Low-permeability gas sands are often cased, perforated, and hydraulically fractured in stages. Commingled production is common, and coiled tubing (CT) has become the medium of choice for opening multiple productive intervals between fracture stages and for use as a remedial workover method.

High differential pressures in the wellbore complicate CT intervention considerably. Bridging agents are sometimes used to combat severe lost circulation and associated well control problems. Calcium carbonate may be the most common bridging agent because it is inexpensive and easy to mix; however, removing the damage caused by calcium carbonate slurries to the formation and proppant packs is difficult and costly. Salt pills are widely used because they cause less formation damage, but they are ineffective at controlling severe fluid loss. Furthermore, to prevent dissolution of the pill, saturated brine must be used as a workover fluid, increasing costs and contributing to scaling problems.

A unique fluid-loss control agent has been gaining popularity for temporarily isolating low-pressure, fractured sands. This double-derivatized, crosslinkable, hydroxyethyl cellulose (DDHEC) polymer leaves less than 0.5% gel residue by weight, minimizing impact on production. It has demonstrated a regained permeability of 91 to 93% under laboratory conditions and can be completely removed by acid. The polymer has been used in conjunction with 1.25- and 1.75-in. CT with a high degree of success. It does not require expensive brines, is resistant to solvents, and can be used with foam.1,2 

Eight field applications of the polymer have been performed, none of which have negatively affected production. This paper provides case histories for several of these field applications and defines techniques and selection criteria for applying the polymer under specific well conditions.

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