Saudi Arabian Trilateral Oil Well in an Unconsolidated-Sandstone Reservoir
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 120999, ’The First Saudi Arabian Trilateral Oil Well in Unconsolidated-Sandstone Reservoir,’ by Ali S. Raba'a, SPE, and Anthony S. Johnson, SPE, Saudi Aramco, and Keith Parry and Mohammed A. Abduldayem, SPE, Weatherford, prepared for the 2009 SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, 4-6 August.

Multilateral (ML) wells to achieve maximum reservoir contact (MRC) are used widely in new carbonate-field developments in Saudi Arabia, resulting in substantial financial improvement of these assets. A multidisciplinary approach was used to evaluate, plan, and complete the first trilateral well in a heterogeneous unconsolidated-sandstone reservoir in Saudi Arabia. The objectives of the ML well were to maximize reservoir contact to enhance sweep efficiency, to improve well productivity, and to promote ML-well applications in this complex field to extend the field’s production plateau.    

Introduction

The objective of ML-well technology is to improve well productivity, either by maximizing reservoir contact in a single reservoir or by commingling production from two or more producing zones or formations into a single main wellbore. Successes with this well architecture justified extending its use into an oil field in central Arabia. The Permian heterogeneous unconsolidated-sandstone reservoir consists of well-developed eolian sandstones and closely associated interdune and lacustrine deposits. Maintaining wellbore stability while drilling this friable-sandstone reservoir presents a considerable challenge. Wells must be equipped with downhole sand control and electrical-submersible-pump (ESP) artificial-lift systems, which cannot tolerate appreciable solids loading.

The candidate well for ML drilling was an idle vertical well that had been shut in because of high water cut (WC) and low productivity. Reservoir characterization and fluid-contact information from adjacent wells were uncertain. Before drilling the laterals, a deviated pilot hole was drilled across the entire reservoir, which provided valuable data that helped optimize placement of the laterals. Re-entry of an existing well to drill and steer three long horizontal open drain holes into the reservoir imposed several constraints and added challenges.

The well completion involved installing an expandable sand screen (ESS) in the main bore and standard sand screens in the two laterals to facilitate sand-free commingled production from all three laterals. The lateral completions included a wash-down capability in the high-build-angle laterals and incorporated swell packers positioned just inside the laterals to ensure sand-tight conditions at the Technology Advancement Multilateral (TAML) Level-3 junctions.

Horizontal-Well Infill Strategies

Several drilling strategies have been applied in the field. Initially, the field was developed with vertical wells at 1-km well spacing and with peripheral water injection. Most wells are equipped with an ESP for oil production. After 5 years of production, a new horizontal-sidetrack infill strategy was implemented to target unswept oil, access low-permeability pay, reduce the WC, and accelerate oil production. Geosteering to intersect the top of the reservoir (shallow horizontal sidetracks) or to follow individual channels was found to be ineffective because of the heterogeneous nature of the reservoir (low vertical conformance) and difficulties in predicting sand presence and continuity. Therefore, the integrated team developed an optimal sidetrack infill strategy of highly deviated wells with minimal geosteering.