Abstract
Formation damage, sand production and a HP/HT sour gas environment are major challenges in the field development of the Sawan gas reservoir in Pakistan. Meeting individual well productivity targets (average of 80 MMscfd) requires minimal-restriction (large bore or monobore) completions, minimizing formation damage via under-balance perforation and maintaining sand production below tolerable limits.
The reservoir sands are extremely heterogeneous with many thin, weak layers. Sand control completion concepts are based either on internal gravel packs (IGP) or, if the weaker layers are less extensive, on selective perforation. To avoid having to kill the wells (which can lead to significant formation damage) the completions are run prior to perforating. This meant that the sand control decision for each development well had to be made in 3 to 4 days - between logging the well at TD and running the completion.
The key elements of this "real time" sand management strategy were:
the application of Fuzzy Logic computing techniques to correlate wireline log responses with core measurements, which enabled a field-calibrated, continuous sand failure prediction tool throughout the reservoir intervals;
coupled well performance and geomechanical models to evaluate if selective perforation could safeguard well deliverability yet ensure sand-free production, standardization of critical completion equipment and simplified nipple-less completion design which provided the necessary operational flexibility, lowered overall completion cost, and reduced the risk of equipment failure.
under-balanced through-tubing perforation with coiled tubing to minimize formation damage.
This integrated completion and sand management strategy has delivered well production rates in excess of 100 MMscfd with sand production significantly below tolerable limits. It has also has created substantial cost savings and reduced completion failure risks compared to conventional cased-hole sand exclusion completions.
