During 1992-93, Davidson et al.1  conducted intense quality control (IQC) operations on 54 hydraulic fracture treatments. Their number one conclusion was that "Modern fracture fluid systems are very complex with viscous properties that are not fully understood". Even though a variety of problems can occur in the field, the most common and most serious problems were usually with the crosslinker and/or the breaker systems. If the gel is overcrosslinked or undercrosslinked, the fluid viscosity decreases, and the created fracture dimensions and proppant transport characteristics are adversely affected. If too much breaker is added, the fluid viscosity decreases, once again adversely affecting both the created fracture dimensions and proppant transport. If too little breaker is added, the fluid may never break or may never clean up. This can significantly reduce the productivity or injectivity of the well.

The statistics generated by Davidson et al.1  indicated that serious problems occurred with crosslinked, water based fracture fluid systems 78% of the time. This is consistent with previous quality control work performed in the industry by others.2 "1  These authors stated that fluid problems occurred in 70-80% of fracture treatments. If IQC operations are applied, these serious problems can be discovered and corrected prior to pumping the fracture treatment.

The IQC operations are performed in the field using special equipment to test the actual fluids and chemicals that will be used during the fracture treatment.4  We have found that to properly test the chemicals, such as buffers, crosslinkers, and breakers, the tests must be conducted at an elevated temperature mat represents formation temperature. 10 ensure that the results are meaningful, one must mix the gels correctly and test them under conditions that simulate mixing, shearing, and temperature changes in the actual field application. The equipment and manpower required to perform IQC tests in the field typically can cost between $5,000 and $15,000 per treatment.

To obtain approval by management to conduct IQC tests, one must determine that the economic benefits of conducting IQC are substantially more than the costs. The Gas Research Institute (GRI) has funded detailed studies to compute the benefit-to-cost ratios for applying new technologies, including IQC operations.5  In the GRI work, it was concluded that under certain conditions, IQC can be very beneficial and can provide a substantial return-on-investment to the operator.

To further illustrate the benefits, we have thoroughly reviewed the field data collected by Davidson et al,1  and have used their results to construct examples illustrating how IQC can affect the ultimate recovery and economics from typical gas wells. The information in the paper by Davidson et al.1  clearly showed how the fracture fluid properties are affected by the chemicals and how they are mixed. In this paper, we want to illustrate how these variations in fluid properties actually affect the fracture dimensions, gas flow rates vs time, and the economics of producing low permeability wells that require fracture treatments to produce under optimal conditions.

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