Study On The Mechanism Of Fracturing Fluid And Reservoir Imbibition In Liaohe Tight Reservoir

Large scale fracturing is one of the technologies of tight oil development.During the fracturing process,the fracturing fluid will stay in the reservoir.Under the action of capillary force,the fracturing fluid will spontaneously seep into the reservoir fractures,displace the oil in the fractures,and improve the oil well production.Therefore,the spontaneous seeping and oil displacement is an important driving mechanism of tight oil reservoir.Therefore,it is of great significance to study the mechanism of fracturing fluid and reservoir imbibition,and determine the imbibition and displacement ability of different types of tight oil reservoirs to improve oil well production.This paper focuses on the study of tight reservoir in Liaohe Oilfield.The first is the fine characterization of the reservoir: quantitative analysis of porosity,permeability,pore size distribution and other physical characteristics of tight reservoir.The influence of fracturing fluid on reservoir characteristics(pore throat distribution,permeability,porosity,etc.)is studied;CT scanning technology is used to observe the internal structure change of core before and after fracturing fluid action;the influence of clay mineral content and sensitive minerals on the damage degree of core is analyzed,and the composition characteristics of clay minerals are given by XRD technology;according to the reservoir space type of tight oil reservoir in the study area,it can be divided into three types: tight type,pore throat dominant type and fracture dominant type.In this paper,based on the theoretical model of fracturing fluid in porous media,the permeability experiments of fracturing fluid and reservoir core are carried out,and the permeability results of different types of reservoirs are obtained from the micro perspective by using NMR,The results show that the proportion of oil signals in small pores decreases from 60.2% to 51.7%,that in medium pores increases from 31.7% to 41.4% and then decreases to 39.7%,and that in large pores increases from 8.1% to 8.3%;The results of permeability and absorption experiments in low permeability tight reservoirs show that the proportion of oil signals in small pores decreases from40.3% to 17.8%,that in medium pores increases from 57.9% to 70.1%,and that in large pores increases from 1.8% to 12%;Through the analysis of the mechanism of the interaction between the fracturing fluid and the fluid in the core pore by the results of nuclear magnetic resonance,it is found that the spontaneous imbibition fracturing fluid preferentially enters the small pore and gradually imbibites the oil in the small pore into the large pore;At the same time,contrast experiments are carried out for the low permeability fracture dominated cores of different reservoirs,and according to the experimental results,"water lock" effect is obtained.This type of core should judge the oil-water imbibition effect according to the actual situation,and through the experiment of the influence of crude oil viscosity on the imbibition effect,it is found that the higher the temperature,the lower the oil viscosity,the better the imbibition effect.