ECS Elemental Capture Spectroscopy Sonde

Wellsite Processing of Lithology and Matrix from Elemental Yields

The ECS elemental capture spectroscopy sonde uses a standard 16-Ci [59.2 × 10¹⁰ Bq] 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).

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 the SpectroLith empirical relationships derived from an extensive core chemistry and mineralogy database.

SpectroLith 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

Applications

• DecisionXpress integrated petrophysical analysis
• Clay fraction independent of gamma ray, spontaneous potential, and density neutron
• Carbonate, gypsum or anhydrite, QFM, pyrite, siderite, coal, and salt fractions for complex reservoir analysis
• Matrix density and matrix neutron values for more accurate porosity calculation
• Sigma matrix for cased and openhole sigma saturation analysis
• Mineralogy-based permeability estimates
• Quantitative lithology for rock properties modeling and pore pressure prediction from seismic data
• Geochemical stratigraphy (chemostratigraphy) for well-to-well correlation
• Enhanced completion and drilling fluid recommendations based on clay versus carbonate cementation
• Coalbed methane bed (CBM) delineation, producibility, and in situ reserves estimation