Screening Criteria For Enhanced Oil Recovery In Sudanese Field

Abstract

Sudan has been producing its petroleum resource commercially since 1999 when Block 1/2/4 started production of its locked oil reserve. This was the major achievement by its Operator, GNPOC, when they commercialize and export crude to foreign buyers via 1500km new pipeline to Port Sudan. Since then, its daily production has increase to maximum of 300 KBOPD in 2006 before it started declining rapidly with increasing water production. Three more operators, Petro-Energy, PDOC and WNPOC started their oil production in 2006. Current total production is 522 KBOPD as of (Dec 2010). Total Sudan oil in place as of 1st January 2009 is estimated at 15.9 billion barrels of which 39% (6.2 billion barrels ) of this oil is in block 3/7 operated by PDOC which contributes about 37% total Sudan estimated ultimate oil recovery. GNPOC holds second biggest oil in place of 5.5 billion barrels but the highest recoverable oil of 1.6 billion barrels, contributing about 45%, of the national reserve. The remaining are in WNPOC and Petro-Energy. The average recovery factor for Sudan is estimated at 23% which is relatively low on international standard. GNPOC's average recovery factor is the highest at 26%, followed by PDOC, Petro-Energy and WNPOC at 21.5%, 23% and 11.9% respectively. This is low recovery factor is attributed to amongst others the quality of the oil and also non-favorable reservoir properties, GNPOC's API is the highest at 33 API, followed by PDOC at 25 API, WNPOC at 21 API and Petro-Energy at 18 API. With declining production and the fact that 67% of the oil will still remain in the ground at the end of field producing life, there is an urgent need to adopt new approach to enhance oil recovery to arrest the declining production. The current production is declining at about 100% per annum, and in next 8 years total national production will reduce to 55% (300 KBOPD) of its current production capacity of 522 KBOPD. Total cumulative production as of end 2008 is 1.05 billion barrels. Today, most oil fields production is on natural depletion and assisted by artificial lift pumps. Only Unity/Talih fields in GNPOC is on water injection to provide pressure maintenance, while a pilot is being implemented in PDOC. In the low API oil and viscous crude production environment, water injection is usually not favorable for application due to the poor mobility ratio which is susceptible to water fingering. And early high water-cut and low oil production rate are expected in heavy oil production. Beside infill drilling, well stimulation and horizontal well drilling to produce the "low hanging fruits" a major step forward is needed to improve oil recovery. Suitable and cost effective enhanced oil recovery technique should be selected for implementation. There are a total of 292 EOR projects implemented in 5 countries namely USA, Canada, Venezuela, China and India. Different technique like CO2 immiscible & miscible, steam, polymer and in-situ combustion is proven technologies. About 1.6 MMSTB/day are being produced from EOR project worldwide of which 49% are from thermal application and 45% are miscible. Only 6% are using chemicals. Miscible are more applicable in the production of lighter API oil. EOR project can significantly increase recovery factor which translates into more reserve and higher production, which prolongs sustainable production and field life; however, it requires huge investment, high risk and operationally more complex than secondary recovery methods. It is estimated that at the current STOIIP figure of 15.9 billion barrels, some 2.9 of reserve can be added from IOR projects 0.5 billion barrels from water injection and 2.4 billion barrels from EOR which corresponds of 3% and 15% assumed increase in recovery factor respectively. At oil price of USD40 per barrel, this is valued at USD 116 billion of which 83% is contributed from EOR. Additional production of 400 KBOPD is anticipated from their applications assuming a decline rate of 5% EUR per year. The objective of this study to make survey for all Sudanese fields through screening criteria to select the suitable EOR method for each block to increase recovery factor and economical analysis for method that applied on the Sudanese fields and also by the end making road maps and wide picture for EOR in Sudan. The study concluded that the implementation of some EOR method in Sudan will lead to maximize the production and recovery factor and it showed the importance of early implementation of these methods to make the gain as long as possible and also to take the lesson learn from the similar cases in other countries.