This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 197290, “Quantitative Seismic Interpretation Work Flow for Sweet-Spot Identification in Organic-Rich Mudrocks,” by Mustafa A. Al Ibrahim, Tapan Mukerji, SPE, and Allegra Hosford Scheirer, Stanford University, prepared for the 2019 SPE Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 11–14 November. The paper has not been peer reviewed.

Estimating the lateral heterogeneity of geochemical properties of organic-rich mudrocks is important for unconventional resource plays. Well-penetration data from emerging plays are sparse and so traditional geostatistical methods will not yield good results. In this study, the authors use a quantitative seismic interpretation work flow (QSI) based on a rock-physics template in estimating the uncertainty of the geochemical properties of organic mudrocks of the Shublik formation of the Alaskan North Slope. By combining the rock-physics template and the results of seismic inversion, multiple realizations of total organic content (TOC), matrix porosity, and brittleness index are generated. These parameters can be used for sweet-spot detection.

Introduction

Data for physical rock parameters are generally restricted to well locations. To extend data laterally, two general directions can be taken: a data-oriented approach and a physics-oriented approach. The data-oriented approach is powerful but requires a large amount of data commonly not available in emerging areas where well penetration is scarce.  Physics-oriented approaches can be used to obtain the desired parameters used in decision-making; however, the results are highly dependent on the inputs, such as TOC and hydrogen index, and these typically are not defined regionally.

The QSI is a powerful tool that can be used to estimate the lateral and vertical heterogeneity of rocks beyond wellbores. QSI combines both of the previously mentioned approaches by using well data to calibrate rock-physics models and then using statistical methods to derive relationships between rock-physics models and seismic data.

In the complete paper, the authors demonstrate a work flow to apply the QSI to organic-rich mudrocks by incorporating a constructed rock-physics template for mudrocks. Joint estimation of rock properties is used to estimate the geochemical and mechanical properties important in determining sweet spots. Multiple possible realizations of Earth models are generated to capture the nonuniqueness associated with the inversion problem.

Study Area

The Triassic Shublik source rock is the main petroleum source in the North Slope of Alaska. The organic-rich calcareous interval is interpreted to be deposited during a marine upwelling period. Lateral and vertical heterogeneity in the Shublik formation has been documented with multiple facies identified.

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