The geo-database was finally developed after a series of steps that included georeferencing, digitization, digital image processing, analysis and interpretation, etc. Once the geo-database was developed, the primary task of exploring hydrocarbons in the FTB was initiated. The study area being at early stages of hydrocarbon exploration, sub-surface data is scanty. Consequently, geological modelling using structural techniques was adopted first. Incorporating into the geo-database, the enormous sub-surface data available outside the study area, enhanced the interpretations. The structural trends and hydrocarbon play concepts established outside the study area were then extrapolated into the study area.
The surface geological data (consisting of the modified geological map and the structural dip domain map) was integrated with the topographic, well and seismic data using standard structural methods. A series of structural cross-sections that are geometrically and kinematically tenable, as well as retrodeformable (Figure 4c is one such example), was then constructed using the technique of “cross section balancing”. The technique includes both extrapolation and interpolation of surface and sub-surface data to decipher the sub-surface structural and stratigraphic disposition of rock units to generate a cross-section that can be validated both by inverse and forward modelling strategies. Following the interpretation of the “serial balanced cross sections” and the pseudo 3-dimensional models of stratigraphic horizons, a number of possible hydrocarbon leads and prospects have been identified. Combining these interpretations with interpretations from well log and seismic reflection data, the hydrocarbon potential
and prospect is now being quantitatively worked out, based on the existing geo-database.
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
The advantage of GIS tools is truly represented in building a geo-database. The layers hierarchy has been built using ArcGIS such that the geo-database can accommodate smooth growth scale from single user to a very large enterprise wide multi-user database.
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.