Calcium carbonate, used as a "sizing" material to aid in fluid loss control during drilling/completion operations, is supplied to Aramco in a number of different pre-ground diameters (e.g., Chips, coarse, medium and fine), by a number of vendor/suppliers. In order to provide "abrasion resistance" (in itself, a nebulous terminology), the drilling carbonate is specified to be supplied as "marble", i.e., metamorphic calcium and dolomitic carbonates. The problem to drilling engineers and fluid specialists has been certification of a supplied product as an abrasion resistant "marble" or simply a low strength, sedimentary limestone/dolomite. Determination of the source or "provenance" of a sample is critical to obtaining a quality product from vendors.

This specification as "marble" has inherent QA/QC problems in that standard XRD cannot differentiate metamorphic carbonate from sedimentary limestone/dolomite. Previous methods relied on petrographic examination (polarizing light microscopy) of thin sections of sufficiently large samples, impossible with finely ground material.

A new method of evaluating drilling carbonate samples to determine their mineralogical provenance has been developed, that can be used on solids of any size, even in samples of solids isolated from the drilling mud during drilling operations. The method uses XRD/XRF data generated on acid insoluble residuals of the drilling solids material. Paragenetic origin can be determined based on the accessory mineral assemblage, which is well defined in the literature. In addition, a new compositional ternary diagram has been introduced, termed the M-C-A (MgO-CaO-AL2O3).

Based on the new technique, 18 carbonate drilling samples were first evaluated for acid solubility, and the residual material (insoluble) used for assessment of mineralogical provenance. The new method has the following characteristics:

  • The new method is a robust QA method for rapid determination of marble provenance.

  • The new method is found to be able to differentiate mineralogical provenance in carbonate samples

  • The new method can quickly screen samples for potential formation damage issues.

  • The samples can come from a fresh batch of carbonate before delivery to the field sites, or the method can be applied forensically by taking samples from the mud pits and shakers for evaluation.

  • Given a sufficient data base, the method will be able to identify IK and OOK quarry sources of metamorphic marbles supplied by vendors

  • The method can be used for rapid QA on new IK sources of metamorphic marble

  • The new method can be easily incorporated into a new standard procedure for drilling marble QA, which should include

    • Solubility in 20 weight percent HCl

    • Mineralogy by XRD/XRF (bulk and accessory minerals, separately)

    • Particle size distribution

    • Crush resistance (e.g., particle attrition tests)

The new method will provide a quick and effective method to certify drilling carbonate as marble, thus having the accepted abrasion resistance.

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