296 PART6-GEOLOGICAL METHODS 21232 ● BOTTOM CTOR SIRE SURE v OUR INTERVAL field western Canada, 1974 and 1975. Contour Interval is 2750 kPa.(After Jardine and wishart, 1987. Water Saturation The water saturation(Sw)within the net pay interval is typically estimated from well logs. Water saturations can also be derived from capillary pressure testing of cores to determine the relationship of water saturation versus heigl above the oil-water contact(see the chapter on"Capillary Pressure"in Part 5). Like porosity, the water saturation data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring (Figure 5). The averages should be weighted by porosity Figure 2. structure of the base of the humber unconformity( top of the Brent Group), Dunlin fleld, U. K. Northern North Sea Oil Saturation mapped with 1979 and 1989 vintage data. Contours are marked in ft subsea x 100; contour Interval is 100 ft( From Braithwaite In an oil-water system, the water saturation and oil eal,198) saturation(S)sum to 1. Therefore, once S,, has been determined, oil saturation can be calculated and mapped as S=1-S should be contoured using well control points and interpolated or extrapolated using available seismic and wel test data and the geologists interpretation of depositional and MAPPING FOR RESERVOIR MANAGEMENT diagenetic history (see the chapter on"Effective Pay Deter- A variety of maps are used to predict or monitor reservoir mination"in Part 6)implies that some formation thickness has been excluded from consideration by either(1)occurring below an oil-water contact(or above a gas-water contact), or Permeability )having porosity and /or permeability values below a cutoff limit for productivity. Not all net pay is necessarily Permeability ()can also be mapped and contoured(see productive at a given well spacing. Discontinuous productive Transformations and Porosity-Permeability Relationships"in horizons between wells might be described, for example, by Part 5). As for saturation values, some care must be exercised concept of net pay to net connected pay ratio(Poston, n mapping permeability because values must be derived from indirect measurements. Typically, permeabilities are Porosity The porosity (o)in a reservoir zone can be determined Permeabilities can be reported at ambient laboratory from log and/or core data(see the chapter on"Porosity"in conditions of pressure or adjusted to reservoir conditions of Part 5). The data in an individual well within the net pay confining pressure. Similarly, permeabilities can be absolute interval can be averaged arithmetically and posted on a map permeabilities to air(nitrogen )or liquid or effective for contouring. The averages should be weighted by permeabilities to oil in the presence of irreducible water thickness Permeability values in an individual well are thickness296 PART 6—GEOLOGICAL METHODS Figure 2. Structure of the base of the Humber unconformity (top of the Brent Group), Dunlin field, U.K. Northern North Sea mapped with 1979 and 1989 vintage data. Contours are marked in ft subsea x 100; contour interval is 100 ft. (From Bralthwaite et al., 1989.) should be contoured using well control points and interpolated or extrapolated using available seismic and well test data and the geologist's interpretation of depositional and diagenetic history. "Net" pay (see the chapter on "Effective Pay Deter￾mination" in Part 6) implies that some formation thickness has been excluded from consideration by either (1) occurring below an oil-water contact (or above a gas-water contact), or (2) having porosity and/or permeability values below a "cutoff" limit for productivity. Not all net pay is necessarily productive at a given well spacing. Discontinuous productive horizons between wells might be described, for example, by the concept of net pay to net connected pay ratio (Poston, 1987). Porosity The porosity ((ji) in a reservoir zone can be determined from log and /or core data (see the chapter on "Porosity" in Part 5). The data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring. The averages should be weighted by thickness. - V MARCH 1974 / w f [• ym •"*^^ r T\I* f • * *^v» rAjivSt \N VX V J V* •\r1 K •/" * " .V^ * ' / * \ \ vlnn *V"-*j<tf* * * yV*"""! * It ft»* J^?"- " i* r*'~^t \R&jEfiB3$y / • \?jS • • y 7 ••" • y ^y 5km • BOTTOM WATER INJECTOR . PERIPHERAL ' WATER INJECTOR PATTERN WATER INJECTOR CONTOUR INTERVAL 2750 kPa • PRESSURE 'SIN< K I PATTERN I FLOOD AREA Figure 3. Map of pressure response to pattern flood, Judy Creek field, western Canada, 1974 and 1975. Contour interval is 2750 kPa. (After Jardine and Wilshart, 1987.) Water Saturation The water saturation (Sw) within the net pay interval is typically estimated from well logs. Water saturations can also be derived from capillary pressure testing of cores to determine the relationship of water saturation versus height above the oil-water contact (see the chapter on "Capillary Pressure" in Part 5). Like porosity, the water saturation data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring (Figure 5). The averages should be weighted by porosity. Oil Saturation In an oil-water system, the water saturation and oil saturation (S0) sum to 1. Therefore, once S w has been determined, oil saturation can be calculated and mapped as S„ = l-S„ , MAPPING FOR RESERVOIR MANAGEMENT A variety of maps are used to predict or monitor reservoir performance. Permeability Permeability (k) can also be mapped and contoured (see the chapters on "Permeability" and "Core-Log Transformations and Porosity-Permeability Relationships" in Part 5). As for saturation values, some care must be exercised in mapping permeability because values must be derived from indirect measurements. Typically, permeabilities are derived from wireline log porosities transformed on the basis of core permeability versus porosity cross plots. Permeabilities can be reported at ambient laboratory conditions of pressure or adjusted to reservoir conditions of confining pressure. Similarly, permeabilities can be absolute permeabilities to air (nitrogen) or liquid or effective permeabilities to oil in the presence of irreducible water. Permeability values in an individual well are thickness