Research And Application Of Coalbed Methane Microbubble Drilling Fluid In Baode Block

Baode coal seam gas field is located in northern part of flex belt in west shanxi,the eastern edge of the Ordos Basin,where coal seam gas resources are rich.With the deepening of block exploration and development,Baode block mainly uses polymer drilling fluid system,the probability of drilling fluid leakage occurred in the drilling process is 15.38%,after drilling into thecoal seam horizontal wells generally leakage.The main leakage layer is Shanxi Group 4 plus5 coal seam,Taiyuan Group 8 plus 9 coal seam,the average single well leakage time is 105 h.The type of leakage is generally a loss-type leakage,the main solution is blocking the mud leakage or top leakage drilling.The failure to plug the leak of part of the well even leads to the project scrapping.The well leakage problem of coal seam section gradually becomes a bottleneck affecting the drilling project,so the study of a microbug drilling fluid system applicable to the Baode block coal seam gas drilling project is of great significance.In this paper,according to the actual situation of the coal seam geology of Baode block,combined with the technical difficulties of drilling engineering,the research direction of coal seam bubble drilling fluid is determined.Based on the polymer drilling fluid system,the addition optimization of adhesives,foaming agents,foam stabilizers and inhibitors was carried out,and a formula for adjustable micro-foam drilling fluid system with a density of 1.05-1.09g·cm^-3 was developed.Through relevant experimental methods,the static leak-proofing ability,dynamic leak-proofing ability,strat layer matching and reservoir protection performance are evaluated.The field configuration method and maintenance process of micro-bubble drilling fluid are studied,and the control measures and aggravating ability of gas intrusion are studied.The results show that the micro-bubble drilling fluid can effectively block the leakage channel and enhance the pressure-bearing capacity of the formation,prevent leakage and plug the leak well by relying on the"filling"and"stacking"of micro-bubbles.The NTU value of the micro-bubble drilling fluid mixed with the coal seam formation water is less than the NTU value of the stratum water in the coal seam of the original Baode block,and the mixture of micro-bubble drilling fluid and the coal seam formation water is good with the formation water.The recovery value of coal heart permeability after micro-bubble drilling fluid pollution is greater than 85%,which means the damage to coal reservoir is small.The configuration method and maintenance process are simple,convenient and efficient,and the density of drilling fluid can be adjusted widely using aggravating materials to meet the well control requirements of coal seam gas drilling without affecting the pulse signal transmission of directional instruments,and the engineering performance is good.The on-site test shows that the micro-bubble drilling fluid can be reused,the cumulative leakage of the test well drops by 22.82%,verifiesthe correctness of the low density anti-collapse control leakage theory of micro-bubble drilling fluid,solves the technical problems of coal seam leakage prevention,leak-blocking and anti-collapse in the coal seam gas drilling process,and the field application effect is good.