TABLE OF CONTENTS Primary methods using natural producing mechanisms, i.e., liquid and rock expansion and solution gas drive, leave behind 80% or more of the original oil in place. Figure 1-1 and Table 1-1 present some characteristics of natural producing mechanisms of oil reservoir. Consequently, a vast amount of hydrocarbon remains unrecovered in the United States and elsewhere in the world.
| Mechanisms | Reservoir Pressure | GOR | Water Production | Efficiency | Others |
|---|---|---|---|---|---|
| 1. Liquid and rock expansion | Declines rapidly and continuously P i (initial pressure) > b (bubble point pressure) | Remains low and constant | None (except in high S w reservoirs) | 1-10% Avg.3% | |
| 2. Solution gas drive | Declines rapidly and continuously | First low, then rises to maximum and then drops | None (except in high S w reservoirs) | 5-35% Avg. 20% | Requires pumping at an early stage |
| 3. Gas cap drive | Falls slowly and continuously | Rises continuously in up-dip wells | Absent or negligible | 20-40% Avg. 25% or more | Gas breakthrough at a down dip well indicates a gas cap drive |
| 4. Water drive | Remains high. Pressure is sensitive to the rate of oil, gas, and water production | Remains low if pressure remains high | Down-dip wells produce water early and... |
