**Source**

**Conference**

**Theme**

**Author**

- Allegar, Norman (1)
- Andersen, Ole B. (1)
- Barnes, Gary (1)
- Barraud, Joseph (1)
- Beno, Ján (1)
- Berry, P.A.M. (1)
- Childers, Vicki A. (1)
- Colombo, D. (1)
- Dalstørm, Bjørn (1)
- Davies, Mark (1)
- Davis, Kristofer (1)
- Factor, John (1)
- Farquharson, Colin G. (1)
- Fernando, Fernando J.S. Silva (1)
- Foss, Stig Kyrre (1)
- Gao, Zhiliang (1)
- Goussev, Serguei (1)
- Gram, Christian (1)
- Halldórsdóttir, Heiða (1)
- Hallinan, S. (1)
- He, Lanfang (1)
- He, Zhanxiang (1)
- Holmes, Simon (1)
- Hurich, Charles A. (1)
- Jain, Mukesh (1)
- Jiang, Fan (1)
- Joa˜o, B.C. Silva (1)
- Karcol, Roland (1)
- Kass, M. Andy (1)
- Keller, G. Randy (1)
- Kenyon, S. (1)
- Kenyon, Steve (1)
- Knudsen, P. (1)
- Krahenbuhl, Rich A. (1)
- Krahenbuhl, Richard A. (1)
- Le, Wan (1)
- Li, Wenming (1)
- Li, Xiong (1)
- Li, Yaguo (1)
- Li, Yaoguo (1)
- Lumley, John (1)
- Mantovani, M. (1)
- Marusiak, Ivan (1)
- Meyer, Thomas J. (1)
- Mikuska, Ján (1)
- Mohanty, S.N. (1)
- Mosher, Craig R.W. (1)
- Pardo, Jessica M. (1)
- Pasteka, Roman (1)
- Pavlis, N. (1)
- Pavlis, Nikolaos (1)
- Rhodes, Mark (1)
- Roman, Daniel R. (1)
- Rowe, Jeff (1)
- Saad, Afif (1)
- Shi, Baoping (1)
- Shields, Gordon (1)
- Smith, Dru A. (1)
- Strack, Kurt (1)
- Tulinius, Helga (1)
- Vale´ria, C.F. Barbosa (1)
- Virgilio, M. (1)
- Wang, Yan M. (1)
- Welbon, Alastair (1)
- Winester, Daniel (1)
- Wu, Jiangsheng (1)
- Yalamanchili, S.V. Rao (1)
- Yu, Gang (1)
- Zhang, Jian (1)
- Zhdanov, Michael S. (1)
- Zumberge, Mark (1)
- Ádám, László (1)

**Concept Tag**

- accuracy (1)
- activity (1)
- adaptive learning (1)
- Advancement (1)
- advantage (1)
- aerogravity (1)
- altimetry (2)
- analysis (2)
- Andersen (1)
- anomaly (5)
- Artificial Intelligence (5)
- AUV (1)
- Bachu Upheaval (1)
- Bachu Upheaval region (1)
- basement (2)
- basin (2)
- borehole (2)
- Brine Injection (1)
- Cambrian (1)
- China South Sea (1)
- COB (1)
- Colombia (1)
- Comparison (1)
- contrast (2)
- equation (2)
- exploration (2)
- fault (2)
- formation evaluation (7)
- FTG (1)
- Galveston (1)
- geologic modeling (2)
- geological modeling (2)
- geology (2)
- geophysics (3)
- Grace (1)
- gradient (3)
- Gradiometer (1)
- Gravimetry (1)
**gravity (21)**- Gravity Survey (1)
- Hilbert transform (1)
- Horizontal (2)
- Horizontal Gradient (2)
- Imaging (1)
- interpretation (2)
- inversion (8)
- joint inversion (2)
- Jotun Field (1)
- Knudsen (1)
- las vegas (3)
- magnetic field (2)
- magnetization (2)
- method (2)
- Mineral Exploration (1)
- model (7)
- Nahavandchi (1)
- Northwest China (1)
- observation (5)
- Oceanography (1)
- Pannonian (1)
- Pannonian Basin (1)
- Pre Stack Depth Migration (1)
- problem (2)
- profile (4)
- project (2)
- region (2)
- regularization (2)
- Reservoir Characterization (19)
- reservoir description and dynamics (21)
- resistivity (2)
- Resolution analysis (1)
- salt (3)
- satellite (2)
- Satellite Altimetry (2)
- Scenario (1)
- Scripp Institution (1)
- sediment (2)
- seg las vegas (5)
- seismic processing and interpretation (9)
- signal (3)
- source (2)
- Station (1)
- StatoilHydro (1)
- structural geology (4)
- structure (2)
- study (3)
- surface (4)
- survey (6)
- survey line (2)
- system (2)
- Tarim basin (1)
- technical program committee (2)
- Uncompahgre uplift (1)
- University (1)
- Upstream Oil & Gas (19)
- US government (3)
- vector (2)
- Visualization (1)
- Worldwide (1)
- Zhdanov (1)

**File Type**

The borehole gravity technique has been well established in hydrocarbon exploration geophysics since the 1970’s. The concept behind borehole gravity is simply to measure the variation in the Earth’s gravitational field while traveling along a borehole. Densities both close to and far from the borehole can be derived from such measurements. However, the borehole gravity technique has not yet been routinely used for mineral exploration because gravimeters that fit in the narrower diameter holes used in mineral exploration have not existed. Such gravimeters are now being developed. Complementary investigation and development of interpretation procedures for borehole gravity data in a mineral exploration context are required. Here, preliminary results are presented of a study inverting synthetic borehole gravity data for three-dimensional, mineral exploration relevant Earth models. The forward-modelling on which the inversion is based is a finite-difference solution of Poisson’s equation. The inversion is performed using a standard minimum-structure algorithm. The intention is to demonstrate what we can expect to determine about the density variation around and between boreholes given varying amounts and locations of down-hole and surface data.

Measuring the Earth’s gravitational field down a borehole is a technique that has been used in hydrocarbon exploration for the past several decades (see, e.g., Nabighian et al., 2005). From these measurements, formation bulk densities can be determined (e.g., LaFehr, 1983), and estimates of densities tens or hundreds of metres into a formation can be made. The borehole gravity technique has rarely been used for mineral exploration because the gravimeters developed for hydrocarbon exploration do not fit down the narrower boreholes typically used in mineral exploration. However, a gravimeter for these slim holes is currently being developed (as a CAMIRO consortium research project). Interpretation techniques for the data that will be provided by these gravimeters in the mineral exploration context are therefore required. Here we investigate the use of minimum-structure inversion for the interpretation of such data.

The application of minimum-structure inversion has proven successful in the interpretation of gravity, magnetic, electric, and electromagnetic survey data, especially in areas with complex geology. A typical minimum-structure inversion procedure for gravity (e.g., Li and Oldenburg, 1998; Portniaguine and Zhdanov, 1999) parameterizes the Earth’s subsurface into cubic cells that hold the physical property, in this case density, and aims to recover the parameters of the model which has the least spatial variability. The process is generally reliable and robust, and produces models which have a limited amount of artifacts due to noise in the observations. This approach deals well with the non-uniqueness of the inverse problem. However, the models obtained are typically of smeared shapes and do not exhibit the sharp interfaces that are usually assumed to separate subsurface geologic structures. Ways to incorporate a priori knowledge of the subsurface to aid with issues of non-uniqueness have been studied by Li and Oldenburg (1998) and Farquharson et al. (2008), and techniques for developing sharper interfaces in models have been described by Last and Kubik (1983), Portniaguine and Zhadov (1999), and Farquharson (2008).

borehole, equation, exploration, formation evaluation, geologic modeling, geological modeling, geophysics, gravity, inversion, mesh, Mineral Exploration, minimum-structure borehole gravity inversion, minimum-structure inversion, observation, Reservoir Characterization, reservoir description and dynamics, seismic processing and interpretation, subsurface, technique, Upstream Oil & Gas, vertical component

**Summary**

This paper presents an integrated, multi-disciplinary approach to exploration in a complex salt basin. The construction of the interval velocity/depth model and the resultant depth migrated seismic data were constrained by gravity/magnetics and, uniquely, by structural restoration of both seismic data and interpretations to ensure consistency between geophysics and geology. This proved invaluable as it placed boundaries on interpretation possibilities in areas where poor seismic imaging persisted. A 1D basin modeling exercise was also performed adding to the complete understanding of the basin. As this work flow allowed for “what-if” scenarios, estimates of uncertainty in image quality, trap, sand distribution, etc. were also provided and used in prospect risking. The project was completed in the same time frame that it would take to complete a conventional pre stack depth migration project yet delivered far more than just depth migrated seismic data.

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

DNSC07 is a new global ocean wide satellite altimetry derived gravity field computed at the Danish National Space Center (DTUDenmark) with a spatial resolution of 1 arc-minute by 1 arc-minute covering all marine regions of the world including the Arctic Ocean up to the North Pole. For more than a decade satellite altimetry has been used to determine the marine gravity field. All present satellite based global marine gravity fields are based on the GEOSAT and ERS-1 Geodetic Mission (GM) data combined with other satellite derived datasets. The most urgent outstanding problem with most existing marine gravity fields (i.e. KMS02, Sandwell and Smith V12, NTU 01, GSFC00) was to improve the coverage of the data and the quality of the satellite observations in order to gain higher accuracy of the derived marine gravity field in particularly high latitudes and in coastal regions where many sedimentary basins are found. By using a new double-retracking system for the entire ERS-1 GM mission using a highly advanced expert based system of multiple retrackers and subsequently repacking/retracking we have been able to obtain both higher quality data but also many more data than seen before. Especially in coastal and ice-covered regions the new DNSC07 global marine gravity field is superior to other satellite based global marine gravity fields. We will present the high resolution new global marine gravity field and comparison with existing marine gravity surveys in several regions of the world (Indonesia, Florida Keys and East Greenland) and demonstrate how much accuracy have been gained by retracking the satellite observations compared with existing global marine gravity fields.

altimetry, Andersen, anomaly, Artificial Intelligence, Comparison, danish national, field, global marine gravity field, gravity, high resolution global marine, Knudsen, national space center, observation, polar region, Reservoir Characterization, reservoir description and dynamics, satellite, Satellite Altimetry, surface, system, Upstream Oil & Gas

Industry:

- Information Technology (0.70)
- Energy > Oil & Gas > Upstream (0.37)

Our integrated geological and geophysical study of the Wet Mountains region is focused primarily on expanding our knowledge of the tectonic evolution of this area and the Southern Oklahoma aulacogen in general. Gravity and magnetic surveys were conducted that covered an extensive area over the Gem Park and McClure Mountain mafic and ultramafic complexes in the Wet Mountains of Southern Colorado. These results, when merged with regional gravity and magnetic data, indicate that a large (>500 km2) portion of the Wet Mountains is underlain by Cambrian mafic igneous rocks. Furthermore, NW-SE trending regional lineaments align with known trends of the Southern Oklahoma Aulacogen (SOA).

In addition, regional seismic refraction/wide angle reflection data from the Continental Dynamics of the Rocky Mountains Project (CDROM) were used to support the above interpretation by correlating the northern Wet Mountains with high velocity (~6.20 km/s) material that extends from near the surface to a depth of about 10 km.

ancestral rocky mountain, gem park complex, geophysical study, gravity, las vegas, map, region, Reservoir Characterization, reservoir description and dynamics, residual gravity, residual gravity map, seismic processing and interpretation, southern colorado, southern oklahoma aulacogen, structure, Uncompahgre uplift, University, Upstream Oil & Gas, US government, wet mountain

Industry:

- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > US Government (0.30)

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Time-lapse gravity surveys directly detect mass changes and offer unique means for monitoring the dynamics of the subsurface. As wider application of the method is emerging, survey design and model appraisal are key steps in developing a meaningful interpretation. We first examine what the optimal station spacing should be, in theory and in inversion-based simulations given a scale-length feature. We then examine the resolving power if the data spacing has been established in order to have an appropriate model mesh.

In recent years, there has been an emergence of 4D gravity surveys, particularly for reservoir monitoring. In such cases, it is important to set up the survey in order to gain as much information about the target as possible. In other words, one should ask the question ’what is the appropriate data spacing in order to resolve the reservoir?’ We look at the theory behind this question and where the standard assumptions are no longer valid, then perform inversion-based simulations to understand how to calculate the best station spacing with a given expected noise threshold. Once data is collected (or if previously collected) it is important to set up an appropriate model space in order to recover a model that has the optimum-sized cell discretization. We investigate the resolution of models with different data spacings using a synthetic example and apply it to a field study.

When designing a gravity survey to investigate a particular depth, the optimal data spacing can be bounded by an analysis of the decay of wavenumbers with distance from the source. Intuitively, the deeper the source, the less high-wave number signal can be represented at the surface. We follow a similar approach to Reid''s (1980) note on aeromagnetic survey design to investigate this bounding station spacing. Given the assumed infinitely small source dimension, Equation (1) essentially states that the wavenumber response very close to the source is white (all wavenumbers contain equal energy) whose amplitude is scaled only by the gravitational constant and the mass. As the obervation height increases, the higher wavenumber bands will have progressively smaller energy. By examining power as a function of the reciprocal of wavenumber (the period) on a decibel (dB) scale relative to the power near the source for some observation height, the required station spacing is immediately seen. We chose to use a 4 dB roll off as our cutoff wavenumber-any wavenumbers higher than the 4 dB roll off are considered insignificant. Therefore, to accurately represent the signal due to a point mass at the surface, we use twice that cutoff wavenumber for our station spacing to honor the Nyquist Theorem. The result is the standard rule-of thumb; station spacing for a gravity survey should be roughly equivalent to the depth depth. Numerical results with the 4 dB roll off actually indicate that station spacing 8% wider than depth will accurately represent the field at the surface. However, it is important to note that this result is strictly valid only for noiseless data.

analysis, cell, design, formation evaluation, gravity, increase, inversion, model, model appraisal, noise, regularization, Reservoir Characterization, reservoir description and dynamics, resolution, Resolution analysis, resolution matrix, source, Station, study, survey, Upstream Oil & Gas, wavenumber

SPE Disciplines:

**Summary**

Although the gravitational effect of Earth’s atmosphere has relatively small values it is generally recommended to account for it in precision gravimetry. Since the effect is height-dependent, it is especially worth considering when the survey covers a broad range of gravity station heights and where the survey is performed close to a continental coast. Previously, the Earth''s topography was not considered significant when calculating the atmospheric correction for subtraction from the theoretical ellipsoidal gravity at the station. In fact the Earth''s surface is not flat over the continents and this variation in height must produce an additional influence upon the values of such a correction. We show using several examples that accounting for the Earth’s topography significantly changes the values from those calculated in the conventional way. The necessary calculations can be efficiently performed using a newly derived formula for the gravitational effect of a spherical shell with variable density.

atmosphere, atmospheric correction, calculation, calculation point, earth, formation evaluation, formula, Gravimetry, gravitation effect, gravitational effect, gravity, gravity station, las vegas, method, model, Nahavandchi, Reservoir Characterization, reservoir description and dynamics, topography, Upstream Oil & Gas

SPE Disciplines:

We present a 3D gravity inversion for estimating the location and geometry of 3D salt bodies. Iteratively, our approach estimates a 3D density-contrast distribution by assuming a piecewise constant function defined on a user specified grid of cells. To estimate a unique and stable density-contrast distribution, we look for the solution that fits the observed anomaly within the measurement errors and favors compact salt bodies closest to pre-specified geometric elements, such as axes and points. Our inversion method consists of two nested iterative loops. The outer loop uses an adaptive learning strategy that starts with a coarse grid of cells, a set of first-guess geometric elements (axes and points) and the corresponding assigned density contrast. From the second iteration on, this strategy refines the grid and creates a new set of geometric elements (points only) and associated density contrasts. The inner loop estimates the density-contrast distribution for the grid of cells and for the set of geometric elements defined in theouter loop. Each geometric element operates as the first guess skeletal outline of a particular, homogeneous section of the salt body to be imaged. The algorithm easily incorporates known density contrast information by assigning these values to each geometric element. The iteration stops when the geometries of the estimated salt bodies are invariant along successive iterations. We apply our method to synthetic gravity data obtained from a salt body, whose density contrast with the host rocks varies from positive to negative. We tested two different geologic hypotheses about the geometric elements and the assigned density contrast on the real gravity anomaly from Galveston Island salt dome, offshore Texas, USA. In the first one, we estimated a vertically elongated salt dome with depth to the bottom at 5 km. In the second hypothesis, we estimated a cylindrical salt dome with an associated overhang and depth to the bottom at 4 km.

adaptive learning, Artificial Intelligence, computer based training, contrast, density-contrast distribution, dome, educational software, educational technology, estimate, Galveston, galveston salt dome, gravity, inversion, iteration, machine learning, Reservoir Characterization, reservoir description and dynamics, salt, salt body, salt body imaging, seismic processing and interpretation, static geologic reference model, target, Upstream Oil & Gas, vector

Industry:

- Energy > Oil & Gas > Upstream (1.00)
- Education > Educational Technology > Educational Software > Computer Based Training (0.62)

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.50)

Introduction Full tensor gravity gradiometry is becoming more commonplace within exploration projects where the benefits of high resolution, multi-component data is proving invaluable for discerning both deep and shallow structures. This paper will demonstrate how the signals measured by gradiometers achieve this by presenting a series of simple examples. Exploiting multi-tensor measurements When a full survey is conducted over an area with adequate sampling then, within the limitations of signal to noise and a few constants of integration, it is possible to predict the gravitational potential and any of its associated derivatives using measurements of only a single field quantity. Common methods of achieving this include Fourier transformations (integration and differentiation in the spatial frequency domain) and equivalent source inversions. For these ideal surveys, measuring multiple components of gravity or gravity gradient serves only to increase the accuracy rather than the ...

advantage, anomaly, geologic modeling, geological modeling, geology, gradient, Gradiometer, gravity, gravity gradient, high frequency, high resolution, high resolution gravity gradient, information, inversion, profile, Reservoir Characterization, reservoir description and dynamics, signal, survey, survey line, terrain

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (0.32)

The results of integrated interpretation of geophysical data from the Pacific San Juan Basin and Tumaco Basin areas, of offshore Colombia are presented. Approximately 8100 kilometers of gravity data, 8000 km of magnetic data and 8100 km of seismic data are utilized in this interpretation. One of the primary objectives of this interpretation was to establish the depth to magnetic basement and basement related structural elements, thereby delineating prospective areas for potential hydrocarbon accumulations. The seismic reflectivity from the basement and Cretaceous horizons is not good, making seismic interpretation ambiguous in this area. As the seismic interpretation could not resolve the geological features, such as subduction zone and associated volcanism, gravity and magnetic data interpretation has been carried out. The integrated interpretation of these data worked out well to decipher the subduction zone and thrust belt above the basement as well as other geological features like sediment thickness, volcanism and intrusions.

The qualitative and quantitative interpretations were performed by using several enhancements as well as automated interpretation techniques such as Werner and Euler techniques. These results were further refined with the studies of 2.5-D / 3-D modeling. A number of positive structural features were identified which may provide lead for future hydrocarbon exploration. The sediment isopach map indicates the sediment thickness exceeds 7,000 meters at few places and few significant sediment depocenters were identified having more than 5000 meters thickness. The sediment thickness interpretation is justified in terms of plate tectonics as thinning of the sediments towards the subduction zone and thickening of the sediments towards the mountainous onshore region. This thickening of the basin may be analogous to foreland basin-type morphology, formed due to late compression although this is only an observation and has not yet been substantiated.

Artificial Intelligence, basement, basin, Colombia, fault, gravity, hydrocarbon, hydrocarbon evaluation, information fusion, interpretation, offshore Colombia, orientation, Reservoir Characterization, reservoir description and dynamics, san juan-tumaco, sediment, seg las vegas, seismic data integration, structural configuration, structural geology, subduction, Upstream Oil & Gas

Country:

- South America > Colombia (0.67)
- North America > United States (0.47)

Geologic Time:

- Phanerozoic > Mesozoic > Cretaceous (1.00)
- Phanerozoic > Cenozoic (0.95)

Oilfield Places:

- South America > Colombia > Choco Basin (0.98)
- North America > United States > New Mexico > San Juan Basin (0.94)
- North America > United States > Colorado > San Juan Basin (0.94)

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)

Technology:

A group at Scripps Institution of Oceanography, in partnership with industrial sponsors (primarily StatoilHydro), has developed instrumentation over the past decade that provides new capabilities for deep ocean gravity measurements. The instrument is based on the commercially available Scintrex CG5 quartz spring sensor. We have packaged that sensor in a compact gimbal frame and housed it in a deep ocean pressure case. We have deployed the sensor in two different modes. In the first, we make repeated campaign observations at stationary positions on the seafloor with a Remotely Operated Vehicle (ROV) to monitor changes with time in reservoir density associated with production. In the second, we mount the instrument in an Autonomous Underwater Vehicle (AUV) to facilitate exploratory surveys in the deep ocean, closer to the source than could be experienced with ocean surface observations. The stationary time-lapse surveys have been underway for several years now and we have achieved a precision of about 3 microGal (3 × 10

Artificial Intelligence, AUV, deep ocean, gravity, improvement, instrumentation, microgal, observation, Oceanography, precision, Reservoir Characterization, reservoir description and dynamics, Scripp Institution, sensor, StatoilHydro, survey, technical program committee, underway, Upstream Oil & Gas, vehicle, work

SPE Disciplines:

Thank you!