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Effect of Serpukhian sediments geologic structure and saturation on reservoir fluid flow

UDK: 622.276.1/.4
DOI: 10.24887/0028-2448-2017-5-36-39
Key words: reservoir, limestone, dolomite, porosity, permeability, pores, fissures, caverns, reservoir fluid flow, oil production, watercut
Authors: B.F. Borisov, G.N. Karchevskaya (Giprovostokneft JSC, RF, Samara), G.A. Kovaleva (Samara State Technical University, RF, Samara), A.A. Alexandrov (Volga Department of IGiRGI JSC, RF, Samara), A.M. Tupitsin (BaiTex Ltd., RF, Samara), S.A. Kovalev (Nefteotdacha-Service Ltd., RF, Samara)

The article presents the results of void space study in Baituganskoye field Serpukhian paybed С1s. Recent detailed studies have been carried out for rack samples from 13 wells.

Reservoir С1s is formed by limestone и dolomite. Lasting post-sedimentation transformations finally have resulted in complicated structure of void space – to porous-fissured- cavernous rock type. Oil saturation of reservoir С1s depends on fissures, caverns and partially with reservoir matrix within the zone of fissures and separate reservoir parts adjacent to the top.

Characteristics of rocks with intergranular component have been estimated based on standard-size core analysis data. Average porosity of these rocks is 9.8 %, average permeability – 0.159 Ојm2. Characteristics have been calculated considering boundary capacity equal to 6.3%, filtration characteristic – 0.0022 Ојm2. Fissures and caverns capacity has been calculated together based on difference between total porosity (defined from neutron-gamma method diagrams) and intergranular capacity (defined at cores). On average it is equal to 3.27 %.

In addition, noticeable volume of Serpukhian dense rocks’ variety is observed, which as per well logging data (in accordance with boundary porosity) are distinguished as the reservoir. In this case, tight rock portion has been excluded from oil-saturated volume - as the following ratio: number of dense samples (with off-grade porosity and permeability within reservoir productivity section) versus total number of analyses. Average share of dense part in oil-saturated volume of reservoir С1s is equal to 52.2 %.

Characteristic feature of reservoir С1s is lack of water-free crude production and quick growth of wellstream watercut. Hydrodynamic studies have covered 29 % of well stock, which have shown that (depending on well location) permeability varies within 0.07–1.45 Ојm2. The most successful well are located at pool’s east – high fissuring zone. Hydrodynamic studies have not been carried out for these wells; however, based on yield and drawdown analysis results, permeability is 2.4–7.3 Ојm2. Wells watercut character and 3D simulation results show coning presence from OWC.

Considering the above mentioned occurrence conditions of reservoir С1s, we can recommend fluid’s quick draw-off. After watercut, which can develop within several years, wells may be either converted for overlying bed or used for side-tracking.

References

1. Smekhov E.M., Teoreticheskie i metodicheskie osnovy poiskov treshchinnykh kollektorov nefti i gaza (Theoretical and methodological foundations for the search for fractured oil and gas reservoirs), Moscow: Nedra Publ., 1974, 186 p.

2. Bagrintseva K.I., Usloviya formirovaniya i svoystva karbonatnykh kollektorov nefti i gaza (Conditions for formation and properties of carbonate reservoirs of oil and gas), Moscow: Publ. RGGU, 1999, 285 p.

3. Tkhostov B.A., Vezirova A.D., Vendel'shteyn B.Yu., Dobrynin V.M., Neft' v treshchinnykh kollektorakh (Oil in fractured reservoirs), Moscow: Nedra Publ., 1970, 221 p.

The article presents the results of void space study in Baituganskoye field Serpukhian paybed С1s. Recent detailed studies have been carried out for rack samples from 13 wells.

Reservoir С1s is formed by limestone и dolomite. Lasting post-sedimentation transformations finally have resulted in complicated structure of void space – to porous-fissured- cavernous rock type. Oil saturation of reservoir С1s depends on fissures, caverns and partially with reservoir matrix within the zone of fissures and separate reservoir parts adjacent to the top.

Characteristics of rocks with intergranular component have been estimated based on standard-size core analysis data. Average porosity of these rocks is 9.8 %, average permeability – 0.159 Ојm2. Characteristics have been calculated considering boundary capacity equal to 6.3%, filtration characteristic – 0.0022 Ојm2. Fissures and caverns capacity has been calculated together based on difference between total porosity (defined from neutron-gamma method diagrams) and intergranular capacity (defined at cores). On average it is equal to 3.27 %.

In addition, noticeable volume of Serpukhian dense rocks’ variety is observed, which as per well logging data (in accordance with boundary porosity) are distinguished as the reservoir. In this case, tight rock portion has been excluded from oil-saturated volume - as the following ratio: number of dense samples (with off-grade porosity and permeability within reservoir productivity section) versus total number of analyses. Average share of dense part in oil-saturated volume of reservoir С1s is equal to 52.2 %.

Characteristic feature of reservoir С1s is lack of water-free crude production and quick growth of wellstream watercut. Hydrodynamic studies have covered 29 % of well stock, which have shown that (depending on well location) permeability varies within 0.07–1.45 Ојm2. The most successful well are located at pool’s east – high fissuring zone. Hydrodynamic studies have not been carried out for these wells; however, based on yield and drawdown analysis results, permeability is 2.4–7.3 Ојm2. Wells watercut character and 3D simulation results show coning presence from OWC.

Considering the above mentioned occurrence conditions of reservoir С1s, we can recommend fluid’s quick draw-off. After watercut, which can develop within several years, wells may be either converted for overlying bed or used for side-tracking.

References

1. Smekhov E.M., Teoreticheskie i metodicheskie osnovy poiskov treshchinnykh kollektorov nefti i gaza (Theoretical and methodological foundations for the search for fractured oil and gas reservoirs), Moscow: Nedra Publ., 1974, 186 p.

2. Bagrintseva K.I., Usloviya formirovaniya i svoystva karbonatnykh kollektorov nefti i gaza (Conditions for formation and properties of carbonate reservoirs of oil and gas), Moscow: Publ. RGGU, 1999, 285 p.

3. Tkhostov B.A., Vezirova A.D., Vendel'shteyn B.Yu., Dobrynin V.M., Neft' v treshchinnykh kollektorakh (Oil in fractured reservoirs), Moscow: Nedra Publ., 1970, 221 p.


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