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Evaluating the Impact of Mineralogy on Reservoir Quality and Completion Quality of Organic Shale Plays

Helena Gamero-Diaz, Camron K. Miller, Richard Lewis, and Carmen C. Contreras-Fuentes
3011 Internet Blvd, Suite 200, Frisco, TX

Geochemical logs are fundamental to the evaluation of organic shale plays because they provide mineralogy among other measurements necessary for the petrophysical and geological evaluation of these complex reservoirs. Mineralogy impacts reservoir quality (RQ) and completion quality (CQ), which ultimately governs shale well performance. sCore is a ternary-based classification scheme for organic mudstones that will be used in this paper to define relationships between mineralogy, RQ and CQ within various U.S. shale plays. Ternary plots are useful for discriminating rock types based on normalized proportions of three main end members: i) clay; ii) carbonate; and iii) quartz, feldspar, and mica. When shale RQ parameters, such as effective porosity, total organic carbon (TOC) content, matrix permeability, hydrocarbon saturation, etc., or CQ parameters, such as minimum closure stress, Thomsen's gamma, Mineral Brittleness Index (MBI), etc. are plotted on an sCore ternary diagram, one can make observations as to how mineralogy is impacting RQ and CQ in a particular shale play. The identification of lithofacies having superior RQ and CQ is important information for identifying 'sweet spots' and targeting both vertical and horizontal well completions. A strong correlation exists between mineralogy and CQ in most U.S. shale plays. More specifically, minimum closure stress, Thomsen's gamma and MBI appear to be driven by the mineralogy of organic mudstones. The correlation between mineralogy and RQ is not as strong. Organic mudstones have complex mineralogy, consisting of a mixture of intrabasinal and extrabasinal sources of siliciclastic and/or carbonate debris, affected by diagenetic processes, resulting in highly heterogeneous rocks especially in the vertical direction. RQ in U.S. shale plays appears to be driven by both compositional and textural components of organic mudstones. RQ, as determined by other data types, can be compared to the sCore ternary to aid in interpretation of sediment source. For example, low correlation between effective porosity and silica content may imply dilution via terrigenous input, while a high correlation indicates minimal dilution and more desirable rock.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013