A.L. Hurtado, SPE, PEMEX; M. Asadi, SPE, and R.A. Woodroof, SPE, ProTechnics; and D.D. Casas, SPE, and R. Morales, SPE, O’Jeito S.A. de C.V.
The chemical frac tracing technology is used to evaluate flowback and flowback efficiency. This unique technique utilizes a family of environmentally friendly and fracturing fluid compatible chemical compounds to trace segment-by-segment injection of fracturing fluids. These chemical compounds have unique chemical and physical characteristics that make them detectable at low concentrations of 50 ppt (parts per trillion). These tracers are mixed at a known concentration into individual frac fluid segments as the frac fluid is pumped downhole and into the formation. Upon flowback, samples are collected and analyzed for tracer detection. With the use of the mass balance technique the flowback and flowback efficiency for each fluid segment are calculated. These precise flowback and flowback efficiency calculations yield a more accurate assessment of fracture cleanup efficiency which in turn helps to unravel cleanup problems. This paper presents a case history whereby four different chemical frac tracers were injected into four fluid segments of a frac job. The flowback and flowback efficiency calculations revealed low recoveries of the injected fluid segments through 86 hours of flowback. Based on the flowback results, a recommendation was made to shut in the well for 24 hours. Upon re-opening the well to production, flowback samples were again collected to evaluate flowback enhancement as the result of reservoir pressure buildup and or gel-breaking during the shut-in period. The total flowback efficiency increased by 50% while daily oil production increased by 62%.