Miocene Carbonate Platform Research Articles

The growth and demise of a Middle Miocene carbonate platform in Central Luconia, offshore Malaysia

The evolution and facies distribution of relatively small carbonate platforms, ∼30 km2, are not well documented, even though they are common in ancient and modern carbonate systems. This study investigates depositional facies and evolution of a Miocene carbonate platform in Central Luconia, offshore Malaysia. An integrated approach, including core-described lithofacies, well-log correlation, and seismic analysis, allowed for the mapping of facies through time. The platform was divided into five stratigraphic zones (1 [top], 2 Upper, 2 Lower, 3 Upper, 3 Lower [bottom]) separated by low porosity intervals. Five depositional facies groups were recognized in core samples: (1) bioclastic wacke-packstone facies deposited in a platform interior, (2) bioclastic packstone facies deposited in backreef environments, (3) coral boundstone facies deposited at the reef margin, (4) interbedded shale and carbonate facies deposited on the slope, and (5) argillaceous carbonate facies deposited across the platform as flooding layers. Well D penetrated almost the entire platform, and facies in that well changed upward from mainly bioclastic wacke-packstone at the bottom to mainly bioclastic packstone in the middle to coral boundstone near the top before being covered by interbedded shale and carbonate. Six seismic facies were identified and combined with well data to map the five facies groups through time. The platform shows repeated backstepping of facies at flooding layers followed by aggradation of facies belts up to exposure surfaces, resulting in a long-term backstepping of depositional environments until the platform drowned. Sr-isotopes dating near the top of the platform yielded an age of approximately 12 Ma. This suggests that the platform drowned earlier than other carbonate platforms in Central Luconia (8–10 Ma). More tectonic subsidence in this area during the Middle Miocene is proposed as the main cause of the early demise of this carbonate platform compared to other Luconia platforms.

Evaluation of Carbonate Reservoir with Integration of Petrophysical Analysis and Seismic Impedance Inversion in Banggai Basin, Sulawesi

Banggai Basin is controlled by the collision between Banggai-Sula micro-continent and East Sulawesi ophiolite belt, forming a thrust-sheet anticline structure that has potential to trap hydrocarbon. The Siotu-1 well was drilled right into the thrust-sheet anticline structure targeting Miocene carbonate platform layer. The same structure has proven to be an oil trap at the Tiaka oilfield which is located adjacent to the Siotu-1 well. This study aims to evaluate the presence of hydrocarbon in the Siotu-1 well with characterization of the Miocene carbonate reservoir. It is carried out by integrating petrophysical analysis from the Siotu-1 well log data and 2D seismic impedance inversion of the Tarib-1 line. Five reservoir zones have shale content values range of 21.91-37.53%, effective porosity values range of 9.7-14.62%, water saturation values range of 88.5-98.27%, and permeability values range of 2.53-8.16 mD. The results of the porosity calculation are validated by the model of seismic inversion where the reservoir zone with an acoustic impedance in the range of 7600-13450 ((m/s)/(g/cc)) is a carbonate layer with fair to excellent porosity (10 to> 25%) and reservoir zone with acoustic impedance values range of 13450-16200 ((m/s)/(g/cc)) as carbonate layer with poor porosity (< 10%). The net pay zone in reservoir zone 4 with a thickness of 4.5 feet and a net-to-gross of 0.006 are shown as the lumping result. It is concluded that Miocene carbonate reservoir in the Siotu-1 well met the criteria as a good reservoir rock but insignificant of hydrocarbon potential for further development.

Unravelling Cenozoic carbonate platform fluid expulsion: Deciphering pockmark morphologies and genesis in the Tanintharyi shelf of the Andaman Sea as promising hydrocarbon reservoirs

Pockmarks, intriguing seafloor geological and geomorphological features, are commonly observed in marginal basins with hydrocarbon potential. As a Cenozoic marginal sea, the Andaman Sea is known for its significant petroleum reserves, and exploring its back-arc continental margin has revealed favourable conditions for petroleum occurrences. This study focuses on the Tanintharyi passive continental margin in the Andaman Sea, employing extensive stratigraphic and morphological analyses based on 2D and 3D seismic data interpretation techniques. Specifically, sub-seafloor characteristics of the Tanintharyi shelf region were investigated, focusing on comprehensively understanding pockmark morphologies, including their generation, evolution, migration, preservation, and the complete process leading to seabed leakage. This study revealed the potential of the Oligocene/Early Miocene carbonate platform in the Tanintharyi shelf region as a significant hydrocarbon reservoir for the upwelling buoyant fluids from the deep East Andaman Basin. Besides reservoir function, this carbonate platform serves as a passageway for the migration of fluids from the deep-sea area to the shallow-sea area, thereby playing a pivotal role in supporting fluid expulsion mechanisms in shaping a pockmark train adjacent to truncated sedimentary formations surrounding a geomorphological high on the contemporary seafloor. Additionally, the study examines the influence of changes in sedimentary facies and the tectonic setting of the Andaman Sea on pockmark evolutions, with a specific emphasis on the role of the uppermost shallow marine shale beds in developing sub-seafloor overpressure systems due to their impermeable seal rock properties. The article presents substantial evidence for the initiation of pockmark fields during the Middle Miocene period, followed by their transformation into pockmark trains on the present-day seafloor, attributed to the triggering effect of sub-seafloor overpressure systems due to changes in sedimentary dynamics in the Andaman Sea.

Sedimentary characteristics and controlling factors of a Pliocene shelf-edge delta in the Papuan Basin

The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed by deposition of the Pliocene Orubadi Formation. On the basis of a comprehensive analysis of seismic, wireline and mud logging, and paleontological data, the stratigraphic framework, depositional system and controlling factors on the SED development were established. The Orubadi Formation includes a parallel unconformity. Internally, two third-order sequences (SQ1/SQ2) are identified, and system tracts within the sequence layers are determined by the onlaps. By tracing changes in the shoreline trajectories within the sequence, the SED was divided into six phases in the study area, with seaward advances of ∼1543–5400 m during a single phase. The thickness of the foreset is ∼309–887 m, exhibiting sigmoid or sigmoid-tangential seismic reflections. The stratigraphic patterns and sedimentary system evolution of the Orubadi Formation are determined by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphology. The Coral Sea spreading provided accommodation for the SED. The Miocene–Pliocene uplift and the middle Miocene arc–continent collision in northern PNG, which caused uplift and erosion of mountains in the late Miocene to Pliocene, is the major source of sediments. The large sediment supply and sea-level changes from SQ1–SQ2 indicate an overall relative sea-level fall resulted in rapid shelf margin advancement into the basin, with the Miocene carbonate platform edge providing the necessary slope conditions for material transport. This abundant sediment supply led to the significant development of the SED. This study provides robust insights for deep-water oil and gas exploration in the Papuan Basin. KEY POINTS The Pliocene shelf-edge delta (SED) in the Papuan Basin was formed in a compression setting with arc–continent collision. In the Orubadi Formation, the overall trend of sea-level change is decreasing, and the delta is divided into six stages. The Pliocene SED is controlled by the interplay between sea-level changes, sediment supply, tectonic evolution and paleogeomorphological.

Stratigraphic evolution and drowning steps of a submerged isolated carbonate platform in the northern South China Sea

Drowned carbonate platforms on passive margins present a paradox, because their great growth potential exceeds the typical rates of passive margin subsidence and any relative sea-level rise driven by long-term processes in the geologic record. In this study, manned submersible observations, sampling, and high-resolution acoustic data were used to investigate a drowned isolated carbonate platform cropping out at a water depth of 536–800 m in the northern South China Sea. Based on the results, the Early Miocene strata of the platform are grouped into three units (AU1, AU2, and AU3) that formed on the fault-created topography. The fault-created topography served as a template for the onset of the carbonate platform deposition and as a pedestal for the localization of backstepped platforms in response to accommodation space variations, primarily driven by rapid subsidence and eustatic rises during the Early Miocene. The Middle Miocene strata of the platform are grouped into four units (AU4, PU1, PU2, and PU3), exhibiting a general switch from dominantly aggrading to dominantly prograding platform margins, in tandem with the cessation of faulting. The biostratigraphy and established seismic–stratigraphic correlations indicate that the carbonate platform was submerged during the late Middle Miocene. The banktop consists of a heterozoan carbonate factory dominated by large benthic foraminifera and coralline algae. This facies was deposited during a time interval when summer monsoon-induced upwelling triggered heterozoan factory turnover in other carbonate platforms in the region, such as at well XK-1 (Xuande Platform). The asymmetric backstepping of the platform margins demonstrates that summer monsoon-driven currents influenced the platform drowning. Therefore, summer monsoon-induced upwelling was a major factor influencing platform drowning during the late Middle Miocene. Platform growth did not persist due to the high subsidence rate throughout the Late Miocene. This study provides new insights into the drowning mechanism of a Miocene carbonate platform in the northern South China Sea and a new seismic analog for other ancient, isolated platforms worldwide.

Geological Distribution of the Miocene Carbonate Platform in the Xisha Sea Area of the South China Sea, and Its Implications for Hydrocarbon Exploration

The newly collected seismic data and the existing drilling data provide a good opportunity to better understand the carbonate platform distribution characteristics and the hydrocarbon resource potential in the Xisha sea area of the South China Sea. Based on the seismic data and the reflection characteristics of the carbonate platform’s edge, three boundary indicators were established: abrupt lithological interfaces, fault interfaces, and tidal channels. Combined with the regional geological settings, its spatial and temporal distribution was clearly identified for the first time. The development of the Miocene carbonate platform in the Xisha sea area is divided into six phases, which are further assigned to three evolutionary stages: the bloom stage, the recession stage, and the submerged stage. The sedimentary facies belt of the carbonate platform in each stage is well developed, and the reefs are mainly distributed on the west and southwest edges of the platform. The analysis of the data indicates that the area of the reef and carbonate platform reached 80,000 km2 during the mature period, followed by a retreat period where the scale decreased with the platform’s decline. The Miocene carbonate rocks in the Xisha sea area are widely distributed. They have experienced multiple periods of exposure and infiltration, which further improved the quality of their physical properties for hydrocarbon reservoirs. According to the regional hydrocarbon geological conditions in this area—including the source rock, migration system and the capping layer—the hydrocarbon accumulation potential is preliminarily discussed in this paper. A reservoir model of the reef and carbonate platform is established, which is proposed as typical characteristics of “lower generation, upper accumulation”. It is pointed out that the carbonate platform in the Xisha sea area adjacent to the Huaguang Sag in the Qiongdongnan Basin and the northern Zhongjiannan Basin is a potential area for oil and gas exploration.

Linear polygonal faults initiated Gully system around the margin slope of middle Miocene carbonate platform in the Northwest South China sea

An ancient gully system was revealed in the Northwest South China Sea using high-resolution three-dimensional (3D) seismic data. They are straight, regular, and intensely spaced sediment transporting routines, and are much smaller in size than channels. The gully system was distributed on the margin slope of the peri-carbonate platform in the middle Miocene. Two different types of gullies were identified based on the variation in the seismic response. Among them, most of the gullies are filled by low seismic amplitude reflectors, except a unique one, developed on the east slope of the study area, and is characterised by high seismic amplitude reflectors. The head of this gully reaches the carbonate platform, which provides carbonate clasts to the gully. The other gullies, expressing low seismic amplitude reflectors, develop limitedly on the slope of the carbonate platform and seldom receive source sediments from the carbonate platform. The gullies sit on the polygonal faults of middle Miocene, exhibit same strike with larger-scale linear ones of polygonal faults. These linear polygonal faults elongate from northwest to southeast, perpendicular to the slope contours, and in the same direction as the gullies. The coincidence between gullies and polygonal faults exhibits that the formation of gullies has been triggered mainly by the polygonal fault system (PFS) in the middle Miocene. These findings suggest that the middle Miocene carbonate platform provides favourable fine-grained lithology conditions for the formation of the PFS, while the linear polygonal faults initiate the gully system peri-carbonate platforms. Subsequently, the following gravity flows shape the initial configuration into the final features, while different provenances and different types of gravity flows create various characteristics of gullies.

Withdrawn: Xu, Z.Q. (2022), Spatial and Temporal Distributions of Miocene Carbonate Platform in the Dongsha area of the South China Sea and its Controlling Factors in Acta Geologica Sinica (English Edition)

The above article from Acta Geologica Sinica (English Edition), published online on 03 January 2022 in Wiley Online Library (wileyonlinelibrary.com), has been withdrawn by agreement among the author Zhenqiang Xu, the journal Editor in Chief Zengqian Hou, the Geological Society of China, Acta Geologica Sinica‐English Edition and John Wiley and Sons, Ltd. This Withdrawal was agreed after a request by the author, who noticed after peer review and subsequent publication that some of the data was inaccurate, these inaccuracies impact the analysis and conclusions in the article.

Seismic expression of miocene carbonate platform and reservoir characterization through geophysical approach: application in central Luconia, offshore Malaysia

A substantial proportion of proven oil and gas reserves of the world is contained in the carbonate reservoir. It is estimated that about 60% of the world’s oil and 40% of gas reserves are confined in carbonate reservoirs. Exploration and development of hydrocarbons in carbonate reservoirs are much more challenging due to poor seismic imaging and reservoir heterogeneity caused by diagenetic changes. Evaluation of carbonate reservoirs has been a high priority for researchers and geoscientists working in the petroleum industry mainly due to the challenges presented by these highly heterogeneous reservoir rocks. It is essential for geoscientists, petrophysicists, and engineers to work together from initial phases of exploration and delineation of the pool through mature stages of production, to extract as much information as possible to produce maximum hydrocarbons from the field for the commercial viability of the project. In the absence of the well-log data, the properties are inferred from the inversion of seismic data alone. In oil and gas exploration and production industries, seismic inversion is proven as a tool for tracing the subsurface reservoir facies and their fluid contents. In this paper, seismic inversion demonstrates the understanding of lithology and includes the full band of frequency in our initial model to incorporate the detailed study about the basin for prospect evaluation. 3D seismic data along with the geological & petrophysical information and electrologs acquired from drilled wells are used for interpretation and inversion of seismic data to understand the reservoir geometry and facies variation including the distribution of intervening tight layers within the Miocene carbonate reservoir in the study area of Central Luconia. The out-come of the seismic post-stack inversion technique shows a better subsurface lithofacies and fluid distribution for delineation and detailed study of the reservoir.

Seismic Characteristics and Development Patterns of Miocene Carbonate Platform in the Beikang Basin, Southern South China Sea

AbstractThe Beikang Basin is located in the southern part of the South China Sea (SCS), which is one of most tectonically complex sea areas. It is a deepwater sedimentary basin that was mainly deposited during the Cenozoic era. Owing to data restrictions, the research on carbonate platforms of this area is still in its infancy. High‐resolution seismic data are analyzed to identify the Miocene carbonate platforms and reconstruct the architecture and growth history. The carbonate platforms of Beikang Basin began to develop in the Late Oligocene‐Early Miocene, were extended in the Middle Miocene, and declined in the Late Miocene. The carbonate platform mainly developed during two periods: the Oligocene to the Early Miocene, and the Middle Miocene. The carbonate platforms that developed in the Middle Miocene were the most prosperous. The Middle Miocene carbonate platform in the Beikang Basin can be divided into three stages. In the first stage, the platforms had wide range which were thin. During the second stage, the platforms had a smaller range that was controlled by faults. In the third stage, the platforms were gradually submerged. The platform structure developed in the Middle Miocene at the Beikang Basin was controlled by the rate of rising/falling of the sea level and the carbonate growth rate. Based on an analysis of these changes and relationship, the platform can be divided into several patterns: retrogradation, submerged, aggradation, progradation, outward with up‐stepping, outward with down‐stepping, and down‐stepping platforms. At the top of the carbonate platforms in the Beikang Basin a set of carbonate wings or mushrooms usually appeared. These were formed during a period of relative sea‐level decline. It is believed that the Miocene carbonate platforms in the Beikang Basin are mainly controlled by tectonic and sedimentary environments, and are also affected by terrestrial detritus.

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.

Seismic stratigraphy and sedimentology of a Miocene carbonate platform in Luconia, South China Sea

The internal architecture and evolution of isolated carbonate buildups rely on multiple forcing factors, including tectonics and eustatic fluctuations. These parameters control the developmental phases of carbonate buildups such as initiation, growth, and termination stages, and give insights into other morphologic patterns such as backstepping and exposure events. The current study shows the evolution of a Middle Miocene isolated carbonate buildup of Central Luconia in the southern South China Sea, and describes it from large‐scale to very fine detail (km to mm) utilizing newly acquired (2016) 3D seismic data along with core lithofacies and thin sections. The buildup morphology and seismic facies are linked to core facies that can help to uncover the complex development of the carbonate platform. Core‐seismic calibration was used to create maps illustrating carbonate depositional settings for each stratigraphic unit. Here, we identified five seismic units that constitute the main stratigraphic stages of buildup development: (a) initiation as several isolated buildups, (b) coalescence, progradation, and aggradation, (c) aggradation and retrogradation associated with minor backstepping events and major karstification events, (d) retrogradation associated with major backstepping events, and (e) drowning stage. Our results demonstrate that Miocene reefal evolution and buildup architecture in Central Luconia were distinctly affected by diverse endogenic and exogenic processes. The initiation of localized carbonate growth appears to be strongly controlled by the morphology of the pre‐carbonate basement of Central Luconia where the SSW–NNE horst and graben structures were inherited from the poly‐stage opening of the South China Sea during the Early Miocene. Furthermore, sea‐level fluctuations, local and regional tectonic events during the Middle Miocene controlled the rates of accommodation changes, which directly impacted the stratigraphic architecture of the platform. The detailed seismic and sedimentological study documented in this work will benefit the understanding of the paleogeographic and stratigraphic evolution of carbonate buildups in the Luconia region of SE Asia, and in the current and future exploration for substantial conventional resources.

Unexplored deepwater basins of North Andaman Sea

Deepwater basins of the North Andaman Sea in the northern edge of the Far East Archipelago were assessed recently by state-of-the-art seismic technology. The North Andaman Sea embraces several Tertiary basins consisting of a forearc basin, a volcanic arc, and a back-arc basin. Their massive but largely unknown stratigraphy consists of deeper Neogene lacustrine and deltaic sediments that infill basal synrift half-grabens, blanketed by massive sequences of the Late Oligocene, Miocene, and recent strata. In the extensional forearc, the deeper seismic marker horizons were structurally mapped and identified by acoustic impedance contrasts as carbonates, mass-transport complexes, synrift, and basement. The shallower Pliocene and Pleistocene sequences are dominated by low-seismic-velocity hemipelagic clays that were investigated using seismic attributes and seismic inversion. In the back arc, the relatively larger graben features were affected by tectonic inversion contemporaneous with the foundering of the basin into deep water in the Late Miocene. In the forearc and back arc, main hydrocarbon plays are the rimmed Early Miocene carbonate platforms, the paralic and deltaic sediments beneath the platform, and the deepwater clastics of hemipelagic clays and sands that form the dominant strata of the Mio-Pliocene. This modern seismic exploration involved acquisition, processing, and interpretation to assess the hydrocarbon prospectivity of undrilled deepwater regions in the forearc and back arc.

Facies and geometry of drowning steps in a Miocene carbonate platform (Maldives)

The study of the Miocene carbonate platform of the Maldives allows understanding the controlling factors triggering the stepwise drowning of carbonate platforms. This research presents high-resolution seismic profiles and sediment cores retrieved from Sites U1465, U1469, and U1470 drilled during International Ocean Discovery Program (IODP) Expedition 359. A microfacies analysis of the platform deposits was conducted and correlated with a sequence stratigraphic analysis of seismic reflection data. The Neogene evolution of the Maldives encompasses a series of drowning steps. Two of these steps are compared with regard to the carbonate factory type to unravel if fossil assemblage surviving the first drowning step are different from younger assemblages. In both cases the shallow water carbonate facies are formed by coral-coralline algal boundstone and foralgal floatstone that change basinwards into slope facies dominated by large benthic foraminifera grainstone to packstone, locally floatstone and rudstone. The red algae and large benthic foraminifera assemblages are similar before and after the first drowning step. After this first drowning, the carbonate platform developed under enhanced bottom current conditions, as deduced by the coeval drift deposits. The carbonate platform and the drift deposits were balanced for circa 2 Myr, until a global sea-level fall at 10.6 Ma and later reflooding of the platform, which destroyed the equilibrium between both depositional systems, favouring the current-controlled deposits. The drowning of the Miocene carbonate platform of the Maldives was the result of the combined effect of the fluctuating sea-level during the Neogene and the intensification of oceanic currents due to the invigoration of the South Asian Monsoon during the middle Miocene.

Architecture and Development of Miocene Carbonate Platform in the Beikang Basin, Southern South China Sea

Architecture and Development of Miocene Carbonate Platform in the Beikang Basin, Southern South China Sea

Development and controlling factors of Upper Oligocene–Lower Miocene carbonate platforms and reefs in the Liyue Basin, South China Sea

The architecture and distribution of Late Oligocene–Early Miocene carbonate platforms and reefs are studied for the first time, using reprocessed 2D seismic data in the Liyue Basin, southern South China Sea. The reef complexes developed at higher positions of fault block platform and horst platform. Fault block platforms are the most important for reef development. In addition, most reefs developed in the Northern I Sag, and a few developed in the Middle Uplift. The growth processes of reefs on the platform were subdivided into six reef‐building units and two building stages. The first stage, including units 1–3, displayed slow backstepping and rapid keep up. The second stage was a rapid backstepping process that included the reef‐building units 4–6. Palaeogeomorphology, sea‐level fluctuations, and later volcanic activities were the main controls for reef occurrence. Palaeogeomorphology provided the initial topography for reef growth, and sea‐level fluctuations in combination with tectonic activity influenced reef development including growth and changing facies. Later volcanoes have strongly destroyed the pre‐existing carbonate platforms and reefs. By comparing with the carbonate reservoirs properties of adjacent regions, it is considered there is great potential for oil and gas exploration in the Liyue Basin.

Geology of the eastern slopes of the Simbruini Mts. between Verrecchie and Capistrello (Central Apennines – Abruzzo, Italy)

ABSTRACTThis paper presents the results of a geological mapping project across the eastern Simbruini Mts. and the higher Roveto Valley (Central Apennines). The study area belongs to the Latium-Abruzzi Domain, which is characterized by a Cretaceous and Miocene carbonate platform succession followed by a thick upper Miocene terrigenous succession. A unique feature of the study area is the existence of a thick clastic unit, the ‘brecce della Renga fm.’; this unit was produced by the dismantling of the margins of a large pre-orogenic extensional structural high, which rose within the foredeep basin starting in the early Tortonian. Following the Messinian-Pliocene Apennine chain building phase, the area was subjected to post-orogenic Quaternary extension, related to the opening of the Tyrrhenian sea. A geological map on the 1:20,000 scale illustrates the main stratigraphic and structural features of the area.

Interrelationship Between Facies Association, Diagenetic Alteration and Reservoir Properties Evolution in the Middle Miocene Carbonate Build Up, Central Luconia, Offshore Sarawak, Malaysia

Carbonate build-ups are proven prolific hydrocarbon reservoirs located around the globe. In Southeast Asia, the carbonates are usually associated with grain-rich facies types. Understanding the carbonate reservoirs in terms of their internal characteristics, depositional environment, diagenesis and their impact on petrophysical properties are essential parts of successful exploration and production strategy. The present study provides a detailed work on carbonate reservoir facies, diagenetic history and reservoir quality including qualitative and quantitative analysis of thin sections of the Miocene carbonate platform, Central Luconia. The Central Luconia carbonates are subdivided into eight lithofacies based on specimens collected from five wells. Detailed lithofacies analysis and correlation of carbonate rocks from Well A and Well B allowed us to reconstruct the evolution of sedimentary environments and relative sea-level changes in a platform during the Early to Middle Miocene of Cycle IV and V. Five lithofacies are identified based on texture, sedimentary structure, grain composition, and fossil contents. These include (1) coated grain to packstone (av. O = 6%, av. Kh = 1 mD), (2) coral (m) lime grainstone (av. O = 14.7%, av. Kh = 6 mD), (3) oncolite lime grain to packstone (av. O = 10%, av. Kh = 4 mD), (4) skeletal lime packstone (av. O = 15%, av. Kh = 4.6 mD), and (5) coral (p) lime mud to packstone (av. O = 4%, av. Kh = 0.5 mD), respectively. Micritization, cementation, fractures, compaction, and dissolution are the dominant diagenetic parameters which are identified. The diagenetic features include dolomitization and dissolution (i.e., leaching) making Well A and Well B unique location to study facies distribution and its implication on reservoir potential. By integrating these parameters, facies 2, 3 and 4 are interpreted as a relatively good quality reservoir, whereas facies 1 and 5 are considered as poor reservoir quality. Among all the diagenetic features, dissolution phenomenon contributes to porosity enhancement and reservoir quality, whereas micritization, compaction and cementation have a negative impact on reservoir quality.

Presence of microporosity in Miocene carbonate platform, Central Luconia, offshore Sarawak, Malaysia

The Luconia Province—offshore Sarawak—is a key hydrocarbon province in Malaysia. However, the gas reservoirs in Central Luconia pose unique problems and challenges as they have partially water-filled microporosity that overprint wireline logs. Microporosity in Central Luconia occurs throughout the Miocene carbonates and is a crucial element that influences fluid flow properties and ultimately the recovery of hydrocarbons. Quantification of macroporosity was achieved using petrographic analysis of thin sections and the FESEM images. The point counting technique was used to estimate the amount of macroporosity from the thin section, which was then subtracted from the total porosity to derive microporosity. The qualitative investigation of the Miocene carbonates indicates the presence of three different types of microporosity namely grain-based microporosity, matrix-based microporosity, and cement-based microporosity. Quantification of microporosity showed that the microporosity varies from sample to sample, ranging from 10 to 60% of the total measured porosity. The depositional texture, mineralogy, and microtexture control this microporosity variation including its abundance and type. The microporosity in Central Luconia is diagenetically controlled based on four major diagenetic mechanisms namely (1) mechanical process/endolithic grains/marine diagenesis; (2) leaching/meteoric diagenesis; (3) cementation/shallow diagenesis; and (4) deeper diagenesis environment.

Seismic analysis of early-mid Miocene carbonate platform in the southern Qiongdongnan Basin, South China Sea

The southern uplift of the Qiongdongnan Basin is a deepwater area in which no wells have beens drilled. The Miocene-Quaternary strata in the Xisha Islands, which are located 40–100 km to the south, are composed of carbonate reef formations. Paleotectonic and paleogeographic analyses of the basin suggest that the southern uplift experienced favorable geological conditions for the development of carbonate reefs during the Miocene. The high-impedance carbonates have high amplitudes and low frequencies on seismic profiles. The reefs are distributed on paleotectonic highs and are thicker than the contemporaneous formations. A forward model of the variation in carbonate thickness based on lithological and velocity information from wells in nearby regions can simulate the seismic response of carbonates with different thicknesses. We identified several important controlling points for determining the thickness of carbonates from seismic profiles, including the pinchout point, the λ/4 thickness point, and the λ/2 thickness point. We depict a carbonate thickness map in the deepwater area of the southern Qiongdongnan Basin based on this model. The carbonate thickness map, the paleotectonic and paleogeographic background, and the seismic response characteristics of reefs suggest that the carbonates that developed on the southern uplift of the Qiongdongnan Basin during the Miocene were mainly an isolated carbonate platform peninsula and ramp deposits. It consisted of gentle ramp platform, steep slope platform, platform depression, gravity flow, and reef bank facies.