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Performance analysis and optimization experiment of water-based drilling fluid for horizontal wells

2022-06-01

With the in-depth development of unconventional and tight oil and gas reservoirs, the advantages of horizontal wells have gradually been reflected and promoted. In the process of popularization and application of horizontal wells, there are also many supporting technological problems, such as drilling well trajectory control and completion tool optimization. leak-proof and high-efficiency drilling fluid test, etc. Drilling fluid plays an important role in the drilling process and is the best breakthrough to improve drilling efficiency. At present, common drilling fluids include oil-based drilling fluids, water-based drilling fluids and soilless drilling fluids. Oil-based drilling fluids Due to the high cost and the risk of environmental pollution, the actual use of water-based drilling fluid is less. Water-based drilling fluid is still the type of drilling fluid commonly used in drilling sites. In the process of horizontal well drilling, drilling fluid can effectively control friction. , Reducing the occurrence of leakage and improving wellbore stability are the main considerations in drilling fluid optimization and research and development. Drilling fluid performance analysis includes the analysis of drilling fluid density, dynamic shear force, static shear force and plastic viscosity, mud cake, fluid loss In this paper, the application of water-based drilling fluid in the second-opening completion is generally used in the middle and shallow low permeability reservoirs in the Ordos Basin. , to provide guarantee for efficient drilling of horizontal wells in low-permeability reservoirs.

 

 

1 Optimization of drilling fluid system formulation

 

1.1- Drilling fluid optimization

 

The formula of a 8-3/4" drilling fluid system is as follows:

 

(1) Upper vertical well section: 3%~5% bentonite slurry + 0.2% NaOH + 0.1% Na, CO, + 1-1.5% CMC-LV + 1% COP-HFL (polymer fluid loss additive) + 3% Sulfonated asphalt.

 

(2) After entering the deflection section, on the basis of the upper vertical well section: + 2% non-fluorescent solid lubricant ((graphite) + 0.2~0.5% K-PAM + 2-3% NH, -HPAN or K-HPAN + recrystallization Stone weighted to 1.20.

 

According to the above formula, the on-site drilling fluid material orientation is analyzed, and the compound experiment is said. After the formula is prepared, it is found that the viscosity is large and the formula is changed as follows:

 

3% ordinary soil slurry + 0.1% caustic soda + 0.2% soda ash + 0.8% K-HPAN + 0.5% LV-CMC + 0.3% K-PAM + barite increased to 1.18.

 

Glue formula: fresh water + 0.2% caustic soda + 0.5% K-PAM + 1% K-HPAN.

 

The performance of the modified drilling fluid system after laboratory analysis is shown in Table 1, and the performance of the modified drilling fluid system can meet the field construction requirements.

 

1.2 Optimization of drilling fluid for the second opening

 

The formula of drilling fluid system in Erkai 6" well section is as follows: 1 part of 8-3/4" formula + 2 parts of glue + calcium carbonate weighted to 1.08, the performance is shown in Table 2.

 

Since the viscosity of this system is not enough, 0.5% cmC-LV was added on this basis, and the 6" formula was determined as: 1 part of 8-3/4" formula + 2 parts of glue + 0.5% CMC-LV + calcium carbonate increased to 1.08. Experiment For analytical performance see.

 

 

After optimization, the basic performance of the system meets the field operation performance, the mud cake is thin and tough, and the mud cake has good sealing performance.

 

2. Performance evaluation of drilling fluid after optimization

 

2.1 Evaluation of plugging performance

 

On the basis of the determined basic formula, a plugging agent is added to evaluate the plugging performance of each drilling fluid system. The formula is adjusted as follows:

 

(1) First drilling fluid: 3% ordinary soil slurry + 0.1% caustic soda + 0.2% soda ash + 0.8% K-HPAN + 0.5% LV-CMC + 0.3% K-PAM + 3% 200-400 mesh calcium carbonate + heavy Hedron increased to 1.18. (2) Second-stage drilling fluid: 1 part of 8-inch 6 formula + 2 parts of glue + 0.5% CMC-LV + 3% 200-400 mesh calcium carbonate + calcium carbonate increased to 1.08. (The formula of glue solution is: fresh water + 0.2% caustic soda + 0.5% K-PAM + 1% K-HPAN).

 

The experimental evaluation results of the plugging performance are shown in Figure 2 (the sand disc is a 400 MD sand disc, and the temperature is 60 °C). Generally speaking, the sand disc filtration loss is not large, and it reflects that the plugging effect is good.

 

2.2 Lubrication performance evaluation

 

The EP-B extreme pressure lubricator was used to investigate the lubrication performance of the first- and second-boiler water-based drilling fluid systems. The results are shown in Table 4. The results of the lubrication test show that the extreme pressure lubrication coefficients are large and the lubrication performance is average. Therefore, the amount of lubricant can be increased, or a lubricant with better lubricating effect can be used.

 

2.3 Inhibitory evaluation

 

The reservoir cores were pulverized and ground, passed through 100 mesh, and then dried in an oven at 105 °C for 4 h. The hydration expansion performance of the reservoir rock samples was tested by the new intelligent expansion of JHTP. The results are shown in Fig. 3. The content of swelling clay minerals in the core is less, and the hydration swelling inhibition effect is better.

 

 

3 Conclusion

 

In summary, the drilling fluid system of 8-3/4" drilling fluid for the first opening and the 6" drilling fluid system for the second opening are optimized, and the performance of the optimized drilling fluid is analyzed, which improves the plugging performance and lubricity of the drilling fluid. Provide favorable guarantee for the drilling of horizontal wells with long horizontal sections.