For a tight reservoir, assessment of zonal production contribution is often possible only after the reservoir has been hydraulically fractured. Spinner survey is commonly the tool of choice for diagnosing relative production contribution across perforated interval in a cased-hole and by extension, minimum productive fracture height at the wellbore. However, its limited radial resolution renders such tool unreliable in evaluating flow characteristic within fracture body and across fracture planes. The acquired data is generally insufficient for resolving relative contribution of various productive horizons intersected by the fracture. As the measurements are focused on flow characteristics inside the wellbore, fracture height diagnosis is limited by the extent of perforation interval. Alternatively, radioactive tracing and microseismic survey allow one to see through the casing wall albeit at the expense of heightened cost and operational complexity. Thermal logging, being a cheaper alternative, is time-sensitive and not deployable immediately following proppant placement due to restricted wellbore access. Most importantly, hydraulic and propped fracture heights diagnosed by these methods may not necessarily coincide with effective fracture height that contributes directly to well productivity.
Integrating acoustic logging to conventional production logging measurements may, in addition to increasing resolution for low flow measurement, significantly extend the investigation radius beyond casing wall. Different acoustic characteristics potentially exhibited by flow of different fluid phases may also validate conventional log-derived reservoir fluid types. The paper describes the application of acoustic logging in diagnosing zonal production contribution, fracture height, and reservoir fluid type across hydraulically fractured tight gas condensate and oil reservoirs.
In four naturally flowing wells, zonal production contribution derived from acoustic wave analysis and conventional production log data were both in good agreement. The analysis of depth-specific acoustic wave amplitude provided useful insight in the diagnosis of zonal production contribution and by extension, productive fracture height. In one well, acoustic-derived fracture height could be closely corroborated with that of radioactive tracer data. In addition, one may also observe distinct shape of maximum amplitude of first sound wave arrival in a gas well compared to that in an oil well.