煤层气井造穴射流破岩试验研究

Experimental Study on Rock Breaking by Water Jet for Cavity Building in Coal Bed Methane Well

通过水射流造穴进行洞穴完井是煤层气井重要的完井方式。为了优选造穴射流工具的喷嘴,提高射流造穴直径和效率,通过制备相似煤岩试样,采用室内试验的方法,进行了连续射流和空化射流的破岩效果试验,并在现场造穴施工中进行了应用。结果表明:自由射流条件下,连续射流在喷距为200 mm时破岩效果最好,空化射流在喷距为300 mm时破岩效果最好。淹没射流条件下,连续射流未能冲蚀煤岩试样;空化射流的冲蚀直径则呈先增加后减小并趋于稳定的状态,在淹没深度为200 mm时冲蚀直径达到最大,冲蚀深度随着淹没深度的增加而增加,在淹没深度为300 mm以后,冲蚀深度趋于稳定缓慢减小。研究结果为造穴射流工具的喷嘴选型及结构优化设计提供了依据。

The cavity building by water jet is the important way of coal bed methane well completion. In order to optimize the nozzle for water jet tools to enlarge cavity diameter and improve cavity building efficiency, the similar coal samples were prepared, rock breaking effects were tested by continuous jet and cavitating jet in laboratory and the application was carried out in the field. The results showed that under the condition of free jet, the best rock breaking effects were at jet distance of 200mm and 300mm for continuous jet and cavitating jet respectively. Under the condition of submerged jet, the continuous jet could not erode the coal sample ; the eroding diameter of cavitating jet increased first, then decreased tending to be sta- ble ; and when the submerged depth was 200mm, the eroding diameter reached the maximum. The eroding depth increased with the increase of submerged depth; by the submerged depth of 300mm, the eroding depth was tending to be stable and decreased slowly. This research provides the basis for nozzle selection and optical design of water jet tools.