- Reservoir Management - Schaben Field
- study the effect on well productivities
- stimulation
- well pump rates

- infill drilling program - well placement

Prior to the start of simulation, on a grid-by-grid basis, determine if reservoir parameters (effective porosity and net pay thickness - water saturation) support historical production.

Establish grid pattern that properly defines the reservoir by using any mapping or gridding software (Geographix used to generate the grids for this study)

- Size Of Grid Cells In X & Y Direction
- numerical dispersion reduced - 4 to 5 grid cells between wells
- grid sizes of 220 ft by 220 ft - 5 grid blocks between wells

- reservoir heterogeneity
- schaben field is a dual porosity - dual permeability system
- oil column migrated across multiple zones
- most cores contain vertical fractures
- mini-permeameter results - high & low permeability layers
- production history - initial water free production followed by rapid onset of water production
- current reservoir pressure near original reservoir pressure - suggests strong recharge by aquifer

- multiple completions in isolated reservoirs
- segregate openhole & casedhole completions by layer

Simulation designed as two layer model - a reservoir layer with an underlying aquifer layer. Z-dimension equals pay thickness (top of the reservoir to the OWC, average depth of OWC = -2145 ft subsea)

Layer 1 - Reservoir (gross/net pay thicknesses assumed to be equal)

- difficult to distinguish between productive and non-productive zones
- porosity and permeability averaged over pay thickness

Layer 2 - aquifer provides recharge to reservoir layer (aquifer thickness in Schaben Field approximately 100 feet)

- Pay thickness - grid dimension in z direction
- Porosity
- dual porosity system
- total porosity - from petrophysical logs (Pfeffer)
- total porosity = effective porosity + ineffective porosity
- ineffective porosity saturated with water
- effective porosity saturated with oil, gas, & water
- fluid flow occurs only through effective porosity
- NMR studies on core plugs at reservoir pressure
- core porosity assumed equal to log porosity

- fluid saturations
- dichotomy - Sw from petrophysical logs & production history
- average Sw - 65 to 75%.
- production history - high OWR in early years followed by water break through
- thus all of Sw is not mobile

- effective saturation calculations on grid cell basis
- OOIP = (1-Sw) * grid volume * total porosity
- effective pore volume = grid volume * effective porosity
- effective So = OOIP / (effective pore volume)
- effective So - normalized <= 75% - relative permeability curves indicate Swi = 25%

- effective Sw = 1- (effective So) (water saturation in effective porosity)
- Map of OOIP on a grid cell basis - effective porosity * effective So * grid volume
- Map of cumulative production
- Available production history - 33 years lease production history & well productivity tests.
- Calculate well production - annual productivity tests - distribute lease production to wells. Bo (=1.04) - surface volume to reservoir volume.
- Schaben Field - uniform 40 acre spacing with 36 grid cells per acre.

- Cumulative production per well divided by 36 (grid cells) to allocate production over drainage area to generate cumulative production per grid cell map.
- Map of ROIP per grid cell
- ROIP = OOIP – cumulative production
- remaining So = ROIP / effective pore volume
- remaining So thickness = remaining So * pay thickness
- Soir = 25% (assumption)
- residual mobile So = remaining So - Soir - So => 0 - reservoir parameters consistent with production history
- Sor * t = residual mobile So * pay thickness - buried treasure map - areas with significant production potential

- Map of Recovery Factor - on a grid cell basis – cumulative production / OOIP

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Updated January 1999

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