Continuous Resource Assessment Integrating Volumetric Analysis and Probabilistic Well Simulation
Authors: Hood Kenneth C. , Steffen Kurt J. , Yurewicz Don A. 
Published: May 2016

Abstract
We propose an integrated workflow for evaluating continuous resources that is intended to bridge the varying analysis requirements through successive stages in the business cycle. All stages of the approach are fully probabilistic and transition smoothly from one to the next; each step encompasses and builds upon the uncertainty represented in the previous steps. Probabilistic assessment of in-place and recoverable hydrocarbon volumes is necessary to build an understanding of the hydrocarbon resource but it is rarely sufficient to support specific business decisions. The approach proposed here moves beyond a simple volumetric representation of the resource and builds multiple well simulations based on physics-based models of the reservoir. These simulations predict spatially aware well behavior within the play both in terms of ultimate recovery and hydrocarbon flow rates over time. In addition to standard volumetric inputs, these analyses require engineering parameters linked to specific development scenarios, such as lateral length for horizontal wells, number of fracture stages, and fracture half length. To be robust, the models need to incorporate both spatial variations in geologic and engineering inputs as well as uncertainty in the parameter estimates for a single location.

Introduction
The value of probabilistic assessment of continuous resources has been well established (e.g., Schmoker, 2002; Hood and others, in press). Reliable business decisions require a comprehensive understanding of the range of hydrocarbon volumes that could reasonably be expected - how small or large could the volumes be given that the basic geologic interpretation is fundamentally correct? The volumetric inputs should incorporate value ranges that capture uncertainties due to quantity and quality of interpretative data. Rarely is it sufficient to know only the expected hydrocarbon volume associated with a best estimate or preferred interpretation. Commercial analyses likewise need to consider the range of possible outcomes associated with the preferred geologic interpretation and development strategies. In many situations more than one geologic interpretation or development strategy may be plausible within the constraints provided by the available data. In such cases, alternative scenarios can facilitate the representation of the full range of possible outcomes.
Probabilistic assessment of in-place and recoverable hydrocarbon volumes is necessary to build an understanding of the hydrocarbon resource endowment at a play, basin, country, or global scale, but it is rarely sufficient to support specific business decisions. For continuous plays that will be developed using wells (as opposed to mining), business decisions must consider the volume of hydrocarbons that will be produced by individual wells coupled with the rate at which those hydrocarbons will be produced. Well design becomes an important consideration in these analyses. As an example, a vertical well may be able to access a thick stratigraphic succession of rock over a limited area of drainage, whereas a long, horizontal well may have a much larger drainage area but access a limited stratigraphic interval. Interdependencies among surface access, well cost, production rate, and stratigraphic distribution of hydrocarbons must be considered as part of any economic analysis and must be considered in the commercial context of price forecasts and drilling commitments to hold leases. We propose an integrated workflow that is intended to address the varying analysis requirements through successive stages in the business cycle. All stages of the approach are fully probabilistic and transition smoothly from one to the next; each step encompasses and builds upon the uncertainty represented in the previous steps.