Schlumberger

ECS Elemental Capture Spectroscopy Sonde

Wellsite processing of lithology and matrix from primary formation elements

The ECS elemental capture spectroscopy sonde uses a standard 16-Ci [59.2 × 1010Bq] americium beryllium (AmBe) neutron source and a large bismuth germanate (BGO) detector to measure relative elemental yields based on neutron-induced capture gamma ray spectroscopy. The primary elements measured in both open and cased holes are for the formation elements silicon (Si), iron (Fe), calcium (Ca), sulfur (S), titanium (Ti), gadolinium (Gd), chlorine (Cl), barium (Ba), and hydrogen (H).

From elemental yields to dry-weight concentrations and quantitative lithology

Wellsite processing uses the 254-channel gamma ray energy spectrum to produce dry-weight elements, lithology, and matrix properties. The first step involves spectral deconvolution of the composite gamma ray energy spectrum by using a set of elemental standards to produce relative elemental yields. The relative yields are then converted to dry-weight elemental concentration logs for the elements Si, Fe, Ca, S, Ti, and Gd using an oxides closure method. Matrix properties and quantitative dry-weight lithologies are then calculated from the dry-weight elemental fractions using SpectroLith lithology processing’s empirical relationships derived from an extensive core chemistry and mineralogy database.

SpectroLith lithology processing outputs

  • Dry-weight lithology fractions (from elements)
    • total clay
    • total carbonate
    • anhydrite + gypsum from S and Ca
    • QFM (quartz + feldspar + mica)
    • pyrite
    • siderite
    • coal
    • salt
  • Matrix properties (from elements)
    • matrix grain density
    • matrix thermal and epithermal neutron
    • matrix sigma

Fast petrophysical answers

Quantitative mineralogy and lithology from the ECS elemental capture spectroscopy sonde enables not only identifying the rock grains and matrix—especially the clay fraction determined independently from the conventional analysis of gamma ray, spontaneous potential, and density-neutron—but also supports the accurate determination of porosity, fluid saturation, and permeability.

The DecisionXpress petrophysical evaluation system integrates data from the ECS sonde and the Platform Express integrated wireline logging tool to provide rapid data visualization and reprocessing capabilities at the wellsite or in the office. The result is a robust petrophysical evaluation with minimal user inputs in sand-shale reservoirs for planning coring and sampling operations and designing completion strategies.

Additional processing supports complex reservoir analysis, including geochemical stratigraphy (chemostratigraphy) for well-to-well correlation.

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Finding 50 ft of North Sea Pay with ECS Sonde Mineralogy

Petrophysical evaluation of North Sea well. The net pay flags in the depth track of this DecisionXpress display reveal nearly 50 ft of oil pay near X,150 ft. Track 1 presents the gamma ray curve and lithology determined by the DecisionXpress system. Track 3 show hydrocarbon and water along with intrinsic permeability. Fluid saturations and porosity are shown in Track 4. Detailed mineralogy, presented in Track 5, is determined using the ECS sonde and DecisionXpress processing. As in all DecisionXpress presentations, a gray mask indicates that results are outside tolerance specifications.
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