Solid-Free Brine Drilling Fluid Additive for Coal-Bed Gas Wells

The patent introduces a specially formulated drilling fluid composition containing organic salts (ammonium chloride, ammonium bromide, zinc bromide) as intermediary substances that mediate between the need for high penetration rate and low residue rate. These organic salt-based additives modify the drilling fluid's interaction with the coal-bed gas reservoir, enabling efficient penetration while minimizing harmful residue through their unique solubility and compatibility characteristics.

The patent changes the chemical composition parameters of the drilling fluid by replacing traditional inorganic salts with organic salts (ammonium chloride, ammonium bromide, zinc bromide) and adjusting concentration ratios. This parameter change transforms the drilling fluid's properties to achieve both high penetration rate and low residue rate, as organic salts provide better solubility and less formation damage compared to conventional brines.

The patent extracts and removes solid particles (bentonite, barite) from the drilling fluid composition, creating a solid-free brine system. This extraction eliminates the clogging of seepage fractures and channels in coal-bed gas reservoirs, thereby improving penetration rate while maintaining reservoir protection through the use of carefully controlled brine chemistry and organic salt additives.

The patent utilizes the porous structure of the coal-bed gas reservoir by employing a solid-free drilling fluid that can flow through tight pore spaces and fractures without blockage. The absence of solid particles allows the drilling fluid to penetrate through the porous media effectively, while the organic salt composition prevents formation damage by maintaining appropriate osmotic pressure and chemical compatibility.

The patent adopts a simpler, more disposable-like approach by using a straightforward solid-free brine composition with organic salts that can be easily prepared and pumped without complex foam generation equipment. The drilling fluid serves its purpose effectively during the drilling operation and can be easily displaced or abandoned, reducing the need for complex foam maintenance and handling infrastructure.

The patent employs a hydraulic-based solid-free brine system that relies on fluid pressure and flow dynamics rather than foam aerodynamics. This hydraulic approach simplifies the equipment requirements compared to foam drilling, as it uses standard drilling pumps and fluid handling systems, making the technique more widely adoptable while still achieving good gas output through effective wellbore cleaning and reservoir penetration.