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Introduction

Paterson, Grant & Watson Limited (PGW) has a long history of working in Brasil for the petroleum and mineral exploration market. It has previously undertaken nationwide compilations of magnetic, radiometric and geochemical data on a multi-client basis, and these data now form the basis of the products offered by government agencies in Brazil.

PGW undertook a recompilation of the aeromagnetic surveys flown for PetroBras on behalf of a private client. This work included editing of profile data for errors, sorting out coordinate systems, IGRF correction and microleveling using PGW’s proprietary methods. Grids of total magnetic intensity for each survey were prepared at full resolution, and a merged grid at 500 m resolution was prepared.

Early in 2002, PGW established a new company in Brasil, PGW do Brasil Ltda., based in Rio de Janeiro. It applied to the Agencia Nacional do Petroleo (ANP) for a license to distribute the reprocessed PetroBras aeromagnetic data. The license was granted on November 7, 2002 (authorization number 272). As a result, we are now able to offer potential field data and interpretation packages to aid petroleum companies in their evaluation of the blocks offered by ANP in Brasil Round 5.

Potential Field Data

There are three types of low-cost potential field data available for inclusion in this study. They are:

1. PGW’s reprocessed archive of PetroBras aeromagnetic surveys (Figure 1);

2. Satellite gravity data for offshore areas (Figure 2); and

3. Land and marine gravity data available from various sources (Figure 2).

PGW will window these data to the nine study areas, process them at full resolution, and model and interpret them. The data may be acquired from PGW with or without the interpretation package.

Fugro Airborne Surveys has flown or is currently flying aeromagnetic surveys over portions of the four southernmost Round 5 blocks. These data may be incorporated in the study on a proprietary basis, with the additional costs determined on a case-by-case basis.

Data Packages

The data packages will incorporate the source data (i.e. magnetic line archives if available, gravity station data) as well as a series of grid products at full resolution.

The survey specifications for the aeromagnetic surveys incorporated in each study area are as follows:

Block	Area	Survey	Year	Line Spacing	Profiles?
1	Bacia da Foz do Amazonas	4006	1968	4 km	No
2	Bacia de Barreirinhas	4005	1967	2.5 km	No
3	Bacia Potiguar	4010	1970	5 km	No
		4045	1986	2 and 4 km	Yes
4	Bacia do Reconcavo	4042-4043	1986	2 km	Yes
		4044	1986	3 km	Yes
5	Bacia de Jequitinhonha	4007	1968	4 km	No
		4044	1986	3 km	Yes
6	Bacia do Espirito Santo*	4007	1968	4 km	No
		4054-4055	1990	3 km	Yes
7	Bacia de Campos*	4054-4055	1990	3 km	Yes
8	Bacia de Santos*	4009	1969	5 km	No
9	Bacia de Pelotas*	4008	1969	4 km	No

The magnetic grid products are as follows:

1) total magnetic intensity;

2) pole-reduced magnetic field;

3) first and second vertical derivatives of the pole-reduced magnetic field;

4) total horizontal gradient of the pole-reduced magnetic field;

5) pseudo-gravity field; and

6) analytic signal.

The gravity grid products are as follows:

1) free-air gravity field;

2) Bouguer gravity field;

3) first and second vertical derivatives of the Bouguer gravity field; and

4) total horizontal gradient of the Bouguer gravity field.

The gravity grids will utilise the satellite gravity data primarily, supplemented by land gravity onshore and marine gravity where the resolution and data coherence warrants.

The data will be delivered in digital form, in industry-standard geophysical and GIS formats specified by the client. Likewise, the coordinate system can be in any typical for Brazil. A hard copy map of each image will be prepared at the 1:500,000 scale. A report describing the source data and PGW’s processing will be included.

Interpretation Package

The interpretation will integrate the potential field data with the published geology and terrain/bathymetry data to prepare maps with the following elements:

1) tectonic framework and basin controls;

2) basin and basement structure;

3) intra-sedimentary sources;

4) major lithologic boundaries;

5) depth-to-sources; and

6) petroleum target areas.

The depth analysis will incorporate results from source parameter imaging, Euler deconvolution and forward/inverse modeling.

The interpretation products will be:

1) depth-to-source map;

2) interpretation map; and

3) interpretation report.

The maps will be delivered in digital form, in industry-standard GIS formats specified by the client. Likewise, the coordinate system can be in any typical for Brazil. A hard copy map of each map will be prepared at the 1:500,000 scale. A report describing depth analysis, interpretation elements and petroleum exploration potential will be included.

Costs

The following table provides the costs for the data package, and the interpretation package, on an area-by-area basis (all figures in US dollars).

Block	Area Name	Study Area	Data Package	Interpretation Package*
1	Bacia da Foz do Amazonas	122,000 km2	$2,500	$12,000
2	Bacia de Barreirinhas	72,000 km2	$1,500	$7,500
3	Bacia Potiguar	72,000 km2	$2,000	$9,600
4	Bacia do Reconcavo	28,800 km2	$1,500	$7,500
5	Bacia de Jequitinhonha	65,800 km2	$2,000	$9,600
6	Bacia do Espirito Santo	153,800 km2	$3,500	$16,800
7	Bacia de Campos	112,000 km2	$3,000	$14,400
8	Bacia de Santos	224,000 km2	$4,000	$19,200
9	Bacia de Pelotas	86,100 km2	$2,000	$9,600

If four or more areas are ordered, a volume discount of 15% applies to the total cost. If seven or more areas are ordered, a volume discount of 25% applies to the total cost.

In addition, PGW can provide a national data package, comprising all of the PetroBras aeromagnetic surveys shown in Figure 1, and all of the Brasil gravity data shown in Figure 2, for US$19,000. This data package includes the source data and the twelve grids listed under Data Packages.

PGW has also compiled the CPRM magnetic, radiometric and geochemical data over the hard rock areas of Brazil. Further details and costs are available on request.