Geological And Reservoir Engineering Study Of Xishanyao Low Permeability Sandstone Reservoirs By Oil Stabilization And Water Control In Well Block Cai-9 Of Cainan Oilfield

Cainan oilfield is China's first massive desert oilfield under production. Xishanyao low permeability sandstone reservoir in Well Block Cai-9 is one of the major producing zones in Cainan oilfield, with its OOIP accounting for nearly half of the total OOIP in the oilfield. At present, such problems as low degree of formation pressure maintenance, rapid increase of water-cut, sharp production decline and increasing difficulty in production stimulation, which are unfavorable for stabilized production, exist in the oilfield development. And these led to the result of oil production decreasing from 73.8 104t in 1996 to less than 20 l04t currently, with the ratio of total oil produced to OOIP less than 20% , the total water-cut exceeding 60% and the degree of pressure maintenance of only 65%. This is why it has become critically important to carry out field-scale combined adjustment and management . The project, which is initialed to provide basis for making combined reservoir stimulating plans, restore the reasonable and effective recovery of the reservoir and to realize the final target of ultimate recovery factor of 32%, will be of great significance to continuous production stabilization and further improving the ultimate recovery.On the basis of previous studies, taking the whole reservoir as the target and well groups as a unit, the paper made full use of seismic, drilling, logging, core analysis, formation testing, production test and performance data, to carry out recharacterization of the reservoir using detailed reservoir description in terms of the reservoir structure , fracture distribution characteristics , subdivided sedimentary facies, reservoir characterization, oil, gas and water property and distribution, reservior pressure , temperature, driving types as well as reserves recaculation etc. By means of conventional reservoir engineering and numerical simulation, through in-depth study of the production characteristics suah as oil and water movement, water-cut variation , pressure system , injection-production capability , producing reserves , reasonable injection-withdrawal ratio and water injectivity etc , theproduction technical limits during mid and high water-cut stages of the reservoir have been determined. The development level by waterflooding as well as development effect was evaluated, to find out the major factors affecting reservoir development. The future potential of the reservoir development has been analyzed from three aspects , namely , well pattern infilling adjustment , restoring the production performance of flank high water-cut wells by sidetracking and oil and water stimulation measures. We presented a purposed and feasible plan of stabilizing oil by water control, which aims to stabilize oil production and improve the development effect during the period of "the Tenth Five-Year-Plan" .Economic evaluation indicates that the proposed plan can have a better economic benefit and strong risk-resistant capability. Finally, several suggestions are made to improve the reservoir development performance and maintain the sustainable stabilization of oil production.The study methods and practice of technical countermeasures presented by the paper can be used for reference for development of similar low permeability sandstone reservoirs in china.