Real-Time Formation Fluid Evaluation using Direct Mass Spectrometry

S. Michael Sterner¹, Donald L. Hall¹, and Bruce Warren^2
1 Fluid Inclusion Technologies, Inc, Broken Arrow, OK
² Warren and Christian, Inc, Burns Flat, OK

Advances in portability and durability of analytical instrumentation make possible real-time, high-sensitivity, analysis of formation fluids at the well site via direct mass spectrometry. Compared with conventional techniques of well site gas analysis, direct mass spectrometry affords the ability to continuously monitor a much broader spectrum of compounds such as C1 – C10 HC's, water-soluble species including acetic acid, benzene and toluene, inorganics including H2, He, N2, O2, CO2, Ar and various sulfur-bearing compounds. Correlation of these geochemical indicators with drilling parameters and lithologic data allow real-time evaluation of pay, wetness, petroleum type and quality, reservoir compartmentalization, fluid contacts, seals, etc.

Reservoir compartmentalization has been defined by profiling key molecular fragments indicative of paraffinic, naphthenic and aromatic character of hydrocarbon shows. Abrupt changes in relative abundances of these components over short vertical distances suggests the presence of intra-reservoir seals and are clearly visible in depth profiles prepared from mass spectrometric data.

Anomalous concentrations of water-soluble species like acetic acid, benzene and toluene in uncharged sections suggest the presence of “nearby” hydrocarbon accumulations. These “Proximity-to-Pay” indicators become concentrated down-dip from charged intervals below the oil-water contact, in poorer quality reservoir sections, in seals overlying reservoired hydrocarbons, and in water-saturated, cross-fault equivalents of reservoir sections and are readily monitored via direct mass spectrometry. Water-soluble organics and inorganics at the base of hydrocarbon accumulations have been useful in indicating hydrocarbon-water contacts.

Helium/methane ratios, laterally consistent within a given producing sand, yet variable among sands, have been used in field-wide correlation of regional productivity. Identification of discrete and confined carbon dioxide bearing intervals has proven useful in evaluating pay potential and production strategy in dry gas wells. Mass spec analysis of hydrogen, various sulfur species and even nitrogen under certain circumstances, shows promise in pre-production gas quality assessment with regard to these potential penalty gases.