Statistical analysis of pulsed-neutron well logs in monitoring injected carbon dioxide

Journal Article · 06 June 2018 · International Journal of Greenhouse Gas Control

DOI: https://doi.org/10.1016/j.ijggc.2018.05.023 · OSTI ID:1874354

Azzolina, Nicholas A. ^[1]; Bosshart, Nicholas W. ^[2]; Burton-Kelly, Matthew E.  ^[2]; Hamling, John A. ^[2]; Peck, Wesley D. ^[2]

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1. Univ. of North Dakota, Grand Forks, ND (United States); Univ. of North Dakota, Grand Forks, ND (United States). Energy & Environmental Research Center
2. Univ. of North Dakota, Grand Forks, ND (United States)

Pulsed-neutron well logs (PNLs) were acquired to monitor CO₂ storage associated with enhanced oil recovery. This work quantifies the precision of repeat PNLs using data from four wells and 15 repeat PNLs. Root-mean-square (RMS) precision for the repeat PNLs was less than 3%, indicating good agreement between the baseline and repeat PNLs. Evaluations of scaled relative difference (Scaled-D) showed variation in precision among individual wells and formations. Analysis of false-positive rates (FPRs) across the entire data set showed that a Scaled-D threshold in sandstone formations of approximately ±8% resulted in a 1% FPR. These Scaled-D precision thresholds were used to estimate the value of CO₂ saturation able to be confidently distinguished from baseline. The detection limit for CO₂ is lowest for high-porosity formations filled with saline water and is highest for low-porosity formations filled with fresh water. Thus, detection of vertical out-of-zone CO₂ migration using repeat PNLs is a function of instrument precision, petrophysical properties, and hydrology, all of which must be taken into account as part of the monitoring program. Here, the results of this work provide insight into how PNLs may be included within monitoring plans to detect vertical out-of-zone CO₂ migration along a wellbore or instances of wellbore failure and provide a quantitative basis for establishing detection limits of repeat PNLs to distinguish change from baseline conditions.

• Research Organization: Univ. of North Dakota, Grand Forks, ND (United States). Energy & Environmental Research Center
• Sponsoring Organization: USDOE
• Grant/Contract Number: FC26-05NT42592
• OSTI ID: 1874354
• Journal Information: International Journal of Greenhouse Gas Control, Journal Name: International Journal of Greenhouse Gas Control Vol. 75; ISSN 1750-5836
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
CO2 capture, utilization, and storage (CCUS)
Monitoring, verification, and accounting (MVA)
PCOR
Plains Carbon Dioxide Reduction Partnership
Pulsed-neutron well log (PNL)