A Performance Analysis of Petrotrin's North Palo Seco Steamflood
Authors: Ramlal V. , Lewis K. 
Published: December 2007

Thermal oil recovery was first started in Trinidad and Tobago in Palo Seco in 1966. The field started as a cyclic stimulation project but was later converted to a continuous steamflood in 1975. The project can be considered as one of the most successful thermal schemes in Trinidad and Tobago. The Palo Seco steamflood covers an area of 250 acres in the South Western region of the Island of Trinidad and Tobago. The reservoir being steamed, comprises three elements of the Lower Morne L'Enfer (LMLE) horizon, viz. D, E and F sands. Cumulative injection to date is 54.8 million barrels of steam with a cumulative oil production of 18.8 million STBO which is 38% of the original oil in place. The paper reviews the overall project performance of the steamflood. Predictions of the performance of new patterns are made using the Gooma steam model. The present economics of the project is discussed using the tolerable steam oil ratio approach.

Introduction

The North Palo Seco Thermal Project (NPSTP) is situated in the North \Western section of the Palo Seco field, which is located in the Southern Basin of Trinidad (Figure 1).

This NPSTP is one of several on-going thermal projects being operated by Petrotrin. Oil production from these thermal projects is approximately 30% of Petrotrin's total land production, with the NPSTP contributing about 30% of thermal production and 8% of the total land production. After twenty (20) years of continuous steamflooding this mature steamflood now produces from twenty-five (25) patterns consisting of forty (40) injectors and one hundred and forty-five (145) off-takes covering an area of 250 acres (Figure 2).

The major contributing factors to the success of this project can be attributed to :-The high reserves of shallow heavy oil (average 140 API oil).A reliable constant supply of fresh water and natural gas for steam generation.Reservoir continuity within the project limits.The accumulated expertise gathered over the last 25 years from Petrotrin's predecessor companies.An average oil sand thickness of 180 feet.

Other parameters of permeability, porosity, reservoir pressure depth, dip and oil viscosity are within acceptable limits when compared to some successful steamfloods - Refs. 1-6.

RESERVOIR DESCRIPTION FIELD DEVELOPMENT

For details of the field development and reservoir description refer to Reference 7.

Steam injection has been in the D, E and F sand units of the Lower Morne L'Enfer sand formation. The sand units, separated by shale breaks (5-10 ft) are at subsea depths ranging from 500 feet to 2000 feet with average nett and gross sand thicknesses of 180 and 335 feet respectively. Figure 3 shows the type-log while figures 4, 5 and 6 display the nett oil sand thicknesses of the D, E and F sand units. It should be noted that the "E" sands are the thickest and most well developed sands of the three units. The structure map for this thermal project was drawn on the Upper Coora Silt marker which separates the LMLE "E" and "F" sand units. The reservoir has a 200 sand dip to the southwest (Figure 7).

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