Analytical evaluation of gas/condensate skin in hydraulically fractured wells

The work in this paper is a result of a problem encountered in producing a low permeability formation from a hydraulically fractured well in South Texas. The well was producing from a tight gas condensate reservoir and there was concern about damaging the well if the wellbore pressure fell below the dew point. However, it turned out that condensate damage was not a problem. Lower wellbore pressures only resulted in higher rates. This study employs analytical methods to evaluate production impairment by use of fracture face skin concept, s_ff, which is a permeability reduction normal to the face of the fracture. Due to very tight formation and presence of infinite conductivity fracture which propagates the entire drainage boundary of the well, the flow pattern from the formation into the hydraulic fracture is linear. The reservoir was modeled by a synthetic single phase linear model and the simulation results were compared to analytical solutions. In order to investigate if the analytical equations properly quantify the production impairment, at this stage the single phase fluid model was used to ignore productivity decrease due to condensate damage. Single-phase damage analysis shows that for a linear reservoir producing at constant rate conditions, S_ff is additive to the analytical solutions. It also shows that S_ff calculated in transient and pss periods are identical to that calculated by using Cinco and Samaniego equation. The same analysis for the constant p_wf case assuming that the S _ff is additive to the analytical solutions shows that the calculated skin in transient period changes with time.