The cementing technology of low-density, high-strength tough cement slurry for the deep well ZG112

Well ZG112 is a carbonate development well located in No.1 Tazhong Gas Field. Its single-stage cementing through of Ø200.03 mm casing is faced with the following difficulties. First, lost circulation tends to happen easily in the Permian. Second, the single-stage cementing section is 6 132 m long with irregular calipers in most parts, and the amount of cement slurry and the displacement of drilling fluid are high. Third, the upper-lower temperature difference is 110 ℃, and the compression strength of cement slurry at the top develops slowly. A low-density, high-strength tough cement slurry system for lost circulation was developed according to the close packing theory and the particle-size distribution technology. Its density is adjustable in the range of 1.15−1.35 g/cm³, its thickening time changes little and its stability is good with the compressive strength over 14 MPa under the condition of 80 ℃, 21 MPa and 48 h. Obviously, it can satisfy the requirements of field construction. In addition, the flushing micro-manganese weighted spacer compatible well with cement slurry and drilling fluid was developed. It can clean the faulty filter cake on the borehole wall so as to prevent the contact and contamination between cement slurry and drilling fluid. Combined with the supporting measures (e.g. the cementing technology of 1.88 g/cm³ high-density cement slurry), they were applied to the field cementing practice in Well ZG112. In the process, no circulation loss happened and the cement slurry returned in one trip. And the qualification rate and excellent rate of cementing quality are 91.2% and 70%, respectively. It is indicated that the cementing difficulties of long cementing section with low pressure, lost circulation and large temperature difference in ZG Block are solved effectively.