery was 17.78 MMSTB at 100 ppm, while the lowest was 17.00 MMSTB at 500 ppm. This demonstrates that lower salinity water result in higher oil recovery. The difference in eventual recovery is not substantial when compared to the rate of recovery. Additionally, there is a strong link between incremental oil recovery and kaolinite content as well as the compaction and sand production. Oil is indirectly mobilised because of the clay particle composition. In addition, compaction causes an increase in residual oil saturation and irreversible water saturation. Furthermore, the larger the amount of kaolinite clay, the more oil may be extracted progressively.

Aseismic and seismic impact on development of soft-sediment deformation structures in deep-marine sand-shaly Crocker fan in Sabah, NW Borneo

Soft-sediment deformation structures are present within the deep-marine fan of the West Crocker Formation, Sabah Basin, NW Borneo. Focus of this study is to highlight the impact of seismic and aseismic activities on the development of these structures and their distribution in deep-marine fan. Twenty-nine types of deformation structures were identified during the study of twelve exposed sections. These structures were grouped into five categories: i) water-escape structures, ii) sole marks, iii) clastic intrusions, iv) deformed laminations, and v) syn-depositional brittle and ductile deformation structures. The sediment deformation is interpreted to be caused either by aseismic processes like slope failure, gravity collapse, sediment overloading, density gradient, seismic induced mechanisms such as earthquakes, tectonic uplift, or combined effect of seismic and aseismic events. These structures are classified based on type of features developed during semi-consolidated phase of rock deposition. The seismite structures i.e., clastic intrusions, deformed laminations, and syn-depositional structures are correlated with active collisional tectonics during the Late Paleogene times in the Sabah Basin. In the present work, a generalized conceptual model has also been proposed for the development of soft-sediment deformation structures in a submarine fan environment. Dewatering structurers and rapid sedimentation features are associated with inner fan, load and flame structures are present within middle fan, while contorted layers, slumps and mass-transport deposits are linked with distal fan settings.

Facies Heterogeneity and Lobe Facies Multiscale Analysis of Deep-Marine Sand-Shale Complexity in the West Crocker Formation of Sabah Basin, NW Borneo

Deepwater lobes constitute a significant volume of submarine fans and are primarily believed to exhibit a simple sheet geometry. However, recent studies interpret the geometries of these deep-marine lobes as distinct with respect to the complexity of the facies and their distribution. Hence, a conceptual model of deep-marine sediments is essential to discuss the deep-marine sediments associated with the fan and lobe architecture. The present study highlights the facies heterogeneity and distribution of various lobe elements at a multiscale level by considering a case study of the West Crocker Formation of Sabah in northwest Borneo. The formation was logged on a bed-to-bed scale from recently well-exposed sections, with a total vertical thickness of more than 300 m. The lithological characteristics, bed geometry, sedimentary textures and structures of individual beds were used to categorize the rock units into nine sedimentary lithofacies: five sandstone lithofacies (S1–S5), one hybrid bed facies (H), two siltstone facies (Si1 and Si2) and one shale or mudstone facies (M). These facies were grouped into four facies associations (FA1–FA4), which were interpreted as lobe axis (FA1), lobe off-axis (FA2), lobe fringe (FA3) and distal fringe to interlobe (FA4) facies associations. This study is applicable for the distribution of lobes and their subseismic, multiscale complexities to characterize the potential of hydrocarbon intervals in deep-marine sand-shale system around the globe.

Geothermal Gradient And Heat Flow Maps Of Offshore Malaysia: Some Updates And Observations

An update of the geothermal gradient and heat flow maps for offshore Malaysia based on oil and gas industry data is long overdue. In this article we present an update based on available data and information compiled from PETRONAS and operator archives. More than 600 new datapoints calculated from bottom-hole temperature (BHT) data from oil and gas wells were added to the compilation, along with 165 datapoints from heat flow probe measurements at the seabed in the deep-water areas off Sarawak and Sabah. The heat flow probe surveys also provided direct measurements of seabed sediment thermal conductivity. For the calculation of heat flows from the BHT-based temperature gradients, empirical relationships between sediment thermal conductivity and burial depth were derived from thermal conductivity measurements of core samples in oil/gas wells (in the Malay Basin) and from ODP and IODP drillholes (as analogues for Sarawak and Sabah basins). The results of this study further enhanced our insights into the similarities and differences between the various basins and their relationships to tectonic settings. The Malay Basin has relatively high geothermal gradients (average ~47 °C/km). Higher gradients in the basin centre are attributed to crustal thinning due to extension. The Sarawak Basin has similar above-average geothermal gradients (~45 °C/km), whereas the Baram Delta area and the Sabah Shelf have considerably lower gradients (~29 to ~34 °C/km). These differences are attributed to the underlying tectonic settings; the Sarawak Shelf, like the Malay Basin, is underlain by an extensional terrane, whereas the Sabah Basin and Baram Delta east of the West Baram Line are underlain by a former collisional margin (between Dangerous Grounds rifted terrane and Sabah). The deep-water areas off Sarawak and Sabah (North Luconia and Sabah Platform) show relatively high geothermal gradients overall, averaging 80 °C/km in North Luconia and 87 °C/km in the Sabah Platform. The higher heat flows in the deep-water areas are consistent with the region being underlain by extended continental terrane of the South China Sea margin. From the thermal conductivity models established in this study, the average heat flows are: Malay Basin (92 mW/m2), Sarawak Shelf (95 mW/m2) and Sabah Shelf (79 mW/m2). In addition, the average heat flows for the deep-water areas are as follows: Sabah deep-water fold-thrust belt (66 mW/m2), Sabah Trough (42 mW/m2), Sabah Platform (63 mW/m2) and North Luconia (60 mW/m2).

Stratigraphic evolution of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform Region, Malaysia

The onshore and shallow marine conventional hydrocarbon resources around the world are mostly at the maturation phase and hence, exploration activity globally, showing increasing interest into progressively deeper water hydrocarbon prospects such as South China Sea basins. However, a comprehensive understanding of basin tectonics, depositional history, and petroleum systems of the basin is required to deduce the exploration prospectivity of these deeper reservoirs. The Sabah Basin is a prolific hydrocarbon province in Southeast Asia and has a significant economic impact on this part. Recent discoveries in the deep-water hydrocarbon prospects in the NW Sabah Trough prompted a comprehensive investigation of the surrounding area, e.g., Dangerous Grounds for hydrocarbon prospectivity. Previous studies in the Dangerous Grounds mainly focused on the sparse 2D seismic and gravity-magnetic data analysis. A systematic review of stratigraphic evolution has not been presented thus far in the published literature. In this paper, recently acquired high-resolution 3D seismic data with the core and cuttings and conventional well log data from the adjacent areas have been combined to characterize the stratigraphic evolution of the Dangerous Grounds in the NW Sabah Platform. Seven horizons interpreted from the 7570 sq. km 3D seismic data, calibrated with the global sea - level curve and geological time scale, to establish the stratigraphic evolution in the study area. Based on distinct structural and seismic characteristics, and calibrated with the adjacent regions well data, two mega-sequences, namely, lower syn-rift and upper post-rift mega-sequences, have been identified and evaluated. The Paleocene to Early Oligocene syn-rift sequence consists of clastic sedimentary fill in grabens and half-grabens is overlain by Late Oligocene to recent post-rift sedimentary successions represented by siliciclastic and carbonates deposits. Major depositional units within these two mega-sequences, including carbonate, channel, mass transport deposits, and turbidites have been identified and evaluated. During Late Oligocene to Middle Miocene, the area has witnessed the deposition of carbonate platform and reefs on top of pre-existing structural highs. Late Oligocene to Middle Miocene channel-levee complexes with convex upward sand filling features is prominent in the seismic data. Mass Transport Deposits and turbidites have also been observed above the Middle Miocene Unconformity with distinct seismic characteristics. The pelagic and hemipelagic nature of the sedimentary succession deposited from Pliocene to recent in a passive margin condition have also been interpreted from their unique seismic features. Paleocene-Early Oligocene syn-rift siliciclastic hydrocarbon play, Late Oligocene-Middle Miocene carbonate play, and Late Miocene turbidite play within the study area have been interpreted.

Sequence biostratigraphic framework for the Oligocene to Pliocene of Malaysia: High-frequency depositional cycles driven by polar glaciation

This paper reviews quantitative biostratigraphic data from 101 petroleum exploration wells from the Malay, Sarawak and Sabah basins, and places the stratigraphy of each area into a precise chronostratigraphic framework comprising 41 transgressive-regressive depositional packages which are fully defined here. Each package is ‘fingerprinted’ by foraminiferal, nannofossil and palynological index fossils, and then tied to the global pattern of glacio-eustatic sea level and climate changes based on the global δ18O and δ13C datasets used to calibrate the geological timescale. The result is a tightly constrained chronostratigraphic framework that is applicable from deep to shallow water and is of high accuracy. It is concluded that there is a sedimentation ‘pulsebeat’ across Southeast Asia, independent of local and regional tectonics, driven by patterns of global climate change. For the Oligocene and Miocene, Antarctic glaciation is the key driver, whereas the Pliocene cycles are mainly driven by the expansion and contraction of Northern Hemisphere glaciers. The new chronostratigraphic framework allows unconformities across Malaysia to be better characterised, and the different classification schemes of seismic “Groups” in Malay and Penyu basins, “Cycles” in offshore Sarawak and “Stages” in offshore western Sabah to be correlated. Also, with a clear understanding of the effect of fluctuating sea levels on the stratigraphy of the region, it is easier to make firm judgments regarding the effect of tectonics. The study also characterises systems tracts from shelf to basin floor using biostatigraphic assemblages, which should help in ground-truthing the architecture of depositional sequences in the region based on seismic. The new framework is proposed as an alternative to the outdated TB scheme of Haq et al. (1988), widely used to interpret depositional cycles across Sarawak and Sabah.

Seismic attribute analysis of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform region, Malaysia

The Sabah Basin is a prolific hydrocarbon province in Southeast Asia and has a significant economic impact on this part. Recent discoveries in the deep-water hydrocarbon prospects in the Northwest Sabah Trough prompted a comprehensive investigation of the surrounding area, e.g., Dangerous Grounds for hydrocarbon prospectivity. Previous studies in the Dangerous Grounds mainly focused on the sparse 2D seismic and gravity-magnetic data analysis. A systematic review of detailed depositional history has not been presented so far in the published literature. To achieve this, recently acquired high-resolution 3D seismic data and well information have been used for seismic attribute analysis to establish the structural features and depositional pattern from the Paleocene to recent age. Two major sedimentary sequences have been evaluated from the seismic data, which include syn-rift and post-rift sequence. The pre-rift sequence considered to be the acoustic basement is overlain by syn-rift sequence, deposited during the Paleocene to Early Oligocene age. Spectral decomposition analysis demarcates paleo-lows/depocenters, consist of siliciclastic sedimentary fills in grabens and half grabens with the syn-sedimentary deformation. Geobody interpretation helps to understand the different phases of syn-sedimentary faulting with the presence of antithetic faults in the grabens. Late Oligocene to Middle Miocene carbonate platform and reefs has been observed on top of the pre-existing structural highs. Sweetness attributes enable to appraise the reef structure to demarcate lithofacies boundaries. Variance and amplitude extraction maps reveal the development of reefs on top of the carbonate platform. Amplitude extraction map reflects the Late Oligocene to Middle Miocene channel-levee complex with the convex upward unconsolidated sand filling pattern. Sweetness map helps to delineate the meandering channel boundary, channel geomorphology with ox-bow lake, point bar, and west to east channel shifting. Carbonate and clastic dominated areas have been differentiated in the southwest part. Slides and debris flow Mass Transport Deposits, Late Miocene turbidites have been observed above the Middle Miocene Unconformity and evaluated based on their distinct seismic characteristics. During the Pliocene to recent, the basin has witnessed the deposition of thick pelagic-hemipelagic sediments in the outer-neritic to the bathyal environment in the passive margin condition.

“Fractured basement” play in the Sabah Basin? – the Crocker and Kudat formations as hydrocarbon reservoirs and their risk factors

“Fractured basement” play in the Sabah Basin? – the Crocker and Kudat formations as hydrocarbon reservoirs and their risk factors

Structural Analysis of Northwest Sabah Basin by 2D Reconstruction of Seismic Sections

The tectonic evolution of thrust fold belt and thrust sheet zone in Northwest Sabah basin was described based on balanced reconstruction of seismic sections representing Mid-Miocene to Recent deposits. The study area is located at the center of a wide crustal deformational zone bordered by the Sunda Shelf on the northeast, Sulu Sea in the southwest and the South China Sea in the northwest. Balancing cross section can be applied after the deformed geological structure geometry is accurately determined from seismic sections and 7 seismic stratigraphic unit from 15 Ma until Recent is consecutively restored. There are four steps involved in retro-deformation processes beginning with removing all faults displacements followed by unfolding the folds, isostasy correction and finally the removal of each compacted layer parts or decomposition. Wider fold wavelengths with least thrust faults were observed from south to north in the seismic sections ranging from 12 to 4 km with an average of about 7 km, while smaller fold wavelengths and more thrust faults were observed in the north based on the same seismic sections. In general, the reconstructed cross sections revealed compressional tectonic deformation activity as shown by shortening strain trending NW-SE. Measurement of total shortening shows that thrust fold belt is imbalance by an exceeds of 14.7 km and more active compared to thrust sheet zone which has only 0.9 km. Results of the study also indicate facies destruction due to shortening which is decreasing towards Pliocene or younger deposits.

Application of Simultaneous Inversion Characterizing Reservoir Properties in X Field, Sabah Basin

X field located between the East Baram Delta and Southern Inboard Belt, which is elongated northwest to southeast direction in Middle Miocene Sabah Basin. Previous studies were unable to differentiate the lithology and fluid distribution in the field by using conventional reservoir characterization approaches for example amplitude versus offset (AVO) analysis and post-stack deterministic inversion due to the low contrast in P-impedance between gas sand and shale. Thus, the goal of this approach is to obtain a reliable estimation of P wave velocity (VP). S-wave velocity (Vs), and density (ƿ). From these parameters, we predict the fluid and lithology properties for better reservoir characterization. A feasibility analysis was conducted and the results show that prediction of the hydrocarbon reservoir in X field is feasible using P-impedance and Vp/Vs. Consequently, the simultaneous inversion is carried out to derive the rock properties such as density, P-impedance, S-impedance, Lambda-rho (λƿ) (Incompressibility), and Mu-rho (µƿ) (Rigidity). The results from this study demonstrate the effectiveness of simultaneous inversion and the best parameters for enhancing the resolution and characterizing the hydrocarbon sand layer of the prospect.

Facies Distribution and Petrophysical Properties of Shoreface-Offshore Transition Environment in Sandakan Formation, NE Sabah Basin

Newly exposed outcrop of Miocene shallow marine sandstone in Sandakan Formation, allows characterization of the facies distribution and petrophysical properties of shoreface to offshore transition environment. Six facies are defined: (1) Poorly bioturbated Hummocky Cross Stratified (HCS) sandstone (F1), (2) Moderately bioturbated HCS sandstone (F2), (3) Well bioturbated HCS sandstone (F3), (4) Poorly bioturbated Swaley Cross Stratified (SCS) sandstone (F4), (5) Interbedded HCS sandstone with sand-silt mudstone, (6) Heterolithic mudstone. The sedimentary successions were deposited in upper to lower shoreface, and offshore transition environment. Facies F3, F4 and F5 shows good reservoir quality with good porosity and fair permeability values from 20% to 21% and 14 mD to 33 mD respectively. While Facies F1 exhibits poor reservoir quality with low permeability values 3.13 mD.

Hydrocarbon source potential of Eocene-Miocene sequence of Western Sabah, Malaysia

An evaluation of the petroleum generating potential of onshore Eocene-Miocene sequences of Western Sabah, Malaysia was performed based on organic petrological and geochemical methods. The sequences analysed are the Belait, Meligan, Temburong and West Crocker formations of western Sabah. The Belait Formation which is Stage IV equivalent in the offshore represents one of the major source rock/reservoirs of the petroleum-bearing Sabah Basin. The Eocene-Early Miocene West Crocker and Temburong formations are deepwater turbidites whilst the Miocene Meligan and Belait formations are shallow marine fluvio-deltaic deposits. The vitrinite reflectance and pyrolysis Tmax values show that the Belait samples are generally immature for hydrocarbon generation, whereas the Meligan, Temburong and West Crocker samples are in the mature to late maturity stage of hydrocarbon generation. The overall bulk source rock properties of the Belait and Meligan show fair to good petroleum source rock potential with TOC more than 1 wt %, hydrocarbon yield in the range of 400–1300 ppm and moderately high HI for many of the samples. Most of the samples representing the Temburong and West Crocker formations have TOC less than 1 wt% and have no to fair hydrocarbon generating potential. Interestingly, the samples collected in the West Crocker Formation characterized by slump deposits (MTD) have TOC>2 and possess good to excellent hydrocarbon generating potential. The organic matter present in all of the studied formations is mainly of terrigenous origin based on the abundance of woody plant materials observed under the microscope. Consequently, the analysed sequences are predominantly gas prone, dominated by Type III and Type III-IV kerogen except for minor occurrence of mixed oil-gas prone Type II-III kerogen in the Belait Formation and in the slump mass transport deposits (MTD) of the West Crocker Formation.

Post-Stack Seismic Data Enhancement of Thrust-Belt Area, Sabah Basin

In this paper, an integrated post-stack seismic data processing and interpretation for a complex thrust-belt area was proposed. The sequence was suggested due to poor seismic data quality of the Sabah basin area that was obtained after a pre-stack data processing sequences. This basin consists of a complex geological setting such as thrust-belt with steep dip reflector which is the main features of the region. In this paper, we outlined several methods used in the seismic data processing and interpretation such as amplitude recovery and frequency filtering for enhancing seismic data quality, and relative acoustic impedance, structural smoothing and wavelet coherency were used for attribute analysis. The outcome from this research aims at illuminating the hidden structures such as proper beds termination and faults systems that was heavily affected by low signal-to-noise ratio.

Integrating Mini-DST-Derived Permeability With Other Sources: A Case Study

SummaryPermeability is the cornerstone of any reservoir-flow modeling that leads to field development and production management. Typical sources of permeability include cores, logs, wireline formation tests [or minidrillstem tests (mini-DSTs)], and conventional DSTs. However, integrating various sources of permeability at different scales is problematic. Anchored in mini-DST-derived permeability, this study endeavors to integrate various sources of permeability, leading to reservoir description in a turbidite sandstone reservoir in the Sabah basin, Malaysia.Ordinarily, pressure-transient-test data recorded during a mini-DST operation differ significantly from data gathered during a conventional DST. Even though test quality was excellent, interpretation challenges were numerous in this well. Consequently, multidisciplinary information was brought to bear for integration of data derived from mini-DSTs. Other sources of information included sidewall cores, spot pressure measurements, nuclear magnetic resonance (NMR), and microelectrical imaging logs. This case study demonstrates that, in this particular setting, the use of mini-DSTs was cost-effective and yielded the subsurface information required to plan field-development options.

Spar platform at deep water region in Malaysian sea

Exploration of oil and gas resources has been accelerated towards deeper waters due to depletion of their reserve in shallow water depth. Malaysian sedimentary basins signpost the existence of these energy sources below its sea-bed. In deep sea depth, traditional fixed types of offshore structures to explore these resources have become incongruous and they have resorted to new configurations. Spar platform is treated as a cost-effective and efficient compliant floating platform in this locale for drilling, production, processing and storage of ocean deposits. This study deals with the oil and gas eminence in Malaysian sea along with structural response behaviors of spar platform subjected to hydrodynamic loading. A single model of spar-mooring line combination has been developed. Coupled conduct has been computed under unidirectional wave loading where all non-linearities are incorporated. Solution in time domain approach follows Newmark-beta integration technique. It is seen that the continental shelf offshore of Malaysian waters is divided into seven sedimentary basins, out of which three basins have major ongoing oil and gas exploration and production activity, namely the Malay basin in West Malaysia off Terengganu and the Sabah and Sarawak basins off the two East Malaysian states of Sabah and Sarawak, respectively. Surge, heave, pitch motion response of spar hull and tension in mooring line tension have been evaluated. Spar platform indicates itself as advanced and competent offshore structures to enhance the oil and gas exploration from all the Malaysian sedimentary basins in the deep water region.