Author: bomuo

A permeable rock that may contain oil or gas in appreciable quantity and through which petroleum may migrate. For rocks to contain oil and gas they must have two important properties: (1) a place to store the oil and gas, namely the pores. The more pores the more oil or gas that can be contained in the rock which is measured in terms of a rock’s porosity. Porosity is expressed as the volume percent of the rock that contains open space and can range from 5 to 30%. (2) Permeability – The pores must be connected so that the oil and gas can move through the rock, which is known as the rock’s permeability. Permeability is measured in thousandths of a darcy or millidarcys. Sandstone and carbonate rocks are generally the most porous and permeable rocks

Reservoir risk can be appraised according to the reservoir pressure, which is analyzed by a pressure survey. One of the basic principles of a natural gas reservoir is if you remove one cubic feet of gas from a reservoir that is 100 cf in volume you have taken out 1% of the volume and the pressure should thus drop by 1% because the pressure is linear with the volume. After 5 years if you have taken out 1/3 of the gas from a 15 year field the usual pressure will have dropped equally by 1/3 of the original pressure, so that after 5 years a competent operator would know how much gas he has left in his field. After one year the operator should do a pressure survey then carry out another one annually to see the drop in pressure and just as importantly to establish the trend. If you have an initial pressure of 2000 PSI and after 5 years you have 1500 PSI the operator should conclude that he has 15 years worth of gas left. Reservoir risk can either be borne by the developer or be part of a force majeure clause depending on the strength of the strength of the negotiating parties in a GSA.

The injection of a pressurized fluid (such as air, gas, or water) into oil and gas reservoir formations to effect greater ultimate recovery

Pressure of the fluids in a porous sub-surface reservoir horizon

A representation of a reservoir that incorporates all data pertinent to its ability to store and produce oil and gas. Geoscientists and engineers use reservoir modeling to simulate the movement of the oil and gas under various circumstances to ultimately determine optimal production techniques for the reservoir. The ultimate aim of reservoir modeling is to provide a forecast of reservoir behavior under production conditions. A reservoir model is a mathematical simulation which predicts the production performance of the field and is used to formulate an optimum development plan. One needs to remember this is a model or an estimate, not reality.

The continuing process of integrating and interpreting geological, geophysical, petrophysical, fluid and performance data to form a unified, consistent description of a reservoir.

A subsurface, porous, permeable or naturally fractured rock body in which oil or gas are stored. Most reservoir rocks are limestones, dolomites, sandstones, or a combination of these. An oil reservoir generally contains three fluids – gas, oil, and water – with oil the dominant product. In the typical oil reservoir, these fluids become vertically segregated because of their different densities. Gas, the lightest, occupies the upper part of the reservoir rocks; water, the lower part; and oil, the intermediate section. In addition to its occurrence as a cap or in solution, gas may accumulate independently of the oil; if so, the reservoir is called a gas reservoir. In the typical dry gas reservoir natural gas exists only as a gas and production is only gas plus fresh water

O&G companies are required to keep a report of their oil and gas reserves, mostly focusing on the proven reserves (see proven reserves). The reserve report is for both internal company purposes as well as for the financial world, owners of contiguous territory and the general public. A key problem in structuring information about reserves is that relatively objective estimates of reservoir characteristics must be combined with subjective forecasts of project feasibility and commerciality, since for instance a proven reserve is only as it is nominated if the reserves can be brought to market economically. In its degree of disclosure of information the report should balance the requirement of shareholders to learn more about the underlying value of their investment against the requirement of the company to maintain a level of confidentiality to maintain its competitive edge (see also reserves disclosure)