Characteristics Of Micro-flow Fields In Different Tectonic Environments Of Daqing Sartu Oilfield

Daqing Saltu oilfield has entered the development stage of extra-high waterbearing period.The long-term water injection development of the field has led to the increase of water content within the reservoir,the dispersion of remaining oil,and the increase of difficulty in tapping potential.Previous studies on residual oil mostly studied the distribution characteristics of residual oil from macroscopic perspectives such as well network control,sedimentary phase zone analysis,and reservoir inhomogeneity.However,for the tapping of the highly dispersed and diverse residual oil in the field during the extra-high water period,it is necessary to understand the different microscopic residual oil types and distribution patterns in the reservoir pore space.In order to realize the further development of the remaining oil.The formation and distribution of microscopic residual oil in the reservoir are related to the fluid flow characteristics in the pore throat,and the reservoir pore structure and non-homogeneity are the main factors affecting the microscopic flow field characteristics of the reservoir.Therefore,the analysis of the type and distribution of microscopic residual oil needs to be based on the study of the pore structure,physical characteristics and other microscopic flow characteristics in the reservoir.In this paper,the following results are obtained by studying the micro flow field and its distribution with the micro residual oil in the reservoir under different tectonic environments in the Daqing Saertu Oilfield.By analyzing the characteristics of tectonic evolution and depositional environment in the Songliao Basin,the study selects the PI formation as a weak tectonic environment reservoir and the PII formation as a strong tectonic environment reservoir according to the stress distribution characteristics and geological effects of different types of reservoirs.The study uses scanning electron microscopy to directly observe the morphological characteristics of the cores of different types of reservoirs,the pore throat structure and the morphology and distribution characteristics of different minerals inside the pore throats.The results show that the average pore radius,average coordination number,average throat radius and average throat length of the cores of the PI reservoir formed under weak tectonic activity are larger than those of the PII reservoir formed under strong tectonic activity,and the average values of core porosity and permeability are larger than those of the cores of the strong tectonic activity.The study developed a nμmerical simulation technique of microscopic seepage using fluorescence images of cores as geometric models to simulate the movement patterns of fluids in pore throats within different types of reservoirs.The results of the microscopic flow field simulation show that the pore flow pressure in the core of the PI reservoir formed in a weakly tectonically active environment varies greatly,the duration of high pressure is short,and the high velocity flow is mainly concentrated in relatively narrow throats with strong water washing effect,which is easy to form dominant seepage channels.The high velocity fluid in the reservoir is widely distributed,with small flow velocity differentiation,low degree of large pore channel bypassing,and large effective fluid wave area;the PII reservoir formed under strong tectonic activity environment,with small core pore flow pressure variation,long high pressure duration,and high flow velocity concentrated in relatively wide throat channels.The reservoir has a wide distribution of low velocity fluids,large flow velocity differentiation,weak washing,formation of bypass flow at large pore channels,easy formation of isolated islands at small pore channels,and small effective wave area of fluids.The study quantifies the characteristics of microscopic residual oil distribution in different types of reservoirs.For the P Ⅰ reservoir formed under weak tectonic activity environment,the residual oil content is less,its content is 0.71%,and the distribution of bound residual oil is mainly,and the free state residual oil content is less;for the PⅡreservoir formed under strong tectonic activity environment,the residual oil content is higher,the remaining oil content reaches 1.76%,and the distribution of free state residual oil is mainly.From the Portuguese Ⅰ reservoir to the PⅡ reservoir,the bound and semi-bound state residual oil content decreases and the free state residual oil content increases.The relationship between the microscopic flow field and the formation and distribution of residual oil in the reservoir is analyzed.For the PI reservoir formed under weak tectonic activity,the residual oil in the dominant channel of the flow field is dominated by the distribution of bound residual oil;the residual oil content in the nondominant seepage area of the flow field is 0.57%,which is less than that in the PII reservoir(1.62%),and the distribution of bound and free residual oil is dominated.For the PII reservoir formed under the strong tectonic activity environment,the remaining oil in the flow field dominant channel is mainly in the bound state and free state residual oil distribution;the remaining oil in the flow field non-dominant seepage area is mainly in the bound state residual oil distribution.The formation mechanism of various types of microscopic residual oil is discussed and the main factors affecting the formation and distribution of microscopic residual oil are analyzed based on the flow velocity distribution characteristics of the reservoir microscopic flow field and the flushing and repelling modes of fluids.The extraction techniques for different types of microscopic residual oil after water drive are proposed.