Unraveling the Performance Characteristics of the Most Mature Shallow Gas Reservoir in the Trinidad Acreage in the Columbus Basin

摘要

The BP Trinidad gas fields are located in the Columbus basin, 35-40 miles off the southeast coast of Trinidad in water depths of between 200 to 300 feet. The fields are comprised of highly faulted stacked sandstone reservoir units of varying ages between Quaternary to Pleistocene. Most reservoir units contain original gas in place of less than 0.5 tcf and are usually produced by one or two wells. The shallow gas reservoirs (< 4500 ft TVDSS) constitute a significant percentage of the non- producing BP Trinidad gas portfolio. Reservoir data, such as rock compressibility, and performance data such as recovery factors are lacking in both the local and global database for analogous reservoirs at these depths. Initially these shallow gas reservoirs were considered as drilling hazards for deeper reservoirs therefore well paths and platform locations avoided them as recovery from them were initially expected to be very poor. The shallowest producing reservoir unit to date is from the TP95 reservoir in the Greater Cassia Field Complex and it has one producer. This reservoir depth is 4200ft TVDSS and it has been on production since 2003, exceeding expectations with its recovery. This paper investigates the key uncertainties associated with this reservoir including depth conversion (since it is overlain by other shallow gas reservoirs), rock compressibility and aquifer support. It also shows the well and reservoir performance data, key surveillance data collected as well as types of analysis and modeling performed to help understand and predict the reservoir performance given the aforementioned subsurface uncertainties.