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Web End = Rock Mech Rock Eng (2016) 49:13591368 DOI 10.1007/s00603-015-0807-x
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Web End = Numerical Modelling of Extended Leak-Off Test with a Pre-Existing Fracture
A. Lavrov1 I. Larsen1 A. Bauer1
Received: 19 November 2014 / Accepted: 31 July 2015 / Published online: 7 August 2015 Springer-Verlag Wien 2015
Abstract Extended leak-off test (XLOT) is one of the few techniques available for stress measurements in oil and gas wells. Interpretation of the test is often difcult since the results depend on a multitude of factors, including the presence of natural or drilling-induced fractures in the near-well area. Coupled numerical modelling of XLOT has been performed to investigate the pressure behaviour during the owback phase as well as the effect of a pre-existing fracture on the test results in a low-permeability formation. Essential features of XLOT known from eld measurements are captured by the model, including the saw-tooth shape of the pressure vs injected volume curve, and the change of slope in the pressure vs time curve during owback used by operators as an indicator of the bottomhole pressure reaching the minimum in situ stress. Simulations with a pre-existing fracture running from the borehole wall in the radial direction have revealed that the results of XLOT are quite sensitive to the orientation of the pre-existing fracture. In particular, the fracture initiation pressure and the formation breakdown pressure increase steadily with decreasing angle between the fracture and the minimum in situ stress. Our ndings seem to invalidate the use of the fracture initiation pressure and the formation breakdown pressure for stress measurements or rock strength evaluation purposes.
Keywords Extended leak-off test XLOT Model
Fracture Coupled
1 Introduction
Knowledge of the minimum in situ stress, rmin, is crucial
for choosing the correct mud weight during drilling and for designing hydraulic fracturing jobs during stimulation of oil and gas wells. The need for accurate evaluation of rmin
increases when drilling deepwater or extended reach wells, where the mud weight window becomes narrow. Also, drilling in depleted reservoirs requires a good grip on the actual...