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Research Papers: Petroleum Wells-Drilling/Production/Construction

Analytical Model to Characterize “Smear Effect” Observed While Drilling With Casing1

[+] Author and Article Information
Aniket Kumar

Principal Technologist (Drilling)
Halliburton,
2107 CityWest Blvd
Houston, TX 77042

Robello Samuel

Halliburton Fellow
Halliburton,
2107 CityWest Blvd
Houston, TX 77042

This paper was previously published at the 2013 IADC/SPE Drilling Conference and Exhibition held in Amsterdam, The Netherlands on 5–7 March, 2013.

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received January 2, 2014; final manuscript received February 26, 2014; published online April 25, 2014. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 136(3), 033101 (Apr 25, 2014) (9 pages) Paper No: JERT-14-1002; doi: 10.1115/1.4027156 History: Received January 02, 2014; Revised February 26, 2014

The “Smear Effect” observed during a casing-while-drilling operation helps reduce lost circulation, provides wellbore strengthening, and improves the fracture gradient so we can drill more effectively through depleted reservoirs. Several case studies have been reported confirming the formation of a smear zone around the wellbore wall, due to the plastering of cuttings and added lost circulation materials. However, even after successful application in a number of cases, a thorough understanding of the parameters affecting the formation of the smear zone and the subsequent increase in the fracture gradient is not available. This study analyses the theory behind the phenomenon of the smear effect mechanism using case studies and existing literature, and then applies analytical models to estimate the improvement in the fracture gradient based on the drilling parameters and reservoir properties. The formation of the smear zone has been investigated by modeling the mechanism of initiation of micro-fractures around the wellbore wall due to high equivalent circulating densities (ECDs) occurring during casing while drilling. The effect of plugging of these generated micro-fractures by the drilled cuttings and additional lost circulation material added has then been modelled, to estimate the resultant improvement in fracture gradients expected along the wellbore open hole section. In addition, the appropriate particle size distribution required to successfully plug the micro-fractures has also been presented. These analytical models have then been applied to a simulated field case study and the results have been analysed in the context of recorded field observations to simulate the smear effect using the proposed models. The contribution of the casing size and length, formation properties, and operating parameters on the initiation of micro-fractures and the increase in fracture gradient has also been presented to better demonstrate the mechanism of the formation of the smear zone. This analysis is one of the first of its kind of theoretical study to understand the fundamentals of the smear effect mechanism and can be suitably applied to enhance our understanding of the smear effect to use it better to our advantage.

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References

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Figures

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Fig. 1

Drilling margin for the well undergoing casing while drilling operation

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Fig. 2

Estimated new fracture gradient due to plugging of micro-fractures

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Fig. 3

Improvement in fracture gradient due to increase in wellbore temperatures, Kumar and Samuel [8].

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Fig. 4

Improvement in the fracture gradient due to plugging of micro-fractures having variable lengths

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Fig. 5

Resulting fracture widths for varying fracture lengths

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Fig. 6

Effect of casing diameter/hole size ratios on ECDs with continued progress of drilling activity

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Fig. 7

Variation of ECDs with casing lengths under continued progress of drilling activity

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Fig. 8

Variation of ECDs with depth under continued progress of drilling activity

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Fig. 9

Variation of fracture widths with Young's modulus

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Fig. 10

Variation of improvement in the fracture gradient with fracture toughness of the formation

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Fig. 11

Variation of fracture initiation pressure with Poisson's ratios

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Fig. 12

Variation of ECDs with flow rate at the casing shoe depth of 6400 ft

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Fig. 13

Variation of ECDs with flow rate along the entire open hole section

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Fig. 14

Variation of ECDs with mud weight along the entire open hole section

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