Conventional techniques to analyze probe-type formation test data have been based on the principle of pressure transient analysis or on the equations of steady-state flow. The typical techniques are those associated with the spherical and cylindrical flow regimes and with steady-state drawdown solutions. Due to the intrinsic features of probe-type formation tests, such as the flow line storage effect, variable rate history, and short test duration, these techniques in practice have proven difficult to apply or inappropriate. A better suited analysis is based on the simultaneous analysis of both pressure transient and formation rate data. One technique proposed earlier is the dynamic flow analysis with the Formation Rate Analysis (FRA1,2). FRA is based on the linear relationship between the measured pressure and the calculated sand-face formation rate during the test. In some complex flow conditions, however, non-linear relationships have been observed in actual probe tests. This paper investigates what conditions could cause the non-linear relationship, propose how to analyze such tests, and provide guidelines for repeat tests. To this end, a number of simulated probe-type tests performed under different practical test conditions are used to generate, typical non-linear pressure versus formation rate plots. These non-linear plots may resemble a skewed ellipse, an upward pointing "hockey stick", a downward pointing hockey stick, or a skewed "figure-8". Actual field tests are combined with simulation test data to investigate the conditions that could give rise to such non-linear plots. Analytical solutions are used to justify the findings in this paper. A number of effects are investigated, including low permeability (mobility), high compressibility, high permeability anisotropy, permeability heterogeneity, upper and lower shale boundaries near the probe, duration of the drawdown, test operation parameters, and plugging and cleaning-up processes. The methodology and findings presented in this paper can enhance the post-job analysis of formation tests from challenging environments. Based on these findings, test operation parameters can be optimized for repeated tests in real time if the first test reveals pecial non-linear dynamic flow.
|Number of pages||9|
|State||Published - 2005|
|Event||SPE Annual Technical Conference and Exhibition, ATCE 2005 - Dallas, TX, United States|
Duration: Oct 9 2005 → Oct 12 2005
|Conference||SPE Annual Technical Conference and Exhibition, ATCE 2005|
|Period||10/9/05 → 10/12/05|