软硬煤复合的煤层气水平井分段压裂技术及应用

Technology and application of staged fracturing in coalbed methane horizontal well of soft and hard coal composite coal seam

针对软硬煤复合煤层的煤层气抽采效率低、煤层纵向剖面上抽采不均衡等问题,为了实现大面积快速、整体高效抽采煤层气,以沁水盆地赵庄井田3号煤层为例,对软硬煤分层特征进行精细评价,优化了软硬煤复合煤层中的局部硬煤段,研究了硬煤层中不固井水平井分段压裂开发煤层气技术方法,在对水平井压裂裂缝扩展规律研究的基础上,研究了分段压裂水平井开发煤层气技术对策。研究结果表明:3号煤层软硬煤结构分层明显,软硬煤存在明显的自然伽马和电阻率测井响应特征;硬煤层中水平井压裂能形成一条复杂不规则的垂直裂缝,裂缝易于沿脆性较强的顶板岩层扩展延伸,裂缝能够扩展延伸进入软煤层,提高软硬煤的压裂增产效果;硬煤层中水平井位置和压裂施工排量是影响裂缝扩展效果的两个因素,压裂施工排量影响程度较大、水平井位置影响程度较小。针对这一特点,进一步研究了硬煤层中不固井水平井分段压裂开发煤层气4个关键技术:①水平井射孔、压裂段优选工艺技术;②油管拖动大排量水力喷射防窜流工艺技术;③"大排量、大规模、中砂比"的段塞式清水携砂压裂工艺技术;④气/水分井同步生产精细化排水采气技术。工程试验证明,该技术能大幅度提高煤层气水平井单井产量,突破了软硬煤复合煤层低产技术瓶颈,为软硬煤复合煤层的煤矿区煤层气抽采和瓦斯灾害治理提供了技术途径。

Aiming at the problems of low efficiency of coalbed methane extraction in soft and hard coal composite seam and uneven extraction in coal seam longitudinal section,etc,In order to achieve rapid and overall efficient extraction of CBM over a large area.Taking the No.3 coal seam in Zhaozhuang field of Qinshui basin as an example,this paper analyzes the layered characteristics of soft-hard coal,optimize the local hard coal segment in the composite coal seam.and puts forward the new idea of exploiting CBM through noncementing staged fracturing horizontal wells in layered soft-hard coal seam.On the basis of fracture propagation pattern of fracturing on horizontal wells in layered soft-hard coal seam,the technical measures for the development of CBM by noncementing staged fracturing horizontal wells are investigated.The results show that there are obvious layers of soft and hard coal in No.3 coal seam.and obvious characteristics of natural gamma and resistivity logging response in soft-hard coal.Horizontal well in hard coal fracturing can form a complex and irregular vertical fracture,which is easy to expand and extend along the roof strata with strong brittleness.Hydraulic fracturing can break both hard and soft coal seam,and can improve the fracturing effect of soft and hard coal seam.The location of horizontal wells in hard coal and fracturing construction discharge have an influence on the effect of fracture expansion,the influence degree of fracturing discharge is large and the horizontal well position is small.In view of this characteristic,four key technologies for the successful development of CBM by horizontal wells of staged fracturing are formed:①Optimization technology of perforation and fracturing section in horizontal well;②Pipeline transmission large displacement hydraulic jet anti-channeling technology;③Technology of slug type water carrying sand fracturing with“large displacement,large scale and medium sand ratio”;④Fine drainage and mining technology for simultaneous production of gas and water well separately.The practice proves that this technology can greatly increase the output of horizontal well of coalbed methane,break through the technical bottleneck of low yield of soft and hard coal composite coal seam,and provide a technical way for coalbed methane extraction and gas disaster control of soft and hard coal composite coal seam.