Calcium carbonate scale was detected in the majority of wetproducers in a tight carbonate reservoir in the northern partof Saudi Arabia. Extensive lab work indicated that aphosphonate-type scale inhibitor was effective in mitigatingcarbonate scale, as well as sulfate scale that were found in afew wells. Field application of conventional scale squeezetreatment in this field is not an easy task for the followingreasons:1. The formation is tight and water blockage is aserious concern.2. Formation brine contains high Ca concentrations(up to 19,930 mg/L).3. The formation contains high TDS (up to 231,262mg/L); therefore measuring low concentrations ofthe phosphonate inhibitor is a real problem.4. Nearly 70% of the field is offshore, which imposeslimitation on the volume of fluids that can be used.As a result of these challenges, several modificationswere introduced to conventional scale squeeze treatments,where a large amount of aqueous phase is typicallyintroduced into the formation. Coreflood experiments wereused to evaluate various available options to reduce theamount of aqueous phase introduced into the formation andassociated problems. Based on the results obtained fromthese tests, significant changes were introduced to thepreflush, main treatment, postflush, and soaking time.The new modifications were applied at two wetproducers in this field. Well Z-C is a vertical well with 70vol% water cut, 218oF bottom hole temperature, and 78,540mg/L TDS. Well B is a horizontal well with 5 vol% watercut, 235oF bottom hole temperature and 209,828 mg/L TDS.An extensive wellhead-sampling program was conducted tomeasure residual scale inhibitor in the produced brines.Both wells responded positively to the treatment. Thenew modifications have resulted in better well response.Analysis of phosphonate in the wellhead samples was usedto determine the MIC for this field.
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