Numerical Modeling of Induced Fracture Propagation: A Novel Approach for Lost Circulation Materials (LCM) Design in Borehole Strengthening Applications of Deep Offshore Drilling

Abstract

Lost circulation caused by low fracture gradients is the cause of many drilling related problems. Typically the operational practice when lost circulation occurs is to add loss circulation materials (LCM) to stop mud from flowing into the formations. To improve the treatment for lost circulation caused by low fracture gradients, especially designed materials in mud system are used to seal the induced fractures around the wellbore. This operation is in the literature referred to as wellbore strengthening that has been found to be a very effective in cutting Non-Productive Time (NPT) when drilling deep offshore wells. Size, type and geometry of sealing materials are debating issues when different techniques are applied. Also the phenomenon is not truly understood when these techniques applied in different sedimentary basins. This paper presents development and simulation results of a three-dimensional Finite-Element Model (FEM) for investigating wellbore strengthening mechanism. This study also describes a procedure for designing Particle Size Distribution (PSD) in field applications. To better understand the numerical results, the paper also reviews the connection between Leak of Tests (LOTs) and wellbore hoop stress and how these LOTs can mislead in fracture gradient determination. A comprehensive field database was collected from different sedimentary basins for this study. Results demonstrate that the maximum attainable wellbore pressure achieved by wellbore strengthening is strongly controlled by stress anisotropy. Results also show that Particle Size Distribution (PSD) of wellbore strengthening should be designed in order to seal the fractures close to the mouth and at fracture tip. This will result both in maximizing hoop stress restoration and tip-screening effects. In addition this model is able to show the exact fracture geometry formed around the wellbore that will help to optimize the sealing materials design in wellbore strengthening pills. To support numerical modeling results, near wellbore fracture lab experiments on Sandstone and Dolomite samples were also presented. Laboratory experiments results reveal importance of rock permeability, tensile strength and fluid leak-off in wellbore strengthening applications.

Meeting Name

SPE Annual Technical Conference and Exhibition: Unconventional Wisdom (2012: Oct. 8-10, San Antonio, TX)

Department(s)

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Deep Offshore Drilling; Finite-Element Models; Fluid Leak-Off; Fracture Geometries; Fracture Gradient; Fracture Propagation; Hoop Stress; In-Field; Laboratory Experiments; Loss Circulation; Lost Circulation Materials; Mud Systems; Near Wellbore; Non-Productive Time; Numerical Results; Offshore Wells; Operational Practices; Rock Permeability; Sedimentary Basin; Strengthening Mechanisms; Stress Anisotropy; Wellbore Pressure; Deepwater Drilling; Exhibitions; Experiments; Finite Element Method; Fracture; Numerical Models; Offshore Oil Wells; Oil Field Equipment; Particle Size Analysis; Pelletizing; Residual Stresses; Sealants; Settling Tanks; Tensile Strength; Three Dimensional Computer Graphics Boreholes

International Standard Book Number (ISBN)

978-1622764150

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2012 Society of Petroleum Engineers (SPE), All rights reserved.

Publication Date

01 Oct 2012

Link to Full Text

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