3D gravity inversion of basement relief for a rift basin based on combined multinorm and normalized vertical derivative of the total horizontal derivative techniques

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. G107-G118 ◽  
Author(s):  
Xuliang Feng ◽  
Wanyin Wang ◽  
Bingqiang Yuan
Keyword(s):  
Objective Function ◽  
Gravity Data ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Rift Basin ◽  
Constraint Function ◽  
Vertical Derivative ◽  
Model Constraint ◽  
3D Gravity ◽  
Total Horizontal Derivative

The basement of a rift sedimentary basin, often possessing smooth and nonsmooth shapes, is not easily recovered from gravity data by current inversion methods. We have developed a new 3D gravity inversion method to estimate the basement relief of a rift basin. In the inversion process, we have established the objective function by combining the gravity data misfit function, the known depth constraint function, and the model constraint function composed of the [Formula: see text]-norm and [Formula: see text]-norm, respectively. An edge recognition technology based on the normalized vertical derivative of the total horizontal derivative for gravity data is adopted to recognize the discontinuous and continuous parts of the basin and combine the two inputs to form the final model constraint function. The inversion is conducted by minimizing the objective function by the nonlinear conjugate gradient algorithm. We have developed two applications using synthetic gravity anomalies produced from two synthetic rift basins, one with a single graben and one with six differently sized grabens. The test results indicate that the inversion method is a feasible technique to delineate the basement relief of a rift basin. The inversion method is also tested on field data from the Xi’an depression in the middle of the Weihe Basin, Shaanxi Province, China, and the result illustrates its effectiveness.

3D gravity inversion with optimized mesh based on edge and center anomaly detection

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. G13-G23 ◽  
Author(s):  
Min Yang ◽  
Wanyin Wang ◽  
J. Kim Welford ◽  
Colin G. Farquharson
Keyword(s):  
Edge Detection ◽  
Gravity Data ◽  
Signal Amplitude ◽  
Spatial Extent ◽  
Gravity Inversion ◽  
Unknown Parameters ◽  
Vertical Derivative ◽  
Cpu Time ◽  
3D Gravity ◽  
Total Horizontal Derivative

Gravity inversion is inherently nonunique. Minimum-structure inversion has proved effective at dealing with this nonuniqueness. However, such an inversion approach, which involves a large number of unknown parameters, is computationally expensive. To improve efficiency while retaining the advantages of a minimum-structure-style inversion, we have developed a new method, based on edge detection and center detection of geologic bodies, to help to focus the spatial extent of meshing for gravity inversion. The chosen method of edge detection, normalized vertical derivative of the total horizontal derivative, helps to outline areas to be meshed by approximating the edges of key geophysical bodies. Next, the method of center detection, normalized vertical derivative of the analytic signal amplitude, helps to confirm the center of the areas to be meshed, then a binary mesh flag is generated. In this paper, the binary mesh flag, restricting the spatial extent of meshing, is first undertaken using the two methods, and it is shown to dramatically reduce the number of grid cells from 574,992 for the whole research volume to 170,544 for the localized mesh by the same size of cell, which is decreased by almost 70%. Second, gravity inversion is performed using the spatially restricted mesh. The recovered model constructed using the binary mesh flag is similar to the model obtained using the mesh spanning the whole volume and saves approximately 80% of the CPU time. Finally, a real gravity data example from Olympic Dam in Australia is successfully used to test the validity and practicability of this proposed method. The geologic source bodies are resolved between 250 and 750 m depth. Overall, the combination of edge detection and center detection, and our binary mesh flag, succeed in reducing the number of cells and saving the CPU time and computer storage required for gravity inversion.

scholarly journals 3D Gravity Inversion on Unstructured Grids

2021 ◽  
Vol 11 (2) ◽  
pp. 722
Author(s):  
Siyuan Sun ◽  
Changchun Yin ◽  
Xiuhe Gao
Keyword(s):  
Objective Function ◽  
Unstructured Grids ◽  
Gravity Data ◽  
Depth Resolution ◽  
Continuous Model ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Model Parameters ◽  
Fuzzy C Means ◽  
Fuzzy C Means Clustering

Compared with structured grids, unstructured grids are more flexible to model arbitrarily shaped structures. However, based on unstructured grids, gravity inversion results would be discontinuous and hollow because of cell volume and depth variations. To solve this problem, we first analyzed the gradient of objective function in gradient-based inversion methods, and a new gradient scheme of objective function is developed, which is a derivative with respect to weighted model parameters. The new gradient scheme can more effectively solve the problem with lacking depth resolution than the traditional inversions, and the improvement is not affected by the regularization parameters. Besides, an improved fuzzy c-means clustering combined with spatial constraints is developed to measure property distribution of inverted models in both spatial domain and parameter domain simultaneously. The new inversion method can yield a more internal continuous model, as it encourages cells and their adjacent cells to tend to the same property value. At last, the smooth constraint inversion, the focusing inversion, and the improved fuzzy c-means clustering inversion on unstructured grids are tested on synthetic and measured gravity data to compare and demonstrate the algorithms proposed in this paper.

scholarly journals 3D Gravity Modeling of Complex Salt Features in the Southern Gulf of Mexico

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Mauricio Nava-Flores ◽  
Carlos Ortiz-Aleman ◽  
Mauricio G. Orozco-del-Castillo ◽  
Jaime Urrutia-Fucugauchi ◽  
Alejandro Rodriguez-Castellanos ◽  
...  
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Complex Salt ◽  
Gravity Modeling ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Oil Exploration ◽  
Potential Field Data ◽  
Estimation Algorithms ◽  
3D Gravity

We present a three-dimensional (3D) gravity modeling and inversion approach and its application to complex geological settings characterized by several allochthonous salt bodies embedded in terrigenous sediments. Synthetic gravity data were computed for 3D forward modeling of salt bodies interpreted from Prestack Depth Migration (PSDM) seismic images. Density contrasts for the salt bodies surrounded by sedimentary units are derived from density-compaction curves for the northern Gulf of Mexico’s oil exploration surveys. By integrating results from different shape- and depth-source estimation algorithms, we built an initial model for the gravity anomaly inversion. We then applied a numerically optimized 3D simulated annealing gravity inversion method. The inverted 3D density model successfully retrieves the synthetic salt body ensemble. Results highlight the significance of integrating high-resolution potential field data for salt and subsalt imaging in oil exploration.

Three‐dimensional gravity inversion using simulated annealing: Constraints on the diapiric roots of allochthonous salt structures

Geophysics ◽  
2001 ◽  
Vol 66 (5) ◽  
pp. 1438-1449 ◽  
Author(s):  
Seiichi Nagihara ◽  
Stuart A. Hall
Keyword(s):  
Simulated Annealing ◽  
Gulf Of Mexico ◽  
Gravity Data ◽  
A Priori ◽  
Gravity Inversion ◽  
Inversion Method ◽  
A Priori Information ◽  
Final Density ◽  
Smoothing Effects ◽  
Priori Information

In the northern continental slope of the Gulf of Mexico, large oil and gas reservoirs are often found beneath sheetlike, allochthonous salt structures that are laterally extensive. Some of these salt structures retain their diapiric feeders or roots beneath them. These hidden roots are difficult to image seismically. In this study, we develop a method to locate and constrain the geometry of such roots through 3‐D inverse modeling of the gravity anomalies observed over the salt structures. This inversion method utilizes a priori information such as the upper surface topography of the salt, which can be delineated by a limited coverage of 2‐D seismic data; the sediment compaction curve in the region; and the continuity of the salt body. The inversion computation is based on the simulated annealing (SA) global optimization algorithm. The SA‐based gravity inversion has some advantages over the approach based on damped least‐squares inversion. It is computationally efficient, can solve underdetermined inverse problems, can more easily implement complex a priori information, and does not introduce smoothing effects in the final density structure model. We test this inversion method using synthetic gravity data for a type of salt geometry that is common among the allochthonous salt structures in the Gulf of Mexico and show that it is highly effective in constraining the diapiric root. We also show that carrying out multiple inversion runs helps reduce the uncertainty in the final density model.

scholarly journals 3D Gravity Inversion with Correlation Image in Space Domain and Application to the Northern Sinai Peninsula

2019 ◽  
Vol 1 (2) ◽  
Author(s):  
Xu Zhang ◽  
Peng Yu ◽  
Jian Wang
Keyword(s):  
Density Distribution ◽  
Gravity Data ◽  
Descent Method ◽  
Steepest Descent Method ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Sinai Peninsula ◽  
Space Domain ◽  
Correlation Image ◽  
Starting Model

We present a 3D inversion method to recover density distribution from gravity data in space domain. Our method firstly employs 3D correlation image of the vertical gradient of gravity data as a starting model to generate a higher resolution image for inversion. The 3D density distribution is then obtained by inverting the correlation image of gravity data to fit the observed data based on classical inversion method of the steepest descent method. We also perform the effective equivalent storage and subdomain techniques in the starting model calculation, the forward modeling and the inversion procedures, which allow fast computation in space domain with reducing memory consumption but maintaining accuracy. The efficiency and stability of our method is demonstrated on two sets of synthetic data and one set of the Northern Sinai Peninsula gravity data. The inverted 3D density distributions show that high density bodies beneath Risan Aniza and low density bodies exist to the southeast of Risan Aniza at depths between 1~10 and 20 km, which may be originated from hot anomalies in the lower crust. The results show that our inversion method is useful for 3D quantitative interpretation.

Gravity data as a tool for detecting faults: In-depth enhancement of subtle Almada’s basement faults, Brazil

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. B59-B68 ◽  
Author(s):  
Valeria C. Barbosa ◽  
Paulo T. Menezes ◽  
João B. Silva
Keyword(s):  
Gravity Data ◽  
Synthetic Data ◽  
Normal Fault ◽  
Northeastern Brazil ◽  
Normal Faults ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Basement Faults ◽  
Depth Enhancement ◽  
Fault Displacement

We demonstrate the potential of gravity data to detect and to locate in-depth subtle normal faults in the basement relief of a sedimentary basin. This demonstration is accomplished by inverting the gravity data with the constraint that the estimated basement relief presents local abrupt faults and is smooth elsewhere. We inverted the gravity data from the onshore Almada Basin in northeastern Brazil, and we mapped several normal faults whose locations and plane geometries were already known from seismic imaging. The inversion method delineated well both the discontinuities with small or large slips and a sequence of step faults. Using synthetic data, we performed a systematic search of normal fault slips versus fault displacement depths to map the fault-detectable region in this space. This mapping helps to assess the ability of gravity inversion to detect normal faults. Mapping shows that normal faults with small [Formula: see text], medium (about [Formula: see text]), and large (about [Formula: see text]) vertical slips can be detected if the maximum midpoint depths of the fault planes are smaller than 1.8, 3.8, and [Formula: see text], respectively.

scholarly journals USING THE COMBINATION OF THE 3D GRAVITY INVERSION METHOD WITH THE DIRECTIONAL ANALYTIC SIGNAL DERIVATIVES AND THE CURVATURE GRAVITY GRADIENT TENSOR METHOD TO DETERMINE STRUCTURE OF THE PRE-CENOZOIC BASEMENT ON SOUTHEAST CONTINENTAL SHELF OF VIETNAM

2019 ◽  
Vol 18 (4) ◽  
pp. 393-405
Author(s):  
Nguyen Kim Dung ◽  
Do Duc Thanh ◽  
Hoang Van Vuong ◽  
Duong Thi Hoai Thu
Keyword(s):  
Continental Shelf ◽  
Density Distribution ◽  
Analytic Signal ◽  
Gravity Gradient ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Gradient Tensor ◽  
Gravity Gradient Tensor ◽  
Maximum Value ◽  
3D Gravity

In this paper, we present some new results of the Pre-Cenozoic basement structure on the Southeast continental shelf of Vietnam based on the combination of some modern methods to analyse and interpret gravity data. They are the 3D gravity inversion method, the directional analytic signal derivatives and the curvature gravity gradient tensor. The results obtained include the density distribution, the fault system and the main structural blocks inside of the Pre-Cenozoic basement on Southeast continental shelf of Vietnam. The initial results about density distribution show that it relatively clearly reflects the shape of basins in the area: The contours that have value σ =2.7 g/cm3 and value σ = 2.76 g/cm3 are near the edges of the Cuu Long basin and the Nam Con Son basin, respectively. The density value reaches the maximum at the center of basins. For the Cuu Long basin, the maximum value is σmax= 2.76 g/cm3 and the Nam Con Son has maximum value σmax= 3.0 g/cm3. Many faults that appear in the study area have the existence depth in the wide range from 6 km to 30 km, even above 30 km and the faults that have the existence depth from 8 to 10 km are in the majority. In particular, the boundary of anomalous sources existing in the Pre-Cenozoic basement is shown by the better resolution, at which more edge points are identified than the maximum horizontal gradient amplitude method that is widely used. The results also show that the combination of individual results complements each other and creats the sufficient and clearer picture inside of the Pre-Cenozoic basement.

An integrated geophysical approach for imaging subbasalt sedimentary basins: Case study of Jam River Basin, India

Geophysics ◽  
2007 ◽  
Vol 72 (6) ◽  
pp. B141-B147 ◽  
Author(s):  
V. Chakravarthi ◽  
G. B. K. Shankar ◽  
D. Muralidharan ◽  
T. Harinarayana ◽  
N. Sundararajan
Keyword(s):  
Gravity Field ◽  
River Basin ◽  
Gravity Data ◽  
Sedimentary Basins ◽  
Gravity Inversion ◽  
Data Points ◽  
3D Gravity ◽  
Regional Gravity ◽  
Godavari Basin

An integrated geophysical strategy comprising deep electrical resistivity and gravity data was devised to image subbasalt sedimentary basins. A 3D gravity inversion was used to determine the basement structure of the Permian sediments underlying the Cretaceous formation of the Jam River Basin in India. The thickness of the Cretaceous formation above the Permian sediments estimated from modeling 60 deep-electric-sounding data points agrees well with drilling information. The gravity effect of mass deficit between the Cretaceous and Permian formations was found using 3D forward modeling and subsequently removed from the Bouguer gravity anomaly along with the regional gravity field. The modified residual gravity field was then subjected to3D inversion to map the variations in depth of the basement beneath the Permian sediments. Inversion of gravity data resulted in two basement ridges, running almost east to west, dividing the basin into three independent depressions. It was found that the Katol and Kondhali faults were active even during post-Cretaceous time and were responsible for the development of the subsurface basement ridges in the basin. The inferred 3D basement configuration of the basin clearly brought out the listric nature of these two faults. Further, the extension of the Godavari Basin into the Deccan syneclise and the fact that the source-rock studies show the presence of hydrocarbons in the Sironcha block in the northern part of the Godavari Basin also shed some light on the hydrocarbon potential of the Jam River Basin.

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