L-I, the shallowest hydrocarbon reservoir of Mumbai High field is being exploited as a consistent limestone reservoir. Performance analysis including pressure-production behaviour of the reservoir indicated the possibility of a higher in-place volume. This called for a detailed review of the L-I reservoir and to build a model in order to draw a development scheme for enhancement of production and better reservoir management to improve recovery.

A 3D geo-cellular model of L-I reservoir of Mumbai High North was constructed, incorporating all the well data. While carrying out stratigraphic correlation, a layer with high gamma similar to a sandstone reservoir of the field was identified below the Limestone reservoir in a NE-SW corridor across the field. It was supported by the presence of siltstone/fine grained sandstone in side wall core and the cutting samples of nearby wells falling in this corridor. ECS log recorded in a new well to validate the findings also confirmed it as clastic layer and the CMR log showed maximum permeability therein this layer. In addition, to confirm the lithology, entire L-I column in one of the vertical well was cored. It was confirmed from the core that the identified clastic layer is sandstone of very good porosity and permeability.

Based on all the observations, the L-I reservoir is divided into 3 sub layers- L-Ia, L-Ib and L-Ic- the top two being limestone and the bottom one (L-Ic) as clastic. The revised hydrocarbon estimates from the model resulted in almost doubling the earlier estimated initially In-place volumes. Reservoir simulation studies were carried out which recommended 9 new oil producers targeting L-I clastic layer from existing free slots and sidetracking/recompletion of existing poor producers leading to net recovery of about 33.4%. The Scheme is under implementation and has resulted in four fold increase in oil production from around 2600 to 10000 bopd.

The present study highlights the importance of integration of all the available data along with finer lithological details, obtained through formation evaluation, for reservoir characterization and well placement which plays a vital role in optimal exploitation of the hitherto less understood reservoirs.

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