Non-Destructive Strength Index Testing Applications for Sand Failure Evaluation

  • Daniels G
  • Mcphee C
  • Sorrentino Y
 et al. 
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Abstract Definitive rock strength data for sand failure evaluation are only available from tests on core plugs, however coverage is limited and core condition and geometry may preclude plugging.  This paper presents results from a non-destructive core strength index tester that is less destructive than the Schmidt Hammer and less intrusive, easier, faster and cheaper than the core scratch tester.  The portable index hardness tester measures and compares the impact and rebound velocities of a small steel ball after its collision with a rock surface to determine its hardness which in turn reflects the relative strength of the rock.  The tester is run at regular intervals along the surface of the core to provide additional data that complement and enhance core rock mechanics data.    Several field examples are presented which illustrate the use of the index tester to optimise core sample selection, evaluate controls on rock strength, and to calibrate and constrain the development of wireline log-based strength models.  Importantly, cases are included to highlight exceptions where the tester can produce misleading and even contradictory results. The integration of index test results with core plug data and log analysis enables development of more robust rock strength models.  The methodologies and techniques developed in this work have in turn enabled more accurate sand failure estimates that represent key tools in the development of effective sand management strategies for the reservoir life cycle for a variety of fields throughout the world.   Introduction Sand management, and the decision whether to exclude or accept sand production, requires an understanding of the mechanisms that cause the rock to fail and the development of a field validated methodology to predict the critical conditions for sand production.  The key data to build and populate the geomechanical model used in sand production evaluations are the rock strength, pore pressure and in situ stress.  In this context rock strength refers to the ability of the rock to withstand the stress environment around the wellbore or perforation cavity.  Factors influencing rock strength include density, porosity, rock type, grain size and clay content as well as microcracks and anisotropy inherent in natural rocks. Historically, rock strength evaluation for the reservoir sands is based on log indicators calibrated where relevant against core rock mechanics data.  However core is discontinuous, and plug coverage is further limited due to routine core analysis and special core analysis plugging taking precedence, hence limiting the availibilty of strength test sample sites.  The index hardness tester, which was originally designed for testing the hardness of steel and integrity of welds, has been adopted for use in rock strength testing due to its ease of use, portability and repeatability. It provides the ability to test cored intervals between rock mechanics plug test sites and where plugging is not feasible.

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  • Gill Daniels

  • Colin Alexander Mcphee

  • Yelitza Coromoto Sorrentino

  • Philip McCurdy

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