Abstract

During the last decade, intelligent well completions have evolved to become engineered solutions widely used for both monobore and multilateral horizontal wells. However, a clear understanding of zonal or lateral branch flow contributions still remains an issue. Several SPE papers covering the issue have been published recently.

This paper presents the engineered solution for a TAML level 5 dual-lateral horizontal well that was drilled and completed in the Oseberg Sør field in December 2005. The solution combines hydraulic flow control valves with advanced downhole two-phase flow and density measurement provided by a Venturi-based flowmeter with a gamma ray source and detector. Real-time data were used to optimize the settings of the downhole chokes to obtain a balanced production from the two horizontal wellbores. The completion provides the capability to control and measure, in real time, flow contributions from both laterals and is the first installation of its type. This capability is critical for production and reservoir optimization.

Additional value of the technology is demonstrated by the analysis of acquired downhole data. Productivity Indices are obtained for each of the two laterals without any production loss associated with shutting down the other lateral branch. Data analysis indicated a decrease of the Productivity Index for one of the two horizontal wellbores.

The successful installation of the two-phase flowmeter in an intelligent completion is a significant milestone corresponding to the general trend in the industry to improve inflow control and the understanding of flow contributions in multilateral wells. This solution for flow control and measurement can be applied effectively in both multilateral wells and monobore wells designed for commingled production from different reservoirs where accurate production allocation is a critical issue.

Introduction

Intelligent completions have developed over recent years with increasing functionality to meet specific applications. Norsk Hydro has been particularly active in implementing innovative intelligent completion solutions to meet its objectives.1 This implementation commenced in 1998 with natural gas lift on the Troll field using hydraulic gas lift valves. For the Fram Vest field, an innovative natural gas lift completion was implemented using this field proven technology repackaged for a more efficient, safe, and environmentally friendly completion system.

Several intelligent wells were completed on the Oseberg field with long reach, highly deviated wells having flow control of two to three zones with hydraulic flow control valves. Norsk Hydro then turned its attention to flow control of multilateral wells. A completion solution integrating flow control of the lateral and main bores together with natural gas lift was implemented on the Troll and Vestflanken subsea fields.

There was a growing understanding that downhole production monitoring was needed in order to draw the full benefit of the intelligent multilateral completions. This resulted in the installation of Schlumberger downhole flowmeter in Norsk Hydro multilateral well F-29 on the Oseberg Sør field. The well was completed with flow control of both the main bore and lateral bore with flow measurement of the main bore. Applied downhole two-phase flow and density measurement principles were the same as for BP Harding well PN1.2

Oseberg Sør Field Description

The Oseberg Sør field, operated by Norsk Hydro, is situated 130 km west of the Norwegian coast. The main oil-producing reservoir is the Tarbert formation within the Brent group, which is of variable reservoir quality with permeabilities ranging from 1 D to 1 mD. The 33 API oil was initially slightly under-saturated, but some parts of the field have been heavily depleted. The field comprises several structures that are drained by extended reach and horizontal oil production wells. The development includes both platform wells and two subsea templates that are tied back to the platform. Reservoir pressure is supported by water and gas injection.

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