Research On Formation Mechanism Of Remaining Oil And Enhanced Oil Recovery In LH Reef Limestone Reservoir

Research about remaining oil is currently a hot spot in reservoir engineering and development geology.The formation mechanism and distribution rule of remaining oil and enhanced oil recovery are the key points.Analyzing the factors that affect the distribution of remaining oil,and clarifying the mechanism of remaining oil formation,which are of great significance to accurately predict the remaining oil enrichment area and put forward a practical,targeted method for enhanced oil recovery.The object of this paper is the largest bottom water oil field with marine reef limestone in China.The pore structure of this reservoir is complex,the bottom water flows along the seepage channel,which leads to the high water cut once the well put into production.At present,this oil field has a low production and great potential for the development of the remaining oil.Therefore,it is of great significance to carry out the formation mechanism of remaining oil in the LH reef limestone reservoir and to enhance oil recovery,which is also necessary to the adjustment of the late reservoir development and the improvement of the reservoir development effect.The geological characteristics of the reservoir are analyzed and summarized on the basis of making full use of various geological and experimental production data provided by the oil field.,The formation mechanism and distribution law of residual oil in LH reef limestone reservoir are studied in detail from two aspects of microcosmic and macro aspects by using numerical simulation and reservoir engineering technology.The effect of EOR has been proved.The paper has obtained the following research results:(1)the microscopic pore structure of reef limestone reservoir and the formation mechanism and distribution of micro residual oil after water flooding experiment are studied by scanning electron microscopy,casting thin film and microscopic visualization.Results show that the micropore structure of the LH reef limestone reservoir is complex and mainly develops 4 kinds of space types,which are relatively compact,compact fracture,hole fracture and pore cavity.The wettability of the microcosmic unbalance displacement and reservoir oil in water flooding lead to the flow of water easily along the large pore channel or crack,and the remaining oil is attached to the reservoir.The surface oil is difficult to be affected and the displacement efficiency is low at the same time.(2)The dynamic law of different types of reservoirs and the distribution law of residual oil has been studied by using the single well mechanism model which can reflect the typical reservoir characteristics.And then the formation mechanism of macro residual oil is analyzed in combination with the actual geological characteristics of the reservoir.The result shows that the reservoir of LH reef limestone reservoir has dual medium characteristics.The bottom water flows along the cracks and the dominant percolation channel to the wellbore rapidly,the macro inequilibrium displacement leads to low wave efficiency.Besides that,there exsisted a lot of area where crude oil has not been displaced.(3)This research holds that:?It needs to be continued to implement the side drill to encrypt and adjust the well in greater potential area to solve the problem of low utilization of reserves;?To strengthen the potential of the remaining water drive in the main development area by using continuous packer oil increasing and controlling water completion technology.Which can also solve the problem of the influence of macro and micro heterogeneity on wave efficiency;? This technology has obvious effect on solving the problem of low oil displacement efficiency and low wave efficiency from the seepage mechanism.