Tulsa SPWLA Monthly Luncheon Meeting  

Thursday Jan16 2020

Tulsa University
Helmerich Hall- Room 121
800 S Tucker Dr.
Tulsa, OK 74104

11:30 – 1:30 pm

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Cost - $25 for Professionals and FREE to students with student ID

Crushed Rock Analysis Workflow Based on Advanced Fluid Characterization for Improved Interpretation of Core Data

Presented By: Melanie Durand - Shell

ABSTRACT:

Sustained E&P activity levels and slim margins on highly-valued Permian Basin acreage drive operators to leverage information as much as possible and in ways not seen in the recent past. Data accuracy, especially in this fast-paced, competitive environment, is strongly desired. Core analyses provide subsurface static calibration, but the thick stratigraphic section comprised largely of sub-log scale facies, challenges a cost-effective approach to collect sufficient calibration data.

Saturation determination is a key petrophysical deliverable that has multiple uses, including landing zone assessment. Calibration of saturation models may originate in several ways: proprietary or JV core, industry consortia databases, data trades with other operators, government databases, or publications. Internal and external reviews of subsurface model inputs have repeatedly shown that Permian Basin saturations in particular have a wide distribution and large uncertainty. Accurately measuring core fluid saturations in tight rock continues to pose significant challenges originating from the currently accepted lab methods, assumptions used to interpret those data and more broadly, due to increased relative uncertainty associated with tight, low-porosity formations.

For example, crushing core samples, which enhances fluid extraction in tight rocks, causes systematic fluid losses in the case of core samples of liquid rich mudstone formations which are not typically quantified.  Instead, as-received air-filled porosity is commonly assumed to represent hydrocarbons that were forced from core during acquisition/retrieval due to gas expansion.  Additionally, fluid extraction from commercially available retorting systems have widely variable fluid collection efficiencies (<100%) resulting in significant inconsistencies between the weight of collected fluids and sample weight loss during retorting experiments.  

The Dean-Stark technique removes not only water and oil, but an unknown volume of solvent-extractable organic matter, and it only allows for direct quantification of the extracted water volume.  Finally, fluid and solid losses during handling in the lab are unassessed in current commercial lab procedures. The reconciliation of fluid volumes with fluid and sample weight data delivered by either of the two techniques, i.e. retort or Dean-Stark, requires numerous assumptions about pore fluid properties which are typically not verified through direct measurements. We demonstrate that such assumptions can lead to extreme uncertainty in estimates of water saturation. 

To address such critical uncertainties, a new retort-based core analysis workflow using improved core characterization and fluid extraction techniques was developed.  In one advancement, this workflow employs NMR measurements systematically performed on all as-received and crushed samples to quantify fluid losses during crushing.   This approach also uses a specially developed fluid collection apparatus with close to 100% fluid collection efficiency.  In addition to these advances in measurements, the workflow is optimized to avoid fluid losses during sample handling and includes repeated grain density and geochemical measurements at different stages for QC. As a result, the new workflow reduces the uncertainties in acquired data and better addresses the assumptions (i.e. parameter corrections for fluid losses) in interpreting measured data into core total porosity and core fluid saturations.  The workflow is demonstrated for a set of Delaware Basin Wolfcamp A samples and the results suggest that previous crushed rock core analysis protocols underestimate water saturation by at least 30 % or ~15 su for this liquid rich mudstone formation.

BIO:  Melanie Durand is a Petrophysicist on Shell’s Permian Asset. After joining Shell in 2012, Melanie has worked on projects in Brazil, Argentina, and Colombia before transitioning to the Permian Basin. Melanie has a deep breadth of operational experience in both wireline and core acquisition. She has a B.S. in Mathematics from the University of Louisiana at Lafayette.