Water and gas coning in oil rim reservoirs pose serious hindrance to optimizing oil production in the thin oil beds as unwanted fluids tend to replace the oil in the production stream. This invariably limits the ultimate oil recovery. In this study, Semi-Analytical models of estimating critical rate and optimum horizontal well placement was developed to control coning tendencies in oil rim reservoirs. The models was developed through semi-analytical analysis of applying the principle of Nodal analysis to graphically combine gas-oil reservoir system and oil-water reservoir system respectively; with a view to controlling gas and water coning phenomena in gas-oil-water reservoir system. The result was compared with an existing correlation with field data obtained from the Niger Delta oil field.
The models are simple for fast calculations for reservoirs with thin oil zones sandwiched between gas cap and bottom water.It is concluded that the developed models can be used as a tool to make a first pass assessment in the development of oil rim reservoirs anticipated to experience water and/or gas coning during production.
Oil rim reservoirs refer to reservoirs with thin oil zones sandwiched between gas cap and bottom water. Such reservoirs may contain large volumes of oil. However, this oil is often difficult to produce economically by conventional methods due to the double coning phenomena. The production of water and/or gas from oil wells is common occurrence that increases the cost of operations and may reduce the efficiency of the depletion mechanism and the recovery of reserves. This inadequate production of water and/or gas with oil from the reservoir can result from coning.
Coning refers to the upward movement of water and/or the downward movement of gas in the reservoir, into the perforations of a producing well (Ahmed, 2006). The term is referred to as coning because the shape of the interface resembles an upright (water coning) or inverted cone (gas coning) when the well produces the unwanted phase (Fig. 1). Coning occurs when viscous forces exceed gravity forces near the wellbore of a producing well, which results in a high gas/oil ratio (GOR) in case of gas coning, or high water cut (BS&W) in case of water coning (Fig. 2). Water and gas coning are common in oil rim reservoirs, with attendant consequences of drastic drop in reservoir pressure and the overall recovery efficiency.
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