Development Strategy for Gas Cap Reservoirs with Edge Water and Complicated Faults in Niger

Abstract

In recent years, a great number of stratified reservoirs with edge water and complicated faults have been discovered in Niger. Gas cap reservoirs are typical and common among all the discovered oil-bearing blocks. Making efforts to achieve good development effects of this kind of reservoirs is of great significance for stable production of entire project. There are many factors influencing the development of gas cap reservoirs. Development of gas cap reservoirs with edge water and complicated faults are very difficult and challenging. Several problems including gas breakthrough, interlayer interference and rapid increase of gas–oil ratio are easy to occur. Taking G oilfield in Niger as an example, based on development mechanism of gas cap reservoir with edge water and complicated faults, single sand bodies are specified and reservoir type of sub-layers are detailed researched according to gas cap index. Development idea of oil production prior to gas production is put forward and reasonable oil recovery offtake rate is optimized. In addition, water injection parameters are optimized and development strategy of layer by layer is adopted to realize successively producing remaining oil between layers. Combined with reservoir numerical simulation research and practical production practice, when the initial offtake rate is around 2%, stable production period and recovery factor within contract period is relatively high; according to the gas cap index, different energy layers are divided and commingling production or interlayer interference with different energy should be avoided; when the pressure level drops down to 60–70% of initial state, converting oil production well in side low position to be water injection well is essential; lower E3 and E2 reservoirs are produced in the preliminary stage and later upper E1 reservoirs should be produced integrated with the production–injection well network improvement to ensure the stable production of the oilfield. Successful development of G oilfield provides valuable ideas and references for the effective development of other similar reservoirs in Niger.