Optimal Locations and Performance Prediction of Horizontal Oil Wells in the Oil Rim at Mahogany Field, Offshore Trinidad

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe 21 Sand reservoir in the Mahogany field has a 63-75 ft oil leg overlain by a gas cap and underlain by water. In order to utilize reservoir energy and efficiently develop the field, the oil reserves must be recovered prior to producing the gas which is dedicated to the Atlantic Liquified Natural Gas plant in Trinidad. A horizontal well program was planned to develop the oil leg. An in-house reservoir simulator was used to predict performance of the oil wells.The 21 Sand is 400' thick and has been segregated into 7 stratigraphic intervals. One hundred and twenty feet (120 ft) of core was acquired through these intervals and the petrophysical properties were measured on representative plug samples. This data was then correlated to well log data. Porosity-permeability flow units were then derived for optimum well placement. Modified-Lorenz plots (Ref. 1) were used to identify the units that would contribute to the flow and those that would act as baffles. Three dimensional visualisation models were then used to place the horizontal wells in high quality reservoir rock. Additionally, placement of the development wells for the deep gas reservoirs was designed to provide vital structural and stratigraphic information for potential heel and toe points for horizontal drilling.This paper describes how all this work was compiled into a simulation model which has successfully predicted the current well producing rates and pressure draw down.

Performance of Trinidad Gas Reservoirs (Cassia, Immortelle, Flamboyant, Mahogany, Amherstia and Teak)

“…The field also has two gas reservoirs with a thin oil column and they are the 21 Sand Fault Block V and the 21 Sand Fault Block I. (4) The field contained initial gas reserves of 2.3 tcf. The properties for these reservoirs are also reported in Table 1.…”

Experimental Investigation of Nature Gas Production Rate's Effect on the Reservoirs with Gas Cap

“…Ezzam [6] pointed that both gas production and oil production would lead to changes of oil-gas interface and mutual displacement between oil ring and gas-cap. According to Nandalal [7] and Bayley [8], gas channeling into oil ring has little influence on ultimate recovery of natural gas, but oil reduction is inevitable and under some serious circumstance, only gas is produced without any oil in oil production wells. If crude oil enters gas cap, large amount of oil will be wasted and oil recovery will be influenced.…”

Study on the Reasonable Development Method of Gas Cap Reservoir

“…Ezzam [6] pointed that both gas production and oil production would lead to changes of oil-gas interface and mutual displacement between oil ring and gas-cap. According to Nandalal [7] and Bayley [8], gas channeling into oil ring has little influence on ultimate recovery of natural gas, but oil reduction is inevitable and under some serious circumstance, only gas is produced without any oil in oil production wells. If crude oil enters gas cap, large amount of oil will be wasted and oil recovery will be influenced.…”