Study On Temporary Plugging And Fracturing Law Of Low Viscosity Liquid In Unconsolidated Sandstone

The unconsolidated sandstone has complex physical properties such as high porosity,high permeability,weak cementation and heterogeneity.When the conventional hydraulic fracturing is performed,the pump pressure is low and the fracturing effect is not ideal.Temporary plugging and fracturing technology can effectively reduce the permeability of high permeability reservoirs,reduce fluid loss,increase pump pressure and improve fracturing effect.Therefore,it is necessary to study the temporary plugging and fracturing law of low-viscosity liquid in unconsolidated sandstone.In this paper,unconsolidated sandstone artificial cores are prepared,and through permeability test,porosity test,triaxial rock mechanics parameter test,core displacement test,triaxial hydraulic fracturing test,hydraulic fracturing orthogonal test and numerical simulation,the physical and mechanical properties and fracturing law of unconsolidated sandstone samples are deeply studied.The main study contents and conclusions are as follows:1.Three kinds of fine sand and cementing cement were selected to adjust the proportion of cement,water and sand to prepare unconsolidated sandstone artificial cores with different physical and mechanical properties.Through permeability test,porosity test and triaxial rock mechanics parameter test,the permeability,porosity,modulus of elasticity and Poisson's ratio of artificial cores are obtained,which lays a foundation for the analysis of mechanical properties of loose sandstone and subsequent physical simulation and numerical simulation.2.The core displacement test is carried out on the unconsolidated sandstone artificial cores,and the the plugging effect of the two temporary plugging agents on the cores were evaluated.The appropriate temporary plugging agent is selected for subsequent triaxial fracturing test through comparative analysis of the amount and duration of the two temporary plugging agents.3.A temporary plugging agent was added to the low-viscosity fracturing fluid to carry out a triaxial temporary plugging test on the unconsolidated sandstone cores.The effects of temporary plugging agent amount,pumping displacement and temporary plugging agent concentration on crack initiation and propagation under different confining pressures and rock permeability conditions were studied.The results show:(1)Adding temporary plugging agent can effectively increase fluid pressure in fracture.(2)Selecting different displacement according to different permeability can ensure fracture pressure,save temporary plugging agent and achieve good economic and fracturing effect.(3)With the increase of the concentration of temporary plugging agent,the fracture pressure increases and the amount of temporary plugging agent increases.(4)The fracture pressure increases with the increase of confining pressure and the decrease of permeability.4.Orthogonal test of hydraulic fracturing was designed to study the influence of different factors on the fracturing effect of loose sandstone.The influence of pump displacement and temporary plugging agent concentration on the fracturing pressure and the amount of temporary plugging agent under different confining pressure and rock permeability conditions was analyzed.The results show:(1)The scheme of "displacement 20 ml/min + 4% concentration temporary plugging agent" can obtain higher fracture pressure.(2)The scheme of "displacement 10ml/min + 1% concentration temporary plugging agent" can save the amount of temporary plugging agent.5.Using ABAQUS 2017 finite element software,cohesive element is selected to simulate rock cracking behavior.The influence law of permeability,pumping displacement,fracturing fluid viscosity,horizontal principal stress difference and other factors on rock cracking is studied,and the construction parameters are optimized by physical model test.The results show:(1)With the increase of pump displacement,the fracture pressure increases,and the increasing trend tends to be gentle;(2)With the increase of fracturing fluid viscosity,the fracture pressure increases,but the increasing range is very small.In the actual construction site,factors such as fracturing technology,cost,fracturing effect and pipeline friction should be considered comprehensively,and appropriate pumping displacement and fracturing fluid viscosity should be selected to achieve good fracturing effect and save cost.Through the above research,the test results provide the basis for on-site construction,which has guiding significance for cost saving and fracturing effect.