三交地区煤层气井钻井液技术

三交地区煤气层属低压储层，压力系数为0.5-1.0，钻井过程中极易受到损害，机构强度低，孔隙发育，层理发育，煤岩易压缩，煤层破碎，易城塌，煤液呈酸性，要求钻井液的pH值不大于7.5，否则酸碱中和产生金属盐，堵塞煤层气通道，影响煤层气的开发，针对煤层特点，采用相应的钻井液体系和钻井液技术，即：上部地层采用低固相聚合物钻井液，下部煤气层采用充气钻井液，现场应用表明，充气钻井液防漏效果显著，具有良好的携屑能力及防塌效果，井眼稳定；砂样有代表性，井径规则（井径扩大率为3.2%)，取心，测井顺利；充气钻井液无固相，密度低，提高了钻井速度，保证了平衡钻进，减少了滤液和固相进入储层的机会，有效地保护了煤层气。

Drilling fluid technology for coal bed methane drilling in Sanjiao area, Shanxi

Low pressured coal bed gas reservoirs exist in Sanjiao area of Shanxi province, with the pressure coefficient of only 0. 5-1. 0. As the mechanical strength of the coal bed is low, so it is likely to get broken and collapsed and causes hole sloughing. Pores and fractures, as well as stratifications are very developed in the coal bed, and this can cause hole collapse, lost circulation and furthermore, plugging of the pores in formation. Moreover, as the coal bed formation fluid is sour, thus the pH value of the drilling fluid used must be lower than 7.5, otherwise metal salt will be produced from the neutralization of acid and alkali, and further plugs the communication path of the gas. Suitable drilling fluid systems and technologies were applied in accordance with these characteristics of the coal bed formation. Specifically, low solids polymer drilling fluid was used in the upper formation, and aerated mud was used in the lower coal bed formation. Field using showed that the aerated drilling fluid can effectively prevent lost circulation and hole collapsing from taking place, and it has good cuttings transportation capability. Regular borehole (hole enlargement of 3. 2%) and stable hole condition were achieved, and such operations as coring and logging were smoothly carried out without any trouble, and the cutting samples were very representative. At the same time, as the aerated mud has no solids and low weight, it can improve the penetration rate and realize balanced drilling, thus minimize the chances of filtrate entering into the reservoir, and the risk of formation damage.