Optimization of foam drilling fluid for broken and soft coal seam drilling based on response surface methodology

Abstract:

To address the technical challenges of severe dust hazards， difficulties in coal fines transport， and insufficient anti-contamination and compressive resistance of existing foam drilling fluid systems during air screw drilling in broken-soft coal seams， a foam drilling fluid system suitable for this working condition was developed. Through performance screening， the foaming agent DF-1， foam stabilizer MZ-1， anti-contamination agent MPS， and compression-resistant agent HS plant gum were identified as the core components. Single-factor experiments yielded the preliminary optimal concentrations of these components as 0.9%， 0.3%， 0.4%， and 0.3%， respectively. Subsequently， a four-factor， three-level Box-Behnken experimental model was constructed based on response surface methodology （RSM） to investigate the interactive effects of the components on foam volume and half-life， and formulation optimization was performed considering the circulation time requirements of field drilling. The results indicate that the significance order of factors affecting foam volume is MZ-1>HS plant gum>MPS>DF-1， and that affecting half-life is MZ-1>MPS>HS plant gum>DF-1. Considering the foam circulation requirements of field drilling， the optimal formulation achieving a target half-life of 40 min is determined as 1.1% DF-1+0.1% MZ-1+0.5% MPS+0.3% HS plant gum. Validation experiments demonstrate that this formulation produces a foam volume of 510 mL and a half-life of 46 min， with significantly improved anti-contamination and compressive resistance， FCI reduction rate of 28.91% and compression ratio of 73.33%， effectively meeting the requirements for safe and efficient drilling in broken-soft coal seams. This study confirms that RSM can synergistically optimize multi-component foam systems， and the developed formulation exhibits excellent foaming， foam stability， anti-contamination， and compressive resistance properties， providing technical support for safe and efficient drilling in broken-soft coal seams.