摘要
基于真三轴水力压裂模拟系统,开展已压裂缝内流体压力、段间距、射孔参数、水平应力差和水平井段固井质量对致密砂岩储集层多裂缝扩展形态影响的实验。通过岩样剖分和压力曲线特征的类比分析得到以下认识:已压缝处于临界闭合状态时,高水平应力差和小段间距将导致多裂缝合并,而已压缝内高净压力和缝宽不对称分布可能抑制后续裂缝扩展;较大段间距使得后续裂缝处于诱导应力递减区域,降低应力干扰程度;采用大密度深穿透射孔,有利于降低裂缝起裂压力;缝内净压力一定时,低水平应力差将增大水平应力反转程度,增大后续裂缝偏转角度;水平段固井质量较差时,裂缝在井筒与地层结合处起裂,形成纵向缝;各段裂缝起裂压力呈上升趋势,压力增长幅度可达30%;形成横切缝时,起裂后压力迅速下降,延伸压力低;裂缝发生偏转时,起裂后压力波动下降,延伸压力较高,为迂曲窄缝;形成纵向缝时,压力剧烈波动上升,呈现多峰值特征,起裂阶段和延伸阶段区别不明显。
A novel laboratory simulation method for modeling multi-staged fracturing in a horizontal well was established based on a true tri-axial hydraulic fracturing simulation system.Using this method,the influences of net pressure in hydraulic fracture,stage spacing,perforation parameter,horizontal stress bias and well cementation quality on the propagation geometry of multiple fractures in a tight sandstone formation were studied in detail.The specimen splitting and analogy analysis of fracturing curve patterns reveals:Multiple fractures tend to merge under the condition of high horizontal stress bias and short stage spacing with pre-existing hydraulic fractures under critical closure situation,and the propagation of subsequent fractures is possibly suppressed because of high net pressure in pre-created fractures and asymmetric distribution of fracture width.And the subsequently created fractures are situated in the induced stress decreasing zone due to lone stage spacing,leading to weak stress interference,and perforation with intense density and deep penetration facilitates the decrease of initiation fracture pressure.The deflection angle of subsequent fracture and horizontal stress variation tend to be amplified under low horizontal bias with constant net pressure in fractures.The longitudinal fracture is likely to be initiated at the interface of wellbore and concrete sample with poor cementation quality.The initiation fracture pressure of the different stages increases in turn,with the largest increase of 30%.Pressure quickly declines after initiation with low propagation pressure when the transverse hydraulic fracture is formed.The pressure reduces with fluctuation after the initiation of fracture when the fracture deflects,the extension pressure is high,and the fracture formed is tortuous and narrow.There is a violently fluctuant rise of pressure with multiple peak values when longitudinal fracture created,and it is hard to distinguish the features between the initiation stage and propagation stage.
作者
刘乃震
张兆鹏
邹雨时
马新仿
张一诺
LIU Naizhen;ZHANG Zhaopeng;ZOU Yushi;MA Xinfang;ZHANG Yinuo(CNPC Great Wall Drilling Company,Beijing 100101,China;China University of Petroleum(Beijing),Beijing 102249,China)
出处
《石油勘探与开发》
SCIE
EI
CAS
CSCD
北大核心
2018年第6期1059-1068,共10页
Petroleum Exploration and Development
关键词
致密砂岩
水平井
多段压裂
射孔
缝内净压力
缝间应力干扰
裂缝扩展
tight sandstone
horizontal well
multi-staged fracturing
perforation
net pressure in fracture
stress interference between fractures
fracture propagation
作者简介
刘乃震(1960-),男,辽宁昌图人,博士,中国石油集团长城钻探工程有限公司教授级高级工程师,主要从事钻井、完井、储集层改造方面的研究与管理工作。地址:北京市朝阳区安立路101号名人大厦,邮政编码:100101。E-mail:lmlm1985@163.com。
