This paper presents the results of a theoretical study, supported with the finite element analysis, into potential loss of external integrity around a casing shoe resulting from leak-off testing (LOT) in upper marine sediments (UMS). Three types of possible failures from LOTs were considered: vertical fracture, horizontal fracture, and a channel outside cemented annulus. It is proved in the paper that vertical fracture is the most unlikely failure of the three. The other two types of failure can be distinguished by different values of propagation pressures. Although horizontal fractures are initiated at low pressure in the plastic zone around the wellbore, they cannot propagate beyond the plastic zone until wellbore pressures exceed overburden pressures. Annular channels, on the other hand, may propagate upwards at pressures lower than overburden pressure. The paper shows that these channels are initiated at pressures equal to the contact stress between cement and rock and their propagation pressures are on average 3.5-fold greater than contact stress. It is also explained how to identify the UMS with high risk of annular channeling during LOTs.

Issue Section:
Technical Papers
Topics:
Failure, Leakage, Ocean engineering, Sediments, Testing, Fracture (Materials), Fracture (Process), Pressure, Stress, Annulus, Cements (Adhesives), Finite element analysis, Risk, Rocks
1.
Arifun, and Sumpennpo, W. H., 1994, “A New Approach To Casing Setting Depth Selection In Unocal East Kalimantan,” IADC Well Control Conference of The Americas, Houston, TX.
2.
Bender, C. V., and Bourgoyne, A. T., 1995, “Use of Soil Borings Data for Estimating Break-Down Pressure of Upper Marine Sediments,” LSU/MMS Well Control Workshop. Baton Rouge, LA.
3.
Bourgoyne, A. T., et al., 1991, Applied Drilling Engineering, SPE Text Book Series, Vol. 2, Second Printing.
4.
Christman, S., 1973, “Offshore Fracture Gradients,” JPT, Aug., pp. 910–914.
5.
Constant, W. D., and Bourgoyne, A. T., 1988, “Fracture-Gradient Prediction for Offshore Wells,” SPE Drilling Engineering, June, pp. 136–140.
6.
Eaton, B. A., and Eaton, T. L., 1997, “Fracture Gradient Prediction for the New Generation,” World Oil, Oct., pp. 93–100.
7.
Gnirk, P. F., 1972, “The Mechanical Behavior of Uncased Wellbores Situated in Elastic/Plastic Media Under Hydrostatic Stress,” SPEJ, Feb., pp. 49–59.
8.
Harrison
E.
, et al.,
1954
, “
The Mechanics of Fracture Introduction and Extension
,”
Trans., AIME
, Vol.
201
, pp.
252
–
263
.
9.
Hubbert
M. K.
, and
Willis
D. G.
,
1957
, “
Mechanics of Hydraulic Fracturing
,”
Trans., AIME
, Vol.
210
, pp.
153
–
166
.
10.
Mattews, W. R., and Kelly, J., 1967, “How to Predict Formation Pressure and Fracture Gradient,” Oil and Gas Journal, Feb., pp. 39–43.
11.
Morita, N., 1990, “Theory of Lost Circulation Pressure,” 65th Annual Technical Conference and Exhibition of SPE, SPE 20409, New Orleans, LA.
12.
Obert, L., and Duvall, W. I., 1967, Rock Mechanics and the Design of Structures in Rock, John Wiley & Sons, pp. 172–177.
13.
Risnes, R., et al., 1982, “Sand Stresses Around a Wellbore,” SPEJ, Dec, pp. 883–898.
14.
Rocha, L. A., and Bourgoyne, A. T., 1996, “A New Simple Method to Estimate Fracture Pressure Gradient,” SPEDC, Sep., pp. 153–159.
15.
Rocha, L. A., and Bourgoyne, A. T., 1993, “Identifying Crater Potential Improves Shallow Gas Kick Control,” Oil and Gas Journal, Dec., pp. 93–97.
16.
Steiger, R. P., and Leung, P. K., 1988, “Quantitative Determination of the Mechanical Properties of Shales,” 63rd Annual Technical Conference and Exhibition of the SPE, SPE 18024, Houston, TX, pp. 69–76.
17.
Warpinski
N. R.
, and
Smith
M. B.
,
1989
, “
Rock Mechanics and Fracture Geometry
,”
Recent Advances in Hydraulic Fracturing
, SPE Monograph, Vol.
12
, pp.
57
–
80
.
18.
Wang
Y.
, and
Dusseault
M. B.
,
1991
, “
Borehole Yield and Hydraulic Fracture Initiation in Poorly Consolidated Rock Strata-Part I. Impermeable Media
,”
International Journal of Rock Mechanics, Mineral Science & Geomechanical Abstracts
, Vol.
28
, pp.
235
–
246
.
19.
Wojtanowicz, A. K., and Zhou, D., 1996, “Finite Element Analysis of Soft Sediment Behavior During Leak-Off Test,” LSU/MMS Well Control Workshop, Baton Rouge, LA.
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