Field Application of a Novel Emulsified Scale Inhibitor System to Mitigate Calcium Carbonate Scale in a Low Temperature, Low Pressure Sandstone Reservoir in Saudi Arabia Available to Purchase

This paper describes field application of a novel scale inhibitor squeeze treatment to mitigate downhole scale (calcium carbonate) present in several oil producing wells in a sandstone reservoir in central Saudi Arabia. The sandstone reservoir is weakly consolidated, water sensitive, and sanding problems were noted in several wells. The water cut in the scaled wells ranges from 3 to 80 vol%. To avoid sanding problems, most of these wells were gravel packed. In addition, the reservoir pressure and gas oil ratio are low and, as a result, electrical submersible pumps (ESPs) are used to produce these wells. The sandstone reservoir is heterogeneous and contains up to 14 wt% clay minerals in some zones. The bottom hole temperature is nearly 160°F. A thorough investigation was undertaken to develop a suitable scale squeeze treatment to mitigate the scale, and to assess the effectiveness of the treatment in the field.

Based on extensive lab studies, a new emulsified scale inhibitor treatment was designed and applied in more than fifteen wells. These wells were descaled prior to the squeeze treatment as was detailed by Nasr-El-Din et al.¹  All scale squeeze treatments were conducted using 1.75 or 2 in coiled tubing. Because the formation is water-sensitive, the main treatment, the pre and post flushes were designed to minimize formation damage due to fines migration and clay swelling. Following the treatment, the well was shut-in for two days to give ample time for various reactions to occur. Chemical analysis of well flow back samples was used to estimate the lifetime of the squeeze treatment. In addition, a downhole video camera was used to follow scale formation following the treatment.

The scale squeeze treatment was conducted in more than fifteen wells. The emulsified inhibitor was mixed in the field and was injected into the target zones without encountering any operational problems. Analysis of flowback samples indicated that the treatment did not affect well productivity or water cut in any of the treated wells. Based on field data, it is known that the treatment lifetime is greater than two years. The minimum scale inhibitor concentration, presented as phosphorus, is nearly 1 mg/L.