Non-destructive time-lapse monitoring of pressure depletion for high-temperature gas-condensate reservoirs to optimize infill perforation using pulsed-neutron well logging

Assessing infill-perforation opportunities requires confirming reservoir pressure because depleted intervals may provide lower-than-expected production and increase the risk of early water breakthrough. This study presents a non-destructive assessment of reservoir pressure in unperforated high-pressure, high-temperature gas-condensate-bearing sands using time-lapse pulsed-neutron well logging. Surveys were conducted in 2022 and 2024 in a gas-filled borehole using previous- and next-generation sleeved multidetector instruments. Tool-specific Monte Carlo N-Particle forward models incorporated the completion geometry, borehole conditions, formation volumetrics, fluid properties, and depth-specific in-situ shale correction. The next-generation instrument acquired pulsed-neutron capture data at 20 ft/min, twice the logging speed of the previous-generation tool, reducing exposure to borehole temperatures of approximately 350 °F. The measured RIN13 and RATO13 responses were interpreted within their corresponding tool- and year-specific modeling envelopes rather than through direct comparison of absolute values between surveys. The analyses indicated that the upper target sands retained virgin reservoir pressure of approximately 13,450 psi, whereas the lower sands exhibited an approximately 45% pressure reduction to about 7,400 psi. Formation sigma results indicated no material increase in water saturation in the depleted lower sands, supporting pressure depletion rather than water encroachment as the cause of the ratio changes. Subsequent perforation of the upper target sands confirmed the predicted virgin-pressure condition and increased production by approximately 15,000 barrels of oil equivalent per day. The results demonstrate that integrated time-lapse pulsed-neutron logging and tool-specific forward modeling can support low-risk infill-perforation decisions in HPHT gas-condensate reservoirs.