The Patos-Marinza Heavy Oil Field, located in southern Albania, was discovered in 1928. The reservoir, with oil specific gravity ranging from 0.86 to 1.05 (3 to 33 oAPI), contains one of the largest onshore oil resources in continental Europe. Primary production commenced in the 1930s and reached a peak rate of over 3,300 m3/d in the late 1950s. By June 2004, over 2,400 wells had been drilled, at an average spacing of about 3.6 hectares, and cumulative oil production amounted to about 19 million m3. However, the expected ultimate oil recovery by primary recovery was only about 6% of the original-oil-in-place (‘OOIP’).
In 1999, foamy oil production was successfully tested in the laboratory for field application at Patos-Marinza. Subsequently, progressive cavity pumps ('PCP's) were installed in 12 wells in the northern region of the field completed in the main Driza sands, as a pilot test of Cold Heavy Oil Production (‘CHOP’) technology to improve recovery. In July 2004, an intensive campaign of well reactivations using CHOP technology was initiated under new operatorship.
The performance of the pilot test indicated that foamy oil behavior had been clearly initiated at 5 of the initial test wells as a result of the increased drawdown applied to the reservoir. Oil production rates were increased significantly, by an order of magnitude, between 10 m3/d and 20 m3/d. In addition, sand cuts of between 5% and 20% and foam cuts were reported.
The performance of the wells put on CHOP production since change of operatorship in July 2004, have yielded good results. As of July 2005, the current operator has taken over 76 wells and continues to progressively apply CHOP technology to the field. This paper focuses on the wells that have exhibited clearly defined CHOP performance characteristics and reports the initial results in terms of well production rate responses.
The Patos-Marinza Heavy Oil Field, located onshore in southern Albania, is one of the largest onshore fields in Europe with an OOIP of over 300 million m3. The field has gross dimensions of 5 kmeast-west by 14 kmnorth-south (Figure 1).
The reservoirs of this large oil field are heavily faulted and compartmentalized and comprised of three main oil-bearing sandstone formations, the Driza, Marinza and Gorani, in a large, dipping structure. Key reservoir and fluid parameters have wide ranges, imparting a similar range in reservoir performance. Approximate ranges of various reservoir parameters are:
Depth 60 - 1,800+ m
Oil Density 0.86 to 1.05 tonnes/m3
Porosity 15 - 40%,
Permeability 1 - 2000+ mD
The field has been developed with over 2,400 wells and produced under primary depletion for over seventy years, with an overall recovery factor around 6% and individual well recoveries less than 10%. As of mid 2004, under new operatorship, an aggressive campaign of well interventions and application of CHOP technology has been implemented. This paper presents a review of the initial performance of the CHOP process.