高级检索

顶板水平井分段分簇压裂治理掘进巷道瓦斯模式研究

Study on the model of staged and cluster fracturing to control the gas in driving roadway by horizontal well in roof strata

  • 摘要: 为了解决淮南矿区碎软低渗煤层掘进巷道瓦斯抽采效率低的问题,提出了煤层顶板水平井分段分簇压裂瓦斯治理模式。运用数值模拟方法和物理相似模拟方法研究了煤层顶板水平井水力压裂裂缝扩展过程;运用产能模拟的方法研究了分段分簇压裂的产气效果,对分簇压裂和不分簇压裂进行了剩余瓦斯含量对比分析。裂缝扩展数值模拟结果表明:煤层顶板水平井内的裂缝能够扩展至煤层,将煤层全部压开,且由于煤层的塑性大于顶板砂质泥岩,煤层形成比顶板更为宽泛的压裂缝。裂缝扩展物理相似模拟结果表明:在考虑了泥岩伪顶发育的条件下,水平钻孔布置在碎软煤层顶板的砂岩内,在合理的垂直距离和大排量压裂液施工的环境下,若煤层发育有较薄的泥岩伪顶,裂缝能沿着射孔孔眼穿过直接顶−伪顶界面(粉砂岩−泥岩界面)和伪顶−煤层界面(泥岩−煤层界面),扩展至下伏煤层内,裂缝延伸形成1条弯曲不规则的阶梯型裂缝,能实现对碎软煤层的压裂改造目标。但是,当煤层发育有较厚的泥岩伪顶时,泥岩对水力压裂产生了阻挡作用,导致裂缝难以压开下伏煤层。产能模拟结果表明:在相同的地层环境和施工条件下,经过3 a的抽采,单段不分簇压裂能够产生更大的瓦斯抽采影响范围,但不能均匀降低掘进巷道的瓦斯含量,压裂段之间出现了瓦斯抽采空白带,分簇压裂产生的瓦斯抽采影响范围小,却能够更均匀的降低掘进巷道的瓦斯含量。经过在淮南地区潘谢煤矿的工程验证,在10 m3/min的施工排量下,裂缝长度最长可以达到193.8 m,最大缝高27.0 m,单井日产气量最高达到1 490 m3/d,2 a的瓦斯抽采量达到31×104 m3,说明煤层顶板水平井分段分簇压裂技术是淮南地区碎软低渗煤层掘进巷道瓦斯高效抽采的有效模式。

     

    Abstract: To address the issue of low gas extraction efficiency in driving roadway of broken soft and low permeability coal seams in Huainan mining area, a model of segmented cluster fracturing gas management in horizontal wells at the roof of coal seams was proposed. The crack expansion process of hydraulic fracturing in horizontal wells of coal seam roof was studied using numerical simulation and physical similarity simulation methods. The gas production effect of segmented and clustered fracturing was investigated using productivity simulation, and a comparative analysis of residual gas content between fracturing in clusters and without clustering was conducted. The numerical simulation results of crack extension shown that, the cracks in the horizontal wells at the roof of coal seam could expand to the coal seam and open up the coal seam completely. Due to the plasticity of the coal seam was greater than that of the sandy mudstone at the roof, a wider fracturing crack was formed in the coal seam than at the roof. The physical similarity simulation results of crack extension shown that, considering the development of the mudstone pseudo-roof, when the horizontal drilling was placed in the sandstone at the roof of the broken soft coal seam, and under reasonable vertical distances and high-displacement fracturing fluid construction, if coal seam developed a relatively thin mudstone pseudo-roof, the fractures could extend through the interface of direct roof and pseudo roof (siltstone- mudstone interface) and the interface of pseudo-roof and coal seam (mudstone-coal seam interface) along the shot hole aperture and into the underlying coal seam. The fractures extended to form a curved and irregular step-like pattern, which can achieve the goal of fracturing and reforming the broken soft coal seam. However, when the coal seam developed a thick mudstone pseudo-roof, it had a blocking effect on hydraulic fracturing, making it difficult for the cracks to open up the underlying coal seam. The productivity simulation results shown that, under the same stratigraphic environment and construction conditions, after 3 years of extraction, single-stage non-cluster fracturing could produce a larger gas extraction impact range. However, the gas content of driving roadway could not be uniformly reduced, and there was a gas extraction gap between the fractured segments. Fracturing in clusters produced a smaller gas extraction impact, but it could more evenly reduce the gas content in driving roadway. After the engineering verification in the Panxie coal mine in Huainan, with a construction discharge of 10 m3/min, the longest fracture length could reach up to 193.8 m, the maximum height of fracture was 27.0 m, and the daily gas production of a single well reached 1 490 m3/d. The gas extraction volume of 2 years was 31×104 m3, indicating that the segmented and cluster fracturing technology of horizontal wells at the coal seam roof was an effective model for efficient gas extraction in the driving roadway of broken soft and low-permeability coal seams in Huainan area.

     

/

返回文章
返回