Journal of the Earth and Space Physics
Year:2006 | Volume:32 | Issue:3|Papers Count:13

Estimating of various petrophysical parameters and determining of subsurface geology is very important in petroleum reservoir evaluation. Exploration drilling and various well logs normally provide this sort of information. Among the various well logs, the photoelectric (PEP) log is very important as it able to determine the lithology of the reservoir precisely. Therefore for those wells for which this log is not available it is necessary to predict them somehow. In this study it is aimed to use artificial neural network (ANN) ability to tackle this problem. To achieve the goals, a back-propagation ANN (BPANN) is planned to model the interrelationships between seven different well logs, and PEF logs. Data from three wells in the Ahvaz oil field (Asmari reservoir) are organized into training, testing and validation data sets for BP-ANN modeling. Data of the fourth and the fifth wells in the same field are retained as independent data sets for evaluating the ability of the network PEF prediction. Once the designed network has been trained properly, its performance has also been tested. When it has been found that the performance is satisfactory the data set of the fourth and the fifth wells are applied to the trained network. The results of the ANN modeling show that the designed network with three layers and architecture of 7-10-1 can produce the precise PEF log that compares well with the measured PEF logs. This means that the designed network is capable enough to predict the PEP logs for the required wells in the same area.

In this paper the influence of solid tide on the Earth gravity field is considered. In this consideration the Earth can be regarded as either an elastic or inelastic body. Each one of these elastic and inelastic bodies has two main tidal components, Frequency dependent and trequency independent components. In this article how to compute the effect of these components in the Earth's gravity field is presented. In this investigation, an attempt is made to find out whether the Earth should be regarded as an elastic or inelastic body in practical applications. Computations show equivalent effects on the gravity field due to the elastic and inelastic Earth model. The effect of the Frequency dependent component of solid tide due to the elastic and inelastic Earth is much smaller than the Frequency independent components. It depends on time and tidal constituents and it should be considered in precise applications. Comparisons between the solid tides due to the elastic and inelastic Earth model show that the inelastic Earth is contracted at poles about 3mm and expanded at equator about 2.5mm more than the elastic case.

The least-square minimization approaches for determination of depth, shape and amplitude coefficient expressed by Abdolrahman et al. (2001) for sphere and horizontal cylinder is used for rectangular prisms as synthetic models with and without random noises. The method is also applied for real sources producing micro-gravity data .The capability of the method is tested and discussed in this paper.

The loess deposits in central Asia, China, Europe and the USA provide records of past climate, which permits the study of paleoclimatology. Although luminescence dating has had an important role in dating loess, significant challenges still remain. UV-blue emission from polymineral and feldspar suffer from anomalous fading. UV-blue emission from quartz saturates at c.<500 Gy. Fattahi (2001) reported the ability of red thermoluminescence for dating volcanic quartz to c.1.3 Ma.This paper investigates the possibility of applying single aliquot regeneration red thermoluminescence (SARRTL) protocol for dating loess and demonstrating that: 1- It is possible to detect red thermoluminescence from loess. 2- Red thermoluminescence from loess is bleachable.3- SARRTL is able to recover a known laboratory dose.4- Equivalent doses around 1000 Gy are accessible.This information suggests that SAR RTL is a powerful protocol for dating loess which can extend the time range of luminescence dating of unburnt Aeolian sediments.

In this paper to find stable anisotropy direction with minimum error, we attempt to automate the choice of analysis of Moho Ps phase window by performing a grid search over different windows. We have determined the anisotropy direction in the crust of the Alborz region by using 8 events recorded at three BEES seismic broadband stations (i.e. DAMV, THKV and CHTH).Analysis of shear wave splitting of the Ps conversion from the crust-mantle boundary indicates a fast azimuth of anisotropy oriented approximately NE-SW. This strongly suggests coherent crustal anisotropy with a fast direction perpendicular to the strike of mountain block ranges.We estimate the average directions of anisotropy under three stations, DAMV, THKV and CHTH of 42, 55, 55 degree, respectively. Moreover our results show that the magnitude of anisotropy are 0.23, 0.22, 0.27 seconds, respectively, which are in good agreement with the geology and tectonic setting of this region.

Seismic data from the onshore area of Iran over the Darquain structure is used to investigate stratigraphic and structural seismic anomalies inside the Fahliyan formation (Neocomian). The data consists of a 3D grid seismic cube, acquired in the late 1990's. An integrated seismic interpretation and inversion revealed an outstanding feature in the lower part ofihe Fahliyan formation. This anomaly has N-S trend, parallel to Darquain structure and the results of seismic studies predict high porosity for the observed anomaly in the lower part of Fahliyan as a major oil reservoir. Recent drillings based on the results of seismic interpretation proved its potential.

In seismic data acquisition, source and receiver array is used for attenuation of surface waves caused by the source. On the other hand regarding the spatial sampling, to prevent spatial aliasing, the wavelength should not be shorter than twice the trace interval. Therefore by designing a suitable source and receiver array one may suppress waves that are prone to aliasing. Thus, to further attenuate these phenomena (surface waves and aliasing) will be necessary to optimize arrays. One of the ways to optimize source and receiver arrays is spatial convolution. In this method each complex array consists of several simple arrays which make a large array when joined together. By using simple arrays of 2 and 3 elements and putting the notch points of these arrays in side lobes of the final response of the array, the side lobes can be reduced. Considering that both source and receiver arrays can affect the amplitude of the generated waves, and the total effect of these arrays equates the summation of both effects in decibel, it is also possible to compute the effect of the source array on the final response of source and receiver arrays in order to optimize the final response of array.

Comparison of some numerical integration methods of solving the differential equation of motion of a satellite is the main subject of this paper. Since the equation of motion of a satellite is a second order differential equation, therefore, six initial values should be introduced to the numerical solution. These six initial values are the components of position and velocity vectors in an inertial frame respectively. Comparing numerically integrated position and velocity vectors with Keplerian orbit; one can obtain the bias of the numerical integration method in a satellite-centered coordinate system. In this research, three methods of Runge-Kutta, Runge-Kutta-Nystrom, and the predictor-corrector method of Adams-Bashforth and Adams- Moulton are investigated for a low earth orbiting satellite. Numerical results show that with integration size of 30 seconds, the Runge-Kutta method, Adams-Bashforth and Adams-Moulton predictor-corrector algorithms, and Runge-Kutta-Nustrom provide closer orbit to the theoretical orbit respectively.

Geo-stationary orbit has been in use since 1964 for telecommunication purposes. Our investigation on the orbit of such satellites revealed that the radius of geo-stationary satellites are so far computed based on the point mass W=GM/r gravitational model of the Earth. To investigate the effect of more improved Earth's gravitational models on the radius of the Geo-stationary satellites we have considered the following models: (i) Bjerharnmar gravitational potential field, (ii) first term of ellipsoidal harmonic expansion of the Earth's gravitational field, (iii) Somigliana-Pizzeti gravitational potential field. According the results of the computations, the radius of the Geo-stationary satellite computed based on the aforementioned gravitational potential models are deviated from the radius computed based on point mass model W=GM/r, by (i) 0.5km, (ii) 2.15km, and (iii) 2.7km, respectively. Since such an error in the radius of geostationary satellites results in small movements of the satellite in orbit that justifies why the current geo-stationary satellites require fuel and racket engine to fine tune the position of the satellite in its orbit at the specific interval of time. These orbital maneuvers are so important that even the life time of those satellites is determined from the time span that their fuel allows for the fine tuning of the orbit. Based on the computations, the radius of 42, 161, 465.71m, computed based on the Somigliana-Pizzeti gravitational potential field is recommended for the placement of geo-stationary satellites.

This research is an attempt to investigate the blocking systems over the Atlantic Ocean and especially over the Mediterranean sea, which leads to surface cyclogenesis in the east of the Mediterranean Sea, and the influence of their effects over the Iranian region. At the first step of study, Mediterranean topography, local Mediterranean winds and cyclogenesis have studied; then structure and types of existing blocking systems on the synoptic weather maps have been introduced with figures.In the second step of the study, all of the blocking systems that were formed over the Atlantic Ocean were identified from 1989 to 1997, the results of which are shown in the table included in the paper. Of course this part of the work was done with the help of Prof. Colucci from USA and data are given from NCEP.Atmospheric blocking systems can lead to a stagnation of weather patterns where the patterns remain for several days or even weeks at the same location during the blocking system. This case can lead to flooding, drought, above normal temperatures, below normal temperatures and other weather extremes. Therefore, it is important to recognize a blocking pattern in its initial development. With this awareness, one can forecast up to several days in advance with a high degree of accuracy.

In this paper with the method considering the correlation coefficients the order of regional field could be determined. This method can be used for both Bouguer and residual anomalies.Capability of this method is tested in the case of small models which have not been considered in the main paper. Depth estimation is one of the most important aspects in the method.

Recent progress in the field of satellite, airborne, and surface gravimetry has resulted in geopotential models with high resolution. Since the geopotential models are computed based on dense and highly accurate gravity data, they are valuable sources of information for presentation of long and medium wavelength spectrum of the gravity field in the computational algorithm of modem gravity field modeling techniques. Considering the variety of the geopotential models which are currently available, it is necessary to verify their accuracy in synthesizing the gravity functional so that one can select the best geopotential model for a region of interest. In this study 4 geopotential models, namely: EGM96, PGM2000A, Eigen-cgolc, Eigen-Grace2s,are compared for their accuracy in synthesizing gravity functional of the types: (1) astronomical longitude, (2) astronomical latitude, (3) norm of gravity acceleration, and (4) geoid from GPS/Leveling in the geographical region of Iran. Based on the numerical results EGM96 and PGM2000A perform almost the same in synthesizing the aforementioned gravity functionals in the geographical region of Iran.