煤层气洗井中煤粉分散剂对煤岩的影响

Effect of pulverized coal dispersant on coal in the CBM well-washing technology

为了综合优选煤层气洗井液中煤粉分散剂,采用韩城矿区太原组11号煤及不同类型的阴离子分散剂,从分散剂对煤粉悬浮性、煤岩表面性质以及分散剂溶液进入煤储层的影响角度出发,开展了不同分散剂对煤粉分散稳定性、润湿性及分散剂进入煤岩中伤害的实验,探究了不同煤粉分散剂对煤岩的影响。研究结果表明,粒径<300μm的贫煤煤粉在水中分散稳定性差,添加分散剂有助于提高煤粉的分散稳定性。综合不同分散剂溶液的表面张力、溶液在煤表面的接触角、铺展系数和黏附功的分析,不同分散剂对煤粉润湿程度不同,质量浓度为2 g/L的SDS溶液对煤粉表面的润湿性最好。不同分散剂溶液进入煤岩样品,煤岩样品的渗透率均发生变化,且存在水锁效应,渗透率损害程度表现为SDS>CMN>SN。随毛细管力的增加,分散剂溶液对煤储层的渗透率损害程度增大。针对韩城区块,在煤层气洗井液中加入SDS分散剂可使煤粉更易排出,同时也会对煤岩渗透率产生一定的伤害。因此,在洗井过程中,应保持井底流压稳定,尽量避免分散剂溶液进入近井地带的煤储层中。

In order to screen synthetically the dispersants of pulverized coal in CBM well-washing technology, the ex- periments of the dispersion stability of pulverized coal, the wetting characteristics and the coal reservoir damage evalua- tion have been carried out by using the No. 11 coal of Taiyuan formation in Hancheng mining area and different anion- ic dispersants, based on the influences of dispersant solution on pulverized coal, coal surface properties and coal reser- voir. The effects of different dispersants on coal rock have been investigated. The results show that the pulverized coal with a particle size of less than 300 ~xm has a poor dispersion stability in water. Adding a dispersant can help to im- prove the dispersion stability of the pulverized coal. Combined the surface tension of the different dispersant solutions, the contact angle, spreading coefficient and the adhesion work, different pispersants have different wetting degrees to pulverized coal,the best one is the 2 g/L SDS solution. The coal permeability varies due to the invasion of dispersant solution and the effect of water lock of coal. The damage degree of permeability shows a relationship of SDS〉CMN〉 SN. And with the changes of capillary force, the permeability damage rate by the invasion of dispersant solution increa- ses. For the Hancheng block, the SDS dispersant can make the pulverized coal easier to disperse, and it can causesome damage to coal permeability. Therefore, in the well-washing process, the bottom-hole flowing pressure should be kept stable and the dispersant solution should be avoided entering into the coal reservoir in the near-well bore region.