This paper presents the results of a study carried out to identify near-wellbore formation damage in horizontal wells. Formation damage occurs when pore throats are constricted by clay swelling upon contact with incompatible fluids, by clay migration or by plugging with drill solids and mud products. Relative permeability effects can also cause water/condensate blocking and subsequent reduction in loadfluid recovery and productivity.

Extensive laboratory experiments were carried out on cores from wells offsetting four poorly producing horizontal wells in a gas-bearing formation. The results indicated that clay-related near-wellbore formation damage was the primary cause of the low productivity from these horizontal wells. Results from further laboratory investigation indicated that the formation damage could be remedied using an oxidizing material (e.g., hydrogen peroxide).

Based on these laboratory results, a field test was carried out to treat the near-wellbore formation damage using a mixture of oxidizing fluid and acid. The results of this field test are also presented in this paper.

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