Padra field, discovered in 1977, is located in the eastern margin of Ankleshwar-Broach tectonic block of Cambay basin. Padra basement is overlain by thick sedimentary succession of clastic reservoir rocks and shale barriers including Cambay shale (major source rock). The characterization, modelling and flow simulation of fractured basements is complex and entirely different from conventional reservoirs. The paper aims to introduce a unique approach for study of basement reservoirs.

A Discrete Fracture Network (DFN) model is made to represent two fracture set explicitly, based on spatial and non-spatial parameters. Fracture orientation is distributed using statistical model of Fisher. Simulation exercises are carried out wherein; fractures are not explicitly represented but an equivalent virtual medium is created with effective properties (porosity and permeability) representing the dynamic properties of the flowing domain (fractures). Being a type I basement reservoirs, single medium model (single porosity and permeability) is used for flow simulation with effective properties calculated by Oda's method of numerical flow.

This work paves the way to establish workflows that benefit from the merits of complementary methods, which will allow us to characterise the uncertainty in naturally fractured reservoirs more accurately. The case study elucidates the experiences gathered during simulation study of 112 wells, out of which 48 wells have been found to be hydrocarbon bearing. Pressure and water cut trend indicate active aquifer support. Early cessation of structurally higher wells in same as well as different fault blocks has been found to be a prominent anomaly. Also, strong contrast in reservoir performance of nearby wells has been found in a few cases. This indicates a great level of heterogeneity in fracture distribution in reservoir. Ten zones of alternate high and low fracture intensity have been created based on interpretation of 6 FMI logs. The fracture counts (P10, count per length) in wells with FMI should have been used as indicator for fracture intensity (fractures area in a unit volume). Sensitivities on interaction forces and roughness of fracture planes is carried out as a key part of dynamic modeling. The DFN approach allows us to generate multiple realisations of fracture models and condition these to the field observations.

Characterizing fractured reservoirs using borehole core and image logs provides the static description of fracture properties. However, some fracture properties (3D fracture-density) are highly uncertain when they are evaluated using static characterization methods only. Hence, dynamic calibration methods are required to condition geological fracture models and to increase confidence in the adopted conceptual model. Pressure transient analysis integrated with log/core information must be used to characterize the reservoir's flow capacity and for the dynamic calibration.

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