The Application of Advanced Surface Logging for an Integrated Reservoir Characterization
Authors: Hekimoglu Kemal C. , Turrisi Riccardo , Pozzi Alessandro 
Published: October 2018

Our objective is to demonstrate the analytical capabilities of Advanced Surface Logging or Advanced Mud Logging (AML), the results borne from an extensive use of wellsite techniques and their use in time- critical situations. The work revolves around ascertaining and characterizing from the surface the nature of fluids found downhole using a number of integrated analytical techniques on oil samples and rock cuttings. We aim to evaluate the reservoir fluid properties flowing from the fractures and fluids which are suspected to be present within the pores of the reservoir matrix via cross-referencing multiple sample mediums.

The work studies data collected from a well in the Middle East; "Well-A", which was drilled as a producer from the Upper-Middle Jurassic (UMJ) Formations and an appraisal from the porous interval of the Lower Jurassic formation (LJ). The primary target of the operating company was to determine the in-situ fluid characteristics of the UMJ Formations. The communication between these two intervals as well as the contact depth is unknown and crucial at the current stage of the field development.

Reservoir and hydrocarbon fluid characterization was investigated using cuttings samples taken from Well-A. All samples were analyzed in-lab, post-drilling using Advanced Mudlogging (AML) techniques such as Thermal Extraction Gas Chromatography (TEGC), Chemical Elemental Analysis and Mineralogical analysis (the latter two performed using X-Ray based techniques). Additional Mudlogging datasets gathered in real-time during drilling were integrated within the interpretation including Advanced Mud Gas (Methane to Toluene), together with the Computer Processed Image Logs and PVT test data provided by the operator. Finally, three dead oil samples from the tested intervals were analyzed in-lab with TEGC.

The chromatographic analysis of the commercially produced oil from the UJ showed a bimodal distribution which was interpreted as a mix of two different maturity fluids. We were able to trace the individual levels from which these two fluids were most probable to originate, by comparing the chromatographic characteristics of these oils across the TEGC results from the cuttings analysis. Furthermore, the in-lab geochemical analysis supported the understanding of the fluid mechanism within this reservoir interval. This interpretation resulted in potentially identifying a sub interval which could yield a higher gravity oil than initially tested and potentially transform this, now unproductive interval, into a prospect.

The innovative workflow, integrating all formation evaluation data collected from rock cuttings and mud gas data was applied for the first time at this level of complexity. Although prior studies investigated the potential of integrating multiple datasets to determine reservoir fluid characteristics, never before, was such an integrated approach utilized based specifically on surface logging solutions. The case study demonstrated the value of supporting interpreters to bolster their interpretations thanks to data coming from separate independent sources.