Typical analysis of the Leak-off testing (LOT) in wells assumes elastic wellbore and involves identification of diversion points from linear trends of the recorded plots. However, LOTs from wells in the shallow marine sediments (SMS) are inherently nonlinear and their analysis becomes a problem. The paper presents mathematical models of the pressure-volume behavior for two different possible failures around the casing shoe, annular crack (cement-rock parting) and formation fracture. The study submits that these two failure modes would control abnormal LOT patterns. A general pressure-volume model of LOT has been developed including volumetric effects of wellbore expansion, mud loss into the rock, and propagation of an annular crack or plastic fracture. A diagnostic method is proposed to identify LOT-control mechanisms (i.e., formation fracture, annular crack, or mud loss) by analyzing the shut-in section of the LOT’s plot.

1.
Wojtanowicz, A. K., and D. Zhou, 1998, “Borehole Failure Resulting From Formation Integrity (Leak-Off) Testing in Upper Marine Sediments Offshore,” Journal of Energy Resources Technology, June, Vol. 120, pp. 111–117.
2.
Morita, N. M., 1991, “Safety of Casing Shoe Test and Casing Shoe Integrity After Testing,” Presented at the 66th Annual Technical Conference and Exhibition of the SPE, Dallas, TX, SPE 22557, pp. 229–243.
3.
Postler, D. P., 1997, “Pressure Integrity Test Interpretation,” presented at the SPE/IADC Drilling Conference, Amsterdam, Netherlands, March, SPE/IADC 37589, pp. 169–183.
4.
Hazov, V. A., and Hurshudov, V. A., 1993, “Leak-off tests help determine well bore compressibility,” Oil & Gas Journal, Nov., pp. 71–73.
5.
Almeida, M. A., 1986, “Computer-Aided Analysis of Formation Pressure Integrity Tests used in Oil Well Drilling,” Ph.D. Dissertation, Louisiana State University.
6.
Chenevert, M. E., and McClure, L. J., 1978, “How to run casing and open-hole pressure tests,” Oil & Gas Journal, March, pp. 67–76.
7.
Bourgoyne, A. T., et al., 1991, Applied Drilling Engineering, SPE Text Book Series, Vol. 2, Second Printing.
8.
Altun, G., et al., 1999, “New Model to Analyze Nonlinear Leak-Off Test Behavior,” Journal of Energy Resources Technology, Vol. 121, pp. 102–108.
9.
Risnes, R., et al., 1982, “Sand Stresses Around a Wellbore,” SPEJ, Dec., pp. 883–898.
10.
Chen, W. F., and Han, D. J., 1988, Plastic for Structural Engineers, Springer-Verlag New York, Inc.
11.
Obert, L., and Duvall, W. I., 1967, Rock Mechanics and the Design of Structures in Rock, John Wiley & Sons.
12.
Gidley, J. L., et al., 1989, Recent Advances in Hydraulic Fracturing, SPE Monograph Vol. 12, Richardson, Texas.
13.
Sneddon, I. N., and Lowengrub, M., 1969, “Crack Problems in the Classical Theory of Elasticity,” John Wiley & Sons, Inc.
14.
Nelson, E. B., 1990, Well Cementing, Schlumberger Educational Services.
15.
Rocha, L. A., and Bourgoyne, A. T., 1996, “A New Simple Method to Estimate Fracture Pressure Gradient,” SPEDC, Sep., pp. 153–159.
16.
Zhou, D., and Wojtanowicz, A. K., 1999, “Estimation of Leak-off Pressure Gradient from Cementing and Casing Data,” presented at the 1999 SPE Annual Technical Conference and Exhibition, Houston, Texas, SPE 56760.
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