Net Pay — What Is It? What Does It Do? How Do We Quantify It? How Do We Use It?

Abstract

Summary A knowledge of net pay is important for the volumetric estimation of hydrocarbon resources, a practice that underpins the value of the petroleum industry. Yet, there is no universal definition of net pay, there is no general acceptance of its role in integrated reservoir studies, there is no recognized method for evaluating it, and there are disparate views on how to make use of it. Partly for these reasons, net-to-gross pay constitutes a major source of uncertainty in volumetric reserves estimates, second only to gross rock volume. With the aim of improving this unsatisfactory state of affairs, I chart a critical path of net-pay understanding and application to dispel some of the unhelpful myths that abound within the industry and replace them with a defensible rationale to guide the quantification of net pay (thickness). Central to this process is the identification of net-pay cutoffs, themselves the subject of much controversy over the years. The approach is data-driven, in that it uses what we know, and also fit-for-purpose, in that it takes account of reservoir conditions. The outcome is a sounder basis for incorporating net pay into volumetric estimates of ultimate recovery and thence hydrocarbon resources.