Experimental Study On The Preparation Of CO₂ Foam Fracturing Fluid And Its Anti-reflection Performance

As an associated mineral of coal,coalbed methane is rich in geological resources.With the proposal of the concept of"carbon peaking and carbon neutrality",the role and significance of carbon dioxide sequestration has become more apparent.At the same time,coal is the main energy source in my country,and the safety of its production process is particularly important.As an associated organism of coal,gas is the main factor causing gas explosion,gas suffocation and gas outburst accidents.How to reduce mine gas concentration and ensure the safety of mines and personnel is very important.Carbon dioxide foam fracturing flooding CBM technology is currently the main technical means of CBM exploitation.It can not only drive away CBM efficiently,reduce gas hazards and increase CBM production,but also can store CO₂ in the formation to reduce carbon emissions.However,this technology is mainly used in oil exploration and production stimulation activities,and is rarely used in coalbed methane mining technology,and the CO₂ foam fracturing fluid system has not yet matured in coalbed methane mining and utilization.By analyzing the geological occurrence environment of coalbed methane,this paper explores the effect of p H and metal ions on foam fracturing fluid,and develops a CO₂ foam fracturing fluid system that is suitable for the occurrence environment of coalbed methane.Anti-reflection properties of fissures.The main research contents and results are as follows:（1）Exploration of Coalbed Methane Occurrence environment.The experiment takes Heidaigou（HDG）long flame coal in Jungar banner,chengdi（ZCD）coking coal in Gujiao Town,Sihe（SH）anthracite in Qinshui county and Kaiyuan（KY）anthracite in Shouyang County as the research objects.Firstly,the p H of the soaking solution of the coal samples is analyzed.The test results of the soaking solution of the four coal samples are weakly alkaline.At the same time,the content of Mg²⁺in HDG long flame coal was the highest among the four coal samples,reaching 11.9 mg/L;Zgd coking coal has the highest Na⁺content,which is 57.8 mg/L;The Ca²⁺content of SH anthracite is the highest among the four coal samples,reaching 40.7 mg/L.Three kinds of metal ions exist in coal and occupy a certain proportion.（2）Study on the effect of p H on foaming agent.Through the experimental research and analysis of acid and alkalinity resistance of foaming agent,the p H has different effects on 4types of 8 surfactants.With the increase of p H,the foam quality and foam half-life of anionic surfactants A and B are increasing.The foam quality and foam half-life of the remaining 6surfactants decreased.The foam stability of anionic surfactants is good under weak alkali conditions,and the stability of other types of surfactants decreases with the increase of p H.（3）Effect of metal ions on foaming agent.Through the experimental research and analysis of metal ion resistance of foaming agents,the foam stability of 8 surfactants in three metal ions(Na⁺,Mg²⁺,Ca²⁺)foaming base solutions with different concentrations has different change trends.It can be found that metal ions promote the foam quality and foam half-life of anionic surfactants,thereby enhancing the stability of the foam.The other three types of 6 surfactants,under the action of metal ions,reduce the stability of foam to varying degrees.At the same time,molecular dynamics simulation was used to study the diffusion characteristics of water molecules and the hydration of metal ions in the foam wall formed by anionic surfactant SDS in different metal ions.The influence of metal ions on the stability of foam was demonstrated from the microscopic perspective.（4）Optimization and configuration of CO₂ foam fracturing fluid.Through the analysis of influencing factors,the foaming base solution was configured.Based on the configured foaming base solution,the stability of eight surfactants in the unitary state was studied.At the same time,based on the unitary investigation results of eight surfactants,seven of them were optimized for binary compounding.It was found that when the anionic surfactant B was mixed with zwitterionic surfactant E at 1:4 ratio,the overall effect was the best.The foam quality reached83.25%,and the half-life of the foam reached 322 s,all of which were the maximum value in the compound test.At the same time,according to the experimental results before the laboratory,adding twelve alkyl three methyl ammonium bromide 150 mg/L（reversing agent）and 0.48%guar gum（stabilizer）will eventually form the best CO₂ foam fracturing fluid mixture.（5）BET specific surface area analysis.Using the BET-specific surface area analyzer,it can be clearly seen that the corresponding fractal dimension D of the four kinds of coal samples after CO₂ foam fracturing fluid treatment showed a significant downward trend,which means that the pore structure of the coal samples after CO₂foam fracturing fluid has a tendency to change from complex to simple.The treatment of CO₂ foam fracturing fluid reduces the proportion of pores and pores in coal samples,and decreases the fractal dimension,which is more conducive to the desorption of coalbed methane.At the same time,the specific surface area of coal after CO₂ foam fracturing fluid treatment is significantly reduced,which means that the area of coalbed methane adsorption decreases,thus promoting the extraction capacity of coal-bed methane.（6）Fourier infrared analysis.The peak area of each sample was obtained by fitting the peak of the absorptive stretching vibration region(3700-3100 cm^-1)of the coal sample after the treatment of four kinds of coal samples and CO₂ foam fracturing fluid.With the increase of metamorphic degree,the area of hydroxyl vibration absorption peak in raw coal shows a downward trend.Therefore,it can be inferred that the number of hydroxyl functional groups in coal:HDG long flame coal>ZGD coking coal>SH anthracite≥KY anthracite.The hydroxyl peak area of coal samples treated by CO₂ foam fracturing fluid decreased to varying degrees.This shows that after CO₂ foam fracturing fluid enters the coal body,it is combined with the hydroxyl in the coal and adsorbed in the coal body,thus promoting the analysis of the gas and inhibiting the oxidation of the coal body.Therefore,the in-depth study of the adaptability of CO₂ foam fracturing fluid and the occurrence conditions of coalbed methane has practical significance for coalbed methane mining engineering,and has certain reference value for the application of CO₂ foam fracturing technology.Further optimization of foam fracturing fluid provides a theoretical basis.