JOURNAL OF RESEARCH ON APPLIED GEOPHYSICS
Year:2016 | Volume:2 | Issue:1 |Papers Count:6

Estimation of residual statics in complex areas is one of the main challenging problems in seismic data processing. It has been shown that residual statics show itself as random noise in the frequency domain, and hence, can be treated as a denoising problem. Here, we develop an f-x domain denoising algorithm to attenuate the residual statics in seismic data. A subset of low frequencies are selected and denoised individually via a Tikhonov's type filter. The denoised section is cross-correlated trace-by-trace with the noisy one, and then, the maximum shifts are picked and applied to reduce the statics. This procedure is repeated until convergence is accomplished. Numerical tests show good performance of the proposed algorithm to compensate static effects on synthetic and field seismic data.....

Water and Gas injection are two major enhanced oil recovery methods in Iran. Gas (e. g. CO2) injection, is one of the most applicable methods of enhancing oil recovery in oil fields. In order to study the behaviour of seismic attributes, the compatibility of the prediction made by Gassman theory and Greenberg-Castagna equations in the situation of CO2 saturated environment is investigated using lab data. It should be noted that the mentioned equations are based on some assumptions that are not always represent the real situation, thus, some incompatibility is anticipated. Therefore, their predictions are liable to be incompatible with real world wave behaviour. In this research, CO2 in dissolved phase is injected into pressurized sandstone samples in laboratory scale, and elastic waves are utilized in order to investigate the injection process. The variation of the propagation velocity of seismic waves and their amplitudes are studied versus variation of effective parameters e. g. confining pressure (close to reservoir pressure), pore pressure (close to reservoir pressure), transmission wave frequency, and CO2 density and phase. We have also used the collected laboratory data for wave propagation at supercritical saturation state to investigate the compatibility of the prediction made by Gassman theory and Greenberg-Castagna equations. Based on the results of various laboratory experiments, we can conclude that some of the developed equations are useful for estimation of velocity and amplitude of seismic waves. Verifications confirm that compatibility of the developed equations with laboratory results are more than 90 percent, and thus, the developed equations can be preferred to other related popular equations....

Magnetic induction caused by sea characteristics has recently been the focus of attention of several studies. Since water is an electrically conductive liquid, its movement in the Earth's magnetic field produces a transverse magnetic force at each unit of charge. Therefore, it seems essential to identify the factors affecting the fluctuations of these magnetic fields and the effect of these factors on the marine, navy, and military applications. In this research, the changes of magnetic fields caused by sea waves in the Strait of Hormuz have been investigated. For this purpose, we use the waves parameters obtained from numerical model of MIKE21, and then, calculate the magnetic field and observe the magnetic field fluctuations in the study region. The results show that the values of magnetic field vary between 0 and 0. 2 nanotesla. Moreover, magnetic field values in Bandar Abbas coast and Iran shoreline within the study region are less than the magnetic field values in the Islands of Qeshm, Hormuz and Larak. In general, it can be said that the magnetic field fluctuations are completely caused by changes in the waves parameters so that the trend and pattern of changes of three variables of the waves including height, period, and magnetic field within the study region are almost the same. Therefore, due to the low height and low period of the waves in the Strait of Hormuz, the magnetic field caused by the waves is not considerable, and thus, its effect on magnetic field fluctuations is not also noticeable. As a result, in some maritime applications, like determination of the range of magnetic field fluctuations for the purpose of setting sensors of a torpedo and preventing the torpedo deviation from the goal, the effect of waves on the magnetic field fluctuations can be ignored.

This paper introduces a sparse inversion methodology for large-scale magnetic survey data. The minimum support constraint is used in the stabilizer term and leads to models with sharp boundaries. The subsurface under the survey area is divided into a large number of cubes with fixed geometry and unknown susceptibility. In this case, the number of model parameters is much larger than the number of data. Then, transforming from the model space to the data space yields a much smaller system of equations that can be solved quickly. The conjugate gradient algorithm is used to obtain the numerical solution of this system of equations. The proposed algorithm has been applied on a synthetic model consisting of multiple bodies, and also, on real data from Tigh Nuo Ab area in south of Birjand, Iran. Both synthetic and real cases have demonstrated the efficiency of the presented algorithm....

Temporal changes in the earth magnetic field occur in the frequency band of millihertz to a few hertz. Amplitudes of variations above 0. 1 Hz are usually much smaller than 1 nT, changes of 50-100 nT over periods of a few hours are not uncommon. Total-field aeromagnetic surveys typically require days or weeks to complete. An airborne magnetometer measures variations in the magnetic field caused by flying over magnetic geological structures and by temporal variations in the earth magnetic field. The most common method of estimating and removing the effects of time variations is called leveling. The standard procedure of leveling the data requires additional tie-lines flown perpendicularly to the original lines. In this study, a leveling approach is used without the need for tie-lines. The method, used in this paper, utilizes nine-point Hanning filter to creat a smooth representation of the regional magnetic field. The leveling errors are the difference between the flight-line raw magnetic data and the derived regional magnetic field. The magnitude of the error is minimized through least square method with a firstdegree function, and the correction involves only a diurnal correction (DC) shift. The technique is applied to the aeromagnetic data set acquired in Moalleman area, Semnan, Iran. The results show that the stripy effects are removed and the unleveled data is improved....

The improvement of seismic data resolution in hydrocarbon exploration, especially in complex structures is of great importance. There are two types of resolution in surface reflection seismic data: horizontal resolution and vertical resolution. Vertical or temporal resolution is expressed by means of the tuning thickness and horizontal or spatial resolution is expressed by means of the Fresnel zone. Tuning thickness is defined as a quarter of the dominant wavelength at the position of the target layer. It is the minimum thickness by which the top and bottom of the layer is separable. The tuning thickness is related to interval velocity of the target layer and the dominant frequency of traveling wave at the depth of the target layer. Thus, the increase in the dominant frequency of seismic data can help to increase the vertical resolution....