Enhanced oil and gas recovery is going to be the future option for Pakistani reservoirs sooner or later, when conventional gas deposits will be running short and oil reservoirs will not be able to continue production under their current depletion mechanisms.
Reservoir analysed in this study is one of the four vertically stacked heavy oil reservoirs in an oilfield of Potwar region and producing at lower production rate. This work is an attempt to screen the subject reservoir for future decisions. First fluid characterisation was executed using experimental PVT data. History match was performed using available production and reservoir data. Since flowing bottom-hole pressures were unavailable, they were generated using Guo Ghalambor correlation using tubing head pressure information. Afterwards, reservoir screening was performed using available criteria in the literature and updated with world EOR survey. Screening dictated the application of miscible carbon dioxide flooding for the subject reservoir. Also the reservoir pressure was above bubble point, showing the feasibility for CO2 injection. Minimum miscibility pressure was estimated empirically using Alston et al. correlation and numerically by slim-tube simulation. MMPs resulted from both methods well agreed.
Three scenarios were made to analyse the performance of reservoir under the influence of revitalization planning. Additional producer was placed in the subject reservoir, which ceased flow after 16 years adding 1 MMSTB of oil to the reserves. Injecting water enhanced the life of the reservoir to 24 years yielding 2.8 MMSTB of oil while the application of CO2 miscible flooding incremented 3.7 MMTSB of oil in the same duration as waterflood.
Results inferred from this study will prove to be a breakthrough in the field of R&D for welcoming enhanced oil recovery in Pakistan. It also encourages the industry look ahead to the revitalization of mature and aging oil fields.
Field XYZ under study was located in Potwar Region of Pakistan which is home to various oilfields which are producing from light to heavy oils.
The Potwar Basin has been actively explored for hydrocarbons since 1870 and first success came in 1914 when Attock Oil Company discovered oil at Khaur. The Dhulian, Joyamir and Balkassar field were then discovered by the same company in 1918, 1943 and 1945 respectively. In 1978 Amoco was granted the exploration license in the Northern Potwar. In 1982, the concession was granted to the Occidental of Pakistan, who discovered oil from the Eocene formations and later from Paleocene and Permian horizons. Similarly, NOC1 was also granted exploration license in the Northern Potwar Deformed Zone (NPDZ), where it drilled several exploratory, appraisal as well as development wells successively.
In 1990, with the help of 3D Seismic Survey for the first time in the history of Pakistan, Rajpet1 field was explored. Fig. 1 is showing the horizon map of a reservoir in Rajpet oilfield.
Geologically, Rajpet structure is NE-SW trending anticline. The producing part of the structure is pop up block formed between two thrust faults. The closed area is about 12 sq.km bounded by 1800 m.sec contour 2.
Field had four vertically stacked reservoirs and to-date 5 wells had been drilled in this field and 4 were producing (as on 31–12–2010)