Field Implementation of Condensate Bank Removal Using Chemical Treatment
Authors: Al Ghamdi Bander N. , Al-Malki Bandar H. , Al-Kanaan Adnan , Rahim Zillur , Al-Anazi Hasan D. 
Published: March 2015

Productivity of gas-condensate wells decrease as bottomhole pressure drops below dew point and condensate starts accumulating surrounding the wellbore. The deliverability of gas-condensate reservoirs is controlled by transport properties, mainly capillary pressure and relative permeabilities between the fluids in a pore-scale. When condensate drops out in the reservoir, the relative permeability to gas decreases and affects the flow rate.

The productivity of gas-condensate reservoirs can be effectively enhanced by creating hydraulic fractures to reduce draw-down pressure near wellbore. This helps maintaining the flowing bottom-hole pressure above dew point and consequently delays condensate accumulation. In rich gas reservoirs where condensate to gas ratio (CGR) is high, it becomes challenging to keep the pressure above the dew point. Other approach to enhance relative permeability to gas is by altering the system wettability and making it preferential to gas flow. Recently, a chemical treatment was developed by 3M company (3M) in collaboration with the University of Texas at Austin (UT) to remove condensate banking effect. The treatment fluid was tested in the United States and showed promising results.

In this work, Saudi Aramco participated with 3M and the University of Texas Austin to implement a field trial of the chemical treatment on one of Saudi Arabian gas wells that declined in productivity over its production life due to sever condensate banking. The treatment aimed to enhance the relative permeability of the least-wetting phase of the fluids in-place and reduce the effect of condensate-banking was successfully pumped in the candidate well. The initial results of the field implementation demonstrated a significant improvement of gas flow rate and a simultaneous increase in the flowing wellhead pressure.

Key results were consolidated with a Pressure Build-up Test conducted six months later, proving effectiveness of chemical treatment on reducing condensate saturation, increasing relative permeabilities to gas, and modifying wetting conditions to make it preferential to gas, which significantly enhances recovery from such high CGR gas reservoirs.

Introduction

Gas-condensate fluids are mixtures of hydrocarbon molecules that are initially present as a gaseous phase at reservoir conditions. During the depletion of the reservoir fluids as the reservoir pressure falls below the dew point pressure, the liquid phase comes out of the single phase hydrocarbon. When the pressure crosses the dew point pressure, the bonding between the light components and heavy components of the single phase fluid in the reservoir are weakened causing a split between the light and heavy components (Ahmed, 2000). The result of the split enhances the bonding among the heavy components and makes it stronger forming condensate. The condensate thereby keeps accumulating until a maximum liquid dropout is reached. The condensate accumulation takes long time before it reaches the critical condensate saturation allowing the fluid movement. During this time, reduction in gas flow is sensed and is directly reflected on the production performance.