Deserts must be supplied with sediment in order to accrete. The Thar Desert, lying east of the Indus River in South Asia, might be expected to be largely supplied with sediment from that drainage. In this study, we use a combination of major and trace element bulk-sediment geochemistry, together with Sr and Nd isotopes, to constrain the provenance of postglacial dune sand. Our data indicate a stronger influence from mafic source rocks in the Sindh Desert compared to that in Cholistan. Nd isotopes imply sediment was largely derived from the lower Indus River during the early and pre-Holocene post-glacial time. The sand is coarser grained in Sindh and retains higher & varepsilon;Nd values in sediment that eroded from mafic rocks in Kohistan and the Karakorum as a result of deflation of deltaic and floodplain areas in the lower reaches by southwesterly summer monsoon winds. The composition of Cholistan dunes, like that in the Eastern Thar Desert, reveals instead more supply from Himalayan sources and more negative & varepsilon;Nd values. The greater Himalayan influence in Cholistan and the Eastern Thar Desert largely reflects finer grain size, a result of the longer transport from the delta source and a preference for more Himalayan supply in the form of finer sediment.

We present an integrated, high-resolution, biostratigraphical, mineralogical, and geochemical characterization of the well-exposed Upper Paleocene - Lower Eocene stratigraphic succession of the Surghar Range (Baroch Nala section, NE Pakistan). The faunal assemblages from the Baroch Nala section, dominated by hyaline benthic foraminifera and green calcareous algae, along with the significant terrigenous fraction and the presence of terrestrially derived organic matter, testify to the deposition in a low-energy shallow-marine environment. Such environmental conditions, coupled with weak diagenetic effects, allow us to integrate a continuous record of carbon stable isotopes with a detailed account of the biotic response by carbonate-producing assemblages, paleoclimatic information based on clay-minerals, and information on volcanic activity based on mercury concentrations. The environmental evolution from the Late Paleocene up to the Paleocene Eocene Thermal Maximum (PETM) is clearly documented, including the weaker warm excursion that precedes the PETM (i.e. the Pre-Onset Excursion "POE"), and the evolution of large benthic foraminiferal assemblages. The overall record perfectly shows how the turnover in benthic carbonate producers started with the onset of the PETM and was completed by the time the excursion ended, highlighting how (geologically) brief environmental oscillations can have long lasting effects on the biosphere.

The Thar Desert is a major sediment depocenter located in southwestern Asia and bordering the Indus drainage system to its east. It is unclear where the sediment that built the desert is coming from, and when the desert experienced phases of construction. In particular, we seek to establish the role of the South Asian monsoon in the initial formation and subsequent expansion of the desert. Here we integrate bulk -petrography and heavy -mineral data with U-Pb ages of detrital zircon grains to understand how the Thar Desert relates to the major potential sediment sources in the Himalayan orogen and to the large rivers that adjoin it to the west and north. Bulk petrography and heavy -mineral data from eolian sand in Cholistan (NE Pakistan) show closer similarity with that of Himalayan tributaries than eolian sand in Sindh (S Pakistan), which contains heavy -mineral suites close to those of mainstream Indus sand largely supplied by erosion of the Karakorum and Kohistan ranges. Kohistan is a particularly rich source of heavy minerals and is thus over -represented in provenance budgets based on that proxy alone. U-Pb ages of detrital -zircon fail to show a sharp difference between dune sands in Sindh and Cholistan but confirms a somewhat greater supply from the Himalaya in Cholistan and from the Karakorum, Kohistan, and Nanga Parbat in Sindh. Zircon ages are similar in Sindh desert sand and in the Indus Delta, and are most similar to deltaic sand dated as 7 ka or older in the deglacial period. In parallel, the age signature of Cholistan sand resembles more that of older river channels found along the northwestern edge of the desert (e.g., paleo-Ghaggar-Hakra) than that of modern Himalayan tributaries (e.g., Sutlej). Both Cholistan and Sindh sands suggest that sediment supply to the desert was greater during the early Holocene when the summer monsoon was stronger. The southwesterly summer monsoon was the most effective agent of eolian transport and recycling of Indus delta sediments entrained towards the central and northern parts of the Thar Desert.

We investigate the Palaeocene succession of the Hazara Basin (Northern Pakistan) to better understand the impact of climate change on marine carbonate-producing organisms. These shallow-water carbonates, deposited during the Late Palaeocene, before the onset of the Palaeocene-Eocene Thermal Maximum, were studied using a quantitative approach to highlight changes in the skeletal assemblage. We recognise a decrease in the abundance of colonial corals and green calcareous algae and an increase in larger benthic foraminifera and red calcareous algae from the early Thanetian to the late Thanetian. Increasing temperatures may represent a plausible cause for the decline of the more sensitive colonial corals in favor of the more tolerant larger benthic foraminifera. A similar pattern is observed in most successions deposited along the margins of the Neotethys Ocean, suggesting a connection with the Late Palaeocene environmental changes that heralded the PETM hyperthermal event. Our stratigraphic analysis of the Hazara Basin strata suggests that the biotic turnovers occurred during the Palaeocene – Eocene transition started already before the onset of the Palaeocene Eocene Thermal Maximum as recorded by the geochemical proxies.

Exploration for hydrocarbon in shales is an example of unconventional reservoirs for oil and gas resources with huge amount of commercial potential. Porosity and permeability in shale are two important factors that control fluid accumulation and flow. To get the natural shale samples from wells is certainly a hard and crucial job for reservoir fracking studies. To study different factors that influence pore types and geometry in fracking experiments, we carried out X-ray Diffraction (XRD) analysis, surface area analyzer and porosimetry system (SAP), poroperm and tomographic imaging (micro-CT scan) on shale samples from Peninsular Malaysia. The results of synthetic cores through XRD show high amount of clay content (illite/smectite, and kaolinite) and quartz. Other experimental studies reveal that porosity and permeability is heterogeneous and low in the interbedded shale due to very-fine grained matrix. Microscale studies using SEM and CT scan demonstrate different types of pores that are inter/intragranular, intercrystalline, and organic. Our results elucidate that interconnecting pores and their permeability for fluid flow is low due to the obstruction by very-fine grains of clay minerals like illite and kaolinite in shaly sand. The results can be directly applied to labbased fracking experiments that can provide optimal fracking parameters and has great potential in the (oil and gas) O&G industry for understanding hydrocarbon (HC) flow dynamics

Deep‐water massive sandstones (DWMS) are characterized by large volumes of sand accumulations which are considered as potential reservoir intervals in deep‐marine environments. Lithological variations and bed thickness statistics are used to interpret the distribution of massive sandstones in a deep‐marine fan‐lobe system. These massive sandstones are interpreted based on lithological heterogeneities and detailed facies analysis in seventeen exposed sections of the Late Palaeogene deposits in Sabah, NW Borneo. Sedimentary logs containing details of lithology textures and structures were used to recognize nine sedimentary facies of DWMS. These lithofacies were then grouped into three sedimentary facies associations: (1) massive facies association with basal part of turbiditic Bouma sequence, (2) massive facies association having soft‐sediment deformation structures, and (3) massive facies association with erosional features. The facies analysis portrays inner to middle submarine fan deposition and was later applied to reconstruct the distribution of a channel‐lobe complex. Individual sandstone bed thicknesses vary from 1 m to more than 8 m and the number of massive sandstones in submarine lobes range from less than 10% to more than 50%. The thicknesses of massive sandstones in channels are more than 8 m, whereas distal lobes have thicknesses from 1–2 m only. These sandstones are concentrated in channels, proximal and medial lobe settings that can also be verified from calculating the average of all maximum thickness of massive sand intervals that is, 8.91 m. The lithological heterogeneities and the processes associated with the deposition of these massive sandstones are vital for potential hydrocarbon reservoirs in the deep‐marine environments around the globe.

Numerous studies have been done to determine the hydrocarbon potential of Malaysia's formations and basins due to the need to identify more conventional or unconventional hydrocarbon resources. Due to the fact that none of these investigations were carried out with any prior knowledge in the relevant regions with hydrocarbon potential, some of them did not, however, yield the expected results. This study aims to provide researchers with all the necessary information about potential hydrocarbon-producing areas in Malaysia and the various lithologies connected to them by analyzing all earlier studies carried out in Malaysia. This was accomplished by determining patterns in the distribution of organic matter and characteristics of the formations in Malaysia. Total Organic Carbon (TOC), Generic Potential (GP), Vitrinite Reflectance (R-o), and Hydrocarbon Yield (S2) were the most important hydrocarbon generation potential indicators discussed. A heat map was created using a statistical weight ranking with a weight of 45% for the TOC value and 30%, 15%, and 10% for the GP, S2, and R-o values, respectively. According to the data, the Bintulu, Pinangah, Begrih, Liang, and Tanjong formations have the highest potential to generate hydrocarbons in Malaysia, while the Kroh, Setap, Kalabakan, Temburong, and Belaga have the least potential. Majority of formations with high hydrocarbon potential are tertiary in age and consist primarily of coal and carbonaceous shale formations. The most promising formations are mostly immature, with type II or type III kerogen quality. It is recommended that critical exploration activities be focused on the tertiary-aged formations, particularly those in East Malaysia, in order to increase Malaysia's hydrocarbon production.

The Lower to Middle Jurassic sedimentary succession is dominated by siliciclastics with a significant amount of black shales in the Indus Basin, Pakistan. Several outcrop samples have been studied using an integrated approach to interpret the conceptual depositional setting from carbon and oxygen isotopes (δ13C& δ18O), organic geochemistry, and palynofacies with major and trace element analysis. For interpretation of trace element data, various single and elemental ratios have been used in this research to unlock the geological history of the studied strata. Ti/Al is 1.96 for high-potential source rock and 7.82 for non-potential source rock, and Cr (less than 1) indicates low clastic input with low oxygen for stratified and stagnant water. The ratios of V/(V + Cr), V/(V + Ni), V/Mo, V/Ni, (Cu + Mo)/Zn, Mo/Al, isotopic values of δ13C and δ18O and besides the V/Cr elemental ratio, all proxies indicate that there are oxygen-depleted anoxic conditions at high potentials, while in non-potential source rock, these ratios show oxic to sub-oxic settings. In addition to the trace element correlation with total organic carbon, the influx of organic matter is determined by the palynoafacies analysis, which indicates mixed terrestrial and marine organic influx in high-potential source rock and vice versa. Furthermore, the studies of palynofaceis DFPF A-D and SFPF A-B suggest that the depositional setting of black shale occurred in the anoxic proximal to distal shelf. The results suggest that the regional and local occurrence of black shale during the Lower to Middle Jurassic and its geological condition were addressed, and these play an important role in its depositional and paleooceanographic setting in the Eastern Tethys.

In the Sibu-Tatau region of Sarawak, the Belaga Formation (Late Cretaceous- Late Eocene turbidites) is interpreted in relation to a submarine fan model deposited in the extinct ocean basin of the proto-South China Sea. A number of clastic rocks, which include sandstone, siltstone, mudstone, and black shale, define the formation. While it is considered one of the Rajang group's extensive and well-studied formations, yet no comprehensive studies have been carried out on the shales in Sarawak, Malaysia, to interpret their importance as a source rock to oil and gas fields. The present study highlights the prominent lithofacies in addition to the detailed source rock characterization of each member of Belaga Formation to discuss the potential source rock intervals present in these Cretaceous to Eocene rock units. Four major types of shales and mudstones facies were observed in the field, i.e. (i) Variegated colored shale facies (VSF), (ii) Black "Papery" shale facies (BSF), (iii) Gray to black mudstone facies (GMF), (iv) Silty/sandy shale facies (SSF). They show hemipelagic settling in a calm environment to turbiditic deposition at levees as well as distal lobe depositional environment. In this study primary geochemical studies such as Rock-Eval pyrolysis and Total Organic Carbon (TOC) analysis were used to classify the thermal maturity, organic matter richness, and kerogen type of the studied shales. Forty-six selected shale samples were studied from the formation, including samples from members of the Layar (Upper Cretaceous), Kapit (Paleocene to Early Eocene), Pelagus (Early to Middle Eocene), Metah (Middle to Late Eocene) and Bawang (Eocene). The shales of Belaga Formation typically display low to moderate source rock potential, which is obvious by low TOC contents between 0.14 wt% and 7.22 wt% (average of about 2.97 wt%) and show a wide range of maturity (immature to over mature) evident from very low to very high Tmax values ranging from 293 °C to 610 °C. The results show that the kerogen is of type IV, with some units can be potential sources of gas.

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.

Sediment loss is an indispensable geological phenomenon that determines the reduction of mass in time interval with the differential influence of controlling factors. In this study, the competence of rocks is considered as a controlling factor while weathering and erosion are termed as the decaying parameter. Attributed to the reduction of the total mass in unit time. A mathematical model is [proposed for the above-mentioned phenomenon and generalized using the Caputo fractional derivatives approach to better understand and predict the sediment loss. The model is solved for exact solutions using the Laplace transform technique. The results obtained for β and -β are in strong agreement with the field images of selected outcrop sections. The memory effect is also shown with different values of αThe results revealed that the mathematical model better explains the geological processes.

Geostatistical data plays a vibrant role for surface-based reservoir modeling through outcrop analogues,which is used to understand three-dimensional(3D)variability of petrophysical properties.The main purpose of this study is to improvise the surface-based 3D geo-modeling to demonstrate petrophysical characteristics and heterogeneities of Sandakan reservoirs,NW Borneo.We used point cloud data from Light Detection and Ranging(LiDAR)to build high-resolution virtual outcrop modeling(VOM)onto which we mapped 6 different lithofacies.Porosity and permeability of core plugs were measured to determine the average variance of petrophysical properties for each lithofacies.By utilizing the inte-gration of VOMs analogues and petrophysical properties in PetrelTM,we demonstrated the distribution and associations of all lithofacies in pseudo wells that have inherent thin beds heterogeneities in 3D geo-cellular model.The results concluded that the heterogeneity of thin beds in lithofacies is dependent on porosity and permeability with input dataset.According to the final model,cross-bedding sandstone(CBS),hummocky cross-stratified sandstone(HCSS)and trough cross-bedding sandstone(TCBS)show good reservoir quality due to high porosity ranging from:25.6％to 20.4％and,19.3％-14.5％,and permeability ranging from:74.03 mD to 66.84 mD and,64.86 mD to 21.01 mD.In contrast,massive to weak laminae sandstone(MWLS)and bioturbated sandstone(BS)show fair to poor reservoir quality,caused baffling of surrounding mud sediments in the reservoir lithofacies.Results also revealed that LiDAR based VOM with petrophysical properties can significantly reduce the risk and minimize the cost of reservoir modeling in petroleum industry.

Hybrid event beds represent the combined effect of multiple geological processes, which result in complex depositional geometries and distinct facies distribution in marine environments. Previous work on hybrid event beds highlights the classification, origin, and types of hybrid facies. However, in the present study, we discuss the development of hybrid event beds in submarine lobes with an emphasis on the analysis of proximal to distal, frontal to lateral relationships and evolution during lobe progradation. Detailed geological fieldwork was carried out in the classical deep-marine Late Paleogene Crocker Fan to understand the relationship between the character of hybrid bed facies and lobe architecture. The results indicate that hybrid facies of massive or structureless sandstone with mud clasts, clean to muddy sand, and chaotic muddy sand with oversized sand patch alternations (H1–H3) are well developed in proximal to medial lobes, while distal lobes mainly contain parallel to cross-laminated clean to muddy hybrid facies (H3–H5). Furthermore, lateral lobes have less vertical thickness of hybrid beds than frontal lobes. The development of hybrid beds takes place in the lower part of the thickening upward sequence of lobe progradation, while lobe retrogradation contains hybrid facies intervals in the upper part of stratigraphy. Hence, the development of hybrid beds in submarine lobe systems has a significant impact on the characterization of heterogeneities in deep-marine petroleum reservoirs at sub-seismic levels.

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.

The Belaga Formation of the Rajang Group or Rajang Fold and Thrust Belt (Late Cretaceous to Late Eocene) is mostly exposed in Sibu Zone along with some exposures in the Miri Zone of Central Sarawak. This entire turbiditic sequence was believed to have been deposited in a deep marine environment in a basin having an overall passive margin setting, that is, the Rajang Sea. However, the Eocene age‐related stratigraphic record of this group (including Bawang Member) is much more complex, due to the complicated geological and tectonic settings which prevailed during their deposition. Here, we present field observations along with the application of various geochemical proxies and their constraints for the understanding of provenance, palaeo‐weathering, and tectonic evolution of the area during the deposition of Bawang turbidites. Based on field observation, it has been found that this member consists of four main lithofacies, including massive sandstone facies (MSF), thick‐bedded facies (TBF), heterolithic facies (HF), and mud facies (MF). Using geochemical data, chemical weathering indices (CIA and CIW) values and A‐CN‐K plot show that the source area for Bawang turbidites has undergone a moderate to an intense degree of chemical weathering and was influenced by the recycling effect. The slight depletion in sandstones and shales for Cr, Ni, and V values is consistent with the felsic dominated source region; however, La/Sc versus Co/Th and La/Th versus Hf plots show a mixed source (felsic and intermediate volcanic source) with some input of recycled sediments from the older sedimentary to metasedimentary rocks. Various geochemical ratios and discriminant diagrams verify that the Schwaner Mountains and its metamorphic group of rocks were the principal provenances for these sediments, along with some input from West Borneo. The results of the geochemical analysis also show that Bawang turbidite sediments were deposited in a basin associated with an initial active continental margin setting and the basin was shifting towards a passive setting (Late Eocene–Oligocene). The volcanic input in Bawang Member during the Late Eocene also suggests the involvement of some subsequent possible arc setting around the “Bawang subbasin”.

The 3-D seismic dataset is a key tool to analyze and understand the mechanism of structural and stratigraphic hydrocarbon (HC) trapping in the subsurface. Conventionally used subsurface seismic characterization methods for fractures are based on the theory of effective anisotropy medium. The aim of this work is to improve the structural images with dense sampling of 3-D survey to evaluate structural and stratigraphic models for reservoir development to predict reservoir quality. The present study of the Gullfaks Field, located in the Norwegian North Sea Gullfaks sector, identifies the shallowest structural elements. The steepness of westward structural dip decreases eastward during the Upper Jurassic to Lower Cretaceous deposition. Reservoir sands consist of the Middle Jurassic deltaic deposits and Lower Jurassic fluvial channel and delta plain deposits. Sediment supply steadily prevails on sea-level rise and the succession displays a regressive trend indicated by a good continuous stacking pattern. The key factor for the development of reservoirs in the Gullfaks Field is fault transmissibility with spatially distributed pressure. The majority of mapped faults with sand-to-sand contacts are non-sealing, which provide restriction for the HC flow between the fault blocks. The traps for HC accumulation occur between the post-rift and syn-rift strata, i.e. antiform set by extensional system, unconformity trap at the top of syn-deposition, and structural trap due to normal faults. Overall reservoir quality in the studied area is generally excellent with average 35% porosity and permeability in the Darcy range. Our findings are useful to better understand the development of siliciclastic reservoirs in similar geological settings worldwide.

One of the most important influential parameters which controlled the permeability network in the surface and subsurface sedimentary reservoir is ichnofossils. The measured permeability from the Sandakan Formation explain the influences of ichnofossils in primary sedimentary structures of reservoir zones. This work represented three ichnofossils (i.e., Psilonichnus, Skolithos and Cruziana) within the dense ichnofabrics and sedimentary structures. Present research shows that the effective permeability is very high (250mD-950mD) due to the ichnofossils in the bioturbated horizons of sandstone and interbedded mudstone. It also represents the depositional environment of Sandakan Formation that is transitional from back to foreshore setting and extends to very distal fringes of a proximal lower shoreface. This work is important because ichnofossils can increase secondary porosity and enhance pore connectivity in reservoir horizons that play a vital role in the subsurface hydrocarbon reservoirs.

Reservoir studies in the Sandakan sub-basin NW Borneo are challenging and inexplicable due to complex diagenetic effects such as compaction, cementation, dissolution and depositional means including grain size, sorting and packing with reference to clay texture. These diagenetic effects together impart significant amounts of uncertainty on reservoir quality assessment. In this regard, we documented the mineralogical, diagenetic and reservoir properties of sandstones from the Sandakan Formation, NW Borneo through thin sections, SEM, XRD, XRF, He-porosimeter and poroperm. In order to analyze the influential parameters, we used matrix, grain rearrangement and clay coating around detrital grains for the reservoir quality. Our results show that the sub-litharenites to quartz arenite that dominate in the sandstones are drawn from recycled orogenic sand. Furthermore, reservoir properties of the sandstones were ascertained to be controlled by diagenesis, micro quartz with clay coatings and pressure dissolution of feldspar with the alteration of lithic fragments. The result shows that the physical compaction, rearrangements and ductility of grains were the reasons that reduced porosity and permeability. The main reason for porosity reduction in the present study is pressure dissolution that resulted in the form of chemical compaction induced by micas with grain contacts. Nonetheless, through SEM and petrography, clay coatings around the grains and dissolution of feldspar were found to optimally contribute to the preservation of reservoir properties. Dissolution of feldspar and kaolinization resulted in the formation of secondary porosity that allows meteoric water to percolate through the open and detachment spaces of quartz or other grains. This percolation is also responsible in enhancing the pore throat radii in the reservoir media of the analyzed sandstones. These traits are obliging to diagenetic effects on porosity and permeability, which are linked with the physical compaction and clays coating to reduce and preserve the reservoir properties respectively of same type of reservoirs globally.

Permeability network is influenced by ichnofacies in the surface and subsurface sedimentary media, which modifies textural heterogeneity of reservoir rocks by the filling of burrows with the surrounding sediments. In situ measurements of rock permeability from surface analogues of proven subsurface hydrocarbon traps demonstrate the influences of ichnofacies in primary sedimentary structures and resultant high variability within reservoir zones. This work emphasizes on the evaluation of three ichnofacies (i.e., Psilonichnus, Skolithos and Cruziana) that are interdependent and characterized by dense ichnofabrics with sedimentary structures in the exposed rocks of Sandakan Formation. The sedimentary structures associated with ichnofacies are parallel to subparallel, multidirectional trough cross-stratification with current cross laminae and low-angle, undulatory, hummocky cross-stratification (HCS) and oscillation ripple laminated sand with the alteration of silty or sandy mudstones. Results show that the Sandakan Formation was deposited in a transitional environment from a back to foreshore setting and extends to very distal fringes of a proximal lower shoreface or distal delta front to pro-delta. The effective permeability network in the bioturbated horizons of sandstone and interbedded mudstone is very high (250-950 mD). The integration of ichnofacies and sedimentary structures with high permeability profile suggests that the Sandakan Formation has good reservoir potential with the textural heterogeneity. The implication is that the presence of ichnofacies in sedimentary reservoir horizons can substantially increase secondary porosity and enhance pore connectivity; thus, making them valuable and lucrative subsurface hydrocarbon reservoirs.