Study On Residual Oil And Stimulated Measures For Wumishan Fractured-vuggy Carbonate Reservoir

Wumishan reservoir is a fractured-vuggy carbonate reservoir,the characteristics of which are massive fractures and vugs development,good connectivity and strong reservoir heterogeneity.Wumishan reservoir is on the late stage of high water-cut development now.Due to high rising speed of water cut,the reservoir is flooded seriously.Complex oil-water distribution and highly fragmented residual oil make the stimulated measures or technology difficult,thus the effectiveness of reservoir development becomes poor.In this situation,it is necessary to make a study on residual oil distribution.Then according to different types or patterns of residual oil,take effective measures to ensure the reservoir development sustained and stable.Facing to existing problems of reservoir development,this study,based on deepening the basic geological study,is mainly to find out the factors of controlling the remaining oil distribution on the late stage of high water-cut development and find out the characteristics of reservoir water flooding and residual oil distribution by indoor experiment,field test,numerical simulation and production practice.Then make sure types or patterns of residual oil distribution,analyze the cause of formation and summarizes developing methods.At last,based on the above research results,evaluate the measures and effectiveness of reservoir comprehensive control and make a reasonable technical measures and developing methods indicating the direction for reservoir management work in the next step.Comprehensive geological study and field exploration research shows that the structure and the low permeability are the main factors to control the residual oil distribution on the late stage of high water-cut development.The residual oil types can be divided into four types,that is,top weathering crust,low permeable formation on the top of the open hole,low permeability well zone and local high block of residual oil.According to the characteristics of the residual oil distribution and development condition,water-controlling to stabilize oil technology,weathering crust exploiting technology,adjustment wells drilling technology,shut-in well recovery technology and so on.In terms of measure ways,water plugging,increasing production,acidification and weathering crust exploration are still the main measures on the late stage of high water-cut development These main measures have the same mechanism of increasing oil that is controlling the product capacity of larger fractures and vugs to exploit the small fracture or microfracture with high oil saturation by pressure difference.Comparing all kinds of measures and effects,each has advantages and disadvantages,Water plugging and increasing production are used more and make more production,but scattered residual oil and complicate oil-water relation make the measure technology more difficult and shorten the period of validity,while weathering crust exploiting and acidification measures can make higher average single well oil production,but well condition is relatively rigid and working procedure is complex,so relative economic benefit is low.Therefore,it is suggested that water plugging,increasing production and drilled well recovery should be prior used compared to weathering crust and acidification.In addition,tertiary oil recovery study should be made at the same time in order to slow down the reservoir decline and improve the effect of reservoir development.