Why Many Overpressured, Stress-Sensitive Hydrocarbon Reservoirs Should Not Be Abandoned

Most commercial oil sands exhibit shale resistivity ratios (ratio of normal R _shn to observed R _sho ) of less than approximately 1.6 in adjacent shales and can be reached without an expensive string of protection pipe. On the other hand, some experts claim that “no commercial production is found when the shale resistivity ratio reaches and/or exceeds 3.5.” This statement, however, needs further investigation Such wells often are highly productive initially and are characterized by extremely fast pressure depletion. Based on extensive compaction studies of rocks, the authors argue that the latter is due to plastic deformation (irreversible compaction) in undercompacted overpressured rocks with increasing effective stress soon after production is initiated (or during well testing). Thus, well tests could be quite misleading, and many er roneously condemned overpressured reservoirs should be reexamined, reevaluated, and strategies be developed to recover the oil and gas from these stress-sensitive reservoirs.

Keywords:

• overpressured reservoirs
• maximum effective stress
• shale resistivity ratios
• compaction
• abandoned reservoirs