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页岩气储层压后返排特征及意义
杨海,李军龙,石孝志,朱炬辉,邓才,王丹
(中国石油川庆钻探工程有限公司井下作业公司,四川成都 610051)
摘要:
为制定科学的页岩气储层压后返排策略,基于威远地区龙马溪组36口页岩气井压后返排数据,分析压后关井对产量的影响以及返排过程两相流阶段性特征,同时进行页岩气储层液相支撑验证实验。结果表明:压裂液在主压裂结束后一定时间内仍然发挥造缝作用,一定时间的关井有利于提升气井累积产气量期望值;页岩气储层压后返排气液两相流阶段出现气增液降特征点是高产气井的共同特征,根据两相流阶段特征可初步评估气井产气能力;滞留压裂液在页岩储层微细裂缝网络中具有液相支撑作用,使气相渗透率不是含水饱和度的单调函数,存在最优返排率使气相渗透率最大化;可以采用以追求气相渗透率最大化为目标,以控压、控速为原则的页岩气储层压后返排策略。
关键词:  页岩储层  压后返排  最优返排率  返排策略  关井
DOI:10.3969/j.issn.1673-5005.2019.04.012
分类号::TE 357.1
文献标识码:A
基金项目:国家科技重大专项(2017ZX0506304)
Characteristics and significance of flow-back processes after fracturing in shale-gas reservoirs
YANG Hai, LI Junlong, SHI Xiaozhi, ZHU Juhui, DENG Cai, WANG Dan
(Down-hole Service Company of Chuanqing Drilling Engineering Company Limited, PetroChina, Chengdu 610051, China)
Abstract:
In order to optimize the flowback process for a shale-gas reservoir after fracturing, the characteristics of the two-phase flow in the flowback process were analyzed based on the data of 36 shale gas wells located in the Longmaxi Formation of Weiyuan area, and the effect of shut-in operation on well production was studied. Moreover, laboratory testing was conducted in order to verify if the fracturing fluids in the micro-fractures can act as proppant. The results show that the phenomenon of gas production rate increases with deceasing of water production appears in the two-phase flow of the clean-up process is a common feature of shale gas wells with high productivity, and it can be used to evaluate the well productivity preliminarily. The fracturing fluids can be imbibed into micro-pores and fractures to generate new fractures for improving the stimulation effect, thus, a reasonable shut-in is beneficial to increase gas production. The shut-in before flowback can fully utilize shale hydration effect to enhance the fracture network, and the shut-in during the flowback can increase the formation pressure and improve gas flow. The residual fracturing fluids in the micro-fracture network of shale gas reservoir can act as proppant keeping the micro-fractures open, so that the gas permeability is not a monotonic function of water saturation. Moreover, there is an optimum water recovery during the flowback after the fracturing that can maximize the permeability of gas-phase, increasing the expected value of cumulative gas, but it should be emphasized that the optimum water recovery is not only referred to a certain value, more importantly, it refers to an optimum flowback strategy.
Key words:  shale reservoirs  flow-back processes after fracturing  optimum water recovery  flow-back strategy  well shut-in
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