Central Luconia Province Research Articles

Assessment of geological CO2 storage potential in central Luconia province

The objectives of this paper are to evaluate the suitability of the Central Luconia Province as a potential geological storage site for CO2 in Malaysia and to estimate the theoretical storage capacity of the basin by using Carbon Sequestration Leadership Forum (CSLF) and US Department of Energy (US-DOE) methods. The Central Luconia that has a limited faulting and located within seismic-free zone and possessing suitable geothermal condition which is an attractive characteristic for potential site for CO2 storage are found to be suitable for geological CO2 storage in Malaysia. The Central Luconia Province is estimated to be able to store CO2 from 56 Gt up to 75 Gt. The Central Luconia Province is believed to be a potential site for geological CO2 storage and will give much help in reducing CO2 emissions in atmosphere of Malaysia.

Assessment of the Combined Effect of Temperature and Time on Calcium and Magnesium Release in Carbonate Rocks, Central Luconia Province, Offshore Sarawak, Malaysia

Dissolution of carbonate rocks indicated by the release of calcium and magnesium ions was evaluated for a number of six samples of carbonate rocks representing three microfacies. Dissolution was measured progressive periods of time under different temperature ranges. The main objective of this paper was to evaluate the individual and collective effect of time and temperature on the dissolution trends for any facies. The method applied was the surface response method, in which, temperature, and time represented the factors, while amounts of calcium and magnesium released (in ppm) represented the responses. Dissolution was carried out experimentally under a constant pH of 0.1 m Hcl, continuous stirring. The resulting data in terms of concentration (ppm) of the Ca and Mg was used as input data for the model. Response surface method provided models for the dissolution of carbonates, optimization of dissolution, and individual-and-combined effect of each factor (Time and temp).

Relationship between syn-depositional faulting and carbonate growth in Central Luconia Province, Malaysia

Using 3D seismic and well data, detailed seismic interpretation has been conducted on two carbonate Platforms EX and FY located in the Central Luconia Province, Malaysia. The results provide an insight to understand the relationship of faulting with syn-depositional carbonate growth. Five geo-seismic units were interpreted from the Late Oligocene to present day sedimentation in the basin. Structural interpretation of both platforms shows that almost all the faults in the deeper part of the platforms are normal listric faults that resulted from the final rifting stage of the South China Sea. Small-scale, steep normal faults within the carbonate units behave relatively as syn-depositional faults that became the base and template for the reefs to grow as these faults created conjugate and branching faults systems. Apart from becoming templates for the reefs to grow, these syn-depositional faulting events had also interrupted the growth of reefs especially those that were located at the platform margin. Slight movement of the branching faults induced sub-marine landslide to create reefs collapse. The establishment of relationship between faulting and carbonate growth in Central Luconia Province might be useful for revisiting mature hydrocarbon reservoirs.

Remote Sensing Analysis of Recent Carbonate Platforms, East of Sabah: Potential Analogues for Miocene Carbonate Platforms of the South China Sea

DOI: 10.17014/ijog.v7i3.141Recent carbonate platforms may provide useful analogues for fossil platforms and reefs, and could allow the generation of quantitative tools for the prediction of facies distribution, reservoir volumes, and reservoir quality. Data from these modern analogues would greatly enhance our ability to construct more reliable and calibrated reservoir models for carbonate fossil fields, such as the Miocene carbonate platforms of Central Luconia Province, Sarawak. In this study, carbonate facies maps and quantitative reservoir data will be generated by using remote sensing techniques. Satellite imageries over the carbonate platforms east of Sabah have been acquired and processed for generating facies maps. In order to produce a reliable facies map, the composition and grain size distribution of the sediments that make up individual facies must be known in order to determine the classes that have been identified on the initial facies maps. Samples collected from the Gaya and Selekan platforms were analyzed and the results of grain size analysis are illustrated.

Present‐day stress orientations and tectonic provinces of the NW Borneo collisional margin

Borehole failure observed on image and dipmeter logs from 55 petroleum wells across the NW Borneo collisional margin were used to determine maximum horizontal stress (σH) orientations; combined with seismic and outcrop data, they define seven tectonic provinces. The Baram Delta–Deepwater Fold‐Thrust Belt exhibits three tectonic provinces: its inner shelf inverted province (σH is NW‐SE, margin‐normal), its outer shelf extension province (σH is NE‐SW, margin‐parallel), and its slope to basin floor compression province (σH is NW‐SE, margin‐normal). In the inverted province, σH reflects inversion of deltaic normal faults. The σH orientations in the extension and compression provinces reflect deltaic gravitational tectonics. The shale and minibasin provinces have been recognized in offshore Sabah. In the shale province, σH is N010°E, which aligns around the boundary of a massif of mobile shale. Currently, no data are available to determine σH in the minibasin province. In the Balingian province, σH is ESE‐WNW, reflecting ESE absolute Sunda plate motions due to the absence of a thick detachment seen elsewhere in NW Borneo. The Central Luconia province demonstrates poorly constrained and variable σH orientations. These seven provinces result from the heterogeneous structural and stratigraphic development of the NW Borneo margin and formed due to complex collisional tectonics and the varied distribution and thicknesses of stratigraphic packages.

What are the Spratly Islands?

Seismic records, combined with dredged samples and a core, indicate that the Spratly Islands of the Dangerous Ground Province are constructed of presently active carbonate build-ups, known to extend back continuously at least to the Pleistocene and presumed to have initiated in the Miocene, most likely upon the crests of sea-floor cuestas that trend north-east–south-west parallel to the sea-floor spreading magnetic anomalies of the contiguous abyssal plain of the southern part of the South China Sea. The cuestas range from spectacular to subdued, constructed of Triassic and Cretaceous strata and no older rocks have been identified from dredges. The cuesta axes plunge towards the south-west away from the islands, suggesting that the reefs began colonising their more elevated parts, but the timing is uncertain. The highest seismically recorded cuesta crest is in 440 m of water and the islands and reefs are generally closely surrounded by water deeper than 1500 m. Since the so-called Mid-Miocene Unconformity (MMU), the region has been undergoing post-rift thermal subsidence. However, the nearby seismic lines show no evidence of drowned carbonate reefs. It is suggested that the coral-algal reefs colonised the crests of the most elevated cuestas that have maintained stability as shown by the 165 m core of one reef indicating periodic exposure with caliche horizons. Deepening water has protected the build-ups from extinction by post-rift draping strata in contrast to the Central Luconia Province, and the build-ups have been able to keep up with regional thermal subsidence. The dredged Mesozoic strata indicate that the Dangerous Ground is not exotic and should be interpreted as an integral part of the pre-rift Sundaland continent that included South China, Vietnam, Peninsular Malaysia, western Sarawak and possibly part of Sabah. Igneous and metamorphic samples have been dredged. Although individual spot K/Ar dates cannot be accepted at face value, such rocks can also be interpreted as an integral part of Sundaland. Post-MMU dredged samples are predominantly deep-water calcareous mudstones typified by the draping strata of the Ocean Drilling Program (ODP) Site 1143 cored from Recent to Late Miocene.

Three dimensional reservoir geological model and multiple scenario volumetrics of the F23 Miocene carbonate buildup, Luconia Province, offshore Sarawak

Typically, the geology and production behavior of gas reservoirs in the atoll shaped Miocene carbonate structures of the Central Luconia province, offshore Sarawak, are best constrained in the center of the field due to a biased distribution of wells. Control over the reservoir architecture, pore volume and fluid flow behavior decrease significantly towards the reservoir flanks introducing uncertainties for an optimized reservoir management. An integrated reservoir geological study was initiated with the objective to decrease uncertainties and increase the understanding of their impact on static and dynamic reservoir models. Data from an integrated core, seismic and petrophysical evaluation, including lateral seismic porosity prediction and the application of geostatistics, were combined to a 3-D fully computerized reservoir model. The core and seismic evaluation reveals a complex internal reservoir architecture strongly influenced by paleo-wind pattern and sea-level fluctuations with backstepping, progradational and aggradational growth phases. Transgressive systems tracts are represented by dense argillaceous limestones, which form more or less continuous blankets possibly isolating gas volumes and influencing vertical water movement. During repeated periods of flooding the platform back-stepped up-wind only to prograde down-wind again during sea-level high stands until re-reaching the previous platform margin. An uncertainty tree was constructed for the F23 field in order to assess the impact of combined and individual uncertainties on static and dynamic reservoir models. Parameters considered in the uncertainty tree are the top carbonate structure, the porosity distribution, the hydrocarbon saturation and the gas expansion factor. Most likely, low and high cases were used in order to assess the parameters with the most impact on the uncertainty of hydrocarbon volume and fluid flow, in particular possible flank water encroachment. Results from the volumetric calculations arrive at a most likely GIIP close to that derived from material balance analysis. However, low and high cases significantly exceed the uncertainty range of the material balance GIIP. While the geology of the reservoir flank is now better constrained using refined seismic interpretations, uncertainties in these areas remain high.

Multidiscipline Studies of the Depletion Behavior of the F23 Gas Field, Offshore Sarawak, East Malaysia: ABSTRACT

The F23 gas field is located 178 km north-northwest of Bintulu in the central Luconia province, offshore Sarawak. The accumulation consists of a late Miocene layered platform-type carbonate buildup 22 km[sup 2] and a maximum gas thickness of over 1000 ft. Eleven development wells and one observation well were completed in 1983, with initial gas delivery to Malaysia LNG in October 1983. Annual TDT surveys are conducted in the observation well to monitor the movement of the GWC in the central area of the field. As of April 1992, a cumulative rise of 25 ft was observed. This contrasts with material balance calculations predicted rise of some 60 ft based on Sgr of 50% inferred from core measurements. Among the potential explanations were irregular bottom-water encroachment, preferential flank water advance, or larger GIIP. As all had potentially important consequences to depletion strategy and ultimate reserves, multidiscipline studies were initiated. Time-lapse seismic data were used to better determine the existing fluid levels across the field and reservoir simulation studies were used to match observation well data and predict future reservoir behavior. Concurrent reservoir and simulation studies suggested that the material balance and observation well data could be reconciled by (1) amore » reduced aquifer, and/or increased GIIP, and/or a lower residual gas saturation, or (2) preferential flank water influx due to internal low-permeability layers. As (1) would not lead to early water breakthrough, the simulation effort was aimed to investigate (2), the possibility and implications of early edge water breakthrough via the flank zone.« less

FMS/FMI Borehole Imaging of Carbonate Gas Reservoirs, Central Luconia Province, Offshore Sarawak, Malaysia: ABSTRACT

The Central Luconia Province, offshore Sarawak, is a significant gas province characterized by extensive development of late Miocene carbonate buildups. Some 200 carbonate structures have been seismically mapped of which 70 have been drilled. FMS/FMI borehole images were obtained from three appraisal wells drilled in the [open quotes]M[close quotes] cluster gas fields situated in the northwestern part of the province. The [open quotes]M[close quotes] cluster fields are currently part of an upstream gas development project to supply liquefied natural gas. Log facies recognition within these carbonate gas reservoirs is problematic due mainly to the large gas effect. This problem is being addressed by (1) application of neural network techniques and (2) using borehole imaging tools. Cores obtained from the M1, M3, and M4 gas fields were calibrated with the FMS/FMI images. Reservoir characterization was obtained at two different scales. The larger scale (i.e., 1:40 and 1:200) involved static normalized images where the vertical stacking pattern was observed based on recognition of bed boundaries. In addition, the greater vertical resolution of the FMS/FMI images allowed recognition of thin beds. For recognition of specific lithofacies, dynamically normalized images were used to highlight lithofacies-specific sedimentary features, e.g., clay seams/stylolites, vugs, and breccia zones.more » In general, the FMS/FMI images allowed (1) easier recognition of reservoir features, e.g., bed boundaries, and (2) distinction between lithofacies that are difficult to characterize on conventional wireline logs.« less

Reservoir Development in Miocene Carbonates, Central Luconia Province, Offshore Sarawak: ABSTRACT

Reservoir Development in Miocene Carbonates, Central Luconia Province, Offshore Sarawak: ABSTRACT

A Completion Design for High-Capacity Offshore Gas Wells

Summary Sarawak Shell Bhd. (SSB) is currently developing two offshore gas fields to supply about 1,200 MMscf/D (34.3 × 10(6) std m3/d) to a liquid natural gas (LNG) plant being built at Bintulu, Sarawak. Both fields are plant being built at Bintulu, Sarawak. Both fields are carbonate buildups with very high productivities but, because of their relatively shallow depth, only moderate reservoir pressure. The produced gas is lean, With CO2 content of up to 7.3% and H2S content of about 8 ppm. Because the wells are offshore, there is increased risk caused by the proximity of other wells and the possibility of platform damage. Being offshore also means high costs for drilling, compression, and workover. This paper discusses the completion design developed to cope with these conditions. Safety considerations, the prevention of corrosion, and tubing stress analysis are prevention of corrosion, and tubing stress analysis are discussed. The final design uses 7-in. (17.8-cm) tubulars, including 13% Cr steel at points where corrosion may be severe, and uses a fire-resistant Christmas tree and wellhead design. Introduction As operator for the Malaysian national oil company, Petronas, SSB currently is developing two offshore gas Petronas, SSB currently is developing two offshore gas fields in the Central Luconia province of Sarawak to supply about 1,200 MMscf/D (34.3 × 10(6) std m3/d) to an LNG plant at Bintulu. Development drilling started in the El I field in May 198 1. Drilling in the second field, F23, should begin in Dec. 1982. Ten to twelve wells are planned initially for each field with the possibility that planned initially for each field with the possibility that four additional wells could be required in E11 field at a later stage. The development of a third field, F6, depends on the production performance of E11 and F23 and the increase in market demand. Both E11 and F23 ar-e carbonate buildups with very high productivities. Planned deviations for development wells require Planned deviations for development wells require kickoff between 500 and 2,000 ft (152 and 610 m) subsea, 2 1/2 degrees/100 ft (0.00143 rad/m) buildup to a maximum of 45 degrees (0.785 rad), and a tangent section to total depth. The casing scheme selected for E11 and F23 wells comprises a 9 5/8-in. (24.4-cm) production string and a 7-in. (17.8-cm) liner across the productive zone. This paper describes the completion design developed for the two fields. The Fields Ell field is a pinnacle-type carbonate buildup, and gas will be produced from the interval of 4,740 to 6,477 ft (1445 to 1974 m) subsea. Reservoir pressure is 2,885 psia (19.9 MPa) at 6,000 ft (1829 m) subsea, and psia (19.9 MPa) at 6,000 ft (1829 m) subsea, and pressure at top carbonate is equivalent to a 0.59 psi/ft pressure at top carbonate is equivalent to a 0.59 psi/ft (13.35-kPa/m) gradient. CO2 content of the gas is 7.3% and the H2S content is 7 ppm, giving partial pressures of 211 and 0.02 psia (1.45 MPa and 0. 14 kPa), respectively. The calculated maximum production rate from the top zone at initial conditions is more than 200 MMscf/D (5.7 × 106 std m3/d) per well. Other technical considerations limit the planned production rates to 75 MMscf/D (2.1 × 10(6) std m3/d) per well from the top zone and 50 MMscf/D (1.4 × 10(6) std m3/d) per well from the bottom zone. F23 field is a platform-type carbonate buildup. JPT P. 688