Abstract

The purpose of this study is the development of smart lost circulation materials (LCMs) to deal with wide-opened natural fractures encountered during drilling in naturally fractured formations. Due to the limitations on the size of LCMs pumped through bottom-hole assembly (BHA) equipment, simply enlarging the size of particles is not an applicable idea. We benefit from the shape memory effect of polymers and downhole temperature as an external stimulus to produce small enough LCMs which can be transformed to elements with about one order of magnitude larger sizes after exposure to the high temperature. Polymeric particles and filaments are used to prepare permanent shapes which are thermomechanically programmed to fix temporary shapes, such as, compressed particles, disc shapes, and bended star shapes. Permanent shapes are designed and programmed in such a way that a combination of different categories of LCM including granular, fibrous, and planar, are achieved after activation. One of the important factors in the design of LCM elements is their capability to get entangled and form a mat-like bridge over the fracture opening. Then, particles can get trapped inside the interwoven network and provide sealing.

Introduction

Lost circulation is defined as the total or partial loss of drilling fluids or cement slurries into highly permeable zones, cavernous formations, and natural or induced fractures during drilling or cementing operations. This issue is more prominent in naturally fractured formations. During drilling, the operating pressure should be maintained within the drilling margin to ensure the well integrity. Otherwise, the formation will be fractured, and the drilling fluid can be lost if the equivalent circulating density (ECD) exceeds the fracture gradient. Operating outside the drilling margins can result in non-productive time (NPT) and drilling problems such as kicks, pipe sticking, or loss of the well. Economically speaking, about 25–40% of total drilling costs are spent on drilling fluids (Lécolier et al., 2005). In addition, lost circulation problems account for around $800 million, and the products used to prevent or remediate a lost circulation event cost over $200 million (Ivan et al., 2003).

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