Research On Structural Features And Evolution For The North Of Urxun Sag

On the basis of the predecessors'study, the paper studies the structural interpretation of seismic data for the northen area of Urxun sag. By the application of structural Geology, Sequence stratigraphy theory and advanced geophysical techniques, we can identify the regional unconformity interface and trace it exactly. We will develop the fine interpretation of the seismic data and establish the isochronal stratigraphic frame work; we establish the 3D velocity field and extract the average velocity of the intended interval through the application of the velocity spectrum, and the velocity logging. We can study the distribution of the faults that control the formation of the sag; we analysis the tectonic pattern and the characteristics of the tectonic in different Evolutionary stages and predict the beneficial hydrocarbon accumulation area.On the basies of sequence stratigraphy theory, we can identify the bedding interface by the combination of seismic and well data, which is on the basies of synthtic; furthermore, according to the step control of cycle and detailed interwell correlation, we can define the bedding interface of bed set. After the summary of lithologic association and logging feature, by the synthtic and seismic reflection feature, we define the identification sign of interface of each bed set. According to man-machine integration system of Landmark, we develop the structural interpretation of 3D seismic data, and through the lateral section and dip combination faults, we obtain the feature of fault plane disttribution.Through the study of structural feature for this area, we find that thefeature is tectonic zonality, from east to west it displays zonality, from south to north it is blocking. It develops longitudinal, northeast, east north east and north north east syructure, and the longitudinal, northeast, east north east faults are early faults which control subsidence and present crosscutting relationship on surface. Partly structure presents apparent zonality, it can be divided into four structural belts: they are Huangqimiao, Surennuoer, Wuxi and Tongbomiao structural belt. Fracturing action can be divided into three phases: before T22 it primarily presents control sag or uplift; between T22 and T04 it presents tensional fault of middle- superficial strata; after T04 the action of tensional fault apparently become diminution, and the base presents differential settlement according to the action of magmatic activity, which makes long-range inherited down fault reverse, and become reversal structure.On the basies of structural feature and fracturing action, we study the structural evolution, this area can be divided into three phases: fault subsidence; transform of fault sag and sunken phases, it also can be divided into five epoch:they are intensely tensional fault depression, quick settling fault depression, sustained fault depression, faden fault depression and consumption of fault depression.Through the application of the above theory and technique, according to the analysis of structural feature and structural evolution of Urxun sag, we find that in this area oil-gas mainly accumulate in the local structure zone.Faults worked as oil and gas migrating channels and shield. The development of structure and fault is the important factor to the hydrocarbon accumulation. By the multidisciplinary analysis of structure, deposition, oil-gas examination, well drilling demonstration, we forecast two favorable hydrocarbon structural belts.