Scale formation and deposition (CaCO3) in production facilities is a problem encountered in the Ghawar Field in Saudi Arabia. The scale deposition causes production loss and safety hazards. Downhole scale inhibitor squeeze treatments have proven successful in controlling this scale accumulation. However, weak producers (low oil rate and high water cut wells) could not be squeezed due to the difficulty anticipated in re-starting production from these wells because of the high volume of water normally needed to squeeze the inhibitor into the formation. Starting in 1994, an alternative method (the encapsulated inhibitor treatment) was tried for selected weak wells.
This paper presents the design of the encapsulated inhibitor treatment, treatment procedure, a field case history with scale inspection results, economical analysis of this treatment versus the regular downhole treatment and the future plans. To-date, more than ten treatments have been performed in Saudi Arabia. Regular visual inspection of selected wells revealed no scale accumulation up to 24 months after the treatment. Current plans are to treat more wells for further evaluation.
Calcium carbonate CaCO3 scale is the most common scale encountered in the Ghawar field production wells. Its deposition in surface and subsurface equipment causes loss in oil production and major operational problems. The scale control program was started in the Ghawar Field in 1986, and since then, conventional scale inhibitor squeeze treatments have been successful in controlling scale accumulations. Saudi Aramco field experience has shown that weak oil producers, especially high water cut wells (WC >70%), when treated using a conventional scale inhibitor squeeze, require several reviving attempts before the wells can be put back on production and in some cases the wells might remain dead. This is mainly due to the hydrostatic head created by the large treatment fluid volumes normally pumped during a conventional treatment where the inhibitor is squeezed into the formation to a predetermined radius.
In 1994, a new scale inhibitor treatment "Encapsulated Inhibitor Treatment" was introduced to Saudi Aramco. The main advantage of this treatment is the placement of the treatment fluids in the rathole rather than squeezing it into the formation. Therefore, the encapsulated scale inhibitor treatment is suitable for the weak wet oil producers with high water cut. To-date, more than ten wells in the Ghawar Field and an offshore field have been treated with the encapsulated inhibitor, without any difficulty in bringing the wells back on production. Some of these wells are being closely monitored for rescaling by performing regular visual inspections. To date none of these treated wells have shown scale redeposition after up to two years following the treatment of the first well.