Polyanionic cellulose (PAC) and sodium carboxymethyl cellulose (CMC) have different application environments in oil drilling, as follows:
1. Polyanionic Cellulose (PAC):
1.1 Brine Wells and Offshore Oil Drilling: PAC has low salt sensitivity and strong resistance to salt, calcium, and magnesium. It can be used as a rheology modifier and filtrate reducer in brine drilling fluids, seawater drilling fluids, and saturated brine drilling fluids. It can quickly adjust the rheology of drilling fluids under low dosage conditions, carry away drill cuttings, maintain a low solids content, and form a dense mud cake, reducing the damage of filtrate to oil and gas reservoirs.
1.2 Calcium-Treated Drilling Fluid Environments: Calcium-treated drilling fluids prepared with PAC have good calcium resistance, preventing excessive flocculation of clay particles in the system caused by calcium ions, and maintaining stable solids content and rheological properties of the drilling fluid.
1.3 Wells with Complex Geological Conditions: PAC-formulated drilling fluids exhibit excellent fluid loss reduction, inhibition, and high temperature resistance. They can be used in mud systems where solid content is difficult to control and varies widely, making them suitable for complex formations such as salt-gypsum layers and high-temperature environments, as well as challenging drilling conditions in marine and desert environments.
Fracturing Operations: PAC-formulated fracturing fluids can withstand 2% KCl solution, exhibiting good solubility, requiring only small addition amounts, and producing no residue. They effectively reduce fracturing fluid loss and possess good salt and temperature resistance, resulting in superior fracturing performance in low-permeability formations.
2. Sodium Carboxymethyl Cellulose (CMC):
2.1 Collapsible Shale Formations or Low-Pressure Leaky Formations: CMC forms a dense colloidal filter cake on the wellbore surface, effectively preventing water and solid particles from the drilling fluid from leaching into the formation, thus protecting wellbore stability. It is particularly suitable for easily collapsible shale formations or low-pressure leaky formations.
2.2 Shallow and Medium-Depth Wells: High-substitution CMC exhibits excellent chemical stability in low-to-medium temperature (≤120℃) well sections, is not prone to thermal degradation, and can maintain its filtration loss reduction effect for a long time, making it a commonly used additive in drilling fluids for shallow and medium-deep wells.
2.3 High-Angle or Horizontal Wells: The three-dimensional network structure formed by CMC molecular chains and clay particles can maintain the suspension of the system in a static state. In high-angle or horizontal wells, it can prevent cuttings from accumulating at the bottom edge of the wellbore, ensuring wellbore cleanliness.
2.4 Areas with Strict Environmental Requirements: Low-toxicity, biodegradable CMC is suitable for areas with strict environmental requirements, such as onshore oilfields and offshore drilling, and is compatible with water-based environmentally friendly drilling fluid systems, reducing pollution to the formation and the environment.
