Chemical Stimulation of Gas Condensate Wells (2007)

Abstract Gas wells are susceptible to sub-optimal performance due to accumulation of liquid in the near wellbore region of the producing well. This liquid may arise when the bottom hole flowing pressure drops below the dewpoint pressure of the fluid and a gas condensate bank (retrograde condensate) forms in the near wellbore region of the producing well. Alternatively, water may be present from many natural and man-made causes, ie, connate water, water from an aquifer, bottom water, crossflow from another zone, completion/fracturing fluids, etc. In a worst case scenario, both of these situations can occur and cause severe liquid blocking of the gas. In all instances, capillary forces trap some of this liquid in the pores resulting in a high liquid saturation and a reduction in the relative permeability of both the gas and the condensate, which is the root cause of the loss in production. Even for lean gas (1% liquid dropout) significant liquid condensate saturations can build up near the wells and can decrease production by a factor of two or three. Firoozabadi and co-workers first proposed using chemicals to alter the wettability of the formation in the near wellbore region to mitigate the damage caused by condensate blocking. Most gas reservoirs are thought to be water wet. It is predicted that by changing the wettability to neutral wet (contact angle of ~90°), the steady state relative permeability of the condensate and gas would both increase, thus resulting in substantial increases in the productivity of gas wells with condensate flowing into the well. Due to the requirement of a contact angle of ~90° versus a hydrocarbon fluid, it was deemed that a fluorochemical would be needed. For such a treatment to be effective it needs to be durable for long periods of time at high temperatures and high flow rates. This previous work has focused on utilizing fluorinated alkoxysilanes that would form covalent bonds to a sandstone formation. However, it was felt that reactive chemistries could be difficult to reliably deliver as desired under some reservoir conditions. It is commonly known in the oil industry that surfactant flooding may result in the loss of surfactant due to adsorption onto the formation. We chose to take advantage of this phenomenon to create a chemical treatment that will adhere to the substrate. The work described in this presentation utilizes non-reactive chemistries to address this problem. These materials do not react in solution and interact with the substrate under reservoir conditions. The interaction between this type of molecule and the substrate is due to adsorption out of solution, controlled in part by the cloud point of the material. Since the molecule does not contain a reactive moiety, incidental damage to the formation should not occur. Materials were obtained from 3M Company, St. Paul, MN, USA. The materials, L19945 and L19973, are ~2wt% solutions of a fluorinated, nonionic, polymeric species that is solvated in organic solvents. Experiments were conducted using the pseudo pressure method to obtain steady state gas and condensate relative permeabilities. This method and apparatus schematic has been described in detail elsewhere. Essentially by controlling the upstream and downstream pressure a gas mixture can be flashed into the experimental core to produce gas condensate. This core can contain previously placed water or additional pumps can be used to inject flowing water for various studies. The pressure drop is measured prior to treatment and then after treatment to determine the ?P for the treatment. The ratio of the pressure before treatment to after treatment is the improvement factor or PI ratio.