Physical and Analytical Studies of Sand Production from a Supported Wellbore in Unconsolidated Sand Media With Single- and Two-Phase Flow
Authors: Nouri A. , Vaziri H. , Kuru E. , Belhaj H. , Islam M.R. 
Published: March 2010

Use of expandable technology for sand control has rapidly grown in recent years. While several expandable systems have been developed, assessment of their long-term performance and effectiveness has hitherto not been objectively completed. To address some of the concerns and uncertainties on this front, this paper provides criteria for the assessment of sanding from wellbores completed by expandable completion techniques. It also provides an in-depth understanding of the mechanism under which expandable screens control mobilization of sand grains.

A series of experiments were conducted using hollow cylinder unconsolidated sand samples. The primary objective was to assess the influence of the opening size relative to the grain size in dictating the operational limits. A stiffener, representative of a general expandable completion technique, supported the central hole. The stiffener contained a network of small perforations. Experiments were conducted on both single- and two-phase flow media. This was to explore the possible effect of a second phase in sand production in the presence of the stiffener.

Experiments showed that the mobilized friction between the grains plays a major role in preventing sand production. The experiments also confirm that even with a large aperture size of an order of magnitude greater than the maximum grain size, sanding did not take place under routine operational conditions in a two-phase medium. On the contrary, instant sanding from the sandpack in single-phase experiments took place, which emphasized the important role of capillarity.

Introduction

Several expandable techniques have been implemented by the oil industry(1–5) and their application is experiencing a rapid growth. Although expandable completion techniques have been used in over 1,000 wellbores(6), few experimental research studies have been reported on their interaction with the medium around them. This paper bridges a gap in the literature on several important issues surrounding supported wellbores.

This paper presents insights into the hollow cylindrical experimental implementation of an expandable completion and uses both single- and two-phase fluid flow. Field observations have indicated there are strong ties between sand production and water influx(7–11). A formulation is suggested for the evaluation of the stability of unconsolidated media under single- and two-phase flow conditions. The validity of the formulation is examined by experimental observations.

This research used unconsolidated sand in a comprehensive experimental program. The importance of studying the response of unconsolidated and weakly consolidated sandstones to expandable completions is realized by estimations that approximately seventy percent of the total World's oil and gas reserves are found in poorly consolidated reservoirs(7).

Experimental Setup

The testing equipment included the loading unit, the flow setup unit, the sand weight measurement unit and instrumentation. A schematic of the testing equipment is depicted in Figure 1. A steel 12 mm thick shell restrains a hollow cylinder sample surrounded by 7.5 mm thick gravel pack. The samples were 125 mm in

FIGURE 1: A schematic of the consolidation chamber (Available in full paper)

FIGURE 2: Grain size distributions of the fine and coarse sand used in sandpack samples (Available in full paper)

diameter and 250 mm in height.