Water injection provides efficient pressure support and increases oil recovery in field developments worldwide. The success of water injection comes from its cheap and simple application. However, waterflooding is an energy intensive operation. Typically, more than one third of total energy use in offshore platforms is allocated for water injection. Since many offshore platforms still rely on gas turbines as their main energy source, waterflooding thus accounts for a substantial portion of total CO2 emissions. The quantity of CO2 emitted depends on the injection strategy being adopted; both on the well placement and on the injection rates and pressures during production life. Traditional optimization of drainage strategies has given little heed to the cost of emissions. In this work this emission cost will be an integral part of the injection strategy optimization, as we will include the cost of emissions into our optimization objective. We formulate the optimization objective (net present value) so that it incorporates the cost of CO2 emission: Our augmented objective function includes not only revenue and cost of production, but also carbon tax proportional to CO2 emitted. Moreover, we introduce a scheme for quantifying CO2 emissions corresponding to a particular injection strategy. This scheme is based on an integrated subsurface-topside model and utilizes reservoir simulation results for calculating the energy spent by the water pump and treatment systems. This energy is then used to estimate the fuel consumption for water injection and the corresponding CO2 emissions. We conduct the optimization study using a two-dimensional numerical reservoir simulation model. In addition, we optimize over a range of CO2 tax rates and investigate how the different tax regimes affect the optimal solution and associated carbon emissions. Our results indicate that the optimal well placement is dependent on the CO2 tax rate. A higher CO2 tax rate moves the optimal injection location towards higher permeable zones. This leads to lower oil production and lower emissions. However, the relative reduction in emissions is larger than the relative reduction in oil production.

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Early production of gas reservoirs is usually associated with a volumetric gas driving mechanism with no water production. Aquifer activity is minimal as well during the early life of the reservoir. In this paper, we will discuss about the good engineering practices based on several shut-in pressure data to observe and maximize marginal gas field value. We will also discuss about the possibility of water drive behavior in this field. Shut-in pressure data plays an important role in determining the in-place and reservoir dynamics of the gas reservoir. High shut-in pressure usually indicates high gas reserves. On the other hand, it shows a very strong water drive existence. The study takes place on a sandstone gas reservoir with an abnormal pressure regime on it. Production performance was then analyzed using the rate transient analysis (RTA) to determine its properties and gas in place and crosschecked with shut-in pressure data. From these steps, we can determine the trend of both static and flowing material balance (FMB) analysis to predict the reservoir dynamics. During the early life of production, it is clear that volumetric reservoir plays an important role in the reservoir dynamics since it produces no reservoir water. However, after 1 year of production, it starts to produce reservoir water. Monitoring starts when the first shut-in pressure shows a quite unexpected value. It puts a sense of both high gas reserves and aquifer activity. After applying all the pressure and production data on FMB and p/Z plot, it shows that both high gas reserves and aquifer activity exist in this field. The results of this study change the development strategy of this field, preventing doing major investment on high capital expenditure (CAPEX) with low results due to high aquifer activity. We can conclude that good reservoir monitoring and analysis combining several analytical methods can enhance our insight into reservoir dynamics. Combining FMB and p/Z, geologist starts to compare aquifer volume based on geological data and found to be similar with the results coming from analytical data. 3D reservoir simulation also confirms similar results based on those analyses.