SPE 148717 Effects of Fluid and Rock Properties on Reserve Estimation Kegang Ling, SPE, Zheng Shen, SPE, Texas A&M University Copyright 2011, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Eastern Regional Meeting held in Columbus, Ohio, USA, 17–19 August 2011. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract Oil and gas reserves are the most important assets for oil companies. An accurate estimation of reserves not only helps listed oil companies prepare solid annual reserves reports required by SEC, but also guarantees the good reward from divesting assets or reasonable price to farm-in asset. A precise reserves calculation is the fundamentality for production forecast, which is vital to the sale contract, thus the feasibility of project. It controls the cash flow and most of all the sustainable development of the company. The importance of reserve estimation cannot be overemphasized whatsoever. We know that in the practice of exploration and production, all efforts are to obtain fluid and rock properties such as porosity, permeability, saturation, rock and fluid compressibility, viscosity, fluid gravity, gas z-factor, saturation pressure, reservoir pressure and temperature. Due to the instrument sensitivity, limitation, measurement error, environmental effect, sample interval, location, the representative of sample, and Mother Nature of these properties, there is always uncertainty. In this research, a systematic study on the effects of fluid and rock properties on reserves estimation had been conducted. Effect of each property on reserves estimation is quantified through sensitivity analysis. As a result of this study, a comprehensive picture of how fluid and rock properties affect the reserves was brought to engineers. Reserves evaluator can use this to estimate the range of reserves as a consequence of uncertainty. With this study, we realized their different impacts on reserves. Therefore main efforts should go to the variables that affect the reserves most. Introduction Fluid and rock properties are always key parameters that control original hydrocarbon in place and recoverable oil and gas. It is observed that uncertainty and error are unavoidable due to the instrument sensitivity, limitation, measurement error, environmental effect, sample interval, location, and the representative of sample. Shafer et al. (2008) indicated that formation pressures at some wells are higher than 20,000 psia in the Gulf of Mexico. Therefore the measurement of rock properties under reservoir condition is very hard, if not impossible, to be conducted by existing technology, not mention the unknown error in the lab experiment. Ling et al. (2009) investigated the gas viscosity at high pressure and high temperature and found out that existing viscosity correlations estimate up to 10% error for gas viscosity at high pressure and high temperature condition. Although a few former studies had tried to put some light on the link between these properties and reserves, they just touched the surface with limited analysis; none of them approaches the problem with a thorough or systematic investigation. Hernandez et al. (2002) used reservoir simulation to analyze the sensitivity of viscosity and indicated that the common assumption of the accuracy of fluid viscosity has a marginal influence on the reservoir performance is false. Their results show that ±1% error in viscosity will produce a ±1% error in cumulative production for heavy oils. It is difficult to find a neat real field with all required data to analyze the effects of rock and fluid properties of recoverable oil and gas due to the fact that operators usually do not opine to publish field data. In our study, we want to investigate the most representative case so that the outcome of the study can be used widely for future application. As a result, a synthetic field was built. It is an oil field with aquifer support. The initial reservoir pressure is higher than the bubble point pressure. To imitate the worldwide oil field development practice and make the analysis simple and easy to be understood, one reservoir system was studied at this time. The production scenario follows ordinary operation procedure. Initially five