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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
1 Exploration, Greater Nile Petroleum Operating Company Ltd, Vth floor, Exploration Dept.,
Khartoum tower, Al gamhouria street, Khartoum, 12527, Sudan, phone: 00249912394176, fax: 00249183760048,
[email protected]
2 Exploration Dept., Basin Studies Group, Greater Nile Petroleum
Operating Company, Vth Floor, GNPOC tower, Al-gamhouria street, P.O. BOX 12527, Khartoum, Sudan
Reservoir characters are major consideration for formulating any test design. Permeability dictates test flow rate and
duration of the test. Test flow rates and flow times must satisfy several criteria. (1)Test must be long enough to obtain data
beyond near-well
bore
effects, such as wellbore storage distortion, formation damage, or stimulation.(2) Test must also
reach desired radius of investigation and evaluate a representative volume of the formation. In low -permeability reservoirs,
flowing time required to satisfy both criteria can be prohibitive, especially when flaring gas. Duration of wellbore storage
period depends on wellbore volume and fluid compressibility, reservoir porosity, permeability, net pay thickness, and fluid
properties. Reductions in wellbore storage period can be achieved by running bottom hole valves in the tubing string, which
allows to shut in the well just above the sand face rather than at the surface. Time to reach a desired radius of investigation
in a reservoir increases with decreasing permeability. Drawdown varies directly with flow rate and inversely with
permeability. For higher permeability wells, a given flow rate will cause a smaller pressure drawdown than in lower
permeability wells. To increase the pressure drawdown, a higher rate must be used. Higher rates will require larger
separators and meter runs at the surface. Higher flow rates will also waste more gas through venting and flaring unless well
is connected to a pipeline. Higher rates can create larger pressure drawdown which may result in retrograde condensation
in gas condensate reservoirs or formation sloughing in unconsolidated sandstones damaging the reservoir immediately
adjacent to the well
bore
. Authors with the help of case history built out a reservoir model and standards for testing the wells
effectively in most economical methods.