Anlysis, Interpretation, and Design of Inter-Well Tracer Tests in Naturally Fractured Reservoirs

摘要

In order to understand the complex fracture network that controls water movement in a developed area within Spraberry Trend in West Texas and to better manage the on-going waterflood performance, a field scale inter-well tracer test was implemented. This test presents the largest inter-well tracer test in naturally fractured reservoir reported in the industry and includes the injection of 13 different tracers and sampling of 110 producers in an area covering 6533 acres. This inter-well tracer test generated a total of 598 tracer responses from 52 out of the 110 sampled producers. Tracer responses showed a wide range of velocities from 14 ft/day to ultra-high velocities exceeding 10,000 ft/day with same-day tracer breakthrough. Re-injection of produced water has caused the tracers to be re-injected and added an additional challenge to diagnose and distinguish tracer responses affected by water recycling. This paper investigated analytical, numerical, and inversion modeling approaches in order to categorize, history match, and connect tracer responses with water-cut responses with the objective to construct multiple fracture realizations based entirely on water-cut and tracers' profiles. In addition, the research highlighted best practices in the design of inter-well tracer tests in naturally fractured reservoirs through lessons learned from this test. Results indicated that tracer responses could be categorized based on statistical analysis of tracer recoveries with each category showing distinguishing behavior in tracers' movement and breakthrough time. In addition, it showed that tracer and water-cut responses in the lease are dominantly controlled by the fracture system revealing minimum information about the matrix system. Numerical simulation studies showed limitations in dual porosity formulation/solvers to model tracer velocities exceeding 2200 ft/day. Inversion modeling using Gradzone Analysis showed that east and north-west of the developed area have significantly lower pore volume compared to south-west.