Estimating reliable gas rate with transient-temperature modeling for interpreting early-time cleanup data during transient testing

• Novel gas rate estimation method formulated with rigorous depth-dependent temperature superposition principle.
• Estimated rates help interpret early-time DST pressure data gathered during cleanup period.
• Good permeability estimates made during early test period, leading to fine-tuning test sequence.

In drillstem testing (DST), analyses of transient data are generally restricted to the post-cleanup period because rates often go unmonitored at early times during the cleanup phase, unless aided by multiphase flow metering. The value of early-time production data monitoring may be overlooked for two reasons: first, transients may be difficult to interpret because of two-phase flow in the formation; second, two-phase flow metering becomes a requirement.The objective of this study is two-fold: to estimate rate from multipoint-temperature sensor (MTS) data available for downhole telemetry with a rigorous transient analytical model, and to show the possible use of the computed rates to perform transient analysis for both the pre- and post-cleanup periods. Comparing and contrasting permeability estimates from the two periods provides guidance on the suitability of this approach. To that end, this study compares and contrasts rate computation with analytical methods. The new methods entail transient-temperature modeling with and without superposition effects. Two field examples strengthened the new rate-computation methods introduced here, and simulated examples probed the possibility of extracting meaningful information from the cleanup data.