Through-the-Bit Logging Technology Enables Improved Reservoir Characterization in the Orinoco Belt, Venezuela: 3D Structural Model Integrating Advanced Logs in a Multiwell Study

Rodriguez, Ricardo (PDVSA) | Villavivencio, Elvio (PDVSA) | Bellorin, Pavel (PDVSA) | Rendon, Lerrys (PDVSA) | Orozco, Jose (Schlumberger) | Quintero, Andreina (Schlumberger) | Chapellin, Alvaro (Schlumberger) | Mutina, Albina (Schlumberger) | Bammi, Sachin (Schlumberger)



The Orinoco Oil Belt (Faja) is the largest known heavy oil reserve in the planet. Geologically, its reservoirs are composed mainly of sequences of shales and unconsolidated sands. The properties of the sand units such as shale volume, water saturation, porosity, and thickness can present lateral heterogeneity at a few hundred feet scale. The high viscosity of the oil and its variation both laterally and vertically is one of the key features of the Faja. Prediction of water saturation from resistivity can be difficult due to multiple reasons, including the low salinity of the formation water and wettability changes.

For the field development, Faja reservoirs are drilled following a specific drilling pattern called a “macolla”. A macolla is composed of a vertical stratigraphic well followed by a group of two to four highly deviated wells (slant wells). These deviated wells play a fundamental role in cluster delineation, because they are key calibration points in the trajectory planning of the subsequent set of horizontal wells, which are completed with a slotted liner to maximize production.

Usually, in Faja, only vertical stratigraphic wells include comprehensive logging suites. These suites include elemental gamma ray spectroscopy, microresistivity images, sonic, dielectric, and magnetic resonance measurements at multiple depths of investigation. Moreover, due to the complexity of logging highly deviated wells in unconsolidated formations, many slant wells are not logged or logged only for correlation (gamma ray and resistivity logs). The ability to acquire more log data in the slant wells improves reservoir description and reduces the uncertainty in the planning of horizontal production wells.

The case study presented here illustrates the value of integrating data from vertical and slant wells in a macolla cluster. Comprehensive logging suites acquired in the vertical wells are complemented with through-the-bit logging suites acquired in the slant wells. Through-the-bit technology has recently been introduced in Venezuela and has proved to enable the acquisition of high quality logs through unconsolidated sand shale sequences in highly deviated boreholes. Rig time due to the logging operation and the risk of sticking of the logging string was also reduced.

This case study presents the workflow for and the results of the multiwell data integration in which different formation properties, including lithology-based facies, are propagated and incorporated into a 3D structural model. This workflow provides critical input to reservoir characterization and facilitates significantly the planning of horizontal wells.