Abstract

The use of expandable screens simplifies completion proce-dures. Many operators perceive that screen performance de-pends on whether it is fully compliant with open hole; how-ever, it is impossible to guarantee total compliance. Evidence indicates that, in addition to filling the micro-annuli and plug-ging the screen, mobile fines and sand have the potential to create hot spots and erode the screen, thus creating sand-production problems.

This paper presents laboratory results that illustrate the feasibility of applying a curable, low-viscosity composition to stabilize and strengthen unconsolidated formations. Over-displacement is not necessary in this process. The composition forms a tacky, ultra-thin film, creating bonds between grains that cure with time and temperature once coated onto the sur-faces of formation particulates. Unconsolidated formation sands, even those with high content of clay fines, were con-solidated with negligible loss of initial permeability.

The results obtained from this study demonstrate the im-portance of stabilization of the formation. The screens, whether wire-wrapped, pre-packed, expandable, or simply slotted pipes, serve as a mechanical support to prevent col-lapse of the wellbore. A combination of treating unconsoli-dated formations with an ultra-thin, curable composition and installing a mechanical liner should provide an economical and reliable means for sand control. The use of such curable sand-stabilization treatments may therefore eliminate the per-ceived need for compliant expansion, placing a premium on the mechanical strength of the sand-control technique selected.

Introduction

Wellbore instability often results from a combination of me-chanical and chemical instability; however, mechanical factors play a dominant role in wellbore instability during the drilling phase of operations. Drilling a well in a formation changes the initial stress state and causes stress redistribution in the vicin-ity of the wellbore. The redistributed stress state may exceed the rock strength and cause failure.[1, 2]

Once a wellbore or a perforation tunnel is introduced into a friable sand formation, a plastic zone develops and formation failure can follow. Production and cyclic loading are the main reasons a plastic failure zone expands into a formation. For-mations that are considered soft or poorly consolidated are often plagued by sand production. Formation sand production can result in

  1. plugged gravel packs,

  2. plugged sand screens,

  3. plugged tubulars, and potentially sand fill in the surface flow lines and surface equipment, as well as

  4. lost production.3–6 In addition to damage caused by plugging, sur-face equipment can be eroded because of abrasive, sand-laden fluid flowing from the well.

In a worst-case scenario, sand-production problems can cause total well failure or the need for recompletion resulting from casing collapse, openhole col-lapse, or both.

Conventional treatments for sand-producing wells include gravel packing, frac-packing, formation consolidation, and squeeze treatments using resin-coated sand slurries. These treatments control sand production and are based on gravel-packing technology that relies on the creation of stable bridges at the face of the formation to minimize damage to the pack. The filtering mechanism provided by the gravel pack is effec-tive for controlling sand production, but the permeability of the pack can decrease over time. This decreased permeability results from a continuous migration of formation fines toward the wellbore, which causes progressive plugging and results in high skin damage and reduced productivity.

Sand-Control Screens

The primary function of screens is to provide mechanical support to prevent proppant or gravel placed in the perforation tunnel and formation from flowing back into the wellbore. Keeping proppant in place will support the perforation tunnel and/or fracture thus maintaining a highly conductive flow path into the wellbore. In all gravel pack and frac-pack comple-tions, the gravel and proppant act as the primary filter to help prevent fines migration and sand production.

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