【摘要】 页岩气藏清水压裂形成的缝网中存在大量非支撑剂充填裂缝,粗糙裂缝面的剪切错位是其主要的导流机理。理论分析了剪切裂缝形成条件及裂缝错位程度,并通过实验研究了缝面错位程度和粗糙度对导流能力的影响。理论分析表明,水力裂缝诱导天然裂缝发生剪切滑移的条件是裂缝内净压力超过地层水平主应力差。高应力差、低杨氏模量和低泊松比地层中的天然裂缝易形成较大的错位程度。在压剪闭合状态下形成最大错位的有利天然裂缝角度是arccotKf/2。实验结果表明,页岩裂缝发生滑移错位,导流能力可提高2个数量级以上;但错位程度的影响存在随机性。粗糙度较大的裂缝更易形成高导流能力,但没有绝对的相关性,粗糙度对剪切裂缝导流能力仅在低闭合应力条件下影响显著。软页岩缝面凸起易破碎,粗糙度相近情况下软页岩错位裂缝的导流能力可比硬页岩的低一个数量级以上。更多还原

【Abstract】 Shear dislocation of rough fracture surface is the main conductivity mechanism for many unpropped fractures in the network formed by water-fracturing in shale gas reservoirs.Formation conditions,displacement of shear fracture and the effects of displacement,roughness on fracture conductivity are investigated by theoretical analysis and experimental test respectively.Theoretical analysis shows that net pressure exceeding horizontal differential principal stress is required for hydraulic fracture inducing natural fracture shearing slippage.Natural fracture is likely to slide a big displacement in formation with high stress difference,low Young modulus and Poisson’s ratio.The advantageous fracture azimuth to form maximum displacement for closed fractures is arccotKf/2 degree.Experimental results show that fracture conductivity is improved more than 2 orders magnitude when shear-slip occurs,but the effects of fracture displacement on conductivity are random.Fractures with large roughness are likely to provide high conductivity,but there is no absolute correlation between conductivity and roughness,except for the low closure stress condition.Asperities-crushing of soft shale is serious,so its conductivity is one order magnitude lower than that of hard shale with the similar fracture roughness.更多还原