Abstract

This paper discusses the first multilateral well drilled in Trinidad and the unique integration of techniques that allowed sand control procedures to be implemented as well. The well 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 heavyoil 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 as it not only represents the first multilateral well in Trinidad but also is the first in the area that integrates sand control into a multilateral.

After reviewing many possibilities, horizontal openhole gravel-pack technology had been selected to provide sandexclusion. A TAML 4 multilateral well junction was selected originally because it offered a cemented junction with full casing-drift access across the mainbore/lateral interface. When sand was encountered above the junction area, a completion workover was required to convert the existing TAML 4 multilateral junction into a TAML 5 to gain pressure integrity across the junction area.

The paper will present the initial planning, special considerations, methods for implementation of horizontal gravel pack into multilateral technology, and finally, the rework operation later required for junction conversion.

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 (Figs. 1 and 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 casedhole completion that used either gravel packing or frac-andpack 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. The lower lateral gravel-pack assembly would be tied back to the bottom of the 9–5/8-in. production casing. The upper lateral completion would penetrate the 4B sand and would be gravelpacked with a pressure-maintenance, horizontal gravel-pack system. Approximately 850-ft of premium screen would be deployed into the upper lateral and tied back to the 7-in. upper lateral casing. Both laterals would be gravel-packed using 20/40 re-sieved gravel-pack sand.

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