Study On The Imbibition And Damage Mechanism Of Fracturing Fluid And Soaking Time In Fuyu Tight Oil Reservoir

In recent years,as a kind of unconventional oil and gas reservoir,tight oil reservoir has been focused on.It has the characteristics of small pore throat,complex pore throat structure,poor physical properties,etc.,and requires high development and exploration technology.Large-scale hydraulic fracturing is commonly used for the exploitation of tight oil and gas resources.In the post-pressure soaking stage,pressure release promotes fracturing fluid filtration into the reservoir,improves oil-water interface performance and imbibition displacement capacity.In addition,the fracturing fluid has certain damage to the near-fracture reservoir,and reasonable optimization of soaking time during the development process can achieve better stimulation effect on the basis of reservoir protection.Therefore,the study on imbibition displacement mechanism,damage degree of fracturing fluid to reservoir and reasonable soaking flowback time has important guiding significance for improving tight oil reservoir exploitation.Taking the tight sandstone of Fuyu reservoir in Block Z of Daqing as the research object,the XRD whole-rock diffraction experiment,porosity experiment,permeability experiment,mercury injection experiment,contact Angle experiment,dynamic and static imbibition experiment,reservoir damage experiment and soaking flowback experiment were carried out.The characteristics of mineral composition and physical properties of reservoir,dynamic and static imbibition characteristics,permeability damage rate and soaking well flowback recovery of associated fracturing fluid system were obtained.On this basis,a number of fluid flow models and numerical simulation methods were established to calculate the daily oil production and cumulative oil production of different soaking schemes,and the optimal soaking time was proposed.The main conclusions are as follows:(1)In the tight reservoir of Fuyu reservoir,the quartz mineral content,total particles content and interstitial materials content are about 47%,86% and 6?9% respectively.The porosity ranges from 10.56 to 12.38% with an average of 11.46%,which shows that the pores are relatively developed.The permeability ranges from 0.9 to 1.3m D with an average of1.13 m D.The core is a hydrophilic core with dense pore structure,mainly small pores and strong capillary force.(2)Both dynamic and static imbibition rates increased rapidly at the initial stage of imbibition and reached a peak,then began to decline rapidly and gradually reached equilibrium.Nuclear magnetic resonance analysis showed that static imbibition was mainly due to the small pore throats in the core.While,both small pore throats and large pore throats played a role in dynamic imbibition.Besides,the static imbibition rate was higher than that of the static imbibition rate.The results indicated that the associated fracturing fluid system had a certain damage effect on the reservoir,and the permeability damage rate was about 11.9%.(3)The experimental results showed that at the initial stage of soaking well,under the joint action of capillary force and release of soaking well differential pressure,the effect of imbibition and replacement was obvious,and the recovery rate rose rapidly.With the progress of fracturing fluid damage processed,the physical properties of core decreased,and the increase of recovery rate slowed down.The reasonable soaking time of reservoir in the target block was6 days.(4)The simulation results showed that with the increase of soaking time,the pressure diffusion range around fractures increased,the fracture damage radius gradually expanded,the filtration range of fracturing fluid increased,and the cumulative production increased.The soaking time after pressure should not be too long,because the fracturing fluid stayed in the formation for a long time would cause damage to the formation.It was recommended that the reasonable soaking time should be 6-10 days.Applied the soaking time of 6 to 10 days in the S block,and good effect of production and production was achieved.This study has important guiding significance for improving tight oil reservoir exploitation.