Gross

Bulk catalytic materials, in which the gross composition does not... 

However, before extrapolating the arguments from the gross patterns through the reactor for homogeneous reactions to solid-catalyzed reactions, it must be recognized that in catalytic reactions the fluid in the interior of catalyst pellets may diSer from the main body of fluid. The local inhomogeneities caused by lowered reactant concentration within the catalyst pellets result in a product distribution different from that which would otherwise be observed. 

Gross calorific values are high, being about 100000 kJ/m ... 

The carbon atom has a share in eight electrons (Ne structure) whilst each hydrogen atom has a share in two electrons (He structure). This is a gross simplification of covalent bonding, since the actual electrons are present in molecular orbitals which occupy the whole space around the five atoms of the molecule. 

Measuring the gross heating value (mass) is done in the laboratory using the ASTM D 240 procedure by combustion of the fuel sample under an oxygen atmosphere, in a bomb calorimeter surrounded by water. The thermal effects are calculated from the rise in temperature of the surrounding medium and the thermal characteristics of the apparatus. 

In nearly all oil or gas reservoirs there are layers which do not contain, or will not produce reservoir fluids. These layers may have no porosity or limited permeability and are generally defined as non reservoir intervals. The thickness of productive (net) reservoir rock within the total (gross) reservoir thickness is termed the net-to-gross or N/G ratio. 

Keywords deterministic methods, STOllP, GllP, reserves, ultimate recovery, net oil sands, area-depth and area-thickness methods, gross rock volume, expectation curves, probability of excedence curves, uncertainty, probability of success, annual reporting requirements, Monte-Carlo simulation, parametric method... 

GRV is the gross rock volume of the hydrocarbon-bearing interval and is the product of the area (A) containing hydrocarbons and the interval thickness (H), hence... 

The isochore thickness of the total interval ( gross thickness ) "egardless of lithology. 

Connecting the measured points will result in a curve describing the area - depth relationship of the top of fhe reservoir. If we know the gross thickness (H) from logs we can establish a second curve representing the area - depth plot for the base of the reservoir. The area between the two lines will equal the volume of rock between the two markers. The area above the OWC is the oil bearing GRV. The other parameters to calculate STOIIP can be taken as averages from our petrophysical evaluation (see Section 5.4.). Note that this method assumes that the reservoir thickness is constant across the whole field. If this is not a reasonable approximation, then the method is not applicable, and an alternative such as the area - thickness method must be used (see below). 

It is clear that if the area - depth method had been applied to the above example, it would have led to a gross over-estimation of STOMP. It would also have been impossible to target the best developed reservoir area with the next development well. 

This is the method used by the commercial software packages Crystal Ball and RISK . The method is ideally suited to computers as the description of the method will reveal. Suppose we are trying to combine two independent variables, say gross reservoir thickness and net-to-gross ratio (the ratio of the net sand thickness to the gross thickness of the reservoir section) which need to be multiplied to produce a net sand thickness. We have described the two variables as follows ... 

A random number (between 0 and 1) is picked, and the associated value of gross reservoir thickness (T) is read from within the range described by the above distribution. The value of T close to the mean will be randomly sampled more frequently than those values away from the mean. The same process is repeated (using a different random number) for the net-to-gross ratio (N/G). The two values are multiplied to obtain one value of net sand thickness. This is repeated some 1,000-10,000 times, with each outcome being equally likely. The outcomes are used to generate a distribution of values of net sand thickness. This can be performed simultaneously for more than two variables. 

The purpose of this exercise is to identify what parameters need to be further investigated if the current range of uncertainty in reserves is too great to commit to a development. In this example, the engineer may recommend more appraisal wells or better definition seismic to reduce the uncertainty in the reservoir area and the net-to-gross ratio, plus a more detailed study of the development mechanism to refine the understanding of the recovery factor. Afluid properties study to reduce uncertainty in (linked to the shrinkage... 

Take an example of estimating gross rock volume, based on seismic data and the results of two wells in a structure (Fig. 7.2). The following cross-section has been generated, and a base case GRV has been calculated. 

The general list of factors influencing the uncertainty in the gross rock volume included the shape of structure, dip of flanks, position of bounding faults, position of internal faults, and depth of fluid contacts (in this case the OWC). In the above example, the owe is penetrated by two wells, and the dip of the structure can be determined from the measurements made in the wells which in turn will allow calibration of fhe 3D seismic. 

The aquifer response (or impact of the water injection wells) may maintain the reservoir pressure close to the initial pressure, providing a long plateau period and slow decline of oil production. The producing GOR may remain approximately at the solution GOR if the reservoir pressure is maintained above the bubble point. The outstanding feature of the production profile is the large increase in water cut over the life of the field, which is usually the main reason for abandonment. Water cut may exceed 90% in the final part of the field life. As water cut increases, so oil production typically declines a constant gross liquids (oil plus water) production may be maintained. 

Keywords economic model, shareholder s profit, project cashflow, gross revenue, discounted cashflow, opex, capex, technical cost, tax, royalty, oil price, marker crude, capital allowance, discount rate, profitability indicators, net present value, rate of return, screening, ranking, expected monetary value, exploration decision making. 

Once production commences (possibly 3-8 years after the first capex) gross revenues are received from the sale of the hydrocarbons. These revenues are used to recover the capital expenditure (capex) of the project, to pay for the operating expenditure (opex) of the project (e.g. manpower, maintenance, equipment running costs, support costs), and to provide the host government take which may in the simplest case be in the form of taxes and royalty. 

Fixed opex is proportional to the capital cost of the items to be operated and is therefore based on a percentage of the cumulative capex. Variable opex is proportional to the throughput and is therefore related to the production rate (oil or gross liquids). Hence,... 

Royalty is normally charged as a percentage of the gross revenues from the sale of hydrocarbons, and may be paid in cash or in kind (e.g. oil). The prevailing oil price is used. 

Prior to the calculation of tax, certain allowances may be made against the gross revenue before applying the tax rate. These are called fiscal costs and commonly include the royalty, opex and capital allowances (which is explained later in this section). Fiscal costs may also be referred to as deductibles. 

These are deducted from the gross revenues prior to applying the tax rate. 

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