1.3 design principles of low density cement slurry system

According to the close packing theory of particle gradation, the strength and other properties of low-density cement slurry can be greatly improved by optimizing the particle size distribution in low-density mixture and improving the compactness of cement slurry system. Therefore, attention should be paid to the following issues:

1) Good stability: under certain conditions, the cement paste does not separate into layers, and the vertical density distribution of cement paste is basically consistent, with less free liquid and small volume shrinkage.

2) Suitable rheological property and density: the type and grade particle size of the lightening agent should be selected, and the water consumption should not be increased blindly. The water consumption should be strictly controlled within the maximum allowable range of the selected lightening agent.

3) Higher early strength: the rheological properties and filtration control of cement slurry should not be blindly pursued, which will damage the compressive strength and stability of cement slurry. Low density materials with different particle sizes should be selected for tight packing wells with additives to improve the early strength.

1.4 deep water surface cement slurry system and performance evaluation

According to the actual well condition requirements of LW, combined with the development of a new type of deep-water low-temperature admixture, a new type of ZOC-LET^TM LT deep-water low-temperature low-density cement slurry system is used

Jiahua grade G cement, artificial micro bead ZOC-P62S, reinforcing agent ZOC-BT1, deep water cementing accelerator ZOC-DA92S, ZOC-DA93L, fluid loss additive ZOC-DG72S, defoamer ZOC-X60L, dispersant ZOC-F44L, anti channeling enhancer ZOC-GS12L, field drilling water. A lot of formula optimization experiments have been done in the laboratory, and the cement slurry formula for 20 "casing cementing is obtained, and the performance of the cement slurry is evaluated in detail.

2. Field application

LW is located about 260km southeast of Hong Kong. Liuhua 28-4 structure is located in zhuii depression, southern depression of Pearl River Mouth Basin, and northern slope of dongwa in Baiyun sag. A large amount of oil and gas resources were discovered in py-lh reservoir forming area of Panyu Low Uplift in 2011. It is proved that the oil and gas accumulation conditions in this area are very favorable. At the same time, it also reveals the great potential of oil and gas exploration in Baiyun sag Sandstone in the lower part of Zhujiang Formation (2996.0m-3096.0m) and T62 sandstone (3554.0m-3616.0m) of Zhuhai Formation. The water depth is 561 M. three spud operations are carried out: 36 "pipe is put into the first spud; 26" hole is opened in the second for 20 "cementing operation; 17-1 / 4" hole is opened for 13-3 / 8 ", and no cementing operation is conducted for the fourth spud.

Field construction of 20 "casing:

The formation fracture pressure of 20 "shallow casing cementing is low, and there is a risk of cementing loss: the formation is soft, and the additional amount is difficult to determine. According to the existing difficulties, after the casing runs to the designed well depth, the flow rate starts to circulate with 30spm displacement, and gradually increases the displacement to 130 SPM after returning to normal; After circulating seawater for 2 weeks, the display fluid of cementing pump is l0bbl, and the flushing fluid is 60bbl. The cement slurry with mixed pump density of 1.35s. G needs 489 BBL of mixed water and 98T of floating bead cement; 571 BBL of cement slurry with 1.43S.G of mixed pump density is 269 BBL. 86T of floating bead cement; 92.53 BBL of seawater was replaced by cementing pump. No backflow was found during pressure relief inspection.

The waiting time is 10 hours (continuous operation on site, dropping drill pipe and running BOP). The position of probe plug is 1078.5m and the pressure is 20 klbs to confirm. Cobalt casing accessories and cement plug to 1100m, casing pressure test 300PSI / 5min, 1500psi / 15min, qualified 1100m, in line with the design. No cement block was found during the third spud drilling.

3. Conclusion

3.1 the artificial glass bead lightening agent developed by the oilfield business unit is more suitable for deep water and ultra deep water surface cementing operations than natural floating beads.

3.2 the oilfield chemical division independently developed the deep-water low-temperature surface cementing low-density cement slurry system with good comprehensive performance and stable system, which has been well applied in the South China Sea LW field.