Use of Geomechanics for Optimizing Reservoir Completion and Stimulation Strategies for Carbonates in the Campos Basin, Offshore Brazil
Authors: Nagy Zsolt Robert , Pacheco Fabiola , Rosa Marcia R. Da S. , Ribeiro Mauro Torres , Jouti Iwao , Pastor Jorge Aurelio , Grandy Aaron , Fluckiger Sam , Gigena Luis Daniel 
Published: October 2011

A 1D Mechanical Earth Model (MEM) was built for the Albian section of a planned horizontal well in the south Campos Basin area in order to reduce risks for well placement, completion and stimulation in a fast track development program with reduced number of appraisal wells. Mechanical properties and stress profile along the wellbore for the design were determined from multiple data sources including core testing, advanced acoustic, wellbore image, processed petrophysics, micro-fracturing and in-situ formation pressure. These measurements enabled the definition of local correlations for the studied carbonate reservoir, estimation of geomechanical properties, and the creation of input for the completion design. The calibrated geomechanics model was used to evaluate the completion options for a horizontal well in carbonates to optimize reserves and maximize well productivity. Based on field characteristics and mechanical properties determined from this study, the horizontal well placement and drilling design was adjusted and an open hole completion with mechanical isolation was proposed to enable multiple fracturing in one continuous and efficient operation.

Introduction

Heterogeneous reservoirs rocks, such as carbonates, with a broadly varying porosity and permeability have presented a great challenge with regards to completion and stimulation practices in most of the existing carbonate fields in Brazil1, 2. In the planning phase, geomechanics has proved to be a useful tool for characterizing the location of possible barriers to fractures growth and length of fracture propagation in layered formations. The fracture height and length are mainly controlled by the elastic properties (Young's modulus, Poisson's ratio) and stress contrast of reservoir and bounding layers. Specifically, longer-thinner fractures will be dominant when contrast is high and shorter fracture with height growth is more common when contrast is low. In addition, fracture orientation is dependent on the stress state. Fracture always starts along the wellbore due to near-wellbore stress concentrations and eventually turns towards the far-field maximum horizontal stress. This case is common in reservoirs with natural fractures, such as carbonates, that may result in fracture tortuosity.

The prospect was discovered with Well A but carefully planned acquisition program for geomechanics characterization was carried out in Well B, located 8.5 km north. 1D Mechanical Earth Model (MEM) was constructed to understand the mechanical properties and stresses of the Macaé Formation, which was used for basis of the subsequent drilling and completion design of the horizontal well. The paper describes the workflow used to characterize the geomechanics properties of the carbonate play. It also outlines the necessary input data that is required for such an investigation to guarantee a more accurate estimation of the mechanical properties and stresses for fracture design.

The concept of a geomechanical characterization for improving fracture design has already been applied successfully in the Carmópolis and Sirizinho fields, northeastern Brazil 3.