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Quantification of the vertical and lateral heterogeneity of distal submarine-lobe deposits, Wolfcamp formation, Delaware Basin, Texas: implications for subsurface lateral prediction
Aguada, Leonela
Aguada, Leonela
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2023
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2025-06-24
Abstract
Submarine-lobe deposits host important archives of paleo-environmental change and are major targets for exploring and producing hydrocarbons. Traditional conceptualizations of submarine-lobe architecture typically exhibit a systematic decrease in bed thickness, grain size, sand content, and amalgamation from proximal to distal and axis to fringe. However, contemporary interests in these submarine environments, driven by petroleum explorations and carbon sequestration endeavors, have unveiled complex lateral heterogeneities.
This research presents a quantitative bed-scale analysis of core data from the Gas Technology Institute Hydraulic Fracturing Test Site 2 within the Wolfcamp A Formation, Delaware Basin. The study concentrates on correlating vertical and slant core datasets to delineate the vertical and lateral variability and event-bed architecture within a mixed carbonate-siliciclastic sea-floor fan. Data sets from two wells have been provided for this study: (1) A vertical well and (2) a slant well which include well log data, CT scans, core photos, and XRF data. They are situated 380.6 ft and 1007.2 ft apart for the studied interval, ideal for the quantification of lateral heterogeneity in a significantly short distance. Furthermore, this study investigates the correlation between CT-scan data and rock composition, assessing the utility of CT-scan technology in conjunction with XRF data and compositional proxies—Vcarb, Vsil, and Vclay—in heterogeneity analysis. Additionally, the potential of basic Machine Learning techniques for predicting rock composition is also explored (see Appendix).
For the vertical heterogeneity quantification 20 distinct lithofacies were grouped into four Facies Associations (FA-1, FA-2, FA-3, FA-4). Our findings indicate a dominance of Facies FA-3, consisting mainly of pelagites and hemipelagites, followed by Facies FA-1, characterized by Hybrid Event Beds (HEBs), FA-4, composed of hemipelagites influenced by bottom currents and dilute turbidites, and FA-2, featuring turbidite deposits. Among the HEBs, the H3 deposits were the most prevalent, and are characterized by calcium-rich layers at the bottom that progressively transition to silica-dominant layers upwards.
Regarding the lateral heterogeneity, this innovative approach highlights considerable differences in event-bed and background layer thickness and composition over relatively short distances. Trends revealed that background layers diminished in thickness approaching the slant well, whereas event-bed deposits became thinner closer to the vertical well. In addition, the interpreted intervals (A and B) were divided into seven depositional lobe elements, defined by compositional, thickness, and stacking pattern variances. These elements - Axis, Off-axis, frontal fringe, and distal fringe zones - demonstrated specific compositional trends. The distal fringes revealed a gradual shift towards silica-rich sediments, whereas the frontal fringes showed a transition to calcium-rich sediments. The central axis and off-axis regions were predominantly characterized by calcium-rich deposits, whereas the frontal fringes showed a transition from calcium-rich to mixed-deposits. The distal fringes revealed a shift from mixed-deposits towards silica-rich deposits.
These findings underscore the complex dynamics of sedimentary deposition and its implications for petroleum exploration and developing strategies.
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