Steam Injection in Fractured Carbonate Reservoirs: Starting a New Trend in EOR
- Richard K. Penney (PDO) | Riyadh Moosa (PDO) | Gordon Thomas Shahin (Shell) | F. Hadrami (PDO) | A. Kok (PDO) | G. Engen (PDO) | O. van Ravesteijn (PDO) | K. Rawnsley (Shell) | B. Kharusi (Shell)
- Document ID
- International Petroleum Technology Conference
- International Petroleum Technology Conference, 21-23 November, Doha, Qatar
- Publication Date
- Document Type
- Conference Paper
- 2005. International Petroleum Technology Conference
- 5.3.4 Reduction of Residual Oil Saturation, 5.8.7 Carbonate Reservoir, 5.5.8 History Matching, 4.1.5 Processing Equipment, 6.5.5 Oil and Chemical Spills, 3.3.2 Borehole Imaging and Wellbore Seismic, 5.4.10 Microbial Methods, 4.3.4 Scale, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.1.1 Exploration, Development, Structural Geology, 5.7.2 Recovery Factors, 4.1.2 Separation and Treating, 5.4.6 Thermal Methods, 5.2.1 Phase Behavior and PVT Measurements, 1.6.10 Coring, Fishing, 5.1.2 Faults and Fracture Characterisation
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Significant volumes of heavy oil remain in fractured carbonate reservoirsworldwide. Some of these reservoirs are good candidates for the application ofthermally assisted gas-oil-gravity-drainage (TA-GOGD), a novel EOR technique.Unlike a normal steam flood, the steam is used as a heating agent only toenhance the existing drive mechanisms. The elegance of TA-GOGD is that thefracture network is both used for the distribution of steam (heat) and therecovery of the oil. The number of wells can therefore be kept to a minimumcompared to conventional steam floods. Following encouraging pilot results in afield in Oman, a steam injection project is heading for implementation, a firstof its kind on this scale. Studies to date indicate that recovery factors of25-50% with Oil-Steam-Ratios of 0.2 -0.4 m3/ton of steam are feasible. Thesuccess of the project is critically dependent on the field-wide presence ofconductive fractures and the ability to characterize them. Both stochastic anddeterministic studies were tried, but the latter method is now favoured as itallows the use of geological and dynamic understanding as input to themodelling and honours existing faults, deformation mechanism and the conceptualmodel. Fracture characterisation is to some extent still an art and outputs are'only static scenarios'. Therefore results should be validated with dynamicdata as much as possible. The dynamic models are thermal and dual permeability,with compositional dependencies: a complexity that is rarely encountered.Explicit fracture block models are used to verify that the heating rate andGOGD are captured properly, in particular for irregularly shaped fracturepatterns. A new fully integrated workflow of fracture characterisation withstatic and dynamic modelling has enabled uncertainties and risks to be managedin a scenario based approach.
Primary production performance such as that of Qarn Alam Qarn Alam Field islocated in central Oman south of the Shuaiba is only expected to recover some3-5% of the oil in western Hajar Mountains. This large oil accumulation isplace over any reasonable time frame due to low matrix trapped in theCretaceous Shuaiba, Kharaib and Lekhwair permeability and high oil viscosity ongravity drainage rates. limestone units at a depth of around 200-400m sub sea.The Recoveries via matrix floods of water, polymer or steam were anti-clinalstructure is a result of a deep salt diaper, with discounted as developmentoptions due to the pervasive significant crestal faulting and fracturing.fracturing observed in the field which would encourage the
flooding agents to completely bypass the matrix. The field was discovered in1972 and placed on primary production in 1975. The produced oil was found to be16Â° API with a viscosity of 220cP. During the primary production period from1975 to 1995, the first year showed a large peak in oil mainly from emptying ofthe fracture network with a minor contribution from fluid expansion due topressure reduction.
At the end of the first year, production had declined to a very lowsustainable rate interpreted to be from gravity drainage, from a combination ofgas-oil (GOGD) from the secondary gas cap and oil-water (OWGD) below thefracture gas-oil contact (FGOC). The reservoir then consists of a matrix withvery little drainage and a fracture network with a thin oil rim below thesecondary gas cap and above the fracture oil-water contact (FOWC), figure1.
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