Fingerprinting Formation Waters Using Stable Isotopes: Applications to Petroleum Exploration and Production in the Williston Basin

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Eugene Daniels
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1 Fingerprinting Formation Waters Using Stable Isotopes: Applications to Petroleum Exploration and Production in the Williston Basin Serguey V. Arkadakskiy 1, Ben J. Rostron 1,2, and Gavin K. Jensen 2 1 Isobrine Solutions Inc. 2 University of Alberta

2 Talk outline Introduction to stable isotopes Industry applications Water fingerprinting examples from the Williston Basin Most common sampling/analytical problems

3 What is isotope? Protium 1 H Deuterium 2 H (D) Tritium 3 H (T) _ + _ + N _ N + N One of two or more atoms of the same element having different number of neutrons (different mass)

4 What is stable isotope? Protium 1 H Deuterium 2 H (D) Tritium 3 H (T) _ + _ + N _ N + N Stable Stable? m = 1 AMU m = 2 AMU m = 3 AMU mp + mn o 1 AMU >>> me - m 1 H 1/3 x m 3 H!

5 What is stable isotope? Protium 1 H Deuterium 2 H (D) Tritium 3 H _ + _ + N _ N + N Stable Stable Radioactive! Stable isotopes do not undergo spontaneous decay! Therefore, they are not radioactive!

6 Why are stable isotopes useful? Isotopes are not tracers they are the substances themselves (i.e., the H 2 O molecules are combinations of the two 1, 2 H and three 16, 17, 18 O isotopes) The isotope ratios (R) of natural substances change measurably! 1. Physical processes (e.g., diffusion, evaporation) 2. Chemical reactions 3. Biologically mediated reactions (e.g., photosynthesis, hydrocarbon oxidation) The change is called isotope fractionation

7 Measurement and nomenclature Isotope ratios are measured by comparing the isotope ratio of a sample (R sample ) to that of a standard (R standard ). Values are expressed by the δ (delta) symbol: δ = R sample R R standard standard.1000 The δ value is reported in parts per thousand ( ) also referred to as per mil (per mille). Vienna-Standard Mean Ocean Water (VSMOW) is the accepted water standard. (i.e., δ 2 H and δ 18 O of VSMOW = 0.0 )

8 Stable isotopes of interest Hydrogen - δd or δ 2 H (water, natural gas ) Oxygen - δ 18 O (water) Carbon - δ 13 C (natural gas) (Also useful: Sulphur, Nitrogen, Boron, Lithium, and lately Chlorine, Bromine, and etc.,) Why those? Highly abundant Large mass difference (large fractionation) Covalent bonding (site specific fractionation) More than one oxidation state (e.g., CH =C0 2 +2H 2 )

9 Industry applications and methodology Applications Oil reserve assessment Target formation identification Co-produced water source identification Water flood tracking Baseline studies Fingerprinting methodology Basic understanding of stable isotope systematics Background information (basin wide databases!) Local reference points

11 Co-produced water sources

12 Williston Basin Database From 1994 to present Collected & Analyzed samples. 15 % of all sampled wells produce out of zone water

13 Local stable isotope stratigraphy

14 Rostron, 2003

15 Case studies: Lignite Field, North Dakota Lignite field North Dakota - Midale producing field Sampled two wells: Well A: producing since 1956, 46% water cut Well B: producing since 1956, 77% water cut

16 Case studies: Lignite Field, North Dakota Lignite field North Dakota - Midale producing field Sampled two wells: Well A: producing since 1956, 46% water cut δ 18 O = Well B: producing since 1956, 77% water cut δ 18 O = δ 18 O composition of Midale in the area +8 to +9 Well B has brine leaking into wellbore from another formation.

17 Case studies: Pinto Field, Saskatchewan

18 Case studies: Pinto Field, Saskatchewan

19 Case studies: Pinto Field, Saskatchewan

20 Case studies: Recent DST example TDS: 290,000 mg/l (higher than target Formation); solute source: halite dissolution; Percentage of drilling mud in sample 70 %.

21 Case studies: Steelman

22 Case studies: Steelman

23 The most common sampling and analytical pitfalls Sampling and handling: 10 % evaporation +10 hydrogen, +1.0 oxygen!!! Please, do not collect sample from tank! Collect samples in air-tight bottles Send to labs as soon as possible Analytical: Low TDS (<10,000 mg/l) water high TDS water! Send samples only to labs that do high TDS waters/brines!

24 Conclusions: Stable isotopes are reliable natural tracers (no injection needed, no danger of radioactive contamination). Interpretation is simple and straightforward, if proper sampling and analytical methods are used. A comprehensive database for the Williston Basin is already available.

Environmental Isotopes in Hydrology. Woocay substituting for Walton

Environmental Isotopes in Hydrology Oct 7, 2010 1 What is an Isotope? An element is defined by the number of protons (Z) in the nucleus The number of neutrons (N) defines the isotope(s) of that element