3D Geomechanical Modeling Optimizes Drilling in the Llanos Orientales Basin, Colombia

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 138752, ’Drilling Optimization Using 3D Geomechanical Modeling in the Llanos Orientales Basin, Colombia,’ by Ewerton Araujo, SPE, and Rene Alcalde, GeoMechanics International; Darwin Mateus, SPE, Instituto Colombiano del Petroleo; Fermin Fernandez-Ibanez, Judith Sheridan, Chris Ward, SPE, Martin Brudy, and Jose Alvarellos, SPE, GeoMechanics International; and Luz Yamile Ordonez and Felipe Cardona, Ecopetrol S.A., prepared for the 2010 SPE Latin American & Caribbean Petroleum Engineering Conference, Lima, Peru, 1-3 December. The paper has not been peer reviewed. Drilling in tectonically active areas involves nonproductive time (NPT) related to wellbore-stability problems that are very difficult to predict without a clear understanding of the local- and regional-stress magnitude and orientation and their effect on wellbore trajectory. To optimize drilling by eliminating the wellbore-instability NPT, a 3D geomechanical model was built that integrates the geological structural model with relevant well information such as wireline-logging data and drilling reports. A new drilling campaign used the 3D model for wellbore-stability analysis, and the results showed that the associated geomechanical risks to drill the wells have been addressed properly, with a much better drilling experience. Introduction The Llanos Orientales basin, in the northern Andes of Colombia, is affected by light but complex deformation. Wellbore stability is a concern in the area, and it is part of well planning. Ecopetrol S.A. has dealt with this problem for the last 20 years in the Apiay-Suria fields in that every well has shown clear evidence of wellbore instability, as modest-to-severe hole enlargement and related problems such as tight hole and stuck pipe. In extreme situations, some wells with high inclinations had to be sidetracked to reach target depth, not allowing wireline-logging tools to be run. To understand such a challenging drilling scenario and to make appropriate changes in drilling practice to reduce the NPT, a 3D geomechanical model was built by use of structural geological description and information from more than 40 wells drilled in the area. Wireline-logging and borehole-image data and daily drilling reports were sources of information to constrain the orientation and magnitude of local in-situ stresses and pore pressure. The rock mechanical properties were calculated by use of logging-based equations cali-brated with laboratory-test results. 1D Geomechanical Models Individual 1D models for wells in the project were very useful in understanding lateral variation across the area of interest and in confirming features that might exist in one formation but not in another. Because the area has many geological faults, an important aspect was selecting and analyzing wells close to and far away from the main geological faults. This work verified whether the current stress state contributed to reactivation of the faults, which can affect wellbore stability when drilling nearby or when crossing them. An extensive analysis of available image data was performed to identify drilling-induced failures (i.e., breakouts and fractures) at the borehole wall, which was very useful information to constrain the orientation and magnitude of in-situ stresses. A drilling-induced fracture that was generated in a near-vertical well drilled with a mud weight lower than the fracture gradient was a clear indication that the stress regime in the field has a maximum horizontal stress that is higher than the vertical (overburden) stress. Also, significant horizontal-stress anisotropy must be present.