8/7/2019 Wellbore Strengthening Without Propping Fractures

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Copyright 2008, International Petroleum Technology Conference

This paper was prepared for presentation at the International Petroleum Technology Conference held in Kuala Lumpur, Malaysia, 3–5 December 2008.

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AbstractIncorporating particulate lost circulation materials (LCM) into drilling fluids for drilling weak formations to prevent lost

circulation has been in the spotlight in the drilling industry over the last few years. This new technology sometimes is

referred to as “stress cage”. Creating a stress cage1,2 can increase the wellbore pressure containment which effectively widens

the mud weight window. The mechanism has been explained as propping small fractures intersecting the wellbore resulting

in an increase in the hoop stress.

However, a series of studies3,4,5,6

with a numerical method have indicated that increasing wellbore pressure containment does

not necessarily require the propping of the fractures. Merely sealing the fractures alone can also improve the wellbore

pressure containment substantially. This paper presents detailed discussion of those factors related to improving wellbore

pressure containment by sealing the fractures only. Focusing on fracture stability, studies have found that fracture pressure,

fracture length, Young’s Modulus, wellbore radius and sealing location can all affect wellbore pressure containment, and the

fracture width that exists under each condition shows how challenging it could be to achieve the sealing during

implementation.

Introduction

With a greater worldwide demand for energy, drilling activities have been moving into unconventional areas such as deep or

ultra-deep water, deep or ultra-deep wells, extended reach wells, in-field drilling through highly depleted formations, etc.

These drilling activities typically may encounter mud weight windows that are narrower than usual. The possible severe

consequences include hole collapse, lost circulation, stuck pipe, and loss of the drilling interval or even the entire well.

In recent years, a new concept to widen the mud weight window for drilling was introduced1,7,8 and it is now often referred to

as “wellbore strengthening”. While methods for coping with narrow mud weight window challenges can differ, strengthening

the wellbore for higher wellbore pressure containment seems to be the most economical, preferably strengthening the

wellbore to prevent mud losses. 9 A newly introduced wellbore strengthening method to prevent mud losses, usually referred

to as “stress cage”2,10 is a process of adding particulate LCM into drilling fluids to enable the wellbore to withstand a higherpressure without failing. The initially proposed theory has been debated; however, success has been achieved in the field

consistently. While we agree that propping fractures will improve wellbore pressure containment (WPC) based on the

knowledge gained from the research, more studies have found that sealing the fractures alone still will improve WPC

substantially.3

In many cases, the WPC achieved has been high enough to satisfy the drilling needs of a problem interval. In

this paper we will report our findings on the factors that affect achieving a desired WPC by only sealing the fracture. New

understandings9 of wellbore strengthening have provided an improved basis for designing a product and defining its

placement techniques and have led to a series of innovations.10,11 

MethodThis study has been conducted within a linear elasticity domain with the assumptions of rock homogeneity and isotropy.

These assumptions are commonly used in wellbore stability studies.

IPTC-12280

Wellbore Strengthening without Propping Fractures: Analysis forStrengthening a Wellbore by Sealing Fractures AloneHong (Max) Wang, Halliburton, Brian F. Towler, University of Wyoming, Mohamed Y. Soliman, Zhaohui Shan,Halliburton