A new hydraulic fracture screening method has been developed based on quantitative analysis of the mobile oil saturation in the target zone. The traditional selection process was based on analysis of low productivity wells, followed by extensive fracture modeling of leak-off parameters and rock properties. The new screening method defines the best pay zones and uses the saturation profile to govern the size of the fracture treatment.

This method was developed during a 10-acre infill-drilling program on the Central Vacuum Unit during the mid 1990s. Most of the producers were initially stimulated with large, one stage acid treatments. Production declined soon after completion and fell below the levels of offset producers. Texaco analyzed the open-hole logs and discovered a consistent pattern of low in-situ water saturation in the upper San Andres. Log analysis clearly indicated that the infill well production should be much better than the offset wells. Three of the new wells were successfully fracture treated across the entire San Andres interval with excellent results. However, many stimulation candidates were offset by wells producing high water volumes. The new screening method indicated that the upper San Andres should produce nearly water-free after fracturing. The design process also showed that smaller fracs would have substantially better economics and would ultimately produce as much or more reserves as large fracs.

Texaco fractured eighteen more wells in the upper San Andres. Oil production dramatically improved but water production was often unchanged. The new screening method allowed the development of additional reserves that were not recoverable under earlier practices.

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