Abstract

In the petroleum industry, the stress evolution is considered a key factor to understand the geomechanical behaviour of hydrocarbon production fields. Inside the reservoir, changes of stresses have been linked with uniform changes of pore pressure through simple relationships, called reservoir stress paths. However, the stress evolution can also be affected by the mechanical properties and the reservoir geometry. Analytical solutions have been proposed for ellipsoidal reservoir shapes. Enhanced methods based on the theory of nucleus of strain have been developed for arbitrary three-dimensional reservoir shapes, but they cannot provide results inside the reservoir. To overcome this limitation, this paper presents a methodology to assess the evolution of displacements, strains and stresses both outside and inside the reservoir. As an application of this methodology, a synthetic model considering a thick cylindrical reservoir submitted to uniform and non-uniform depletion is shown. The results are discussed through the identification of different geomechanical behaviour inside and outside of the reservoir. Nevertheless, this methodology can be applied to arbitrary reservoir shapes, providing an alternative tool which properly extends the concept of reservoir stress paths to reservoir stress changes.

1. INTRODUCTION

In overall, changes in reservoir pore pressure due to fluid production or injection induce stress changes within the reservoir and its surrounding rocks. These stress changes lead to reservoir swelling or compaction, which in turn can trigger potential geomechanical problems such as surface subsidence, fault reactivation, pore collapse, casing deformation and seismicity.

Inside the reservoir, changes in the horizontal and vertical stresses have been linked with uniform changes in pore pressure through simple relationships, called reservoir stress paths. In general, it is assumed that the reservoir supports the overburden pressure completely. Consequently, the vertical stress path is disregarded and the horizontal stress path occurs under uniaxial deformation. According to Goulty [1], in the reservoir rock three mechanisms can provide different approaches to the horizontal stress path: normal compaction, poroelastic behaviour and normal faulting.

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