Paper: A Primer To DST Chart Interpretation

Qualitative interpretation of drill stem test (DST) pressure-time charts often is more of an art than a science. However, logical and efficient interpretation can be easily accomplished by understanding the basic factors involved in producing a chart. No two DST charts are exactly the same, and thus the guidelines given in this paper are designed to be general in nature. With knowledge of the basic DST shapes and forms in mind, even complicated charts can be broken into components and satisfactorily interpreted. A DST is a temporary completion of an interval within a well to help determine as much useful reservoir information as possible about the interval. The fluids recovered from a DST help describe the fluid type available from the reservoir and how well it may flow. The pressure-time chart is a valuable record of the test events and serves to validate the test results. At the wellsite, a properly interpreted DST chart also can give an indication of important reservoir parameters, such as productivity, permeability, pressure, and wellbore damage. In addition, determination of reservoir characteristics such as depletion, supercharge, permeability anomalies, and multiple zones often is possible when the chart interpretation is coupled with information such as reservoir geology. Finally, the quantitative pressure-time DST data can be analyzed using standard industry pressure transient analysis methods. These can yield valid numerical approximations of important reservoir parameters, and further support the chart interpretation. Quantitative analysis will not be covered in this paper.