Study On Tidal Gravity Of Oil And Gas Reservior

The studying on tidal gravity of oil and gas reservoir is a completely new issue inland. The river, ocean and ground water bring tidal phenomenon at the effect of universal gravitation, which brought some Russian scholars considered that the liquid in oil and gas reservoir would also arose tidal phenomenon. By some reasons, there is little research of the model mechanism, observation method, data processing, datum interpretation of the idea inland. Based on the information of oil-geology and geophysics, we put forward a numeric oil and gas reservoir model firstly, and calculate tidal gravity accordingly. Diff-density model has been advanced in the paper to better discuss the relationship which is between the tidal gravity and the numeric model. And then we analyze the course of observation and processing of the practical data. Combining with the oil-geology information of the work area, the results have been interpreted simply. At the end of this paper, an improved high precision apparent density inversion method is advanced to meet the order of work of high precision in the gravitational prospecting, the downwards continuation operator in the method was substituted by iterative-downwards continuation technique, which was exploited by Xu Shizhe. The method was used to inverse diff-density of an oil and gas reservoir.1. Anticline, which is the basic of the paper, is one of the most familiar types in the family of oil and gas reservoirs. At first we import tidal mechanism of ground water, and put forward a model, which is comparatively accorded to the fact, by analyzing the characteristics of oil and gas reservoir know from ground water(such as great deepness, good enclosing, nonuniform density in the reservoir etc)in order to study tidal gravity of oil and gas reservoir. We consider that the high density component of nonuniform liquid in the reservoir will assemble in the east effected by universal gravitation when the heavenly bodies (Sun or Moon) set up.2. We used the Parker method to forward gravity abnormity from numeric oil and gas model in this paper; with this understanding we calculate the model's tidal gravity. And then we analyze the relationship between the model parameters and the tidal gravity. The relationship is complex correspondingly: The more model interface rise, the more maximum (minimum) of tidal gravity become bigger, also they are linear. The tidal gravity curve will smooth down with the depth increasing of model, the distance between the maximum and minimum of it will augment with the depth increasing of model, but the relationship of the anticline depth and maximum (or minimum) is not line variation yet. All of the results above obtain from model forward. To obtain better explaining purpose, we advance a diff-density model, which is the virtual source that arouses the tidal gravity on the ground.3. Before tidal gravity surveying, studying geological structure is the most important work in the schedule. Based on the known geological structure, corresponding to those models were work out to judge that whether it is possible to tidal gravity surveying in the area. Then we should design several east-west lines on the structure boundary. There are two sixty-four-dollar questions to which should be paid more attention after all the preparations done: confirm the survey manner and time. After analyzing the up and down of the heavenly bodies and the changing with time of the tide-generating force, we consider that two rules should be observed: one is that the survey time should be in the several hours fore-and-aft the time heavenly bodies up or down, another is that the survey time should be after the time when tide-generating force reach maximum (or minimum). The first rule assures that the cutting force reach maximum, and the second rule is adopted because of the lag relationship between hydrocarbon migration and tide-generating force. In order to obtain optimal datum, two manners could be adopted: fixed point manner and line manner. The former is a more accurate, but it is more expansive either. The later is a cheaper manner oppositely, and its precision improved by adopting a back and forth synchronous manner. We should adopt the later manner in practice.4. On one hand, tidal gravity belongs to high precision gravity surveying; some corrections used in high precision gravity surveying are the same with tidal gravity, such as solid tidal correction, zero correction etc. On the other hand, because we obtain the temporal change component of the gravity abnormity, some corrections in high precision, which contact with space change, are invalid, such as topographic-correction, spherical external correction, free-air correction, normal field correction etc. The course of calculating tidal gravity is lattice-valued change->tidal gravity correction->calculating the change of data from each instrument->calculating the difference of data from two time of each instrument->smoothing->averaging. And then we estimate the correction level of the results.5. Frequency apparent density inversion is a fast method, because that the core operation is an unstable downwards continuation operator, the method could not meet the order of high precision gravity measure now. An iterative-downwards continuation technique, which was exploited by Xu Shizhe, was used to substitute the downwards continuation operator in the method to improve the precision and stability of the method. We have forward two numeric models in the paper: one is a 2D density-layer model whose top plane and bottom plane are horizontal. The other is a 3D density-layer model whose top plane is up-and-down. Contacting the inverse density and the model density, we know that the precision will below 5% if the change of density continuous, even if the change of density breaks, the precision will below 10%.6. There are two sections in the tidal gravity interpretation: primary qualitative interpretation and inversion interpretation. Analyzing the four tidal gravity curves, we consider that the third of them reaction oil or gas, and the curves are high Signal-to-Noise. The No. 1 and No.4 curves lay on the west boundary of the construct, putting up positive abnormity. The No.3 curve lay on the east boundary of the construct, putting up negative abnormity. Because of some reasons, the No.2 curve could not present oil or gas. After the primary qualitative interpretation, we inverse the No.4 curve to gain the diff-density distributing of oil and gas reservoir,...