Application of Well Pattern Adjustment for Offshore Polymer Flooding Oilfield: a Macro-Scale and Micro-Scale Study

The early polymer flooding development technology has been applied to the Bohai Bay oilfield. However, about 50% of the residual crude oil remains in the formation after polymer flooding. The ways to improve the effect of polymer flooding needs to be further investigated. In this paper, we simulated the development effect of well pattern adjustment technology during polymer flooding through laboratory experiments and analyzed the development effect of oil displacement and the distribution of remaining oil from macroscopic and microscopic aspects. The micro-electrode technology was applied to the macro-scale physics experiment to study the development effect and residual oil distribution. In this experiment, nine-spot injection pattern was changed to line-drive pattern during polymer flooding. The micro-scale physics experiment uses nuclear magnetic resonance technology to study the micro-scale distribution of residual oil in the high and low permeability core pores before and after polymer flooding. The experimental results show that in heterogeneous reservoir, the remaining oil is mainly concentrated in the large pores of the medium and low permeability layers at high water cut stage. During the polymer flooding stage, the polymer is squeezed into the large and medium pores of the high-permeability layer and small pores of the low-permeability layer, effectively increasing the sweeping area and displacement efficiency of the low-permeability layer. The residual oil remains mainly in the large pores of the medium and few permeability layers. During the subsequent water flooding stage, the medium permeability layer demonstrates the strongest displacement effect. The increase in yield of the low permeability layer was mainly due to the displacement of oil in the large pores in low permeability layer. After long-term water injection development, the oil recovery of large pores in the low-permeability layer is similar to that in the high-permeability layer. The remaining oil is concentrated in the small pores of the high-permeability layer and the medium and small pores of the low-permeability fiver. The low-permeability layer still has potential for development. Changing the well pattern system is conducted to provide uniform displacement of polymer solution, improving and enhancing the displacement effect of polymer flooding and subsequent water flooding, especially improving the displacement effect in the low permeability layer. In this experiment, the oil recovery of well pattern adjustment was increased by 4.77%. Through experimental research, we believe that polymer flooding with well pattern adjustment can not only expand the flow area by changing the flow field, but also further play the role of polymer profile control. The two mechanisms complement each other, 'effectively improving the unevenness of displacement and enhancing the oil recovery. The experimental results can provide new ideas and technical support for further improving the development effect of polymer flooding in offshore oilfields.