Interpreting of Magnetic and Gravity Anomalies for Regional Oil and Gas Prognosis

Instabilities and the large matrices which are common to inversions of regional magnetic and gravity anomalies often complicate the use of efficient least‐squares matrix procedures. Inversion stability profoundly affects anomaly analysis, and hence it must be considered in any application. Wildly varying or unstable solutions are the products of errors in the anomaly observations and the integrated effects of observation spacing, source spacing, elevation differences between sources and observations, geographic coordinate attributes, geomagnetic field attitudes, and other factors which influence the conditioning of inversion. Solution instabilities caused by ill‐posed parameters can be efficiently minimized by ridge regression with a damping factor large enough to stabilize the inversion, but small enough to produce an analytically useful solution. An effective choice for the damping factor is facilitated by plotting damping factors against residuals between observed and modeled anomalies and by then comparing this curve to curves of damping factors plotted against solution variance or the residuals between predicted anomaly maps representing the processing objective (e.g., downward continuation, differential reduction to the radial pole, etc.). To obtain accurate and efficient large‐scale inversions of anomaly data, a procedure based on the superposition principle of potential fields may be used. This method involves successive inversions of residuals between the observations and various stable model fields which can be readily accommodated by available computer memory. Integration of the model fields yields a well‐resolved representation of the observed anomalies corresponding to an integrated model which normally could not be obtained by direct inversion because the memory requirements would be excessive. MAGSAT magnetic anomaly inversions over India demonstrate the utility of these procedures for improving the geologic analysis of potential field anomalies.

Download Full-text

Magneto‐gravity response function and its application to the Daito Ridge

Geophysics ◽

10.1190/1.1451383 ◽

2002 ◽

Vol 67 (1) ◽

pp. 110-116 ◽

Cited By ~ 1

Author(s):

Yoshio Ueda ◽

Ryuji Kubota ◽

Jiro Segawa

Keyword(s):

Response Function ◽

Sediment Cores ◽

Phase Relationship ◽

Gravity Anomalies ◽

Common Source ◽

Constant Density ◽

Magnetization Direction ◽

Gravity Response ◽

Normal Magnetization ◽

Magnetic And Gravity Anomalies

A magneto‐gravity response function, which shows a phase relationship between magnetic and gravity anomalies caused by a common source body with a constant density‐to‐magnetization ratio, is derived for determining the magnetization direction of a source body for 2‐D and 3‐D cases. The validity of the method is demonstrated through application to test data and to field anomalies from the Daito Ridge. The Daito Ridge is found to be magnetized in the present main field direction, contrary to shallow inclinations suggested by studies of Deep Sea Drilling Project (DSDP) sediment cores. The strong normal magnetization is ascribed to high magnetic susceptibility and/or viscous remanent magnetization.

Download Full-text

Magnetic and gravity anomalies of polyhedra

Geoexploration ◽

10.1016/0016-7142(76)90003-x ◽

1976 ◽

Vol 14 (2) ◽

pp. 93-105 ◽

Cited By ~ 19

Author(s):

J.H. Coggon

Keyword(s):

Gravity Anomalies ◽

Magnetic And Gravity Anomalies

Download Full-text

A COMPREHENSIVE SYSTEM OF AUTOMATIC COMPUTATION IN MAGNETIC AND GRAVITY INTERPRETATION

Geophysics ◽

10.1190/1.1438736 ◽

1960 ◽

Vol 25 (3) ◽

pp. 569-585 ◽

Cited By ~ 54

Author(s):

Roland G. Henderson

Keyword(s):

Effective Means ◽

Gravity Anomalies ◽

Comprehensive System ◽

Diagnostic Features ◽

Special Cases ◽

Desk Calculator ◽

Concentric Circles ◽

Gravity Interpretation ◽

Magnetic And Gravity Anomalies ◽

Derivatives Of

In the interpretation of magnetic and gravity anomalies, downward continuation of fields and calculation of first and second vertical derivatives of fields have been recognized as effective means for bringing into focus the latent diagnostic features of the data. A comprehensive system has been devised for the calculation of any or all of these derived fields on modern electronic digital computing equipment. The integral for analytic continuation above the plane is used with a Lagrange extrapolation polynomial to derive a general determinantal expression from which the field at depth and the various derivatives on the surface and at depth can be obtained. It is shown that the general formula includes as special cases some of the formulas appearing in the literature. The process involves a “once for all depths” summing of grid values on a system of concentric circles about each point followed by application of the appropriate one or more of the 19 sets of coefficients derived for the purpose. Theoretical and observed multilevel data are used to illustrate the processes and to discuss the errors. The coefficients can be used for less extensive computations on a desk calculator.

Download Full-text

Magnetic and gravity anomalies of a triaxial ellipsoid

Exploration Geophysics ◽

10.1071/eg986189 ◽

1986 ◽

Vol 17 (4) ◽

pp. 189-200 ◽

Cited By ~ 37

Author(s):

D. A. Clark ◽

S. J. Saul ◽

D. W. Emerson

Keyword(s):

Gravity Anomalies ◽

Triaxial Ellipsoid ◽

Magnetic And Gravity Anomalies

Download Full-text

PROSPEK SUMBER DAYA ENERGI BERDASARKAN ANALISIS POLA ANOMALI GAYA BERAT DI DAERAH BIAK DAN SEKITARNYA, PAPUA

JURNAL GEOLOGI KELAUTAN ◽

10.32693/jgk.13.2.2015.264 ◽

2016 ◽

Vol 13 (2) ◽

pp. 87 ◽

Cited By ~ 1

Author(s):

Saultan Panjaitan ◽

Subagio Subagio

Keyword(s):

Gravity Anomaly ◽

Oil And Gas ◽

East Coast ◽

Gravity Anomalies ◽

Source Rocks ◽

Reservoir Rock ◽

Ultramafic Rocks ◽

Reservoir Rocks ◽

Northern City ◽

Fluid Reservoir

Hasil penelitian gayaberat di Pulau Biak menghasilkan anomali gayaberat yang dikelompokkan kedalam 2 (dua) satuan yaitu anomali gayaberat 50 mGal hingga 120 mGal membentuk rendahan anomali mencerminkan cekungan. Kelompok anomali gayaberat 120 mGal hingga 220 mGal membentuk tinggian anomali. Pola tinggian anomali sisa 0 mGal hingga 2 mGal diduga sebagai perangkap struktur migas yang terdapat di daerah Kota Biak utara, Mandon dan lepas pantai timur P. Pai. Batuan bertahanan jenis rendah antara 0 - 16 Ohm-meter yang mengindikasikan batuan reservoir jenuh fluida terbentuk di kedalaman 2500 meter. Kedalaman batuan dasar terbentuk antara 7000-8500 meter, dengan rapat massa batuan 2.9 - 3.1 gr/cm3 bertahanan jenis tinggi 1000-8200 Ohm-meter diduga sebagai cerminan dari batuan ultramafik kerak samudera. Batuan yang menyusun di daerah penelitian terdiri atas lapisan batuan Tersier dengan rapat massa 2.45 gr/cm3, batuan Pra-Tersier dengan rapat massa 2.75 gr/cm3 dan batuan dasar dengan rapat massa 3.1 gr/cm3. Batuan sumber adalah serpih Formasi Makat berumur Miosen dengan rapat massa batuan 2.45 gr/cm3, sedangkan batuan reservoir terdiri dari batupasir Formasi Mamberamo. Kata kunci Gayaberat, cekungan, migas, anomali sisa, rapat massa, sesar, antiklin, batuan sumber, tahanan jenis. Gravity research on the island of Biak gravity anomalies are grouped into two (2) units is a gravity anomaly 50 mgal up to 120 mgal is basin reflecting. Gravity anomaly 120 mgal up to 220 mgal formed heights anaomaly. Altitude residual anomaly from 0 mGal to 2 mgal is oil and gas as trapping structures contained in the northern City of Biak, off the east coast Mandon and P. Pai. The rocks is of low resistivity between 0 -16 Ohm-meter that indicates the saturated fluid reservoir rocks are in the depths of 2500 meter. The depth of the bedrock formed between 7000-8500 meters, with density 2.9 - 3.1 gr / cm3 is heights resistivity types of 1000-8200 Ohm-meter interpreted as a reflection of ultramafic rocks oceanic crust. The rocks in the study area consists of Tertiary rocks layers with a density 2.45 gr / cm3, the Pre-Tertiary rocks with density 2.75 gr / cm3 and bedrock with density 3.1 gr / cm3. The source rocks is of shale from Makat Formation Miocene age with density 2.45 gr / cm3, and the reservoir rock consists of sandstone Mamberamo Formation. Keywords: Gravity, basin, oil and gas, recidual anomaly, density, fault, anticline, source rocks, resistivity.

Download Full-text