Integrated Petrophysics and Geosteering Reservoir Characterization in the Initial Development Phase of a Carbonate Reservoir - Campos Basin, Offshore Brazil
Authors: Ribeiro Mauro Torres , da Costa Vagner Luis Ferreira , Bomfim Raimundo Antonio Guedes , Ferraris Paolo , Guedes Ana Beatriz Felicio , Bitencourt Priscilla Reuters 
Published: October 2011

A successful exploration campaign has been achieved using innovative concepts and top technology. The results of the last two years are proving the success of this work philosophy marking a new era for Brazilian Petroleum Industry. In this scenario, the first horizontal producer well was drilled in albian carbonate reservoirs of Quissamã Member (Macaé Formation), anticipating reservoir dynamic understanding and the development phase.

Since traditional logs could not capture the textural differences characterizing the most prolific zones, formation evaluation and geosteering challenges were addressed using new Logging While Drilling Technology. Differentiating measurements were Nuclear Magnetic Resonance (NMR), Spectroscopy and high-resolution images. An S shape pilot well was first drilled to identify target zones, establish potential layers and identify water/oil contact. A sideway horizontal well section was consequently drilled navigating through the intervals with best porosity/permeability properties and open fractures.

To best benefit from real time data availability and to guarantee drilling efficiency, a full time monitoring and decision team was assembled in the well owner's headquarters, receiving streaming data from the rig. The Real Time NMR properties allowed evaluation of Net-to-Gross and reservoir quality; images were used to compute dips and adjust borehole inclination and effective porosity was determined using neutron/density and spectroscopy.

Memory Data Formation Evaluation was performed using Multi-Mineral petrophysical analysis further supported by Neural Networks, trained using a data subset with NMR permeability and free fluid as targets and spectroscopy channels as input. The method was validated and applied with success over the complete horizontal section.

Indication of movable fluids using NMR information was compared to the water fractions computed with independent methods (resistivity and sigma) leading to the conclusion that all water was irreducible along the wellbore.

Testing this methodology in this first successful well founded the basis for effective formation evaluation of the complex shallow water carbonates in Brazil and will be used systematically in the upcoming wells.

Introduction

A field development project with horizontal wells, supported by limited appraisal drilling, requires a variety of high quality data for reservoir evaluation to guarantee success. Carbonate reservoirs involve extra challenges for horizontal well placement due to their depositional complexity and diagenetic susceptibility. Matrix density (and consequently porosity), rock texture, structural features (faults and open or closed fractures), pore connectivity and permeability cannot be characterized with enough precision only using a traditional log suite, composed of gamma ray, resistivity, neutron, density and sonic. To decrease the level of formation uncertainty and drilling risks, a cost effective solution is to include advanced measurements like magnetic resonance (NMR), resistivity/ultrasonic images and spectroscopy (ECS) in the evaluation plan.