A 4?-in.liner cementation in a high-profile exploratory well was executed for a major onshore operator in UAE in a challenging environment. More recently,a 4?-in.liner was cemented in a 6-in.vertical hole at a depth of 11,930 ft across the Arab and Diyab formations.Corrosive substances,including high concentrations of CO2&H2S,were present in this well.The H2S level was expected to be as high as 340,000 ppm and the CO2 around 12,000,000 ppm.Adding to the complexity,the BHT of the well was 345 deg.F. This extremely challenging and hostile down-hole environment was addressed by using a“fit for purpose”CO2/H2S-resistant cement system designed to isolate the targeted zone and ensure the integrity of the wellbore for the entire life of the well. The margin between the open-hole fracture pressure and the maximum predicted ECD in the wellbore during the job was extremely tight,and losses were to be expected.In an attempt to offset this,a proprietary lost circulation spacer was pumped ahead of the CO2/H2S-resistant cement system to mitigate the potential for losses and control any additional induced losses while cementing.The spacer had the dual capability of maximizing hole cleaning and strengthening the formation face in the wellbore ahead of the heavy 16.7 ppg(125 pcf)cement slurry. Software was used to optimize the ECD,centralizer spacing and drag/torque calculations based on the available data received from the customer.In addition,temperature modeling was performed to improve the prediction of wellbore and formation temperatures during fluid circulation and cement slurry placement. This paper will address the procedures followed from the slurry and spacer design phases through to the placement of the cement slurry that ultimately led to the successful execution of the job. From an operational and technical standpoint the job was considered a success in that it met all the objectives identified and defined during the well planning stage.The well was logged approximately 48 hours after the cementing operation and the cement bond log was judged to be good and was accepted by the operator.
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