Laboratory measurements of tight rocks is essential for petrophysical evaluation for hydrocarbons-in-place, maturity, and flow capacity. The high cost of acquiring cores can be challenging for oil producers when oil prices are low. Cuttings are readily available in both vertical and horizontal wells.
Our methodology provides the following objectives: New techniques to clean cuttings to minimize native fluid loss; Workflow to measure total porosity, oil and water saturations on drilling cuttings using high frequency NMR; Ancillary laboratory measurements of mineralogy(XRD,FTIR),geochemistry(XRF,LECO, Rock-Eval),pore-size distribution (BET,SEM,NMR,MICP) and pressure-decay permeability, extract GC, etc. for comprehensive evaluation of petrophysical rock properties.
Cuttings are rinsed by solvents based on type of drilling mud (oil based/ water based).These solvents remove mud/solids from the cuttings and vaporize due to their volatility leaving samples saturated with in-situ fluids.
To obtain fluid saturations, NMR T2 and T1T2 scans are done for: a. Sample in mud; b. Sample rinsed with solvents; c. Samples after solvents volatize.
Some sample is tested for LECO TOC, RockEval. Bulk volume is measured by Archimedes using a fluid which is non-intrusive and invisible to NMR. Water porosity is also measured using Karl Fischer Titration. Porosities are also measured using solvent extraction. Mineralogy (XRD,XRF,FTIR), pore-size distribution (BET,SEM,MICP) and pressure decay measurements are also acquired. Measurements done on core plugs to verify validity of results.
NMR scans on the cuttings after removing mud was compared to scans done on the companion core plug which is completely saturated due to alternating cycles of water and oil imbibition. Water and oil porosities between the two scans were found comparable within ±1 p.u. indicating that the cleaning process to remove mud is efficient and the water and oil saturations in these drill cuttings closely represent in-situ saturations.
These porosities also come in close agreement (within ±1 p.u.) to those measured using solvent extraction methods.
Geochemical (XRF,LECO, RockEval) results on drill cuttings were similar to companion core plugs with small variations based on the type of drilling mud used for testing.
XRD, FTIR measurements on cuttings and core plugs are also comparable.
High-frequency NMR spectroscopy provides high SNR, high accuracy quantification of fluids on small volume of rock samples; irrespective of shape or size.
Total Porosity and fluid saturation measurements have been successfully conducted and validated on cuttings samples from Wolfcamp, Spraberry and Eagle Ford formations.
This complete suite of measurements allows for comprehensive petrophysical modeling solely using cuttings.
Performing such an elaborate set of measurements on drill cuttings can help operating companies where coring operations are not financially viable.