An Integrated Deterministic/Probabilistic Approach to Reserve Estimation: An Update
Authors: Nangea Avi G. , Hunt Elizabeth J. 
Published: December 2007

Abstract
As reported in SPE 28329, Mobil Corporation utilizes a unique methodology for reserve and resource evaluation. The approach integrates both deterministic and probabilistic methods to evaluate reserves and establish the full hydrocarbon potential of fields/prospects. We believe both methods have valid justification for utilization, but when used jointly provide greater insight into the recoverable hydrocarbon volumes and the probability of recovering those volumes.
Continuing dialog, within the international industry, which Mobil strongly supports, has resulted in several proposals to develop "accepted industry practices," such as the SPE/WPC Approved Reserves Definitions. Mobil is also continually testing new methodologies that provide further clarity to determining the quantity of hydrocarbon volumes and the associated value.
This paper provides an update on new insights into Mobil's methodology utilizing actual examples and hopes to serve as a catalyst in the continuing dialog to develop "accepted industry practices."

Introduction
The changing landscape in the petroleum industry calls for innovative practices. These "practices" were generally not recognized as essential requirements just a few years ago. Each "stakeholder", whether it be the host country, operating company, service contractor, financial institution (and others), require a common "language" for business dialog. We can lend body to this language through "definitions", "guidelines", and "industry accepted practices"; and several international bodies have participated in this endeavor. But, in the end, the industry must have an accepted set of "norms", which evolve with time (and need) to form the foundation.
Since recoverable hydrocarbon volumes are the "base" asset for each of the "stakeholders", an understanding of the magnitude, the risks, and the value from their own and each other's perspective is essential. This need for understanding, combined with the evolution of technology, has focused greater effort towards improved nomenclature to achieve consistency.
Industry organizations, professional societies, and governmental agencies continue to address these issues. Of particular note, are the recently published SPE/WPC Definitions. These efforts are laudable, and need to be progressed.
As mentioned earlier, the changing business environment where the industry undertakes new and technically challenging projects, requires sophisticated classification systems and evaluation methodologies. Many of these projects have non-traditional financial and political risk, which test the limits of current classification of hydrocarbon volumes. Many companies, facing these challenges, continue to review their internal procedures and systems to enhance the system's utility for external reporting while providing a strong link to business plans. This process is accelerating with a realization that not all barrels have equal value, when looking at them in tandem with the associated risks and uncertainties.
A strong dialog is ongoing, within the industry, to promote a better understanding of the salient issues and thereby support further evolution. We strongly support the continuing efforts to develop "standards" and "industry accepted practices." Mobil is continually testing new methodologies that provide further clarity to determining and representing the quantity of hydrocarbon volumes and the associated values. The purpose of this paper is to provide a discussion of current practices being used within Mobil, in keeping with our desire to further support the ongoing exchange of ideas.
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