A well is said to reach an "economic limit" when revenue from production does not cover the operating expenses, including taxes. If the economic limit is increased, the useful life of the well is shortened and proven oil reserves are lost. Conversely, when the financial limit is lowered, the life of the well is lengthened. When the economic limit is reached, the well becomes a liability if not
abandoned. At the economic limit, a significant amount of unrecoverable oil is often left in the reservoir. It might be tempting to defer physical abandonment for an extended period, hoping that the oil price will increase or that new supplemental recovery techniques will be perfected. In these cases, wells are merely shut in, or temporary plugs may be placed downhole. There are thousands of "temporarily abandoned" wells throughout North America, waiting to see what the market will do before permanent abandonment. However, lease provisions and governmental regulations often require quick abandonment; liability and tax concerns also may favor abandonment. Theoretically, an abandoned well can be re-entered to restore production (or converted to injection service for supplemental recovery or downhole hydrocarbon storage), but reentry is often difficult mechanically and expensive. Traditionally elastomer and cement plugs have been used with varying degrees of success and reliability. Over time, they may deteriorate, particularly in corrosive environments, due to the materials from which they are manufactured. New tools have been developed that make re-entry easier; these tools offer higher expansion ratios than conventional bridge plugs and higher differential pressure ratings than inflatable packers, all while providing a V0-rated, gas-tight seal that cement cannot provide. == Reclaim and reuse ==