Abstract
Daqing Oilfield is a heterogeneous multi-layer sandstone oilfield. The main pay zone of the oilfield has entered into high water-cut (over 90%) development stage after more than 30 years of water injection. According to intrusive mercury tests on 104 pieces of sealed coring samples, permeability increased by 32% after water flooding; the pore volume increased by 5.9%. This may indicate a change in pore structure affected by long-term water injection. In thick layers, water bypasses oil and flooding efficiency decreases.
Fine geology research results show that in main pay zones and thick layers of non-main pay zones, there are certain amounts of remaining oil. Vertically, the remained oil gathers on the top of positive rhythm thick formations. For this portion of the remaining oil, it is difficult to develop by conventional stimulation measures. Therefore, study on nitrogen foam injection technology was carried out to control fingering. Core experiments indicated that nitrogen foam injection is suitable for enhancing oil recovery rate of heterogeneous reservoirs. Field pilot gave positive results.
This paper briefly introduces profile modification mechanism of nitrogen foam to control fingering and enhancing oil recovery rate. Static tests of foam adaptability to temperature, salinity, and oil saturation are evaluated in the paper.
Nitrogen foam can select automatically the high permeability zone and high water cut layer and realize fluid diversion after foam plugging, and then the gas component may provide gravitational differentiation when the foam bubbles break off, so as to increase the sweep volume and enhance the flooding efficiency[1][2] [3] [4] [5]. At present, Sabei Oilfield in Daqing has entered into the extra high water-cut development with its total water-cut up to 96%. Vertically, the water out behavior in layers differs greatly and massive water injected advances suddenly along high permeability positions, resulting in serious channeling. Therefore, in view of the geologic characteristics and fluid properties, three sets of foam system are developed, and the field pilots for nitrogen foam injection technology to control water fingering are conducted successively in Xing 7-1-33 and Bei 2-Ding 2-59 well cluster in Sabei Oilfield.
