Formation Evaluation in Lower Eocene Reservoirs in Upper Assam Basim: An

Oil India Limited's (OIL) operational areas, in Upper Assam-Arakan Basin, are located in a seismically active thrust fault zone (Bora et al., 2010). Multiple stacked layers, highly faulted anticlines and large number of compartments make the structural setting of these fields very complex. In terms of lithology, some of these reservoirs are low resistivity pays, leading to ambiguities in interpretation due to fresh water environment and complexities in evaluation of hydrocarbon-bearing and water-bearing sands (Koithara et al., 1973, Borah et al., 1998). Greater Nahorkatiya and Greater Jorajan, since the inception of commercial production in the 1950s, have been intensively studied to find prospective sweet spots, perforation intervals for new well locations and potential workover candidates. These forecasts, guided only by dynamic numerical model results, have had mixed results when implemented in the field. A validation of the dynamic model forecasts with near-wellbore saturation logs, can help to reduce uncertainty. This paper describes the success stories in field implementation of workovers, guided by dynamic reservoir model results and cross-validated with Pulse Neutron Tool (Roscoe et al., 1991, Schnorr, 1996) log recordings. The intricacy of delivering a precise dynamic reservoir model was managed by state-of-the-art seismic-to-simulation workflows, an integrated approach to improve the quality of the geological model and specific analytical techniques to fill in the data gaps. The calibrated model was analyzed for workover opportunities of zone transfer. In zones with high confidence, (i.e. high Hydrocarbon Pore Volume (HCPV), high porosity, permeability, etc., perforation intervals were recommended for hydrocarbon saturation monitoring to confirm the near-wellbore saturation predicted by the model. This workflow was followed in 8 wells which added immense value both technically and economically. The validation of model predictions with near-wellbore saturation was carried out in old wells which helped in making informed decision about tapping bypassed hydrocarbon pockets. It helped to avoid non-hydrocarbon bearing zones, which were removed from the existing workover plan. Moreover, it introduced confidence in the dynamic model which will be used in future for more aggressive economic development of the fields. This approach resulted in better understanding of the reservoir characteristics which led to identification of some potential reserves which could be characterized as "Reserve Growth".

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Resolving Development Strategy by Integrating Geophysical, Geological and Pressure Transient Test Data: A Case Study of Heterogeneous Lower Eocene Sand of Upper Assam Basin, India

Lama

Phukan

Neog

et al. 2003

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA multi-disciplinary approach had been adopted to resolve the exploitation and development strategy for Deohal and its extension oilfield having mainly the deep Eocene clastic reservoirs which is geologically complex, over pressurized stack of thin sands [by 30-40 Kg/cm 2 (assuming 0.1 Kg/cm 2 /m hydrostatic gradient] interbedded with shale/ carbonaceous shale. An accurate delineation of individual sand in such reservoirs is beyond the resolution of seismic as these occur at a depth of 3600 to >4000 m and its thickness vary from 2 to 4 m only. The Lithostratigraphic correlation based on well log is often unreliable/ difficult due to thin and extreme heterogeneous nature of the sediments. Moreover, areal extent of reservoir as a single unit is difficult to ascertain. The petrophysical properties viz. porosity and permeability substantially deteriorate with increase in depth i.e. below 4000 m.Initially 3D seismic data was showing a broad faulted anticline with fault 500 m to 800 m away from the crestal part. Analyses of pressure transient data showed barrier nearby and reinterpretation of 3D seismic data confirmed the presence of minor faults having limited extension.The Paper presents how transient well test data in conjunction with static 3D seismic data, wireline log and dynamic pressure-production data have helped to workout development strategy for a geologically complex and heterogeneous Lower Eocene thin sand reservoir in one of the oilfields in Upper Assam Basin, India.

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Formation Evaluation in Lower Eocene Reservoirs in Upper Assam Basim: An

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Oilfield geothermal resources of the Upper Assam Petroliferous Basin, NE India

Oilfield geothermal resources of the Upper Assam Petroliferous Basin, NE India

A Novel Approach to Rejuvenate Brown Field by Validating Dynamic Model Response with Near-Wellbore Saturation Monitoring

Resolving Development Strategy by Integrating Geophysical, Geological and Pressure Transient Test Data: A Case Study of Heterogeneous Lower Eocene Sand of Upper Assam Basin, India

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