COMPARATIVE STUDY OF VOLUMETRIC METHOD AND DECLINE CURVE ANALYSIS OF HYDROCARBON RESERVES ESTIMATION
CHAPTER ONE
INTRODUCTION
- BACKGROUND OF THE STUDY
The total estimated amount of oil in an oil reservoir, including both producible and non-producible oil, is called oil in place. However, because of reservoir characteristics and limitations in petroleum extraction technologies, only a fraction of this oil can be brought to the surface, and it is only this producible fraction that is considered to be reserves. Therefore, reserves are said to be estimated remaining quantities of oil and gas and related substances anticipated to be recoverable from known accumulations based on analysis of drilling, geological, geophysical, and engineering data; established technology; and specific economic conditions (Vol. 1, Canadian Oil and Gas Evaluation Handbook). Thus, reserves must satisfy four criteria: discovered, recoverable, commercial, and remaining ( Cronquist, 2001).
        According to Demiren(2005), The petroleum engineer is often faced with the challenges of accurately determining this volume of hydrocarbon that is contained and the volume that is economically recoverable. Petroleum reserves cannot be measured directly. They are estimates of future production under certain conditions which may or may not be well specified, but which include economic assumptions, knowledge of the feasibility of projects to extract the resources, and geological information estimation of oil and gas reserves for a field is continuous throughout the producing life of the field. These reserves estimates involve input on:
Economics (information about current costs, prices and taxes, for ‘proven’ reserves; assumptions or predictions about future costs, prices, taxes, for other categories);
Feasibility (the feasible development schemes, which assume development technologies available and environmental impact constraints); and
Geology (the petroleum initially-in-place estimates and reservoir characteristics)
          The volume of hydrocarbon reserves is a primary component of an energy company’s value. Estimating that volume is a complicated, but essential and regulated part of the resource industry’s business. Unlike the estimates of oil or gas in place, which are estimates of oil or gas in place, which are estimates of physical measurements, estimates of oil or gas reserves are therefore really predictions of production in the foreseeable future, combined with the record of past production, if any.
          An accurate description of the volume of fluid present is very important in quantifying the resources and selection of production techniques, production rates and overall management of the reservoir throughout its life and also enhances adequate schedule control. The information obtained is also the basis for resource development and plan making.
All reserve estimates involve uncertainty depending on the amount of reliable geological and/or production data available and the interpretation of those data. Because the geology of the sub-surface cannot be examined directly, indirect technique must be used to estimate the size and recoverability of the resources. While new technologies have increased the accuracy of these techniques, significant uncertainties still remain. These uncertainties reduce from the exploratory stage to the ultimate recovery and abandonment as a result of acquisition of more data that enhance description of the reservoir (Olatunige, 2007).
The level of uncertainty in making such estimates is affected by the following factors
- Reservoir type,
- Source of reservoir energy ,
- Quantity and quality of the geological, engineering, and geophysical data,
4. Assumptions adopted when making the estimates,
5. Available technology, and
6. Experience and knowledge of the evaluator.
The magnitude of uncertainty, however, decreases with time until the economic limit is reached and the ultimate recovery is realized.
COMPARATIVE STUDY OF VOLUMETRIC METHOD AND DECLINE CURVE ANALYSIS OF HYDROCARBON RESERVES ESTIMATION
