The Study On Fluid Tracing Technique In The Typical Tight Sandstone And Shale Reservoir

The unconventional oil and gas reserves in China are very abundant,but mining is relatively difficult,the production practice requires the implementation of the hydraulic fracturing technology to produce complex artificial fractures network,to increase the tight hydrocarbon flow channel.So,the study of fluid flow mechanism in unconventional tight hydrocarbon reservoirs is helpful to improve the reservoir recovery.In this paper,ERT21 high density resistivity method and spontaneous inbibition experiment were used to study the flow of fluid in tight sandstone and the pore structure and connectivity in shale reservoir.So as to reveal the internal structure and the fluid flow mechanism in the tight reservoirs.The high density resistivity method is a non-invasive test technique which forms a stable electric field through the electrode to apply the excitation current to the measured sample,and then collects the potential of the electrode in the region,to obtain the sample cross-section electrical characteristics.It can be get the test area of time and space date as the resistivity distribution image,and can obtain the rule of the resistivity change in the time domain.In this paper,through a large number of experimental analysis and comparisons,the application of the technology for the tight sandstone fluid flow mechanism is in depth study.A large number of indoor tests were carried out on the flow of the tight sandstone fluid,and the electrical characteristics of the sandstone were obtained.The distribution of the apparent resistivity was plotted on the measured data by using softwares.Spontaneous inbibition is a common natural phenomenon that occurs in porous media and is particularly common in the use of hydraulic fracturing and horizontal drilling techniques in the exploration and development processes of tight hydrocarbon reservoir.Pore structure and mineral composition are important factors that affect the spontaneous inbibition of hydrocarbon reservoirs.In this paper the influence of pore connectivity,pore direction and mineral compositions on the spontaneous inbibition rate of shale reservoirs was studied by using the spontaneous inbibition curve of shale samples.The pore connectivity was evaluated quantitativly by spontaneous inbibition curve.The main results of this paper are as follows:a.ERT21 high density resistivity imaging method as a new technology to detect fluid flow in the sandstone is feasible to study the mechanism of sandstone fluid migration,The apparent resistivity distribution image drew by the data obtained through the instrumentation which is visually reflecting the flow path of the fluid flow is consistent with the direct observed condition.b.Due to the heterogeneity of tight sandstone samples,the rate of fluid flow is different.Where there is a high permeability area,the fluid is easy to enter and the apparent resistivity decreases rapidly.In other dense regions,However,lag phenomenon is apparent.Analyses and comparisions of the resisitivity distribution image can be reflect to a certain extent,the existence of micro-cracks.c.In the unconventional tight hydrocarbon reservoir,the slope of the spontaneous inbibition curve can reflect the connectivity of the shale reservoir.The higher the slope,the better the pore connectivity of the shale reservoir,and the smaller the slope,the more poor the connectivity in the pores of the reservoir,the poor connectivity of the pores may be due to pore and throat in the clay minerals in the filling,resulting in pore and throat blocked.d.The direction of the shale lamellation will also have an impact on spontaneous inbibition,under normal circumstances,the slope of the spontaneous inbibition curve is higher,but there are individual samples showed that the slope of the spontaneous inbibition curve is similar to that of the spontaneous permeability curve,which may be due to the higher content of hydrophilic minerals in shale reservoirs,so that the direction of migration of water in shale reservoirs is weakened.The higher the slope of spontaneous inbibition curve in unconventional tight hydrocarbon reservoir,the better the permeability,the more favorable to the development of unconventional tight hydrocarbon reservoir.e.The shale rich in organic matter,or transformed by the role of oil and gas fluid,pore wall has a great change in its microporous interface due to the different contents of lipophilic hydrophobic minerals,hydrophilic interface and lipophilic interface are uneven distribution,is the key factor affecting the length of fluid flow path.