Here are the differences in the application of low - viscosity polyanionic cellulose (PAC - LV) with different purities in drilling.
The purity of PAC - LV has a significant impact on its performance and application effects in the drilling process:
I. Differences in Drilling Fluid Performance
1. Filtration Control Effect
High - purity PAC - LV: It contains a high proportion of active ingredients (cellulose derivatives) with intact molecular chain structures. This enables it to more effectively adsorb onto the surface of clay particles, forming a tight filter cake and reducing the filtration loss of drilling fluids (the lower the filtration loss, the better the protection for the formation). For example, in high - temperature (such as above 120°C) or high - salinity environments, high - purity products can still maintain stable filtration control capabilities. Low - purity PAC - LV: It may contain more unreacted cellulose raw materials, salt impurities, or by - products, and the molecular chains are prone to breaking, resulting in poor filtration control effects. Especially in complex formations (such as easily collapsible shale formations), the filtration loss may significantly increase, leading to unstable wellbore conditions.
2. Rheological Control
High - purity PAC - LV: It has a more precise influence on the viscosity and shear force of drilling fluids. The low - viscosity type (PAC - LV) itself has limited thickening effect, but high - purity products can moderately increase the dynamic shear force of drilling fluids by optimizing the dispersion of clay particles, improving the ability to suspend cuttings, while avoiding excessive viscosity increase. Low - purity PAC - LV: Impurities may interfere with the interaction between clay particles, leading to unstable rheological properties. For instance, inorganic salt impurities may cause abnormal decreases or increases in the viscosity of drilling fluids, affecting pump pressure and cuttings - carrying efficiency, and even triggering downhole complex situations (such as sand settling and pipe sticking).
3. Contamination Resistance
High - purity PAC - LV: It has a stable chemical structure and stronger resistance to calcium, magnesium ions, and organic matter contamination. When drilling through gypsum layers or oil - gas layers, it can maintain the stability of drilling fluid performance and reduce the repeated addition of treatment agents. Low - purity PAC - LV: Metal ions (such as Na⁺, Ca²⁺) in the impurities may react with other treatment agents in the drilling fluid (such as polyacrylate), weakening the overall contamination resistance and causing the deterioration of drilling fluid performance (such as flocculation and delamination).
II. Construction Efficiency and Cost
1. Dosage and Maintenance CostsHigh - purity PAC - LV: With a high content of active ingredients, to achieve the same filtration control effect, its dosage is usually 30% - 50% less than that of low - purity products, reducing material costs. At the same time, due to its stable performance, the maintenance frequency of drilling fluids is low, saving labor and equipment energy consumption. Low - purity PAC - LV: It needs to increase the dosage to achieve the desired effect, and frequent formula adjustments (such as adding filtration control agents or diluents) may be required due to performance fluctuations, leading to cost increases.
2. Downhole RisksHigh - purity PAC - LV: It forms a filter cake with good quality (thin and tough), and the stable rheological properties of drilling fluids can reduce the risks of wellbore collapse and differential pressure sticking, especially suitable for the construction of highly deviated wells or horizontal wells. Low - purity PAC - LV: The filter cake is thick and loose, prone to causing sticking during tripping; unstable rheological properties may lead to excessive surge pressure, increasing the risk of lost circulation and extending non - productive time (NPT).
III. Environmental Protection and ComplianceImpurities and Environmental Requirements
High - purity PAC - LV: It has a more refined production process and low impurity content (such as heavy metals and residual solvents), meeting the standards of environmental drilling fluids (such as API Spec 13A and ISO 13503 - 2), and is suitable for environmentally sensitive areas (such as water source areas and offshore drilling). Low - purity PAC - LV: It may contain excessive harmful impurities, facing compliance risks in areas with strict environmental regulations, and even leading to the suspension of construction.
IV. Recommended Application Scenarios
High purity: Recommended for deep wells, high - temperature wells, high - salt/calcium formations, and operations with high environmental requirements. The typical indicators (for reference) are purity ≥95% and filtration loss ≤15mL (API standard).Low purity: Recommended for shallow wells, simple formations, and cost - sensitive projects. The typical indicators (for reference) are purity 70% - 85% and filtration loss 18 - 25mL (API standard).Conclusion: In drilling engineering, high - purity low - viscosity polyanionic cellulose is more suitable for complex geological conditions and operations with high environmental requirements due to its stable performance, efficient filtration control capabilities, and contamination resistance. Although low - purity products have lower costs, their performance defects may increase construction risks and comprehensive costs. When selecting, it is necessary to comprehensively evaluate based on formation characteristics, well depth, environmental standards, and budget, and give priority to high - purity products to ensure drilling safety and efficiency.
