Abstract
Abstract
It is often difficult to adequately treat the entire perforated interval in a damaged, gravel packed perforated interval in a damaged, gravel packed well. Foam was evaluated in the laboratory as a diverting technique for hydrofluoric acid treatments, and encouraging results led to field evaluation of foam diverting in 12 wells in the Gulf of Mexico. Generation of stable foam at low pump rates was aided by the use of a coil tubing unit, which further enhances treatment results by enabling the various fluids to be spotted at or below the perforated interval. Two different techniques were perforated interval. Two different techniques were used in these treatments: staged foam injection and foam injection during the first third of the treatment. Production data was used to evaluate the foam diverting technique. Also, temperature logs were run before and after one treatment to provide further information on the benefits of foam. Advantages and disadvantages of foam diverting as well as treatment design procedures, laboratory data, and production data relating to foam diverting in matrix hydrofluoric acid treatments are presented in this paper.
Introduction
Many wells in the Gulf of Mexico are completed in multiple lobed, poorly consolidated, high permeability sandstones, and are usually gravel permeability sandstones, and are usually gravel packed to control sand production. Their packed to control sand production. Their productivity in the absence of formation damage is productivity in the absence of formation damage is adequate; however, while drilling or during their productive life most of these wells will experience productive life most of these wells will experience formation damage, either organic or inorganic.
Following the determination of the damage mechanism(s), a treatment must be designed which effectively eliminates the damage over the entire completion interval, while minimizing the formation of secondary damage.
Commonly, inorganic damage in Gulf Coast formations is caused by a combination of clay dispersion and fines migration, and requires treatment by a hydroflouric acid system to remove the damaging silicates. A successful stimulation treatment requires that unspent hydrofluoric acid contact the formation following a hydrochloric acid preflush, and the formation is then overflushed to minimize the occurrence of damaging precipitates. Fluids pumped into the well will flow most easily into the pumped into the well will flow most easily into the high permeability, possibly undamaged, portion of the completion. Thus, without any modification, the damage removal treatment may not be successful in removing damage from the entire interval.
Diverting agents are often added to the acid system to promote acid flow into the entire perforated interval. Materials used for diversion in the past include sand, oil soluble resins, graded rock salt, and benzonic acid fines. In a gravel packed well, these solids must be sized fine enough to pass through the pack and filter out on the formation to provide effective diversion, and becomes more of a provide effective diversion, and becomes more of a problem as wells are packed with finer mesh gravels. problem as wells are packed with finer mesh gravels. Should a hydrofluoric acid stimulation designed to treat a gravel packed interval in a Gulf Coast sandstone not be sufficiently diverted, the possibility exists that completion failure due to possibility exists that completion failure due to gravel pack dissolution could occur.