Determination of reservoir characteristics from formation pressure created by underbalanced perforating may enable an operator to decide whether a well is commercially productive prior to permanent completion. With the use of several existing techniques, it is possible to analyze such data.
With closed chamber testing techniques, wellhead pressures are used to calculate variable sandface rates during and shortly after the well is underbalance perforated. Superposition is employed to create a rate-time function for plotting with bottom hole pressure data. The straight-line portion of the pressure versus ratetime function plot can be fitted using linear regression to solve the radial flow equation. Calculated parameters include effective permeability, skin effects and initial reservoir pressure.
Also presented, is a method proposed by Soliman to analyze short producing time data. Delta pressure versus total time data is plotted on a Log-Log graph where the time axis combines producing time with build up time. A negative one (−1) slope on this plot indicates the existence of radial flow, from which reservoir characteristics can be calculated if the flow regime is known. A cartesian plot can be used to estimate initial reservoir pressure.
This paper illustrates the use of the aforementioned techniques on data collected from a multi-well project in the Gulf of Mexico. Analyses of oil wells were investigated. The results of these analysis methods for oil cases are compared with buildups performed after the wells were completed.
These analysis techniques have also been applied to formation back surge data with similar results.