pleted and fluid pressures decline, some of the fractures will close and become inactive. Figure 3 shows the SRV imaged during well stimulation and the APV for the same well after two months of production. The APV is about 40 percent smaller than the SRV. Both volumes are shown along with the natural fracture network. The most active locations along the wellbore in the APV are where active natural fractures intersect the wellbore. Monitoring APV over years of production shows that the size of the volume and the active locations along the wellbore change over time. Though the characteristics of these changes appear to vary among reservoirs, the example in Figure 4 shows typical results for the wells in one unconventional reservoir. The SRV and two APVs are shown. The first APV was measured after two years of production and the second was measured after three years of production. There is a decrease in the size of the volume of rock activated by production over time, as production declines. FIGURE 5 1,000 ft. Potential production volume (left) and a combination of APV for 2.5 years of production (center) are shown as map-view projections of the volumes. The APV is overlaid on the potential volume at right. Monitoring Production Potential production volumes can be generated from data collected before a well is drilled. The volumes show activity associated with the pre-existing fracture network, which appears to exert strong control over future production. Figure 5 shows a potential production volume generated from data recorded two months before the well was drilled. SPE Hydraulic Fracturing Technology Conference 9-11 February 2016 * The Woodlands, Texas, USA Register Now! www.spe.org/go/16HFTC JANUARY 2016 85