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Research Papers: Petroleum Engineering

Experimental Study of the Impact of Drilling Fluid Contamination on the Integrity of Cement–Formation Interface

[+] Author and Article Information
Nnamdi Agbasimalo

Craft & Hawkins
Department of Petroleum Engineering,
Louisiana State University,
Baton Rouge, LA 70803
e-mail: agbasimalo@gmail.com

Mileva Radonjic

Craft & Hawkins
Department of Petroleum Engineering,
Louisiana State University,
Baton Rouge, LA 70803
e-mail: mileva@lsu.edu

1Present address: 11 Aibu Street, Surulere, Lagos, Nigeria.

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received October 3, 2013; final manuscript received February 8, 2014; published online November 10, 2014. Assoc. Editor: Andrew K. Wojtanowicz.

J. Energy Resour. Technol 136(4), 042908 (Dec 01, 2014) (5 pages) Paper No: JERT-13-1279; doi: 10.1115/1.4027566 History: Received October 03, 2013; Revised February 08, 2014; Online November 10, 2014

Flood experiments were conducted over 30-day periods at 14.48 MPa (2100 psi) confining pressure and temperature of 22 °C (72 °F) with cement–sandstone composite cores and brine at a flow rate of 1 ml/min. Higher pH values were observed in the effluent brine from the 10% mud contaminated core than the 0% mud contaminated core due to increased dissolution of cement. Microtomography revealed higher porosity at the interface zone of the 10% mud contaminated core. These show that mud contamination has a deleterious effect on the cement–sandstone interface and may create pathways for interzonal communication as well as sustained casing pressure.

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Figures

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Fig. 1

Actual composite core

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Fig. 2

Schematic of experimental setup

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Fig. 3

CT images of 1 in. × 12 in. cement–sandstone composite cores. The brighter half is the cement while the darker half is the sandstone. Longitudinal and cross sectional views of the image reveal effective bonding between the cement and the rock before and after core flooding. White arrows show where cross section was taken from: (a) 0% mud contaminated core before core flood; (b) 10% mud contaminated core before core flood; L: Longitudinal view of composite core, C: Cross section of composite core.

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Fig. 4

Axial slices of micro CT images of 3 mm diameter mini cores drilled from the cement–sandstone interface of the composite cores (inlet and outlet) after 30 days of core flood and also from control samples. The cement in the control samples shows the neat cement layer with uniform density (uniform color) and contaminated layer with varied density (dark and bright regions). The post core flood images, on the other hand, reveal presence of large pores in the 10% contaminated core and small pores in the 0% contaminated core. The pores appear as black spots in the images.

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Fig. 5

Pressure profile for the core flood experiments. The 0% contaminated core exhibited fairly constant increase in pressure differential throughout the core flood while the 10% contaminated core had alternating periods of increase and leveling off in pressure differential.

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Fig. 6

View of inlet face of composite cement–sandstone core: (a) before core flooding and (b) after core flooding. A layer of brown pastelike material is visible on the post experiment core and is clearly absent on the pre core flood core.

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Fig. 7

XRD plot for the brown deposit found on the face of composite cores after core flood. The plot has no identifiable peaks showing absence of crystalline components.

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Fig. 8

Plot of pH measurements of effluent samples taken daily. The pH values for effluent from 0% contaminated core were generally lower than that of 10% contaminated core throughout the experiments.

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