Applied Geophysics

We  present  a  new  method  of  regularization  of  seismic
data using the finite offset common reflection source (FOCRS)  traveltime  approximation.  This method fits  curves
of common  reflection source to the reflection events and
stacks all the amplitudes in a given aperture. The stacked
amplitude, afterwards, is allocated to the time coordinate
in the trace to be interpolated. We applied this method to
three  synthetic  velocity  models  and  the  results  showed
the capability for regularizing  converted seismic waves in
stratified medium.

Metamorphic processes, leading to mineralogical and structural changes of the rocks in response to physical (pressure, temperature) and chemical conditions, can be associated with the development of sin-metamorphic or post-metamorphic fractures. The post-metamorphic ones are directly related to tectonic stress. In addition, tectonic stress may cause the reorientation of minerals on a direction perpendicular to the stress direction, generating foliations (schistosity).
This paper presents a structural analysis of the pre-Alpine metamorphic basement and its relations with the sedimentary cover by using geophysical data recorded in an exploration well located in the North Dobrogea Promontory (Romania). The analysis was based on Quad-Combo wireline logs, spectral gamma ray, sonic cross-dipole and borehole electrical imaging data. The imaging analysis allowed the identification and characterization of metamorphic foliations, sedimentary bedding, natural fractures and the determination of tectonic stress orientation. A brittleness index was computed by means of elastic parameters derived from density and sonic compressional and shear logs. Also, a fracture intensity characterization by using fracture area per volume of rock was conducted. The integration of geophysical logs with mud logging and drilling data allowed us to carry out a detailed analysis of the metamorphic basement in the studied area.

An inexpensive infrared beam barrier and proximity detector has been designed and analyzed using solid state discrete components. The result showed that a security system using infrared technology is possible and viable where the breaking of an infrared signal by objects including humans passing or wandering within restricted premises can be effectively monitored. The design was achieved with the help of IR Module and LEDs, a 555IC timer which oscillates at about 38kHz, a regulating IC which regulates a 9V dc to 5V, transistors, and variable resistors that contribute to the strength of the IR signal generated together with some other passive components. The completed device designed only requires an external power supply when the relay is to be used in triggering an external alarm or switching of bulbs. The design results also showed that the 555IC timer can be used to produce accurate timing ranging from microseconds to hours if the variable resistors can be reduced while the capacitors across it is increased. More so, it was evident from this study that the infrared which has a very small wavelength in micrometers as recorded in the electromagnetic spectrum, can be optimized to travel farther distances of over 250cm.

The study area is located in the northern and western parts of Moldavian Platform, the oldest platform unit of the Romanian territory and representing the margin of the East European Platform. Two hydrocarbon systems are recognized in the Moldavian Platform: a thermogenic system of Paleozoic age and a biogenic system of Miocene age. The Miocene biogenic system comprises significant natural gas fields (including dry gas with more than 98% methane), reservoired especially in Sarmatian (late Middle Miocene) deposits, where suitable conditions for accumulation and sealing are encountered. The Sarmatian stage was marked by permanent changes of the sedimentary conditions, passing from a predominantly marine environment to a transitional one, of deltaic type with lacustrine-continental influences. The gas accumulations are usually hosted in sands/sandstones (observed as good seismic reflectors with continuous or discontinuous character) that pinch out forming lithostratigraphic traps. The sand beds or sand bodies formed during the deltaic construction, especially when they overlap and alternate with pelitic sequences, offer the most favorable settings for such accumulations.
The integrated analysis of recent geophysical well logs (conventional logs and high-resolution electrical imaging logs) and seismic reflection surveys, together with mud logging data and well flow test results, allow a better characterization of the Sarmatian deposits, particularly the gas reservoirs, from the study area. The correlation of three exploration wells along a NW–SE profile indicates that a low-energy, fine-grained depositional environment is developing towards SE, with a prevalence of claystones and with fewer sand reservoirs, if any. This may reflect a deltaic transition from distributary channels and mouth bar sands towards prodelta offshore silts and muds. The processed electrical imaging data recorded in the northernmost exploration well show two dominant dip azimuths (142 and, subordinately, 218 degrees) in the shale intervals. Most likely, these indicate NW to SE and NE to SW sediment paleotransport directions, related to seaward delta progradation. The electrical imaging results also reveal the presence of two high-angle faults (48–54 degrees dip values), which might have provided pathways for gas migration from deeper levels up to shallower Sarmatian reservoirs.

Depositional environments are characterized by their sedimentary lithology, sedimentary structures, paleocurrent patterns and fossils. Sedimentary facies are bodies of sediment that originate simultaneously in adjacent depositional environments. Such environments can be reconstructed using core data, well log information, and outcrops, and other available geologic information. In a study of four oil wells, depositional environments were inferred from the gamma ray log shapes identified on the gamma ray log motifs in combination with the density-neutron trends principle and sonic log high or low spikes. The Multi-Regressive Graph-Based Clustering approach was also used to compliment interpretations. The results obtained show that sand bodies that display an aggradational stacking pattern may be inferred to be channel sand deposits, regressive barrier bars, prograding delta deposits, and alluvial/ fluvial channel, or of transgressive shelf sand. A combination of Multi Regression Graph –Based Clustering and well log motifs has thus been shown to be a reliable tool in depositional environment reconstruction and lithofacies prediction.

In this study, we assessed recent GOCE-based Global Geopotential Models (GGMs) and EGM2008 in Niger. The combined GGMs EIGEN_6C4, GECO and EGM2008 were evaluated up to their maximum degree and order (d/o) 2,190 to select the one for gravity database densification. The following pure satellite GGMs were assessed for the modelling of the long and medium wavelengths in geoid computation: GGM05G, ITU_GGC16, EIGEN_6S4v2 and the fifth releases from
direct (DIR5), space-wise (SPW5) and time-wise (TIM5) approaches. The GGMs are compared to terrestrial gravity data and geoid heights from GNSS/Levelling points before and after applying spectral enhancement method (SEM) by residual terrain model (RTM) for combined models and by RTM and the coefficients of selected combined GGM for pure satellite models. The agreements of combined GGMs with terrestrial gravity data and GNSS/Levelling points, in terms of root mean
square (RMS) are about 4.88 to 5.02 mGal and 0.14 to 0.16 m, respectively. EIGEN_6C4 was selected as it showed the best
performance in terms of geoid height differences and the probability of 3-sigma rule for gravity anomaly differences. At d/o 200, DIR5 showed a good agreement with terrestrial gravity data (5.04 mGal) and GNSS/Levelling points (0.15 m) after applying SEM, it was then retained. All GOCE-based models exhibited a good performance in long and medium wavelengths confirming the good recovery of the gravity field by the spatial gravity mission in these spectral bands.