Trinidad's First Multilateral Well Successfully Integrates Horizontal Openhole Gravel Packs
Authors: Lougheide Delano , Lutchman Krishna , Anthony Elred , Flores Denar , Ramsook Vishnu , Sahadeo Khemraj 
Published: October 2008

The first multilateral well in Trinidad was recently drilled and completed in the 759 area of the northern Soldado Field, offshore Trinidad in approximately 60 feet of water. A multilateral completion was selected over conventional well construction to horizontally access heavy-oil reserves in the Forest 4B and 4C sands, located at true vertical depths of 3850- and 4000-ft respectively. Since the formation parameters included poorly sorted, non-uniform formation characteristics, the completion would have to employ some method of sand control.

This well represents several "firsts" for this area. It is not only the first multilateral well in Trinidad but is also the first in the area that integrated sand control with a multilateral technique.

This paper will discuss the planning, special considerations, and implementation of the techniques chosen to interface sand control into a multilateral well.

After reviewing many possibilities, horizontal openhole gravel-pack technology was selected to provide sand-exclusion. A TAML 4 multilateral well junction was selected because it offered a cemented junction with full casing-drift access across the mainbore/lateral interface.

In addition to the planning, special considerations, and implementation of horizontal gravel pack into multilateral technology, the paper will discuss lessons learned and future considerations.

Introduction

The S-836 heavy oil development well is located in the 759 area of the northern Soldado field, which is approximately eight (8) miles northwest of Point Fortin, Trinidad (Fig. 1-2). The water depth in the area is 60 feet. The target reservoirs were the Forest 4B and 4C sand bodies, which are part of the Pliocene geological period, and were deposited in tidally influenced, fluvial-deltaic environments that comprise a series of complex channel systems. The depths of the sand bodies range from 2800 to 4000 feet true vertical depth (TVD). The surface oil viscosity of the 4B and 4C sands is 5100 and 360 centipoise (cP), respectively.

The hydrocarbon in place in the 759 area is estimated at 22 MMBO with a recovery factor of 16 percent. Prior to constructing the S-836 multilateral well, the traditional well construction method had been a vertical-to-deviated cased-hole completion that used either gravel packing or frac-and-pack sand-control methods. Submersible pumps and gas-lift production systems were typically deployed to provide artificial lift in heavy-oil applications.1

The S-836 well construction strategy had multiple objectives. First, the well path was to provide optimal reservoir exposure into the 4C and 4B sand bodies. Optimal reservoir exposure meant horizontal well paths through each sand body. Effective formation sand exclusion was another objective. Due to the highly unconsolidated nature of the reservoir rock, horizontal gravel-packs would be required to provide effective sand control while maintaining high production rates. In addition, an effective sand-control system would maximize reservoir depletion and minimize maintenance and remedial workover expenditures. The last and most important objective was achieving economic success through maximized production rates. Both sand bodies would be commingled and produced to surface using a progressive cavity pump (PCP).

The lower-lateral gravel-pack would consist of approximately 1700-ft of premium screen and would penetrate the 4C sand. A pressure-maintenance, horizontal gravel-pack system would be used to perform the gravel pack sand.