Establishment Of Velocity Field Of Igneous Strata Constrained With Lithology And Litholigical Vaniation

H area of Tarim Basin area has good geological conditions for hydrocarbon accumulation present, it has already deployed hundreds of wells and the target layer is given priority to with the Ordovician carbonate rocks. In the process of drilling, igneous rocks are commonly drilled in Permian. The lithology and lithofacies of igneous rocks changes quickly, and the eruption of igneous rocks if frequent and fast. These have a great effect to implement low-amplitude traps and velocity-variable mapping, also it can easily lead to the spatial offset of string beads. In this paper, geological data and seismic data of Ym area located in south of H area, are fully used to divide the seismic facies of igneous rocks, and select several seismic attributes that are sensitive to igneous rocks. Then seismic iversion methods are applied to study spatial distribution and establish accurate Velocity field of igneous rocks.Firstly, we analyze the base data and study the geology of YM area on the basis of previous work. The main work is to eliminate the system error of logging data in working area, and standard process the snic curve and density cure via the method of Gaussian distribution. Then DT-GR fitting coefficients are estimated from those logs with density curves based on different lithology of igneous rocks, and it obtains a good imitative effect. What is more, log crossplot like DT-GR and DT-SP can distinguish the three igneous rock types well and lay a good foundation for subsequent lithologic analysis and inversion of igneous rocks.Secondly, Seismic facies are analyzed by using waveform classification based on self-organizing neural network algorithm. In order to get the best classification of seismic facies, we use different time windows in different igneous lithologies areas and this time it totals eight time intervals to extract seismic facies for analyzing. On the other hand, this paper selects several seismic attributes that are sensitive to igneous rocks distribution and lithological mutation, such as Average Absolute Amplitude and Average Reflection Strength. Then combined with the geological data and seismic data, we could identify the development characteristics and distribution regularity of igneous rocks, and well describe arc structural belt, which consists mainly of intermediate-acid dacite.Finally, study on the velocity modeling of work area. This paper chooses the constrained sparse pulse inversion, which rely more on seismic data. In order to achieve the optimal inversion results, we analyze the key parameters in the process of inversion for many times such as well-seismic calibration, wavelet extraction, initial impedance model construction, and QC parameters setting. Meanwhile, the log curves are reconstructed with wavelet transform based on SYM4, which can complement the high frequency information under the premise of keeping the low frequency information. This method can better reflect the detail change of igneous rocks lithology and improve the resolution of the inversion results. This paper establishes the velocity field based on the wave impedance field and combined with DT-GR fitting coefficient estimation. The error analysis shows that the transformed velocity field has a high precision, and the error cortrol in about 2%, which has reached the requirement of practical production.To sum up, in this paper, combining various seismic data and geological data, we have carried out detailed researches on YM igneous rocks lithological and lithological mutation using seismic facies, seismic attribute and seismic inversion. Ultimately we established an accurate velocity field, which would make a strong groundwork to carry out the Subsequent exploration and development.