四川盆地威荣区块深层页岩气水平井压裂改造工艺

四川盆地南部威荣区块由于地质条件复杂、最大水平主应力和垂向主应力差异小、水平应力差值大、施工泵压高、敏感砂比低等原因,页岩气水平井的压裂施工面临诸多难题。为此,通过剖析该区深层页岩气水平井的工程地质特征及压裂改造难点,借鉴国内外页岩气水平井体积压裂的技术思路,确定了对该区页岩气水平井实施压裂改造的主体思路及技术对策,并在后续页岩气水平井的压裂改造中加以应用。研究结果表明:(1)威荣区块页岩气水平井采用常规压裂工艺形成的裂缝复杂程度低、整体改造体积偏小,射孔簇有效性难以保证,加砂强度低导致压裂后气井的稳产能力较差,并且难以应对套管变形井的压裂改造;(2)针对该区深层页岩气水平井的压裂改造难点,形成了"超高压、大排量、大液量、缝内暂堵转向、变排量"工艺、"分段多簇射孔优化+大排量"及"缝口暂堵转向"技术、"大排量、高黏度、低砂比、低密度、小粒径连续加砂"工艺和"连续油管快速处理+小直径桥塞、射孔枪分体泵送"的套管变形井压裂改造技术;(3)将所形成的压裂工艺应用于该区块5口页岩气水平井,压裂后获得的页岩气无阻流量平均值为26.11×104 m3/d,改造效果较好。结论认为,该研究成果可以为深层页岩气水平井的压裂施工作业提供借鉴。

Fracturing technologies of deep shale gas horizontal wells in the Weirong Block,southern Sichuan Basin

Stimulation of hydraulic fracturing of horizontal shale gas wells in the Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions, small differences between the horizontal principal stress and the vertical principal stress, high working pump pressures, and low sensitive sand ratios. In view of this, by combing the geological structure, engineering geological characteristics and the difficulties of fracturing of deep shale gas wells in the Weirong Block, learning from the general idea of volumetric fracturing for shale gas reservoirs at home and abroad, we determined the main ideas and technical countermeasures for fracturing in the area and applied them to the subsequent fracturing practices of shale gas wells. And the following achievements were obtained. First, the conventional fracturing technology applied to the shale gas wells in the Weirong Block resulted in low fracture complexity, small stimulated reservoir volume (SRV), difficulties in guaranteeing the effectiveness of perforation clusters, low strength of proppant adding, difficulties in obtaining higher conductivity, poor stable production capacity after stimulation, and difficulties in meeting the need of well fracturing with casing deformation. Second, in view of the difficulties of fracturing stimulation in deep shale gas wells of the Weirong Block, super high pressure, huge displacement, large fluid volume, steering temporary plugging in fracturing, and variable displacement technology can effectively increase SRV and the complexity of fractures in distant wells. The effectiveness of multi-cluster perforation can be guaranteed by comprehensive utilization of multi-cluster perforation optimization technology, big displacement technology and steering temporary plugging & fracturing technology at slots. The continuous proppant-adding technology with large displacement, high viscosity, low sand ratio, low density and small particle size can improve sand adding strength and fracture conductivity. Besides, the stimulation technology for casing deformed wells using coiled tubing fast processing + small diameter bridge plug and separate pumping technology of perforating gun have been formed. Third, after the above fracturing technologies have been applied in five shale gas horizontal wells in the Weirong Block, the average absolute open flow（QAOF）reached 26.11×104 m3/d, indicating a good stimulation effect. In conclusion, this paper can provide meaningful reference for the development of deep shale gas wells of the similar type.