Development of poorly swept and hard-to-recover oil reserves by changing fracture orientation

Enhanced oil recovery is a vital issue for all petroleum companies. As is well known, recovery of oil reserves is non-uniform across the field, with recovery factor rarely exceeding 0.4, which is especially notable in reservoirs of complex geology. Drainage of oil reserves is also significantly affected by discrepancies in directions of regional horizontal stresses. Movement of injected water and propagation of natural and hydraulic fractures go along thedirections of maximum stresses, thus increasing poorly swept areas. Changing fracture propagation patterns enables better stimulation of the pay zone and recovery of bypassed and dead-end oil as well as extraction from lenticular and semi-lenticular beds, increment of recovery factor, expansion of candidate well selection criteria, and maintaining oil production levels.
Materials and methods
Two-stage hydraulic fracturing in the wells of Povkhovskoye field. DSI (dipole shear sonic imager) logging.
Results
Having reviewed actual performance of wells and well survey results upon completion of two-stage hydraulic fracturing, it is a fair assumption to saythat we have succeeded in changing the direction of fracture propagation, which helps to recover reserves from poorly swept and dead-end compartments of a reservoir. Implementation of such fracturing technique has changed the main criteria used for selection of wells to be fractured, which may be defined as follows:
1. Water cut of up to 100%.
2. Elimination of such adverse factor as location of a candidate well relative to injectors, with minimum distance between producers and injectors reduced to 150-200 m.
3. Selection of a candidate well is less determined by high cumulative oil output.
4. Reservoir compartmentalization (more than 3 compartments), geologic heterogeneity.
Сonclusions
This technology has helped to reactivate over 100 idle wells, most of which are spaced at 250-300 m from injectors and poorly placed relative to maximum regional stress directions. Underthe above conditions, conventional fracturing may increase the risk of water breakthrough. 10 applications have revealed incremental oil production rate of more than 10 tons per day with an average rate of 14.2 tons per day, which is comparable to production rates of lateral wells at Povkhovskoye oilfield. As of today, about 95% of all hydraulic fractures utilize a two-stage fracturingtechnique. The latter is being successfully implemented in other companies ofOOO "LUKOIL-West Siberia".