Reprint of: Comparison of modern fluid distribution,pressure and flow in sediments associated with anticlines growing in deepwater (Brunei) and continental environments (Iran)

Differences in fluids origin, creation of overpressure and migration are compared for end member Neogene fold and thrust environments: the deepwater region offshore Brunei (shale detachment), and the onshore, arid Central Basin of Iran (salt detachment). Variations in overpressure mechanism arise from a) the availability of water trapped in pore-space during early burial (deepwater marine environment vs arid, continental environment), and b) the depth/temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development. Chemical reactions associated with smectite rich mud rocks in Iran occur shallow (∼1900 m, smectite to illite transformation) causing load-transfer related (moderate) overpressures, whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore Brunei. The basal detachment in deepwater Brunei generally lies below temperatures of about 150 °C, where chemical processes and metagenesis are inferred to drive overpressure development. Overall the deepwater Brunei system is very water rich, and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines. The result is a wide variety of fluid migration pathways and structures from deep to shallow levels (particularly mud dykes, sills, laccoliths, volcanoes and pipes, fluid escape pipes, crestal normal faults, thrust faults) and widespread inflationary-type overpressure. In the Central Basin the near surface environment is water limited. Mechanical and chemical compaction led to moderate overpressure development above the Upper Red Formation evaporites. Only below thick Early Miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms. Fluid leakage episodes across the evaporites have either been very few or absent in most areas. Locations where leakage can episodically occur (e.g. detaching thrusts, deep normal faults, salt welds) are sparse. However, in both Iran and Brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds.     

Comparison of modern fluid distribution,pressure and flow in sediments associated with anticlines growing in deepwater (Brunei) and continental environments (Iran)

Differences in fluids origin, creation of overpressure and migration are compared for end member Neogene fold and thrust environments: the deepwater region offshore Brunei (shale detachment), and the onshore, arid Central Basin of Iran (salt detachment). Variations in overpressure mechanism arise from a) the availability of water trapped in pore-space during early burial (deepwater marine environment vs arid, continental environment), and b) the depth/temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development. Chemical reactions associated with smectite rich mud rocks in Iran occur shallow (∼1900 m, smectite to illite transformation) causing load-transfer related (moderate) overpressures, whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore Brunei. The basal detachment in deepwater Brunei generally lies below temperatures of about 150 °C, where chemical processes and metagenesis are inferred to drive overpressure development. Overall the deepwater Brunei system is very water rich, and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines. The result is a wide variety of fluid migration pathways and structures from deep to shallow levels (particularly mud dykes, sills, laccoliths, volcanoes and pipes, fluid escape pipes, crestal normal faults, thrust faults) and widespread inflationary-type overpressure. In the Central Basin the near surface environment is water limited. Mechanical and chemical compaction led to moderate overpressure development above the Upper Red Formation evaporites. Only below thick Early Miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms. Fluid leakage episodes across the evaporites have either been very few or absent in most areas. Locations where leakage can episodically occur (e.g. detaching thrusts, deep normal faults, salt welds) are sparse. However, in both Iran and Brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds.     

Haze and Health in Brunei Darussalam: The Case of the 1997‐98 Episodes

A study of the impacts of the 1997‐98 haze episodes in Brunei Darussalam was carried out in two districts between September 1997 and September 1998 through random surveys of households. The aim of the study was to understand health problems caused by haze; whether such health impacts differed amongst different groups in the population; and the nature of the differences that might exist. The study also sought to understand whether health impacts of haze varied between urban and rural areas. Furthermore, the study aimed to understand respondents' perception of the haze problem. Some hypotheses formulated to establish the existence or otherwise of significant difference between health conditions during haze (September 1997 and January‐June 1998) and haze‐free periods (January‐June 1997 and September 1998) were verified through the p‐value statistical approach. The conclusions from the verifications are that adverse health effects of the haze were statistically significant and were not uniform with respect to different groups in the population. For example, the deleterious effects of haze appeared skewed towards the young (age 1‐5 years) and the aged (≥60 years). A higher proportion of urban population was more adversely affected than in rural areas and, other things being equal, a higher proportion of outdoor workers was more adversely affected by haze than their indoor counterparts. The paper suggests cooperative efforts amongst ASEAN governments to reduce poverty in communities that burn forests; improve their socioeconomic opportunities; lessen their dependence on land; and share information related to haze to prevent or mitigate its adverse effects. There is a need to intervene especially in the private sector with respect to work schedules of those who work outdoors (e.g. construction workers) and the housing of immigrant workers occupying makeshift structures to escape rents in proper accommodation. There is also a need for greater and sustained programme of educating the public on environmental hazards to mitigate their adverse impacts on society.     

Climatic patterns in a tropical rainforest in Brunei

Meteorological parameters were monitored on an hourly basis over ten months during 1991–2, from altitudes of 45 and 913 metres in an undisturbed tropical rainforest in Brunei, near the north-west coast of Borneo. In general, the observed characteristics of the climate accorded with the regional meteorological systems and with published results from other studies in northern Borneo, although a greater degree of temporal variability was apparent. The seasonal variability was probably enhanced by the El Niño Southern Oscillation event of early 1992. Rainfall events were typically highly variable in nature, although storm intensity profiles were broadly similar. High magnitude and high intensity events are common among the large total number of events. More rain, of generally higher intensity, fell on the mountain. The total daily solar energy receipt was similar at both altitudes owing to greater cloud cover on the mountain. Temperatures varied significantly with season at both altitudes and the mean lapse rate was 4.5°C/km. Relative humidity at 913 metres tended to be significantly higher during the day and significantly lower at night than at 45 metres. Wind directions were dominantly controlled by local mountain and valley wind systems. Wind speeds were significantly higher during the dry seasons and at the higher altitude. Previous studies have shown that small but significant variations in meteorological parameters can have distinct ecological responses, and rainfall characteristics are important controls on geomorphological processes.     

WATER TABLE AND REDOX CONDITIONS IN DEEP TROPICAL PEAT

Changes in redox potential(RP)are the resultof the combined effects between many chemical,physical and biological processes in the soil.Soil oxi-dation and reduction depend on soil respiration,diffu-sion of oxygen and carbon dioxide in soil and onchanges …     

Brunei Darussalam: Characteristics of selected petroleums and source rocks

The development of three Tertiary deltaic complexes has resulted in the deposition of up to 10 km of sandstones and shales comprising the sources and reservoirs for crude oils that occur onshore, near-offshore and, with future exploration efforts, those likely to be encountered in deepwater reservoirs north of the Brunei coastline. We examined a series of offshore oils and onshore rock samples in Brunei Darussalam (a) to delineate oil family groups and their source rock characteristics, and (b) to assess the source potential of the sedimentary sequence with respect to lithology and depositional setting. Twelve offshore oils and 53 shales, coaly shales and coals were examined. The oils contain indicators of allochthonous (e.g. bicadinanes, oleananes) and autochthonous (e.g. cholestanes and methylcholestanes) components in the source organic matter. Predictable geographic variations of this mixed input are clearly evident in the sample set (e.g. allochthonous input appears to increase in offshore Brunei to the northeast). Although this molecular source signature is relatively clear, migration of these oils from deep (and unidentified) source rocks has resulted in extensive migration-contamination with respect to the tetracyclic and pentacyclic hydrocarbons. This contamination has resulted in strong correlations between certain molecular maturity indicators and the present-day temperature of the reservoirs. Liquid hydrocarbon source rock potential is present in the tidal and coastal embayment facies, and is greatest in the Miocene coals. Neither the shales nor coaly shales contain significant oil generative potential. The thermal immaturity of the sample set precludes valid oil–source rock correlations without conducting artificial maturation experiments on the coals.     

Variation in vertical stress in the Baram Basin, Brunei: tectonic and geomechanical implications

The vertical or lithostatic stress is an important factor in tectonic and geomechanical studies and is commonly used in the prediction of pore pressures and fracture gradients. However, the vertical stress is not always calculated in situ and the approximation of 1.0 psi/ft (22.63 MPa/km) is often used for the vertical stress gradient. Vertical stress has been determined in 24 fields in the Baram Basin, Brunei, using density log and checkshot velocity survey data. The Baram Basin shows a variation in vertical stress gradient between 18.3 and 24.3 MPa/km at 1500 m depth below the surface. This variation has a significant effect on in situ stress related issues in field development such as wellbore stability and fracture stimulation. The variation is caused by a bulk rock density change of 2.48–2.07 g/cm³ from the hinterland of the delta to its front. Differential uplift and erosion of the delta hinterland and undercompaction associated with overpressure are the interpreted causes of the density and hence vertical stress variation.