Free Yourself from Seismic Uncertainties While Drilling with the Deep Directional Resistivity Tool: A Success Story from West African Offshore

Abstract

To meet the increasing energy demand of the world and with the advent of new technologies, operators have been drilling increasingly challenging hydrocarbon pockets to increase recovery of existing assets. New technologies have been developed to achieve a higher degree of accuracy in well positioning and ministering the aspiration supporting the objectives of producing from otherwise impossible targets. Total E&P Angola, operator in Block-17 in offshore Angola, had launched the CLOV development over four fields: Cravo, Lirio, Orquidea and Violeta, located approximately 140 km from Luanda in water depths ranging from 1050 m to 1400 m. With a focus to develop a highly faulted compartment of the Orquidea field, the ORQ-554 well was planned through a series of faults to achieve the desired drainage length within the unconsolidated channel sands of the Oligocene reservoir. The lack of drilling information for the compartment along with poor seismic resolution of the highly faulted structure owed a high level of uncertainty of ±30 m true vertical depth (TVD) in positioning the well and thus the well could miss the target reservoirs if not calibrated with respect to the structure. The above challenges, in addition to uncertainty in the reservoir position, orientation, and overall geological structure, were necessitated a technology that could bridge the gap between conventional logging and seismic data. A new directional electromagnetic (EM) logging-while-drilling (LWD) service with a radial depth of investigation on the order of ±30 m has been introduced to allow early detection and mapping of the approaching reservoir with sharper resolution than obtained with seismic measurements and to add important new pieces to the reservoir characterization puzzle. The multilayer inversion coupled with deeper depth of investigation, allowed for the marriage in of seismic and borehole data, leading a more effective and productive wellbore. This paper will highlight why deep directional resistivity is a step change for doing proactive well placement of highly deviated wellbores as well as for gaining a larger-scale reservoir understanding. Based on the BHA design, the tool was able to provide a resistivity map of the reservoir up to 20m away from the wellbore, detecting multiple layers to improve understanding and in turn support the characterization of the reservoir beyond seismic structural and near-wellbore petrophysical information. In addition, the improved reservoir delineation resulted in more accurate geological models, reserve estimates, and potential improvements to the completion design.