Three-dimensional constrained gravity inversion of Moho depth and crustal structural characteristics at Mozambique continental margin

Mozambique's continental margin in East Africa was formed during the break-off stage of the east and west Gondwana lands. Studying the geological structure and division of continent-ocean boundary(COB) in Mozambique's continental margin is considered of great significance to rebuild Gondwana land and understand its movement mode. Along these lines, in this work, the initial Moho was fit using the known Moho depth from reflection seismic profiles, and a 3D multi-point constrained gravity inversion was carried out. Thus, highaccuracy Moho depth and crustal thickness in the study area were acquired. According to the crustal structure distribution based on the inversion results, the continental crust at the narrowest position of the Mozambique Channel was detected. According to the analysis of the crustal thickness, the Mozambique ridge is generally oceanic crust and the COB of the whole Mozambique continental margin is divided.

The distribution of deep source rocks in the GS Sag:joint MT-gravity modeling and constrained inversion

The coal-bearing strata of the deep Upper Paleozoic in the GS Sag have high hydrocarbon potential. Because of the absence of seismic data, we use electromagnetic （MT） and gravity data jointly to delineate the distribution of deep targets based on well logging and geological data. First, a preliminary geological model is established by using three-dimensional （3D） MT inversion results. Second, using the formation density and gravity anomalies, the preliminary geological model is modified by interactive inversion of the gravity data. Then, we conduct MT-constrained inversion based on the modified model to obtain an optimal geological model until the deviations at all stations are minimized. Finally, the geological model and a seismic profile in the middle of the sag is analysed. We determine that the deep reflections of the seismic profile correspond to the Upper Paleozoic that reaches thickness up to 800 m. The processing of field data suggests that the joint MT-gravity modeling and constrained inversion can reduce the multiple solutions for single geophysical data and thus improve the recognition of deep formations. The MT-constrained inversion is consistent with the geological features in the seismic section. This suggests that the joint MT and gravity modeling and constrained inversion can be used to delineate deep targets in similar basins.

One-dimensional constrained inversion of electrical source transient electromagnetic method

The damped least squares inversion principle is applied to the transient electromagnetic one-dimensional inversion of electrical sources,and a new model is obtained by continuously iterating the initial model,thereby fitting the observed transient electromagnetic response,and performing one-dimensional inversion through induced electromotive force play.In this paper,in the damped least squares inversion,constraints are added to the Jacobian matrix,and simultaneous constraint equations and conventional inversion equations are solved.By weighting the constraint parameters,the difference between adjacent resistivities and layer thicknesses is minimized.Finally,K-type and H-type theoretical models were used to verify the reliability of the algorithm,and compared with the conventional transient electromagnetic damping least squares inversion.

Comparison between several seismic inversion methods and their application in mountainous coal fields of western China

With the objective of establishing the necessary conditions for 3D seismic data from mountainous areas in western China, we compared the application results of wave impedance technology in the lithology and exploration of coal fields. First, we introduce principles and features of three kinds of inversion methods. i.e., Model-Based Inversion, Constrained Sparse Spike Inversion (CSSI) and Geology-Seismic Feature Inversion. Secondly, these inversion methods are contrasted in their application to 3D seismic data from some coalfields in western China. The main information provided by the research includes: improving the vertical resolution of coal deposit strata, inferring lateral variation of the lithology and predicting coal seams and their roof lithology. Finally, the comparison between the three methods shows that the model-based inversion has the higher resolution, while CSSI inversion has better waveform continuity. The geology-seismic feature inversion requires information from a large number of wells and many types of logging curves of good quality. All three methods can meet the requirements of seismic exploration for lithological exploration in coal fields.

Using Walkaway VSP technology to improve inversion resolution

Walkaway VSP technology is commonly seen in the seismic development stage in the middle and late stages of the oilfield.Its advantage over conventional zero-offset VSP and non-zero well-source distance VSP is mainly due to the higher coverage of the Walkaway VSP acquisition process and the larger acquisition range.The resolution and signal-to-noise ratio are higher.Walkaway VSP technology has a very good application effect on solving complex structural problems and thin interbed reservoir problems.This paper mainly introduces a VSP constrained sparse spike inversion method based on high-precision VSP data.For the data acquired by the eight-azimuth Walkaway VSP in a work area of Bohai Gulf,a new method of 3D seismic-VSP joint seismic inversion is established.In the application of the actual work area,good inversion results based on Walkaway VSP data were obtained,and a new R24 small layer above the top boundary of the NmRIll oil group was depicted.This result meets the needs of development seismic technology and is used to solve thin interbed reservoirs exploration problems that have very important practical significance.

Property Identification of Anomalous Seismic Bodies by GMES Techniques, A Case History

What are the anomalous seismic reflection bodies at depths of over 6000m？Are they reefs or igneous rock？This is a difficult problem for seismic techniques,but the GMES technique can handle it .The GMES technique is a joint exploration technique combining gravity,magnetic,electrical,and seismic techniques.The specific procedure is to conduct a 2D interface-constrained CEMP inversion using 2D seismic and log data followed by a property parameter inversion of the anomalous bodics using gravity and seismic data by the stripping technique.We then estimate the physical properties ofthe anomalous bodies,such as density,susceptibility,resistivity,velocity,and etc.to deduce the geological features of the bodies and provide a basis for drilling decisions.The work in the TZ area reported in this paper shows the applicability of the technique.

The forward and inverse problem of cardiac magnetic fields based on concentric ellipsoid torso-heart model

This paper constructs a concentric ellipsoid torso-heart model by boundary element method and investigates the impacts of model structures on the cardiac magnetic fields generated by both equivalent primary source--a current dipole and volume currents. Then by using the simulated magnetic fields based on torso-heart model as input, the cardiac current sources--an array of current dipoles by optimal constrained linear inverse method are constructed. Next, the current dipole array reconstruction considering boundaries is compared with that in an unbounded homogeneous medium. Furthermore, the influence of random noise on reconstruction is also considered and the reconstructing effect is judged by several reconstructing parameters.

Crust and Upper Mantle Density Structures beneath the Eastern Tianshan Region and Its Tectonic Implications

The deformation mechanisms of the Tianshan orogenic belt(TOB)are one of the most important unresolved issues in the collision of the Indian and Eurasian plates.To better understand the lithospheric deformation of the eastern Tianshan orogenic belt,we combined the S-wave tomography and gravity data to develop a three-dimensional(3D)density model of the crust and upper mantle beneath the eastern Tianshan area.Results show that the crust of the eastern Tianshan is mainly characterized by positive density anomalies,revealing widespread subduction-related magmatism during the Paleozoic.We however have also observed extensive low-density anomalies beneath the eastern Tianshan at depths deeper than~100 km,which is likely linked to a relatively hot mantle.The most fundamental differences of the lithosphere within the eastern Tianshan occur in the uppermost mantle.The uppermost mantle layers in the Bogda Shan and Harlik Shan are relatively dense.This is likely associated with an eclogite body in the uppermost mantle.The most significant negative anomaly of the uppermost mantle is however found in the Jueluotage tectonic belt and the central Tianshan Block and is possibly associated with depleted mantle material.We suggest that these differences related to compositional changes may control the strength of the lithospheric mantle and have affected the uplift of the northern and southern segments of the eastern Tianshan after the Permian.

The research on method of interlayer modeling based on seismic inversion and petrophysical facies

Currently,the three-dimensional distribution of interlayer is realized by stochastic modeling.Traditionally,the three-dimensional geological modeling controlled by sedimentary facies models is built on the basis of logging interpretation parameters and geophysical information.Because of shallow gas-cap,the quality of three-dimensional seismic data vertical resolution in research area cannot meet the interlayer research that is below ten meters.Moreover,sedimentary facies cannot commendably reveal interlayer distribution and the well density is very sparse in research area.So,it is difficult for conventional technology to finely describe interlayers.In this document,it uses L1-L2 combined norm constrained inversion to enhance the recognition capability of interlayer in seismic profile and improve the signal to noise ratio,the wave group characteristics and the vertical resolution of three-dimensional data and classifies petrophysical facies of interlayer based on core,sedimentary facies and logging interpretation.The interlayer model which is based on seismic inversion model and petrophysical facies can precisely simulate the distribution of reservoir and interlayer.The results show that the simulation results of this new methodology are consistent with the dynamic production perfectly which provide a better basis for producing and mining remaining oil and a new interlayer modeling method for sparse well density.