Sodium carboxymethyl cellulose (CMC) plays a key role in completion fluids: thickening, reducing fluid loss, and stabilizing the wellbore. It also protects the reservoir, making it a crucial water-soluble polymer treatment agent in completion fluids.
Its specific functions can be categorized into the following four areas, all centered around the core requirements of completion fluids: ensuring wellbore safety and minimizing reservoir damage:
1. Thickening and Sand Carrying: CMC significantly increases the viscosity and shear force of the completion fluid, enhancing the fluid's ability to carry cuttings and solids, preventing cuttings from settling and clogging the wellbore or causing sticking, thereby ensuring smooth completion operations.
2. Fluid Loss Reduction and Filter Cake Formation: CMC molecules adsorb onto the pore surfaces of the wellbore rock, forming a thin, dense filter cake. This effectively reduces fluid loss into the reservoir, minimizing damage such as swelling of water-sensitive clays and clogging of reservoir pores. 3. Wellbore Stabilization: It maintains pressure balance in the fluid column within the wellbore through thickening. Its adsorption properties also coat clay particles in the wellbore wall, inhibiting clay hydration, expansion, and dispersion, preventing wellbore collapse and ensuring wellbore stability.
4. Reservoir Protection: High-quality CMC (such as low-viscosity, high-substitution types) is highly biodegradable, and the filter cake it forms is easily broken down and flowed back by subsequent operating fluids (such as fracturing fluids and flowback fluids). This minimizes damage to reservoir permeability and maximizes oil and gas production capacity.
