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

Extent: 15p.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.Rosalind C. King, Mark R. P. Tingay, Richard R. Hillis, Christopher K. Morley, and James Clar

Origin and petrophysical log response of overpressures in the Baram Delta province, Brunei.

The ‘window’ of safe mud weights between pore pressure and fracture pressure is narrower in overpressured sediments than in normally pressured sediments. This ‘window’ also controls the maximum buoyancy pressure, and hence the maximum height of hydrocarbon columns. Therefore, accurate pore pressure prediction is of critical importance for hydrocarbon exploration. Accurate pore pressure prediction is especially important in the rapidly depositing (3000 m/Ma) Tertiary Baram Delta Province where all economic fields exhibit overpressures, often of high magnitude and with narrow transition zones. A database of pore pressure information was compiled for 157 wells in 61 fields throughout Brunei. Overpressures are observed in 54 fields both in the inner shelf deltaic sequences and the underlying pro-delta shales. Porosity-vertical effective stress plots from 31 fields reveal that overpressures are primarily generated by disequilibrium compaction in the pro-delta shales, but have been vertically transferred into the inner shelf deltaic sequences.Sediments overpressured by disequilibrium compaction exhibit different physical properties to those overpressured by vertical transfer and hence, different pore pressure prediction strategies need to be applied in the prodelta shales and inner shelf deltaic sequences. Sonic and density log data detects overpressures generated by disequilibrium compaction and pore pressures are accurately predicted using an Eaton exponent of 3.0. Sonic log data detects vertically transferred overpressures, even in the absence of a porosity anomaly, and pore pressures are reasonably predicted using an Eaton exponent of 6.5

In situ stress and overpressures of Brunei Darussalam

ix, 271 leaves : ill. (chiefly col.), maps (col.), photographs (col.) ; 30 cm.This thesis analyses in situ stress and overpressure throughout Brunei. The resultant in situ stress and pore pressure data is applied to establish the neotectonic evolution of the Baram Delta province and resolve a variety of current geomechanics issues affecting petroleum exploration and production in the regionThesis (PhD) - National Centre for Petroleum Geology and Geophysics, 200

An open-access stress magnitude database for Germany and adjacent regions

Knowledge of the crustal stress state is important for the assessment of subsurface stability. In particular, stress magnitudes are essential for the calibration of geomechanical models that estimate a continuous description of the 3-D stress field from pointwise and incomplete stress data. Well established is the World Stress Map Project, a global and publicly available database for stress orientations, but for stress magnitude data only local data collections are available. Herein, we present the first comprehensive and open-access stress magnitude database for Germany and adjacent regions, consisting of 568 data records. In addition, we introduce a quality ranking scheme for stress magnitude data for the first time

The Radio Variability of the Gravitational Lens PMN J1838-3427

We present the results of a radio variability study of the gravitational lens PMN J1838-3427. Our motivation was to determine the Hubble constant by measuring the time delay between variations of the two quasar images. We monitored the system for 4 months (approximately 5 times longer than the expected delay) using the Australia Telescope Compact Array at 9 GHz. Although both images were variable on a time scale of a few days, no correlated intrinsic variability could be identified, and therefore no time delay could be measured. Notably, the fractional variation of the fainter image (8%) was greater than that of the brighter image (4%), whereas lensed images of a point source would have the same fractional variation. This effect can be explained, at least in part, as the refractive scintillation of both images due to the turbulent interstellar medium of the Galaxy.Comment: To appear in AJ (8 pages, including 4 figures

Global crustal stress pattern based on the world stress map database release 2008

The World Stress Map (WSM) project is a global compilation of information on the contemporary crustal stress field from a wide range of stress indicators. The WSM database release 2008 contains 21,750 stress data records that are quality-ranked using an updated and refined quality-ranking scheme. Almost 17,000 of these data records have A–C quality and are considered to record the orientation of maximum horizontal compressional stress SH to within ±25°. As this is almost a triplication of data records compared with the first WSM database release in 1992, we reinvestigate the spatial wave-length of the stress patterns with a statistical analysis on a global 0.5° grid. The resulting smoothed global stress map displays both; the mean SH orientation that follows from the maximum smoothing radius for which the standard deviation is 2000 km) exist for example in North America and NE Asia. These have been used in earlier analyses to conclude that the global stress pattern is primarily controlled by plate boundary forces that are transmitted into the intraplate region. However, our analysis reveals that rather short wave-length of the stress pattern <200 km are quite frequent too, particularly in western Europe, Alaska and the Aleutians, the southern Rocky Mountains, Basin and Range province, Scandinavia, Caucasus, most of the Himalayas and Indonesia. This implies that local stress sources such as density contrasts and active fault systems in some areas have high impact in comparison to plate boundary forces and control the regional stress pattern

Present-day stress orientation in the Molasse Basin

The present-day maximum horizontal stress orientation in the Molasse Basin is broadly perpendicular to the strike of the Alpine front, indicating that the stress pattern is probably controlled by gravitational potential energy of Alpine topography rather than by plate boundary forces. The present-day maximum horizontal stress orientations determined herein have important implications for the production of hydrocarbons and geothermal energy in the German Molasse Basin, in particular that hydraulically-induced fractures are likely to propagate N–S and that wells deviated to the north or south may have reduced wellbore instability problems

Stress map of the Mediterranean and Central Europe 2016

The Stress Map of the Mediterranean and Central Europe 2016 displays 5011 A-C quality stress data records of the upper 40 km of the Earth’s crust from the WSM database release 2016 (Heidbach et al, 2016, http://doi.org/10.5880/WSM.2016.001). Focal mechanism solutions determined as being potentially unreliable (labelled as Possible Plate Boundary Events in the database) are not displayed. Further detailed information on the WSM quality ranking scheme, guidelines for the various stress indicators, and software for stress map generation and the stress pattern analysis is available at www.world-stress-map.org