Evaluation of Alcohol-Based Treatments for Condensate Banking Removal

Abstract

Abstract The use of stimulation treatments based on alcohol to remove liquid blockage or condensate banking in the near well zone date from sixties. Among the proposed mechanisms to explain the enhancement in gas effective permeability and also the higher degree of cleaning and liquid removal obtained in laboratory and field studies, are interfacial tension reduction and the miscibility characteristics reached between the treatment fluids and the formation fluids. This paper presents the results for compatibility and displacement tests carried out among reservoir fluids, alcohol and inhibited diesel based treatments and formation cores from main Cupiagua field. These tests are focused about the behavior of these treatments when they are applied in core flooding tests to reduce liquid saturation and also to increase the gas effective saturation in a porous media. The offered results can be interpreted as a preliminary sight about the use of these treatments on lab scale before applying them as stimulation fluids on a field project. The study consists in assess the alcohol-based and inhibited diesel treatments' efficiency through the gas effective permeability before and after of the treatment injection into a core. The objective was focused to study the use of alcohol and inhibited diesel to remove formation damage by liquid blockage and their application in condensate gas reservoirs. The alcohol-based treatments show consistent results about their effectiveness both on core tests carried on Mirador formation, Cupiagua Main Field - Colombia, and Berea sandstone. In general, the results show up an increase on the gas effective permeability, the lower the core permeability the higher the gas effective permeability enhancement reached after the treatment. The alcohol labeled 21-NE-06 and inhibited diesel treatments increase the gas effective permeability both in Berea and Mirador cores. Both Alcohol 21-NE-06 and inhibited diesel based treatments are effective for removing liquid phases that cause a liquid blockage to gas flow. The stimulation degree is higher in Mirador than in Berea cores. Some treatments did not show any stimulation degree, instead, they generate additional gas effective permeability impairment. Introduction The reservoirs of condensate gas had been subject of study with emphasis in last years because the growing participation of this kind of hydrocarbons in new reserves. Gas condensate reservoirs as a result of fluids' production process and related with the production rate magnitude diminish their pressure below the dew point pressure. This situation is more evident at near production wells' zone, where due to the reduction of radial gas flow area produces an additional pressure drop. Gas condensate reservoirs are very prompted to show up formation damage at the near well zone. [1–6] If the fluid flowing pressure is below of dew pressure, liquid drop-out accumulations would present in the reservoir, and in a higher degree near to the producing wells. It results in an increasing on reservoir liquid saturation what is called as formation damage by liquid blockage. This liquid blockage remains due to capillary forces and also due to the high gas-liquid mobility ratio. Some authors propose the existence of three flow's regions on gas condensate reservoirs, which appears sequentially or simultaneously along production time depending of pressure profile. When the flow pressure is higher than dew pressure, only exists gas flow. This region exists in any point of the reservoir where this condition is met, but its existence is evident at early production times. When the reservoir pressure drops below dew point pressure, fluid condensation results in the formation of liquid banking. In this region and at early time during liquid condensation process only exists gas flow due to temporal immobility of liquid. Near zone to producer's wells, where the pressure drop is higher and also when the condensation process last for longer times, the liquid saturation achieves mobility levels and then simultaneous flow of gas and condensate exists, Figure 1.