ABSTRACT: 3D seismic in field development - a few examples from Indian basins

Josyulu, B. S., V. Singh, and G. Sen , Oil and Natural Gas Corporation Ltd., India, Dehradun, India

Around fifty prospects, located in widely varying geological settings occuring at 2-3Km, in the petroliferous basins of India have been covered by 3D seismics in the last decade. This paper portrays four such case studies drawn from unpublished work. Borholla-Changpang, located in Assam shelf is producing from fractured basement. Tectonic complexity adversely affected field development. 3D surveys brought out the Wrench related structure which had divided the area into five blocks of which the intensely faulted central block was demarcated as the only prospective area. Khoraghat prospect located in the Dhansiri valley in Assam-Arakan basin was identified as a fault closure hosting 5-20m thick fluvio-deltaic Miocene reservoirs. Drilling surprises necessitated 3D coverage, which brought out the stratigraphic style of entrapment. Amplitude anomalies integrated with geoscientific data established the presence of a system of stair like offshore bars cut by tidal channels. Drilling data validated this model. Prospective Oligo-Eocene carbonates of Bombay offshore basin wedges on the southern flank of Bombay high. Optimal exploration and field development necessitated mapping of strati-structural field limits and porosity trends. Only 3D surveys could achieve this, with the dense 3D coverage providing necessary stratistrutural details and sequence attributes providing the porosity trends resulting in an optimal exploitation strategy. Seventeen wells drilled prior to 3D surveys in Nada field located in the western flank of Cambay basin, indicated that 4-18m thick sands are deposited as elongated lenticular sands and are discrete in nature with variable OWC/OSC's. Horizon slices at pay sand level could bring out the network of distributary channels with increased tidal influence in the south resulting in substantial cost benefits in field development. Some more complex problems emanating from thinness of sands and tectonic complexity still remain unsolved. Technology upgradation in depth imaging, reservoir characterization and multi-component surveys are expected to resolve these problems.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia