Simulation of Single-Well Tracerflow

Single-well tracer flow has been studied using a compositional reservoir simulator, UTCHEM. In order to investigate single-well tracer flow in the absence of drift, a two-dimensional (r-z) radial coordinate opotion has been added to UTCHEM. This option models flow to and from a single well and retains all of the existing features of UTCHEM, including extensive physical property modelling and a high degree of vectorization. In order to investigate fluid drift-affected single-well tracer flow, simulated reservoir configurations have been developed for cartesian coordinates. These configurations minimize the required number of grid blocks while producing accurate results. Two single-well tracer tests have been developed as part of this research. The wettability-determining tracer test estimates the relative permeability, capacitance, and capillary pressure behavior of a reservoir. Because the effects of wettability on these properties have been established in laboratory experiments, wettability can then be inferred. The test consists of successive injection/shut-in/production sequences, with one injecting reservoir brine with an ester (reacting tracer) and the other injecting reservoir crude with an ester. The second test is the permeability-determining tracer test. This test uses fluid drift to measure the layer permeabilities in a layered reservoir. This test consists of injecting a small amount of tracer and then shutting in the well for several days before producing. The locations of peaks in the produced tracer concentration history are sensitive to the layer permeabilities. An analytical model has been developed which aids in the design and analysis of the test. Because the permeability-determining test is also sensitive to the average drift velocity, a relatively quick single-well tracer test has been developed to measure this quantity. By performing this test prior to the permeability-determining test, much uncertainty can be eliminated from the design and analysis of the permeability-determining test.