Evolution of Wellbore Strain in Horizontal Wells for Production Evaluation

ABSTRACT The azimuthally resolved wellbore strain and geometry change provides a direct measure of the wellbore locations that are depleted due to production. As pore pressure decreases due to production, the stress field around borehole changes resulting in casing deformation which can be measured by field-scale downhole tools with high azimuthal resolution. It is shown that the shape of the wellbore is different in producing sections/clusters and non-producing sections/clusters along the well. A pad-scale geomechanically fracturing-flow simulator is used to perform life-cycle simulation of a horizontal well, from dynamic fracture propagation to long term pressure depletion. High levels of mesh refinement are used to obtain very fine meshes in the near wellbore region to simulate the deformation of the rock and the casing along the wellbore. Axial and radial strain is obtained as a function of space and time. The results show: a) the total stress around the casing is larger than the wellbore pressure, which leads to compressive deformation of the casing. The magnitude of the casing deformation is different along and around the casing due to the non-uniform pore pressure distribution; b) producing sections/clusters of the wellbore deform less but show larger ellipticity; c) resolution needed in the deformation measurements lies in the precision range of current downhole tools; d) bending deformation can occur due to non-symmetric fracture geometry or pressure depletion. Measurement of the ellipticity of the borehole as a function of measured depth should allow us to identify sections of the wellbore that are depleted (producing fluid) and sections that are not. INTRODUCTION The application of hydraulic fracturing in horizontal well contributes to the production of hydrocarbon resources from unconventional reservoirs with ultra-low permeability in the past decade. In contrast to vertical wells generally stimulated with only one single fracture, horizontal wells have many fractures created in a sequence of stages. During the stimulation treatment of each stage, multiple perforated clusters are fractured simultaneously along the horizontal wellbore, creating high-conductivity pathway between the tight rock matrix and wellbore. Therefore, the surface area available for the transport of hydrocarbon is increased by 3 orders of magnitude, leading to a corresponding rise in production rate.