Petroleum Conference on Production and Reservoir Engineering, 20–21 March, Tulsa, Oklahoma
Fracturing has become an important stimulation method both for production and injection wells in secondary recovery operations. The increased percentage of oil produced by secondary recovery makes studies of the effect of fracturing increasingly important.
There are several reasons why secondary recovery wells should be fractured. Fracturing often makes possible recovering more oil from the reservoir than could otherwise be produced. A reservoir's permeability is so greatly increased that a faster flow of fluid through the reservoir can be obtained under given differential pressures. This condition extends the reservoir's productive life.
In some cases fracturing reduced injection well operating pressures, perhaps eliminating the need for high pressure injection equipment. Fracturing often makes profitable oil recovery possible in a reservoir which otherwise could not be considered commercial. Such a situation may occur after prolonged waterflooding or early in the life of a water flood project.
Several factors should be considered in selecting wells to be fractured. After water injection is started, several months may elapse before the formation's void spaces are filled. Many operators use as a rule-of-thumb that a product ion well should be fractured if it has not responded satisfactorily after one and a half times the calculated fill-up volume has been injected into off-set wells. This rule-of-thumb has been used frequently, and, in most cases, the fractured wells have responded immediately.
If an individual production well has begun to produce large amounts of water it should not be fractured. A fracturing treatment would probably increase water production, rather than oil production. However, a repair job [for example using latex-cement or plastic] may successfully shut off the water and make a fracturing treatment feasible.
In case of injection wells, fracturing treatments are often performed simply because the well does not accept water properly. This situation may occur when production wells are converted to injection wells or when new injection wells are drilled.