采取岩石力学分析法，计算页岩气藏中天然裂缝张开压力和延伸后沟通压力，分析层理对岩石强度的影响，并给出层理薄弱面形成剪切裂缝的力学条件。结果表明：以前的设计所需井底压力较高，当考虑地层中天然裂缝的张开和延伸沟通后，在较低的井底压力下，就能够形成复杂的裂缝网络；页岩层理会降低岩石的整体强度，在一定的井底压力下，岩石发生破碎，有利于形成缝网；页岩层理薄弱面在较低的压力下容易产生剪切裂缝，这是页岩气藏形成复杂缝网系统的重要基础。因此，对于天然裂缝和层理比较发育的页岩气藏，可以不需要达到以往的较高设计和施工压力就能形成缝网。%The opening pressure and interacting pressure of natural fractures are calculated by use of rock mechanics analysis method,and the effect of bedding planes on rock strength is analyzed.At the same time,the mechanical conditions for shearing fractures between wake bedding planes are presented.Results are as follows:The bottom-hole pressure is required higher for pre-vious design,but when the opening and link-up of natural fractures are considered,the network fractures can be created at lower bottom-hole pressure;Shale bedding can reduce the whole rock strength,and rocks are broken at certain bottom-hole pressure, favoring formation of fracture networks;Shearing fractures are easily formed between weak bedding planes at lower pressure,and thus,they are the basis for fracture networks’forming in shale gas reservoirs.Our results indicate that,fracture networks can form in shale gas reservoir with abundant natural fractures and bedding,not requiring higher pressure as designed in common method.
展开▼
