Results of oil deposits secondary development in Samara region after long-term conservation
UDC: 622.276.1/.4
DOI: -
Authors:
KOZHIN V.N.
1,
DEMIN S.V.1,
BAKIROV I.I.2,
YUSUPOV A.F.2,
BAKIROV A.I.3
1 SamaraNIPIneft, Samara, Russia
2 Kazan Scientific Center, Kazan, Russia
3 Kazan affiliate of FBU "GRC", Kazan, Russia
Keywords: secondary operation, coning, oil displacement, reservoir reformation, reserves consolidation, oil-water factor, forced fluid withdrawal, flushing rate, gravitational pressure drop
Annotation:
A characteristic feature of oil production in Samara region in recent years is introduction into industrial development of fields previously temporary abandoned due to high water cut and low oil flow rates. The authors of the article analyze the results of secondary exploitation of seven Devonian and eight Carboniferous deposits confined to terrigenous reservoirs of oil fields in the Samara region after a long-term conservation (from 5 to 28 years). The authors studied the efficiency of such development for two groups of deposits that differ in the mechanisms of oil displacement: the first group is displacement due to the rise of the water-oil contact (WOC) with the formation of water cones and the second group is displacement by bedding, with water linear filtration.
The authors for the first time use two independent approaches to quantitatively assess the efficiency of re-entering a deposit:
– increment of the oil recovery factor for cumulative production ΔКИНнд;
– increment of the recovery factor ΔКИНхв, estimated using displacement characteristics (DC). This approach allows objectively judging the efficiency of the method, eliminating the ambiguity of the recoverable reserves nature.
The parameters characterizing the operating mode are introduced:
– degree of change of the flushing ratio nKпром = Kпром2 ∕ Kпром1
(ratio of the flushing multiplicity after secondary operation Kпром2 to primary Kпром1);
– coefficient of efficiency of forced liquid extraction KФОЖ = Kн/Kж (ratio of the relative growth of oil flow rate to the relative growth of liquid flow rate during the deposit repeated entry). Additionally, the so-called gravitational pressure drop ΔРгр = kgΔρh, characterizing the effect of gravitational forces, is calculated for each deposit. The authors studied the effect of the above-listed parameters on the efficiency indicators. The nature of the revealed dependencies indicates that the efficiency of the secondary development is determined primarily by hydrodynamic factors associated with the additional involvement of the remaining mobile oil, rather than by the static properties of the formations. The decisive role is played by the volume of the fluid additionally pumped through the formation and the degree of intensification of oil recovery. Conclusions are made about the importance of long-term conservation and secondary exploitation with forced fluid recovery (FFR) for the first group, a short-term conservation with subsequent exploitation with FFR is proposed for the second group of deposits, and limitations are identified.
The studies did not confirm the hypothesis of spontaneous reformation of oil deposits due to the migration of film oil under the influence of gravitational and capillary forces. At the same time, the authors emphasize that gravity played a positive role (the first group), contributed to the gravitational alignment of the OWC (separation of the water cone from the well bottom) and the concentration of oil in the upper part of the formation due to the pressure of bottom waters.
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