Experimental and Pilot Tests of Deep Profile Control by Injecting Small Slug-Size Nano-Microsphere in Offshore Oil Fields

Abstract

In order to test the effectiveness and efficiency of nano-microspheres which can be used to effectively reduce water cut with a small slug size, a series of experimental tests have been conducted to evaluate the performance of nano-microspheres and factors affecting the performance. Those tests include hydration swelling characteristics, blocking and migration characteristics, salt resistance, shear resistance and so on. Based on the experimental study, detailed pilot test design were conducted by considering the different reservoir pore structures and microsphere sizes used for oil displacement, so that the slug size is minimized while the net revenue is maximized. Since 2009, deep profile control technology by injecting small slug-size nano-microsphere has been developed in offshore oilfields in Bohai Sea. The main mechanism of nano-microsphere is different from the traditional approaches which increase the water phase viscosity to improve mobility ratio. In nano-microsphere deep profile control technology, nano/micron level microspheres were dispersed in the water phase. Along with the water injected into formation, microspheres swell under the formation condition, plug the water channels, reduce the permeability of high permeable zone, dynamically change the water flow paths, thus increase the water sweeping efficiency. Since 2009, a total of 17 well patterns have implemented in QHD, BZ28, BZ29 oilfields in Bohai Sea. In all those tests, small slug sizes in the range from 0.01 to 0.02 PV were used. Water cut is reduced from 80% to 70% and cumulative oil production was increased by 13.1×106m3. The economic evaluation suggests that for every one dollar investment on this technology, 3.1 dollar can be made even when the oil price is $30 per barrel. So the project has a good technical and economic outcome even in extreme low oil prices.