Abstract
Calcium carbonate scale was detected in several vertical wells in a sandstone reservoir in Saudi Arabia. The scale was detected downhole, plugging gravel packing screens and the intake of submersible pumps. Scale build-up caused a significant decline in oil production from this field. The sandstone reservoir is water-sensitive and has a bottom hole temperature of 160°F.
An emulsified-type scale inhibitor (phosphonate-type) treatment was designed to mitigate scale in this field. The treatment was successfully applied in thirty wells. Some of these wells were de-scaled before the treatment, while other wells were treated before scale detection.
The objectives of the present paper are to assess the outcome of this treatment based on field data and examine the impact of the acid descaling treatments that are usually conducted prior to the scale squeeze treatments. Samples of produced water from these wells were collected and analyzed over the last few years.
The emulsified scale squeeze treatment was successfully conducted in thirty wells with water cut that ranged from 3-80 vol%. Extensive analysis of samples collected following the treatment highlighted the need to completely lift the spent acid from the formation following acid descaling treatments. Field data indicated that the presence of dissolved iron may adversely affect the performance of the scale inhibitor. Finally, the concentrations of key elements (calcium, iron and phosphorus) in the flow back samples were affected by water cut and whether the well was descaled prior to the squeeze treatment.
