Perched water is a phenomenon which exists in nature but is difficult to recognize in seismic data. For this reason, it is almost never modelled until proven from well results. Once found above the modelled HC contact, perched water has the potential to raise many questions including those related to areal connectivity, potential impact in volumes and associated revisions to the reservoir development plan. Using the example of an offshore gas field in Egypt, it will be demonstrated how the 13th well of the field showed an apparent HC contact, much shallower than what was expected from amplitude shut-off and in turn used for the 3D model. The well was found depleted, hence in communication with the rest of the field and on a well-established P/Z trend. The unexpected anomalous contact was investigated in detail to determine whether it was the field HC contact or perched water, trapped by clay barriers during the migration of gas inside the reservoir. Analysis of logs, RFT and production data supported this hypothesis, eventually confirmed by 3D dynamic simulations. This work is aimed to demonstrate how static and dynamic data can be analysed in order to discriminate between perched water and regional HC contacts in order to make sound reservoir development decisions.
Red Field is a gas field located in the offshore Egypt. The field was discovered by R-2 well that found gas bearing sands with a remarkable thickness. Production started-up in 2015 with rates in the order of millions of Sm3/d. By the very beginning of 2018 other twelve wells were drilled and put on production, reaching a rate of some tens of millions Sm3/d. The field is composed by three separated pools: Main area, East area and West area, most of the GIIP (~95%) is located in the Main area. The hydraulic separation of the pools is suggested by wells and pressure data and confirmed by production data (Fig. 2 and Fig. 5).
The Gas-Water Contact (GWC) of the two minor zones was inferred from logs, at -X288 m ssl and -X282 m ssl respectively. In the Main area the GWC was not found by any of the first 10 drilled wells and the deepest clear Gas Down-To (GDT) was detected at -X325 m ssl in RW-2 well, based on logs response.