We performed intense quality control (JQC) on 54 hydraulic fracture treatments during 1992-93. Our detailed fluid testing in the field has indicated the complex nature of fracture fluid systems currently used by the industry. This paper documents our experience with fracture fluids blended in the field and tested under in-situ conditions. Several problems were encountered while performing intense quality control operations on these wells, including overcrosslinked gel systems and contaminated additives. Many of these problems became apparent only after evaluating the fracture fluids at bottomhole temperatures and shear rales. Many fluids that failed viscosity tests at bottomhole conditions looked to be adequate when tested at surface conditions.

The importance of quality control in stimulation operations has been investigated and its importance recognized by the industry.1-4  Intense quality control is performed on location using equipment carried in a rheology van. The rheology van contains two Fann Model 50 viscometers that we use to evaluate the fracture fluids at bottom hole temperatures and shear rates, and a complete wet chemistry lab. Analyses of fracture fluids with the rheology van has been described in a previous paper5  and GR1 publication.6 

Intense quality control is not a new concept. IQC is routinely used in the evaluation of cement slurries. To test recommended mixtures of cement and additives, pilot tests are always performed on cement slurries prior to pumping to test recommended mixtures of cement and additives. Results of the pilot and blend tests indicate if a particular cement mixture will perform as designed. Similarly, we test fracture fluid systems at conditions designed to simulate reservoir temperatures in our IQC work. We use the chemicals and additives that will actually be pumped during the treatment. Using the actual chemicals is a critical part of IQC, and it is the reason that testing must be performed at the wellsite, prior to the treatment. Blended samples are collected during the fracture treatment and tested as the treatment is in progress. The tests performed during the treatment are compared to the pilot tests to ensure the fluid pumped down hole is performing as expected. We inventory all additives before, during, and after the treatment to verify the fracture fluid system is blended accurately.

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