Abstract
In China, the initial development program was "early zonal water injection" for the reservoirs with insufficient natural drives and low formation-saturation pressure differential. At present, the oilfields have successively been progressing into the late development stage with high water cut. Especially in high-permeability reservoirs, water fingering through a single layer results in poor development response. The objective of this paper is to efficiently control invalid water cycling and realize a smooth flooding profile. A technology for whole-process monitoring and controlling in zonal injection has been developed for waterflooding reservoirs based on cable-controlling approach. This technology can constantly monitor real-time flowrate, cumulative volume injected, tubing pressure and casing pressure, as well as intelligently adjust the injection rate according to the allocation in the development program, thereby realizing fine zonal injection. As a demonstration, a typical block characterized by the high permeability (~100 mD in average) and being at the late development stage with high water cut (96.8%), was chosen to conduct the follow-up study and evaluate waterflooding efficiency of high-permeability reservoirs.
There are 54 water injectors connected to 98 oil producers in the demonstration block. The data for one consecutive year upon implementation of the technology were collected and then analyzed. The analysis results illustrated that the water absorption profile was improved and the water fingering was efficiently controlled. The monthly rising rate of the composite water cut in the demonstration block decreased from 0.1% (value before the implementation) to 0.02%, and even to −0.027% in some individual well groups (which means the composite water cut was reduced); 77.5% of sandbody thickness in some individual wells has been producing, compared to 50.7% before the implementation, achieving remarkable effect. As can be seen, this technology is of great guiding significance for waterflooding development of high-permeability reservoirs at the late development stage with high water cut.
