Stimulation Design for Short, Precise Hydraulic Fractures

Abstract

This report discusses the philosophy, design, and implementation of small, precise, hydraulic fracture stimulations as applied in a micellar pilot in Salt Creek field, located in central Wyoming. Wellbore damage and relatively low permeability were resulting in low injection/withdrawal rates in the 1-acre [4046-m2] pilot in this field. Unchanged, these low rates would extend the pilot life by an unacceptable amount and also result in oil production rates too small for meaningful analysis. Accordingly, the decision was made to fracture-stimulate the pilot wells on the basis of reservoir stimulation, which snowed that the creation of very short (90 ft [29.5 m] tip-to-tip) fractures would not "harm" evaluation of the pilot's performance. Normal stimulation practices in this area would not give the control desired for this pilot situation to create a 90-ft-[29.5-m-] long fractures in a formation with a thickness of 100 ft [32.8 m]. The procedure that was developed consisted of measuring bottomhole treating pressure (BHTP) while pumping the pad, using these data to calculate the required sand-laden fluid volume, and then switching directly from pad to heavy sand concentration. A postappraisal of the treatments showed that BHTP measurement was necessary since the pressure varied from theoretical behavior for each well. After initial pressure increases that were predictable, a critical pressure was reached for each case and the value of this pressure (which governed slurry requirements) varied by 25% from well to well. The effects of the treatments also were evaluated with postfracture pressure falloff tests (PFOT). The stimulations performed generally were successful (fracture design/PFOT lengths of 156/146, 90/100, 134/150, and 55/20), confirming that it is possible to create short, controlled hydraulic fractures by using the procedure outlined in this paper.