Changes

  | isbn    = 0891816607

  | isbn    = 0891816607

}}

}}

The production of oil or gas from underground reservoirs involves chemical and mechanical processes that affect the wellbore. Many of these processes can eventually cause a problem with the well, resulting either in a decrease in production or in failure of equipment installed downhole or at the surface. Most of the serious problems can be avoided or delayed through preventive maintenance techniques or early recognition from regular analysis of producing rates, fluids, and the mechanical condition of the well. Such practices can prevent a costly workover that may be required to restore production from the well and may also prevent total loss of the wellbore.

The production of oil or gas from underground reservoirs involves chemical and mechanical processes that affect the wellbore. Many of these processes can eventually cause a problem with the well, resulting either in a decrease in production or in failure of equipment installed downhole or at the surface. Most of the serious problems can be avoided or delayed through preventive maintenance techniques or early recognition from regular analysis of producing rates, fluids, and the mechanical condition of the well. Such practices can prevent a costly [[workover]] that may be required to restore production from the well and may also prevent total loss of the wellbore.

==Water-gas coning==

==Water-gas coning==

===Scales and precipitates===

===Scales and precipitates===

Plugged or inadequate perforations have the same effect as partial penetration; that is, reservoir fluids are restricted from flowing into the wellbore. Perforations can become plugged with scale or other solid particles that are precipitated from formation fluids (see [[Rock-water reaction: formation damage]]). As these fluids are produced, equilibrium conditions of pressure and temperature become altered (especially near the wellbore) causing precipitation of these particles. Some precipitates can form when incompatible fluids come in contact downhole. Workover and completion fluids should be tested with formation fluids for compatibility. Precipitates can also occur in a formation after an acid treatment.

Plugged or inadequate perforations have the same effect as partial penetration; that is, reservoir fluids are restricted from flowing into the wellbore. Perforations can become plugged with scale or other solid particles that are precipitated from formation fluids (see [[Rock-water reaction: formation damage]]). As these fluids are produced, equilibrium conditions of pressure and temperature become altered (especially near the wellbore) causing precipitation of these particles. Some precipitates can form when incompatible fluids come in contact downhole. [[Workover]] and completion fluids should be tested with formation fluids for compatibility. Precipitates can also occur in a formation after an acid treatment.

The most common types of scale are calcium carbonate and calcium sulfate ([[gypsum]]). Sodium chloride (salt), sulfur, and other minerals can also be precipitated under certain conditions. The formation of these scales or solids can be minimized or prevented through use of chemical inhibitors, provided the produced fluids are analyzed ahead of time. If not, it may be necessary to perform a workover to clean out the well.

The most common types of scale are calcium carbonate and calcium sulfate ([[gypsum]]). Sodium chloride (salt), sulfur, and other minerals can also be precipitated under certain conditions. The formation of these scales or solids can be minimized or prevented through use of chemical inhibitors, provided the produced fluids are analyzed ahead of time. If not, it may be necessary to perform a workover to clean out the well.