Short-Term Transient-Rate and Pressure-Buildup Analysis of Low-Permeability Reservoirs

Abstract

Summary A majority of low-permeability wells, both unfractured and fractured, are analyzed with the conventional transient-pressure-buildup test. Application of this technique to wells faced with wellbore storage, even small amounts, can be time-consuming and may not provide accurate answers. Wellbore storage and its effect on the transient regime duration distorts early-time data. Such early-time data could range from a couple of hours to days and weeks. This constraint makes long-term data necessary and does not allow the interpretation of early transients reflective of near-wellbore conditions that are unaffected by outer boundary effects. This paper presents a technique that reduces test time considerably and obtains accurate formation flow properties before any boundary effects are felt. The technique involves measuring transient rate and pressure at the wellbore during the buildup period and a few minutes before the surface shut-in of the well. The technique is called TRAP™ (transient rate and pressure) analysis. Having the transient rate during the pressure buildup allows the engineer to correct the pressure data collected during the early portion and to perform the analysis for permeability, skin factor, reservoir pressure, and other formation characteristics. A field example is presented to show the effectiveness of the technique in analyzing low-permeability reservoirs.