This study evaluates the importance that Biot's coefficient has in the estimation of reserve recovery in the petroleum engineering field of study. Three different types of oil reservoirs are analyzed, and the results indicate that the influence of Biot's coefficient depends mainly on the elastic properties of the actual reservoir in question. The results show that accurate Biot's coefficient values are not necessarily critical to unconsolidated reservoir types for hydrocarbon reserve recovery calculations. However, the significance of accurate Biot's constant values increases as "harder," more consolidated reservoir types are evaluated.
1. INTRODUCTION
For any given application, an accurate value of Biot's constant, known as ß in this paper, is one of the most difficult values to obtain. At a recent workshop held at the Colorado School of Mines, Golden, Colorado, of over forty industry professionals who specialize in rock mechanics laboratory measurements, no topic solicited as much discussion or "lively" conversation as the measurement of accurate Biot's constant values. Almost every expert that attended the workshop had a viewpoint on how poroelastic measurements should be performed, how the samples should be prepared, and what methodology should be used. These various viewpoints did not overlap in many areas, and even if a consensus of these expects could be reached on these issues, the question begs to be asked, "How important are accurate Biot's constant values for any given application?" Is the amount of time and money worth the effort for the values obtained when considering practical application? What is the return on investment?
Very few parameters cross multidisciplinary lines to the extent that Biot's constant and the poroelastic behavior it represents. Petroleum engineers, civil engineers, geophysicists, geological engineers, hydrologists, and a variety of other earth scientists must all address poroelastic effects in their various computations. Even within a given discipline, such as petroleum engineering, the lines are crossed since reservoir engineers need to understand compaction, completion engineers need to understand hydraulic fracturing behavior, and drilling engineers need to understand effective stresses for pore pressures and the associated casing set points.
In order to assess some of the questions posed above, this paper provides a sensitivity study that evaluates the importance of determining the absolute value of Biot's constant for petroleum hydrocarbon reserve determination. For any company that produces petroleum or natural gas, reserve determination is a critical component of assessing its value both internally and externally for stock price evaluation. This paper provides a direct link between the value of Biot's constant and the reserve estimations it can affect.
The paper starts with an overview of the theories of Biot's constant and material balance reserve estimation. It then discusses the development of the model used in this study, which is followed by several test cases that were initially described in a 1989 paper by Morita et al. [1]. Using Monte Carlo simulation, the economic value of the Biot's constant measurement is determined. Finally, a discussion of the results is provided, followed by conclusions.
