Abstract
Sampling process is one of the important tasks in petroleum engineering which is used to specify the fluid type and estimate PVT characteristics. Moreover, to perform geochemical and crude oil analyses, enough volume of fluid is required. To obtain a representative reservoir fluid, sampling should be preferably done at the beginning of the reservoir life i.e., prior to reaching saturation pressure. Above the saturation, the presence of free gas in the oil layer is less probable and the representative reservoir fluid can be acquired. In this study, we propose a detailed step-by-step procedure for the fluid sampling process. According to temperature and pressure conditions at each step, one or more oil or gas properties have been calculated appropriately. Since the down-hole sampling cannot provide sufficient volume for PVT analysis and other fluid calculations, the surface sampling and recombination processes are of great importance. To validate and justify the proposed procedures, we studied a surface recombination process on a volatile reservoir fluid from an oil field in the Middle East. The results indicate reasonable agreements between recombined fluid properties and reservoir fluid properties obtained from routine analysis. The error of 3.2 % has been observed in saturation pressure values compared with the down-hole reservoir fluid.
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Abbreviations
- P :
-
Pressure (psi, mmHg)
- T :
-
Temperature (Fahrenheit, Rankin)
- V :
-
Volume (cc, ft3, bbl)
- GOR:
-
Gas–oil ratio (vol/vol, Scf/Stb)
- Z :
-
Compressibility factor
- \({\rho}\) :
-
Density (g/lit)
- B 0 :
-
Formation volume factor (bbl/Stb)
- V 1 :
-
Volume of liberated gas from separator oil (cc)
- V 2 :
-
v g = gas volume at the standard condition (cc)
- P 1 :
-
Final pressure (mmHg)
- P 2 :
-
Standard pressure (760 mm Hg, 14.7 Psia)
- T 2 :
-
Standard temperature (520 R)
- T 1 :
-
Test temperature (R)
- T L :
-
Laboratory temperature (R)
- GORs-p :
-
Ga–oil ratio from initial pressure (single phase) oil to atmosphere
- v d :
-
Dead oil volume
- GORsep :
-
Separator GOR from field data
- Z f :
-
Field compressibility factor
- Z l :
-
Laboratory compressibility factor
- Z 2 :
-
Standard compressibility factor (1)
- \({{\gamma}_{{\rm f}}}\) :
-
Field specific gravity
- \({{\gamma}_{{\rm l}}}\) :
-
Laboratory specific gravity
- \({{\rho}_{{\rm g}}}\) :
-
Gas density
- \({{\gamma}_{{\rm g}}}\) :
-
Gas specific gravity
- \({{V}_{{\rm s}\text{-}{\rm p}}}\) :
-
Volume of single-phase oil
- V d :
-
Volume of dead oil at standard condition
- V gSC :
-
Gas volume at standard condition
- P cell :
-
Recombination cell pressure
- V cell :
-
Recombination cell volume
- \({{Z}_{{\rm T}\text{-}{\rm CP}}}\) :
-
Compressibility factor at laboratory temperature and cell pressure
- V gRe :
-
Gas volume in laboratory temperature and recombination pressure
- \({{Z}_{{\rm T}\text{-}{\rm Re}}}\) :
-
Compressibility factor in laboratory temperature and recombination pressure
- P Re :
-
Recombination single-phase pressure (Psia)
- V o SC :
-
Oil volume at standard condition
- Cold GOR:
-
Gas–oil ratio at ambient temperature
- V oRe :
-
Oil volume in laboratory temperature and recombination pressure (cc)
- B o :
-
Oil formation volume factor (cc/cc)
- V t :
-
Total volume of oil and gas required for recombination process (cc)
References
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Strong, J.; Thomas, F.B.; Bennion, D.B.: Reservoir Fluid Sampling and Recombination Techniques for Laboratory Experiments. Petroleum Society of CIM. Paper No. CIM 93-54 (1993)
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Williams, J.M.: Getting the Best Out of Fluid Samples. SPE; Science Support Services, E&P Exchange, JPT. September (1994)
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Moayyedi, M., Ahmadi, M., Izadi, M. et al. Volatile Fluid Recombination: A Case Study. Arab J Sci Eng 39, 9277–9282 (2014). https://doi.org/10.1007/s13369-014-1415-x
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DOI: https://doi.org/10.1007/s13369-014-1415-x