Cementing operation is the last process in the process of drilling and completion, and its effect directly affects the life of oil and gas wells and the mining output of oil and gas resources. In recent years, with the continuous exploitation of resources, the phenomenon of gas channeling has become more prominent during the cementing process. A study was conducted on the performance system of cement slurry to address the gas channeling problem in the cementing process of Block D. The research on cementing operations in this block has certain effectiveness and promotion value.

Introduction

After cementing in oil and gas wells, when there is an imbalance between the liquid column pressure in the annular space and the pressure of the formation fluid, it can cause the fluid in the formation to enter the annular space, resulting in longitudinal flow. In cementing operations, gas channeling is generally divided into two types: initial gas channeling and secondary gas channeling. The initial gas breakthrough refers to the phenomenon of gas breakthrough that occurs during or shortly after cementing operations. The phenomenon of annular air channeling is an important factor affecting the quality of cementing. After annular air channeling occurs, it can cause gaps between the formation, cement slurry, and casing, resulting in oil and gas leakage from the wellhead, affecting the normal production of oil and gas wells, and even leading to the scrapping of oil and gas wells.

Block D encountered abnormal gas invasion when drilling to 5967 meters, and a total of 8 gas layers were encountered when drilling to 6777 meters. Based on the situation in Block D, for cementing the tail pipe of the gas reservoir, it is considered to use an anti gas channeling cement slurry system for sealing in Block D. In order to ensure the cementing effect of Block D, it is necessary to select the corresponding anti channeling latex cement slurry system for the formation of Block D.

1.Research on the Anti Gas Channeling Cement Slurry System

1.1 The Effect of Latex Dosage on the Conventional Properties of Cement Slurry

Latex cement slurry is the cement slurry system with the best anti channeling effect, therefore, research mainly focuses on latex cement slurry. Indoor, combined with the actual cementing design of Block D, MX pore support agent is added to the latex cement slurry system to achieve better anti channeling effect. Adding butadiene styrene latex to cement slurry can improve the resistance to gas channeling and corrosion of the cement sheath, ensuring the quality of cementing. Through indoor research, the results of the influence of different ratios of latex content on the performance of cement slurry system are shown in Table 1, and the effect of latex dosage on the mechanical properties of cement paste is shown in Table 2.

Formula: G-grade cement + 35% silicon powder + fresh water + 2.5% CJ56L latex stabilizer + 6% CG88L fluid loss agent + 3% CF44L dispersant + 3% MX + 1.33% H63L retarder + 1% CX66L defoamer + latex (0%~20%).

From the evaluation results, it can be seen that the system composed of impure latex has good strength and rheological properties. However, indoor experiments have shown that in the case of pure latex, the cement slurry will produce a certain amount of free liquid. Therefore, in future experiments, a certain amount of CG88L fluid loss agent should be added to the cement slurry formula. On the one hand, this is to better protect the adhesive and inhibit the production of free liquid, and on the other hand, it can further reduce the water loss of the cement slurry and improve its performance.

1.2 Cement Slurry Lotion Stabilizer

The latex stabilizer used in cement slurry is one of the key technologies of latex cement slurry. Based on the emulsification stability mechanism, the widely used CJ56L latex stabilizer was evaluated indoors. The effect of CJ56L dosage on the performance of cement slurry system is shown in Table 3.

Formula: G-grade cement + 35% silicon powder (300 mesh) + 38% fresh water + 1% CX601L defoamer + 2.5% CF44 dispersant + 33% CG88L fluid loss agent + 1.33% retarder + 3% MXMX + (0-3)% CJ56L latex stabilizer + 10% latex.

From the evaluation results of latex stabilizers, it can be seen that latex stabilizers can effectively reduce the filtration loss of latex systems and improve the rheological properties of cement slurries; At the same time, the addition of latex stabilizers will prolong the thickening time of latex cement slurry, so in actual on-site use, it is necessary to evaluate and determine based on the on-site situation.

1.3 Polymer Fluid Loss Agent for Cement Slurry

The indoor polymerization process was adopted, and after extensive synthesis screening and evaluation, the AMPS polymer CG88L with no thickening reversal characteristics was selected as the fluid loss reducer for the anti gas channeling latex cement slurry system. The dosage of CG88L and the properties of cement slurry are shown in Table 4.

Formula: G-grade cement + 35% silicon powder + 38% fresh water + 2.5% CJ56L latex stabilizer + 10% CGR66L latex + 4% CF44L dispersant + 3% MX + 1.33% H63L retarder + 1% CX66L defoamer + CG88L fluid loss agent (test temperature at 80℃).

The experimental results clearly show the relationship between the dosage of CG88L and the API water loss of cement slurry: with the increase of CG88L dosage, the filtration performance is improved. Research has found that after the concentration of CG88L reaches 5%, the improvement in filtration efficiency gradually tends to be gradual; In general, selecting a dosage of about 5% to 8% can simultaneously balance the filtration performance and the rheological properties of the system. At the same time, it can be seen from the experimental results that the filtration and rheological properties are good when the dosage of CG88L is between 5% and 8% (Table 5).

According to Table 5, the filtration and rheological properties of CG88L in cement slurry are good when the dosage is 7%. As the temperature increases, the filtration loss slightly increases. The cement slurry system prepared with CG88L has a high viscosity, especially the apparent viscosity, but still has good flowability. Compared with PVA modified products, it has better displacement efficiency.

2.Conclusion

In view of the gas channeling problem in the cementing process of Block D, the conventional performance impact test of cement slurry, the stability of cement slurry lotion and the fluid loss agent test of cement slurry polymer were carried out indoors for the gas channeling prevention system, and the cementing slurry system suitable for this block was finally determined as Grade G cement+35% silica powder+38% fresh water+2.5% CJ56L latex stabilizer+10% CGR66L latex+4% CF44L dispersant+3% MX+1.33% H63L retarder+1% CX66L defoamer+7% CG88L fluid loss agent.

The latex stabilizers produced and sold by our company have undergone laboratory tests and years of on-site feedback on their good performance and effectiveness. Please feel free to inquire.