Estimating resource and reserves crosses the disciplines between geoscientists and petroleum engineers. While the geoscientist may well have primary responsibility, the engineer must carry the resource and reserve models forward for planning and economics. Volumetric estimates of reserves are among the most common examples of Monte Carlo simulation. Consider the following typical volumetric formula to calculate the gas in place, G, in standard cubic feet. In this formula, there is one component that identifies the prospect, A, while the other factors essentially modify this component.
Coalbed methane (CBM) is adsorbed onto the coal surfaces exposed through the matrix microporosity and the naturally occurring fracture or cleat system. This cleat system typically is water-filled, often with fresh or slightly saline water, but may also contain some free gas. Calculation of gas-in-place for a unit volume of the coal layers being developed does not follow the "porous media" approach of determining effective: Instead, the gas-in-place is measured physically through the recovery of coal samples, the number and distribution of which are important to the estimation of total gas in place pertinent to the property being evaluated. Cored samples are transferred carefully from the core barrel to canisters, which are sealed immediately and transported to an analysis laboratory. In analysis, two measurements are taken.
The goal of the net-pay calculations is to eliminate nonproductive rock intervals and, from these calculations at the various wellbores, provide a solid basis for a quality 3D reservoir description and quantitative hydrocarbons-in-place and flow calculations. The determination of net pay is a required input to calculate the hydrocarbon pore feet, FHCP, at a wellbore and its input to the overall reservoir original oil in place (OOIP) or original gas in place (OGIP) calculations. The total FHCP at a well is the point-by-point summation over the reservoir interval with Eq. 1. The top and base of the reservoir interval are defined by geologists on the basis of core descriptions and log characteristics. In the FHCP calculation, net pay, hni, at each data point has a value of either 1 (pay) or 0 (nonpay).
The term "petrophysics" was coined by G.E. Archie and J.H.M.A. Thomeer in a quiet bistro in The Hague. By their definition, petrophysics is the study of the physical and chemical properties of rocks and their contained fluids. Petrophysics emphasizes those properties relating to the pore system and its fluid distribution and flow characteristics. The petrophysicist provides answers on products needed and used by team members, as well as physical and chemical insights needed by other teammates. It is easy to define these characteristics and to appreciate their part in the assessment of reserves.