TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAsphaltene deposits were obtained from three high gas/oil ratio (GOR) wells in an offshore field in the Arabian Gulf. The reservoir is saturated and there is a gas-cap present in the field. In many wells the gas cones into the producing wells and causes precipitation of asphaltenes from the crude by stripping. These asphaltenes deposit in the wellbore and have the potential to create plugging problems.This paper describes the results of an investigative study that was initiated to determine the precipitation mechanism and ways to alleviate the deposition problem. Asphaltene precipitation experiments were conducted at reservoir conditions in a special pressure-volume-temperature (PVT) apparatus. The effect of GOR on asphaltene precipitation was determined by titrating the reservoir oil with gas-cap gas. Bulk deposition tests were also performed at different GORs with reservoir fluids. The results demonstrate that the onset of asphaltene precipitation occurs at relatively low GOR values. The amount of asphaltene precipitated at the onset is small. Asphaltene precipitation and deposition increase with increasing GORs. Asphaltene deposition envelopes are provided for the reservoir oil as a function of pressure and temperature. Recommendations were made to alleviate the problem by controlling the maximum producing GORs to less than 1000 scf/stb. Recipes for solvent treatment including asphaltene dispersants are also described in the paper and are currently being considered for implementation in the field.

Gas condensate reservoirs are an essential part of Saudi Arabia's hydrocarbon resources. A good understanding of the effect of water on the phase behavior properties of these hydrocarbons is essential for carrying out accurate forecasts of the performance of these reservoirs using numerical simulators. In addition, the scaling and corrosion tendencies of the produced water are strongly influenced by mass transfer with the hydrocarbon phase. This paper presents unique experimental phase behavior data for a typical Saudi Arab gas condensate three-phase (water/condensate/gas) system. The objective of this work is to quantify the effect of water on gas condensate fluid properties. The results show that appreciable amount of carbon dioxide and methane partition from the gas condensate phase into the aqueous phase. Another important observation was the mass transfer of water into the condensate phase. The mass transfer between the condensate and aqueous phases results in a decrease in the gas/condensate ratio. The carbon dioxide in solution makes the brine acidic, and can dissolve carbonate minerals from the formation, for example, calcium carbonate. In addition, the acidic or sour brine will be quite corrosive. The experimental results are compared with equation-of-state and other correlations published in the literature. Introduction Natural gas reservoirs are an essential part of the hydrocarbon resources of the Kingdom. The phase behavior of such hydrocarbons has been extensively studied, both in-Kingdom and worldwide. One of the factors that have not been studied is the effect of water on the phase behavior of gas condensate systems. This is important since natural gas reservoirs contain interstitial water in equilibrium and are frequently underlain by an aquifer. In addition, the mass transfer between the hydrocarbon and aqueous phases strongly influences their scaling and corrosion potentials. Previous work1,2 on oil/water and gas condensate/water mixtures has shown considerable solubilities of carbon dioxide, hydrogen sulfide, methane and ethane in water. Mass transfer occurs when the oil or gas condensate is contacted with water and these components will partition into that phase (Figure 1). As a result the composition of the hydrocarbon phase is altered and some of its properties (e.g. saturation pressure, gas/oil ratio and formation volume factor) can be altered. Another important aspect is the partitioning of water into the hydrocarbon phase at reservoir conditions. This dissolved water in the hydrocarbon phase may drop out in the lines as the gas condensate is produced and lead to corrosion and/or scaling problems. The literature contains limited data on the solubility of hydrocarbon gases in water, and the available data is for single hydrocarbon-water systems (e.g. methane-water). Even more limited is data on the solubility of complex natural gas mixtures in water and brine. This paper provides experimental data on the effect of contacting one Saudi Arabian natural gas condensate with water. The main effects that are observed are the mass transfer of some of the more water-soluble light components of the gas condensate (carbon dioxide, methane, and to a lesser extent ethane) into the aqueous phase. The loss of these lighter components, especially methane, from the condensate phase leads to a change in its gas-related properties such as the gas/condensate ratio, dew-point pressures and liquid yields. Some water is also partitioned into the gas condensate phase. As a result of this mass transfer the brine can become more acidic due to the dissolution of carbon dioxide and hydrogen sulfide. This can then dissolve some of the carbonate minerals in the formation, which could then precipitate in the well bore or at the surface when the pressure is released3,4. The acidic brine is corrosive4 and large savings can be realized by its effective mitigation5. The experimental apparatus and procedures are described. The properties of the gas condensate and brine used in this study are then presented. Following that, the experimental results are presented. Finally, some conclusions are drawn.

Summary Gas-condensate reservoirs are an essential part of Saudi Arabia's hydrocarbon resources. A good understanding of the effect of water on the phase-behavior properties of these hydrocarbons is essential for accurately forecasting the performance of the reservoirs with numerical simulators. In addition, the scaling and corrosion tendencies of the produced brine are strongly influenced by mass transfer with the hydrocarbon phase. This paper presents unique experimental phase-behavior data for a typical Saudi Arabian gas-condensate three-phase (aqueous/ condensate/gas) system. The objective of this work is to quantify the effect of the aqueous phase on gas-condensate fluid properties. The results show that appreciable amounts of carbon dioxide and methane are partitioned from the gas-condensate phase into the aqueous phase. Another important observation is the mass transfer of water into the condensate phase. The mass transfer between the condensate and aqueous phases results in a slight decrease in the gas/condensate ratio (GCR). The carbon dioxide in solution makes the brine acidic and can dissolve carbonate minerals from the formation (e.g., calcium carbonate). In addition, the acidic or sour brine will be quite corrosive. The experimental results are compared with equation-of-state (EOS) and other correlations published in the literature.