Use of 4D Seismic To Boost The Profitability Of Infill Drilling In An Offshore Sandstone Oil Field

Abstract

This paper presents how 4D seismic was used to boost the profitability of an infill production well (XA) in Field X located offshore Nigeria. Field X has an anticline dome structure with sizeable faults and turbidite sandstone reservoirs. It had under-saturated oil at initial conditions, and has been developed with 4 subsea production wells and 2 subsea water injection wells tied back to a leased FPSO vessel. An Eclipse simulation history match model was constructed in 2012 to support the infill production well proposals XA and XB. The simulation model estimated the oil recovery from infill well XA as 1.57 MMSTB, which was deemed uneconomic. A review of the 2012 simulation model used for the recovery assessment suggested that the XA area was swept by a nearby water injection well (W1). This did not agree with the 4D seismic data. The simulation model water cut in a nearby production well (P1) was also higher than the actual water cut. It was concluded that the simulation model did not represent actual reservoir performance. The simulation model was optimised by improving the XA infill well path penetration in the target reservoir formation. The connectivity between the W1 water injection well and the production wells was also evaluated. A seismic section between W1 and P1 showed a potential flow baffle between the wells. This baffle was added to the simulation model to delay the water between W1 and P1. Production data suggested that W1 was most likely connected to another production well (P3) via a high conductivity channel. The channel was added to the simulation model to divert most of the water from W1 to P3. These actions improved the P1 water cut and 4D seismic water saturation difference history matches, increased the XA infill well oil recovery by over 50%, and made the well economic. This paper presents a standard method of how 4D seismic data was used to support infill well planning, and can also be used to justify 4D seismic data acquisition. It is recommended that reservoir simulation models are history matched with 4D seismic and other geologic and production data prior to using the models for prediction and well placement. In this case study, 4D seismic data was used to improve the simulation history match and boost infill well economics. 4D seismic can also be used to locate sealing faults, evaluate fault seal breakdown, find infill well locations, and improve oil recovery.