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Using Remote Sensing and GIS technologies as an aid for hydrocarbon exploration in the Assam-Arakan fold-thrust belt
Premanand Mishra
pmishra@hoec.com
Sagar N. Mehta
sagar_mehta@hoec.com
Hindustan Oil Exploration Company Limited,
Tandalja Road, Vadodara, Gujarat-390020
Phone: +91-265-233-(0766, 3565 and 3568)
Fax: +91-265-2333567, 2333918
Premanand Mishra
pmishra@hoec.com
Sagar N. Mehta
sagar_mehta@hoec.com
Hindustan Oil Exploration Company Limited,
Tandalja Road, Vadodara, Gujarat-390020
Phone: +91-265-233-(0766, 3565 and 3568)
Fax: +91-265-2333567, 2333918
Introduction
The Assam-Arakan FTB extends all along the India-Myanmar border from the Himalayas in the north to the Bay of Bengal in the south. Petroliferous Tertiary non-marine sedimentary rocks essentially dominate the stratigraphy within the foreland FTB. Like the Himalayan orogenic belt, several fault-bound, stacked-up and longitudinally continuous litho-tectonic zones characterize the Assam-Arakan FTB. Since the late 19th century, workers have adopted various techniques and methods to understand the structures in the FTB, which, in turn, aid in developing hydrocarbon exploration leads. The present work is a consequence of such an activity in the area, undertaken by Hindustan Oil Exploration Company Limited and its Joint Venture partners (Block AAP-ON-94/1, Assam-Arunachal Pradesh, India; Eighth round of exploration bidding announced by Government of India in 1994).
An integrated approach of remote sensing and GIS technologies provides better opportunities not only for geological mapping, but also for geological interpretation and implementation of exploration programs in difficult terrains with greater accuracy and in a cost-effective manner (Everett et al. 2002; Harris and Cooper 2002; Saraf et al. 2002). In assistance with ESRI India (NIIT GIS Ltd.), an extensive GIS database has been build up for the study area through standard procedures, so as to utilize the data not only to generate map outputs, but for various analysis as well. Thematic layers generated by digitization include, settlements, roads, railway network, drainage, topographic contours, geological information, well locations, seismic line locations, oil and gas pipelines, time contours of stratigraphic horizons and depth contours of stratigraphic horizons.
The GIS database generated is currently being used, besides for integration into sophisticated, quantitative structural models, for implementing, documenting and monitoring exploration programs like geochemical prospecting, seismic acquisition and well drilling, besides the environmental impact assessment being carried out for each exploration program.
Data Used The following data sets from different sources were used in the present study:
Figure 1 depicts the various steps undertaken to build up the geo-database. The flowchart also shows how the geo-database is being currently used for various exploration programs.
Figure 1 Flowchart depicting the use of remote sensing and GIS in petroleum ventures.
First, the topographical maps were scanned and then georeferenced in ERDAS Imagine 8.4 to a Lambert Conformal Conic projection system, as had been used for the previous geophysical surveys during seismic acquisition. Then a mosaic of the topographical maps was generated. Settlements, roads, drainage, topographic contours and other geographic information were then digitized from this mosaic of topographical maps. The geological atlas was then scanned and georeferenced in ERDAS Imagine 8.4, also to the appropriate projection system. Reference points were selected from the same maps.
The IRS 1-D PAN and LISS-III images, both obtained from NRSA, Hyderabad, were then also georeferenced to the appropriate projection system in ERDAS Imagine 8.4. Ground Control Points (GCPs) were selected from the mosaic of georeferenced topographical maps and GPS surveys in the field, after the GPS GCPs were matched with the GCPs obtained from the topographical map. By combining Bands 4, 3 and 2 of the LISS-III image, a false colour composite (FCC) was generated. Spatial enhancement was also done to the IRS 1-D PAN and LISS-III images. To take advantage of the spatial resolution and spectral resolution of the IRS 1-D PAN and LISS III images, respectively, both the images were “resolution merged” together to obtain a multi-spectral image having higher spatial resolution. Digital Image Processing was carried out in ERDAS Imagine 8.4. A modified geological atlas (Figure 2) was generated based on interpretations from the multi-spectral image having higher spatial resolution, following image radiometric enhancements. All the information in the georeferenced geological atlas (lithological boundaries as polygon features, faults and axial traces of folds as polyline features and bedding plane dip-strike data as point features) were digitized in ArcGIS 8.1. The road and railway network, settlement, drainage of the region was also updated using the merged satellite image. A land use map was also generated from the merged image following image classification.
The topographic contours and elevation points were interpolated using the Triangulated Irregular Network (TIN) method to generate the Digital Elevation Model (DEM) (Figure 3a), slope map (Figure 3b) and aspect map of the study area. In order to generate Digital Terrain Models (DTMs), the LISS-III, PAN and merged images were draped over the DEM. Figure 3c is a DTM generated by combining the LISS-III image with the DEM. These analyses were carried out in ArcGIS 8.1 using the 3-d Analyst module.
Similarly, all the time and depth structure contour maps of various stratigraphic horizons were interpolated using TIN to produce digital models for better 3-dimensional visualization (Figures 4a and b). A structural dip domain map was also created by IDW (Inverse Distance Weighted) interpolation technique using fault traces and fold axial traces as barriers (Mishra et al. 2002). Based on the X-Y coordinates, well locations and seismic lines were constructed and overlaid on top of all the layers. These steps were also carried out in ArcGIS 8.1.
The geo-database and interpretations made thereof are also being currently used for further exploratory efforts. During geochemical prospecting, the geo-database was successfully used for planning the survey, realizing the logistic requirements and operation documentation and monitoring. The geo-database has also been used for the planning of a new seismic survey. The topographic profile along each line of the seismic grid has been extracted from the DEM, directly indicating the nature of the terrain. The land use pattern in the area of the proposed seismic survey has been deduced from the classified satellite imageries. The land use map would also be used during the survey. The geo-database also gives an indication of the logistics required in the area of the proposed seismic survey. During the seismic surveys, the geo-database would also be used for operation documentation and monitoring. The same geo-database would also be used for planning the location of well drilling, based on a proper understanding of the hydrocarbon potential of the area, the logistics required and the land use pattern in the area. The management of the leased land, and also the operation documentation, monitoring and maintenance of the well would be carried out on the basis of the geo-database. A rapid environmental impact assessment has already been carried out based on the geo-database and field studies before the beginning of the seismic survey. During the seismic survey and also during the drilling of well(s), the geo-database would be used for environmental monitoring.
Conclusion
Orogenic belts, like the Assam-Arakan FTB, are often characterized by complex structures, poor logistics and terrain inaccessibility. Consequently, the surface and sub-surface geological and geophysical data are of poor quality, being discontinuous and scanty. In such areas, it is imperative that proper interpretation techniques be applied for any exploratory effort. The GIS database generated can be used not only for geological interpretations, but also for exploration programs like geochemical prospecting, seismic acquisition and well drilling, besides the environmental impact assessment being carried out for each exploration program.
Remote sensing and GIS technologies are gradually proving to be valuable tools for creating and developing exploration information. Remote sensing and GIS technologies are currently being used by 90 percent of upstream exploration departments across asset teams worldwide (Zolnai, 2002). In fact, from initial exploration through acquisition and production to final divestiture, spatial information is key to any hydrocarbon venture. An integrated approach of remote sensing and GIS can also benefit the entire petroleum enterprise:
References
The Assam-Arakan FTB extends all along the India-Myanmar border from the Himalayas in the north to the Bay of Bengal in the south. Petroliferous Tertiary non-marine sedimentary rocks essentially dominate the stratigraphy within the foreland FTB. Like the Himalayan orogenic belt, several fault-bound, stacked-up and longitudinally continuous litho-tectonic zones characterize the Assam-Arakan FTB. Since the late 19th century, workers have adopted various techniques and methods to understand the structures in the FTB, which, in turn, aid in developing hydrocarbon exploration leads. The present work is a consequence of such an activity in the area, undertaken by Hindustan Oil Exploration Company Limited and its Joint Venture partners (Block AAP-ON-94/1, Assam-Arunachal Pradesh, India; Eighth round of exploration bidding announced by Government of India in 1994).
An integrated approach of remote sensing and GIS technologies provides better opportunities not only for geological mapping, but also for geological interpretation and implementation of exploration programs in difficult terrains with greater accuracy and in a cost-effective manner (Everett et al. 2002; Harris and Cooper 2002; Saraf et al. 2002). In assistance with ESRI India (NIIT GIS Ltd.), an extensive GIS database has been build up for the study area through standard procedures, so as to utilize the data not only to generate map outputs, but for various analysis as well. Thematic layers generated by digitization include, settlements, roads, railway network, drainage, topographic contours, geological information, well locations, seismic line locations, oil and gas pipelines, time contours of stratigraphic horizons and depth contours of stratigraphic horizons.
The GIS database generated is currently being used, besides for integration into sophisticated, quantitative structural models, for implementing, documenting and monitoring exploration programs like geochemical prospecting, seismic acquisition and well drilling, besides the environmental impact assessment being carried out for each exploration program.
Data Used The following data sets from different sources were used in the present study:
- Remote sensing data digital data of IRS-1D LISS-III and IRS-ID PAN.
- Existing geological maps, structure contour maps, and topographical maps (1:50,000 scale).
- Field survey data of existing well and seismic line locations, as well as GPS survey points (used as GCPs during georeferencing).
Figure 1 depicts the various steps undertaken to build up the geo-database. The flowchart also shows how the geo-database is being currently used for various exploration programs.
Figure 1 Flowchart depicting the use of remote sensing and GIS in petroleum ventures.
First, the topographical maps were scanned and then georeferenced in ERDAS Imagine 8.4 to a Lambert Conformal Conic projection system, as had been used for the previous geophysical surveys during seismic acquisition. Then a mosaic of the topographical maps was generated. Settlements, roads, drainage, topographic contours and other geographic information were then digitized from this mosaic of topographical maps. The geological atlas was then scanned and georeferenced in ERDAS Imagine 8.4, also to the appropriate projection system. Reference points were selected from the same maps.
The IRS 1-D PAN and LISS-III images, both obtained from NRSA, Hyderabad, were then also georeferenced to the appropriate projection system in ERDAS Imagine 8.4. Ground Control Points (GCPs) were selected from the mosaic of georeferenced topographical maps and GPS surveys in the field, after the GPS GCPs were matched with the GCPs obtained from the topographical map. By combining Bands 4, 3 and 2 of the LISS-III image, a false colour composite (FCC) was generated. Spatial enhancement was also done to the IRS 1-D PAN and LISS-III images. To take advantage of the spatial resolution and spectral resolution of the IRS 1-D PAN and LISS III images, respectively, both the images were “resolution merged” together to obtain a multi-spectral image having higher spatial resolution. Digital Image Processing was carried out in ERDAS Imagine 8.4. A modified geological atlas (Figure 2) was generated based on interpretations from the multi-spectral image having higher spatial resolution, following image radiometric enhancements. All the information in the georeferenced geological atlas (lithological boundaries as polygon features, faults and axial traces of folds as polyline features and bedding plane dip-strike data as point features) were digitized in ArcGIS 8.1. The road and railway network, settlement, drainage of the region was also updated using the merged satellite image. A land use map was also generated from the merged image following image classification.
The topographic contours and elevation points were interpolated using the Triangulated Irregular Network (TIN) method to generate the Digital Elevation Model (DEM) (Figure 3a), slope map (Figure 3b) and aspect map of the study area. In order to generate Digital Terrain Models (DTMs), the LISS-III, PAN and merged images were draped over the DEM. Figure 3c is a DTM generated by combining the LISS-III image with the DEM. These analyses were carried out in ArcGIS 8.1 using the 3-d Analyst module.
Similarly, all the time and depth structure contour maps of various stratigraphic horizons were interpolated using TIN to produce digital models for better 3-dimensional visualization (Figures 4a and b). A structural dip domain map was also created by IDW (Inverse Distance Weighted) interpolation technique using fault traces and fold axial traces as barriers (Mishra et al. 2002). Based on the X-Y coordinates, well locations and seismic lines were constructed and overlaid on top of all the layers. These steps were also carried out in ArcGIS 8.1.
The geo-database and interpretations made thereof are also being currently used for further exploratory efforts. During geochemical prospecting, the geo-database was successfully used for planning the survey, realizing the logistic requirements and operation documentation and monitoring. The geo-database has also been used for the planning of a new seismic survey. The topographic profile along each line of the seismic grid has been extracted from the DEM, directly indicating the nature of the terrain. The land use pattern in the area of the proposed seismic survey has been deduced from the classified satellite imageries. The land use map would also be used during the survey. The geo-database also gives an indication of the logistics required in the area of the proposed seismic survey. During the seismic surveys, the geo-database would also be used for operation documentation and monitoring. The same geo-database would also be used for planning the location of well drilling, based on a proper understanding of the hydrocarbon potential of the area, the logistics required and the land use pattern in the area. The management of the leased land, and also the operation documentation, monitoring and maintenance of the well would be carried out on the basis of the geo-database. A rapid environmental impact assessment has already been carried out based on the geo-database and field studies before the beginning of the seismic survey. During the seismic survey and also during the drilling of well(s), the geo-database would be used for environmental monitoring.
Conclusion
Orogenic belts, like the Assam-Arakan FTB, are often characterized by complex structures, poor logistics and terrain inaccessibility. Consequently, the surface and sub-surface geological and geophysical data are of poor quality, being discontinuous and scanty. In such areas, it is imperative that proper interpretation techniques be applied for any exploratory effort. The GIS database generated can be used not only for geological interpretations, but also for exploration programs like geochemical prospecting, seismic acquisition and well drilling, besides the environmental impact assessment being carried out for each exploration program.
Remote sensing and GIS technologies are gradually proving to be valuable tools for creating and developing exploration information. Remote sensing and GIS technologies are currently being used by 90 percent of upstream exploration departments across asset teams worldwide (Zolnai, 2002). In fact, from initial exploration through acquisition and production to final divestiture, spatial information is key to any hydrocarbon venture. An integrated approach of remote sensing and GIS can also benefit the entire petroleum enterprise:
- Exploration
- Operation and maintenance
- Production
- Land lease management
- Data management
References
- Everett J. R., Jengo C. and Staskowski R. J., 2002. Remote sensing and GIS enable future exploration success. World Oil, vol.223/11, 59-65.
- Harris R. and Cooper M., 2002. Structural analysis in eastern Yemen using remote sensing data. World Oil, vol.223/11, 52-57.
- Mishra P., Patel K. B., Mehta S. N. and Nath K. K., 2002. Structural analysis in the Assam-Arakan fold-thrust belt using ArcGIS 8.1 3D-Analyst. Fifth ESRI India User Conference, 22-23 January 2002, New Delhi.
- Saraf A. K., Mishra P., Mitra S., Sarma B. and Mukhopadhyay D. K., 2002. Remote sensing and GIS technologies for improvements in geological structures interpretation and mapping. Int. J. Remote Sensing, vol.23/13, 2527-2536.
- Zolnai A., 2002. The second revolution. ArcUser, vol.5/4, 10-11.