Big-hole production well Bulalo 100 is crossflowing while shut-in based on shut-in pressure, temperature, and spinner (PTS) survey results. The apparent crossflow is probably caused by a vertical upflow from the well's deep, less permeable and pressure supported feedzones into its shallow, more permeable and pressure depleted entry zone. Consequently, shut-in wellbore pressures at the entry zones do not represent true static reservoir pressures. Dynamic bottomhole pressures underestimate reservoir pressures at the deep producing zones and overestimate reservoir pressures at the shallow pressure depleted zones.

Crossflowing in Bulalo 100 would explain the large pressure decline rates observed in the field based on static pressure gradient surveys despite the field's uniformly low production decline rates. Reservoir pressures at the permeable zones of Bulalo 100 were then estimated using pressure, temperature and flow data obtained from shut-in and injecting PTS surveys. Linear flow equations that define flow at the well's entry zones at crossflowing and injecting conditions were solved simultaneously to estimate reservoir pressures.

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