Optimization of Water Injection : Case Study Unity Oil Field - Sudan

Abstract

The main objective of this research is to study and evaluate the water injection in sandstone reservoir to provide pressure support and sweep oil out of the pore space to improve oil production. The work focuses on several important issues of reservoir characterization and data integration for water flooding in sand stone reservoir. In determining the suitability of a given reservoir for water flooding or pressure maintenance many factors are important, these factors considered: reservoir geometry, lithology, reservoir depth, porosity, permeability (magnitude and degree of variation), continuity of reservoir rock properties, magnitude and distribution of fluid saturations, fluid properties, relative permeability relationships, and primary reservoir driving mechanisms. Optimization of reservoir development requires a comprehensive evaluation of many decision variables, such as the reservoir properties, well locations and production scheduling parameters, to obtain the best economical strategies. Reservoir simulation studies for East Unity oil field, Muglad Basin, Sudan used to know the best field water injection method. Reservoirs in Unity oil field are resulted of fluvial and lacustrine deposition. The field is a highly complex anticline with major flanking faults to the west and east. Oil is trapped in separated compartments with varying degrees of dip faults closures. On flanking faults the oil-bearing formations are Aradeiba and Bentiu. East Unity oil field sandstone reservoirs is young reservoir started production at 1999. Reservoir is highly heterogeneous, characterized by mid to high porosity and mid to high permeability. The purpose of this simulation study is to determine the suitable water injection method for high cumulative oil production. The simulation model was developed using two-phase, 3D black oil options in ECLIPSE. A good history matching was achieved for the field as general and for the wells one by one. The bottom formation (Bentiu) did not considered or perforated through this study because there are many previous studies suggested to produce from this formation later because water cut will increase by 60% if this zone perforated at the same time with Aradeiba zone. The field now has 9 producers and 4 injectors. The study of the optimum future performance was evaluated through several water injection cases. Cumulative water injection for ten years later for the base case (the actual case) was used as the main control for all the cases. Several cases were tested included cyclic water injection which is a process that improves waterflooding efficiency in heterogeneous reservoirs. Several cyclic water injection scenarios by "injection/no injection" time ratios such as 2:1, 1:1, and 1:2 also were simulated and evaluated using numerical simulation. The cases compared together with the actual case. The keys criteria; cumulative oil production, water cut, and recovery; were used as qualitative indicator to determine the quality of the comparison matches. Simulation shows the optimum water injection rate is about 2835 Sm³/day for every well, using this amount oil recovery will increase by 3.63 %. The study shows adding new injection well has no positive effects in the area although cyclic water injection was failed in East Unity field since water cut from all producers are more than 90 %.