Wells completed in tight-gas sands often produce below expectations after fracture stimulation, with gel filtercake damage cited as a major cause of poor performance. These filtercakes have historically been viewed as immobile and insoluble in flowback water. However, recent field observations demonstrated conclusively that borate-crosslinked filtercakes delink and redissolve in flowback water. A fracture cleanup and chemistry simulator (FCCS) was used to discover and develop an appropriate rate law for the dissolution of gel filtercakes in flowback water. The simulator was validated by matching the observed gel content in the flowback waters from a fracturing treatment. Previous work demonstrated that behavior of gel filtercakes in proppant packs from fracturing treatments was more complex than expected. Particularly interesting were recent observations of significant concentrations of gelling agent across several hundred barrels of flowback fluid from a fracturing treatment with good documentation. Ionic composition of the well returns was first matched with the FCCS. Matching of the gel recovery profile required discovery and development of a rate law for dissolution of gel filtercake by water inflowing from the fracture face. Potential rate laws using flow of water down the length of the fracture were not able to match the observed profile. Parametric studies were then conducted and showed a gel displacement regime and a dissolution regime for gel recovery, with the controlling regime dependent on gel phase saturation in the proppant pack. The gel phase saturation in the proppant pack should be 50% or less to be in the dissolution regime for efficient gel recovery.
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