Downhole scale deposition in producing well bores is becoming a serious problem to most of oil companies, especially when dealing with deep wells. The problem will be greater for those companies that are using water flood to maintain the reservoir pressure as the scale is often Calcium, Barium, and Strontium Sulphates.
The options for the scale removal varies from chemical, mechanical removals and at the worst conditions full rig work over to replace the production tubing could be the only available option. The oil field scale treatment philosophy is "scale prevention is better than curing", accordingly, implementing inhibition programs is generally become the most efficient scale treatment technology. However this inhibition technology is based on many factors to enable an appropriate assessment and reliable conclusions:
How the inhibitor interact with the formation rock matrix.
Thermal stability of inhibitor.
Deployment and return profile.
In this paper, a sever downhole scale problem occurred at Ras Budran field that located at the eastern coast of Gulf of Suez in Red Sea territory, were presented and focused on:
The treatment parameters starting from the traditional chemical & mechanical removal techniques and finalizing by the squeeze inhibition programs.
Inhibition programs and its modification to overcome the formation problems.
Inhibitor deployment, fluid returns monitoring and optimization.
Inhibition lifetimes pronounced improvement for all the scaling wells.
Study different chemistry of scale inhibitors to improve adsorption/desorption profile.
The down hole scale problem is predominate in the Egyptian Petroleum Companies that are using the injected sea water to maintain the reservoir pressure. The producing companies in the Gulf of Suez area have nearly the same formation water composition, which is characterized by very high calcuim Chloride and low Sulphate contents. Also they are using the Red Sea water for water flooding. Accordingly the case history for this paper will be from Ras Budran (R/B) field, Suez Oil Company.
R/B field is located 5 Kms. offshore at the eastern coast of the Gulf of Suez and consists of massive Nubian Sandstone compartmentalized by partially sealing major faults. The field is under saturated and production is maintained by gas-lifting while the pressure is supported by a combined water flooding and limited aquifer drive. R/B formation water is naturally scaling with Calcium Carbonate, later observations following a breakthrough of injected seawater, revealed deposits of Calcium, Barium and Strontium Sulphates contaminated with Iron Sulphide.
The primary factors affecting scale precipitation and crystal growth, nucleation are the solution super saturation, commingling two incompatible waters, change in pressure and temperature. Scale deposited very rapidly may have gas channels, be very porous, and be easy to remove with the dissolution techniques while if the scale deposited slowly it may be very hard, dense and may be very difficult to remove easily with the traditional chemical treatment methods.
Two main dissolution mechanisms for chemical treatment were implemented to dissolve the scales, acid dissolution for Carbonate and organic chelating compounds for both Carbonate & Sulphates; the mechanical cleaning techniques for removing the thick, dense and hard Sulphate scales was also performed for such hard scale.
Scale inhibitors squeeze program were also used in order to manage the scale deposition and prolong the life time and prevent any side effect for the scale dissolvers.
The paper summarizes the historical development of scale formation within R/B field, discuss the different treatment approaches and the inhibition treatment.