Luconia Province Research Articles

Miocene carbonates of the Luconia province, offshore Sarawak: implications for regional geology and reservoir properties from Strontium-isotope stratigraphy

The Luconia Province, offshore Sarawak, Malaysia, is one of the largest SE-Asian carbonate provinces with more than 200 platforms and gas reserves exceeding 40 Tscf. The application of the Sr­ isotope technique integrated with core, log and seismic data significantly refines the stratigraphy of the province despite extensive diagenetic alteration. Based on the new data, a unified concept of platform evolution is tied to global sea-level variations and the regional distribution of reservoir architecture. Evidence is presented for major karstification during and after platform growth and its influence on the regional distribution of reservoir properties. Sr-isotope analyses (ntotaJ = 137; data range: O.7084~.70903 for NBS987 = 0.710230) suggest that the carbonate platforms of the Luconia province are Early to Middle Miocene in age. The Sr-isotope signature is apparently unaffected by diagenetic stabilization from metastable carbonates to low-Mg calcite while dolomitization caused alteration of the isotope ratio. Growth and demise of the province can be correlated with a second-order eustatic sea-level cycle (TB2). Major karst horizons and flooding, aggradation and progradation packages are linked via step-changes in isotope signature to third order eustatic sea-level fluctuations. Simultaneous with the second order sea-level drop (late Middle Miocene) the influx of siliciclastics split the province into a southern part with low relief carbonate banks and a northern part with high relief platforms. All growth terminated at the end of the Middle Miocene. Low relief banks were buried while high relief platforms were karstified prior to drowning (Late Miocene­ Pliocene). The regional distribution of pore types, porosity and permeability is linked to the duration of exposure and burial diagenesis. In the karstified platforms of the northern part drilling losses are common.

Abstract: Sr-Isotope Stratigraphy of Miocene Carbonates, Luconia Province, Sarawak, Malaysia: Implications for Platform Growth and Demise and Regional Reservoir Behavior.

Abstract: Sr-Isotope Stratigraphy of Miocene Carbonates, Luconia Province, Sarawak, Malaysia: Implications for Platform Growth and Demise and Regional Reservoir Behavior.

Geological Factors Controlling Gas Volumes in Miocene Carbonate Buildups - Offshore Sarawak: ABSTRACT

Over 170 independent Miocene carbonate buildups are located within the Luconia Province of offshore Sarawak, Malaysia. They vary in size and shape from small isolated pinnacles through tabular to broad low relief platforms, distributed across nearly 10MM acres of the shallow Miocene shelf. Among the 70-odd buildups drilled to date, over half are gas-bearing. Discovered volumes exceeds 40 TCF of gas-in-place, with gas columns ranging from a few meters to greater than 500 m. Geological factors suspected of controlling the occurrence and volume of gas within each buildup include caprock, source, stratigraphic and structural variables. The source for gas is the (largely uncontrolled) Cycle I/II coastal plain sequence. In practice, only caprock and seismically-derived stratigraphic and structural factors provide sufficient geological/geophysical evidence to characterize and distinguish buildups at the prospect level. Useful caprock-related discriminators include clastictseismic facies, drape, and pore pressure - each reflecting the sealing capacity of the caprock as measured by the gas column height in the reservoir. Factors related to the gas-focusing effectiveness of bedding below the reservoir include the relief and structural configuration of the pre-carbonate section, the areal extent of the drainage area, and faulting. As prospect discriminators, these structural factors are limited by possiblemore » velocity distortions and poor seismic resolution beneath the carbonate section. Five gas accumulations discovered by Occidental since 1992 are compared to show the variety of discernible factors controlling their in-place volumes.« less

The geology of Sarawak deepwater and surrounding areas

A geological and geophysical investigation of several key transects ofthe 1989 vintage seismic grid in the Sarawak deepwater was conducted in order to understand the sedimentation history and structural geology of the area. In the study area, two tectonostratigraphic provinces can be recognised, namely the North Luconia and West Luconia Provinces. The deep sedimentary basin of North Luconia is filled with 7-8 km of Tertiary sediments and are characterised by NNE-SSW trending extensional fault bounded features, buried hills and local occurrences of forced folds. On the eastern boundary, a major, NNE-SSW trending basin boundary fault separates it from the Northwest Sabah Platform. The latter by contrast is an attenuated crustal terrain characterised by NE-SW trending rift systems and generally thinner sedimentary cover of about only 2-4 km thick. To the southeast, the West Luconia Province which is a thick sedimentary basin with up to about 13 km of sediments, contains a very thick pile of post mid Miocene sedimentary section and is characterised by E-W trending growth faults and °a series of slumps and toe thrusts formed by gravity gliding. These overlie an older normal-faulted section at a mid Miocene unconformity. Generally, the crustal extension in the South China Sea and peripheral areas have generated various patterns of rift orientation and extensional axes. In North Luconia the NNE-SSW trending extensional elements parallel some of the basin axes in the N am Con Son Basin, offshore Vietnam. Finally, based on sequence stratigraphic framework, up to five sub-megasequences are recognised in the Sarawak deepwater. The age determination from well controls and correlation with the episodic crustal rifting and seafloor spreading in the South China Sea Basin has provided some insight on the tectonic evolution.

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