A New Approach to Measuring Organic Density
- S. T. Dang (Mewbourne School of Petroleum and Geological Engineering Sarkeys) | C. H. Sondergeld (Mewbourne School of Petroleum and Geological Engineering Sarkeys) | C. S. Rai (Mewbourne School of Petroleum and Geological Engineering Sarkeys)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2016
- Document Type
- Journal Paper
- 112 - 120
- 2016. Society of Petrophysicists & Well Log Analysts
- 6 in the last 30 days
- 354 since 2007
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Shale oil and gas have become important hydrocarbon resources for North America. Despite successful technological developments, formation evaluation faces some significant challenges. Organic matter in shale has multiple roles: it is the source of hydrocarbons; it provides storage, and it may provide preferential hydrocarbon pathways. Organic density remains a critical parameter in the evaluation of shale porosity from logs. The newly proposed experimental procedure combines low-pressure pycnometer (LPP) grain-density measurements, low-temperature oxygen plasma etching, and TOC measurements to estimate the grain density of organic matter in bulk shale. Organic density is clearly a function of thermal maturity, increasing with increasing maturity. Combined results from this study and literature suggest that kerogen density appears to be kerogen-type dependent in shales when %Ro < 2%. Type III density ranges from 1.6 to 1.8 g/cm3. However, when the maturity level reaches the dry-gas window, %Ro ≥ 2, organic density for all kerogen types displays a similar dependence on maturity. The results from the new approach agree well with organic densities measured with other techniques. The advantage of this new technique is that it allows both organic and average grain density to be measured and eliminates the need for kerogen isolation. Additionally, the weight fraction of organic carbon to organic matter, K, can be evaluated; this value seems to be a good independent local indicator of thermal maturity.
Organic matter (OM) complicates and controls the performance of unconventional reservoirs. Surprisingly, as important as the organic density is in well log interpretation— organic density factors directly into porosity estimation, which directly impacts economics—it has been studied very little.
There are three components to total porosity: natural microcracks, inorganic and organic pores (Loucks et al., 2009; Curtis et al., 2012). Sondergeld et al., (2010) and Elgmati et al., (2011) claim organic porosity can account for up to 50% of OM volume. For example, in a so-called good source rock, with TOC of 6 wt% and a typical kerogen density of approximately 1.2 g/cm3, organic porosity can contribute up to 6 to 8% of total rock volume.
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