Wellbore Strengthening in Sandstones by Means of Nanoparticle-Based Drilling Fluids


Drilling operations of both conventional and unconventional oil and gas accumulations are; becoming more challenging especially in deep-water operations. Due to the narrow mud weight window in offshore wells, a proper wellbore stability analysis is required for a cost-effective execution. Wellbore strengthening is an approach used to increase the fracture pressure of the rock, widen the mud window and consequently enhance the well integrity and mitigate mud losses. This paper demonstrates the feasibility of wellbore strengthening in permeable formations using oil-based mud (OBM) containing in-house prepared nanoparticles (NPs) combined with graphite. A significant increase in the fracture pressure was achieved and the predominant wellbore strengthening mechanism was identified. Fracture pressure increase was quantified by carrying out hydraulic fracturing tests on 5 3/4" x 9" Roubidoux sandstone cores. A 9/16" wellbore was drilled, cased and cemented to simulate well conditions. Overburden and confining pressure were applied on the cores while testing to simulate a normalfaulting regime. Two injection cycles were applied allowing 10 minutes of fracture healing between the cycles. The fracture pressure was increased by 65% when calcium-based NPs (NP2) blends were used, whereas it increased by 39% in the presence of iron-based NPs (NP1). Optimum NPs concentrations were established after a comprehensive experimental screening. A strong relationship between wellbore strengthening and mud filtration at high-pressure high-temperature (HPHT) using a filter press on ceramic discs was found. Optical microscopy, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses were conducted on the hydraulically fractured cores. The fractures were seen to be completely sealed from tip to wellbore. Therefore, tip isolation by the development of an immobile mass was identified as the predominant wellbore strengthening mechanism. A 40 micron-seal containing homogeneously dispersed NPs and graphite was observed. In addition, a 300 micron-filter cake was developed around the wellbore also containing homogeneously dispersed NPs.

Meeting Name

SPE Deepwater Drilling and Completions Conference (2014: Sep. 10-11, Galveston, TX)


Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Bathymetry; Cost Effectiveness; Deepwater Drilling; Drilling Fluids; Energy Dispersive Spectroscopy; Fracture; Graphite; Hydraulic Fracturing; Nanoparticles; Offshore Boreholes; Offshore Oil Wells; Oil Field Equipment; Oil Shale; Sandstone; Scanning Electron Microscopy; Well Drilling; Confining Pressures; Deep Water Operations; Energy Dispersive X Ray Spectroscopy; High Pressure High Temperature; Permeable Formations; Strengthening Mechanisms; Unconventional Oil And Gas; Wellbore Stability Analysis; Oil Wells

International Standard Book Number (ISBN)


Document Type

Article - Conference proceedings

Document Version


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© 2014 Society of Petroleum Engineers (SPE), All rights reserved.

Publication Date

01 Sep 2014