a) LEDUC NET PAY ISOPACH MAP (b) CONTOUR INTERVAL.0 1 PORE VOLUME Figure 4.(a)Cross section and (b) net pay isopach map of the Strachan gas field, western Canada. Contour Interval Is 100 ft. Figure 5. Porosity-weighted average water saturation map for (From Hriskevlch et al., 1980. weighted and typically averaged harmonically, arithmetically, or geometrically, depending geometry. Alternatively, Solution Gas to Oil Ratio flow capacity (kH) values derived from pressure transient Engineers forecast ultimate recoverable e reserves by testing can be divided by net pay thickness (H) to yield a applying material balance equations or decline curve analysis quid permeability value for a well to production history records. For example, in type reservoir, the solution gas to oil ratio is sometimes Porosity Thickness plotted versus cumulative oil production on semilog paper Reservoir storage capacity or porosity thickness(H) is the (Garb and Smith, 1987).If such product of porosity and net pay (Figure 6) straight-line relationship, the curve can be used to predict the trend of a cumulative gas or cumulative oil plot to estimate Productivity Index ultimate recovery The solution gas to oil ratio(GOR) is the amount of To avoid coning, sand production, pipe collapse, or other dissolved gas that will evolve from the oil as the pressure is harmful effects, wells might not be produced at the reduced to atmospheric from some higher pressure. GOR maximum wide-open flow rates. Therefore, the ability of a usually expressed in units of SCf gas /STB oil. a barrel of oil well to produce is usually determined by a productivity index and its solution gas at reservoir conditions of temperature and PI(Kimmel and Dalati, 1987). The Pl is a measure of the pressure will usually"shrink"as the fluid is produced and stock tank barrels(STB)of oil produced per day per psi brought to stock tank conditions (normally reported at 60F conditions(see the chapter on"Production Testing"in Part 9). for individual wells can be mapped periodically to identify Changes will show on periodic maps of PI during reservoir areas of the reservoir receiving or not receiving pressure life indicating trends in reservoir depletion or formation support and serving as indicators for reservoir managemenSubsurface Maps 297 Figure 4. (a) Cross section and (b) net pay Isopach map of the Strachan gas field, western Canada. Contour Interval is 100 ft. (From Hriskevlch et al., 1980.) weighted and typically averaged harmonically, arithmetically, or geometrically, depending on flow geometry. Alternatively, flow capacity (kH) values derived from pressure transient testing can be divided by net pay thickness (H) to yield a liquid permeability value for a well. Porosity Thickness Reservoir storage capacity or porosity thickness (§H) is the product of porosity and net pay (Figure 6). Productivity Index To avoid coning, sand production, pipe collapse, or other harmful effects, wells might not be produced at their maximum wide-open flow rates. Therefore, the ability of a well to produce is usually determined by a productivity index (PI) (Kimmel and Dalati, 1987). The PI is a measure of the stock tank barrels (STB) of oil produced per day per psi drawdown under steady-state or pseudosteady-state flow conditions (see the chapter on "Production Testing" in Part 9). Changes will show on periodic maps of PI during reservoir life indicating trends in reservoir depletion or formation damage. Figure 5. Porosity-weighted average water saturation map for Layer 2 of a Middle Eastern carbonate reservoir. Solution Gas to Oil Ratio Engineers forecast ultimate recoverable reserves by applying material balance equations or decline curve analysis to production history records. For example, in a depletion￾type reservoir, the solution gas to oil ratio is sometimes plotted versus cumulative oil production on semilog paper (Garb and Smith, 1987). If such a curve shows a good straight-line relationship, the curve can be used to predict the trend of a cumulative gas or cumulative oil plot to estimate ultimate recovery. The solution gas to oil ratio (GOR) is the amount of dissolved gas that will evolve from the oil as the pressure is reduced to atmospheric from some higher pressure. GOR is usually expressed in units of SCF gas/STB oil. A barrel of oil and its solution gas at reservoir conditions of temperature and pressure will usually "shrink" as the fluid is produced and brought to stock tank conditions (normally reported at 60 T and 14.7 psia). As GOR changes during reservoir life, GORs for individual wells can be mapped periodically to identify areas of the reservoir receiving or not receiving pressure support and serving as indicators for reservoir management action