Abstract
Asmari is the main productive reservoir in Abu Ghirab oilfield in the south-east part of Iraq. It has history production extends from 1976 up to now with several close periods. Recently, the reservoir suffers some problems in production, which are abstracted as water production rising with oil production declining in most wells. The water problem type of the field and wells is identified by using Chan's diagnostic plots (water oil ratio (WOR) and derivative water oil ratio (WOR') against time). The analytical results show that water problem is caused by the channeling due to high permeability zones, high water saturation zones, and faults or fracturing. The numerical approach is also used to study the water movement inside the reservoir. A three dimensional geological and a three phase reservoir model was constructed for Asmari reservoir. The simulation model was used to visualize the water front advance in order to evaluate the water production structurally. The numerical results also show that the channeling is the main cause of water production, as well as, oil-water contact advance problem was noted due to fault sealing behavior effects.
Highlights
Producing water alongside with oil from the reservoir is a normal situation in all natural reservoirs; the water can be either come from a natural resource or an artificial resource
The major reservoir in Abu Ghirab oilfield is Tertiary Asmari reservoir, which is subdivided into three major production formations as, Jeribe-Euphrates, Upper Kirkuk or Buzurgan member and Middle and Lower Kirkuk
Coning can occur if the bottom water raises to the perforations that located near the Water-Oil Contact, while Channeling occurs if a layer(s) in a multi-layers reservoir has a high permeability or high initial water saturation which can affect the speed of water invasion among the reservoir, it is worth mentioning that the channeling can occur due to fractures and faults (Bailey et al, 2000)
Summary
Producing water alongside with oil from the reservoir is a normal situation in all natural reservoirs; the water can be either come from a natural resource (aquifer) or an artificial resource (injection wells). Unit B: this unit represents Upper Kirkuk(including Buzurgan membrane) formation which geologically belongs to Aquitnian to Chattian age / lower Miocene-Oligocene epoch, It exists in barrier complex to shallow marine depositional environment It consist Limestone Intercalated with Argillaceous Dolomite and Sandstone and Claystone. The minimum thickness (75 m) is observed in well AGCS-30, and the maximum (141 m) is observed in well AGCS-44 It is considered as the main producer unit in Asmari formation and better characteristic from the overlying unit due to sand existence, which gives high porosity-high permeability, so most initial oil in place exist within it. This unit is divided into four sub-units, B1, B2, B3 and B4 (Missan oilfield technical report)
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