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glossary.oilfield.slb.com
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Definitions (4869)
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updipLocated up the slope of a dipping plane or surface. In a dipping (not flat-lying) hydrocarbon reservoir that contains gas, oil and water, the gas is updip, the gas-oil contact is downdip from the gas, and the oil-water contact is still farther downdip.
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aThe value a in the relation of formation factor (F) to porosity (phi): F = a / phim. The value a is derived empirically from best fits of measured values of F and phi on a group of rock samples. It has no clear physical significance, although it has been related to grain shape and tortuosity. In the saturation equation, it always occurs associated with the water resistivity as (a * Rw). It is sometimes claimed that a must be 1 since at phi = 1, F must be 1. However, a material with phi = 1 is not a rock: a is essentially an empirical factor for rocks and as such can take any value. A wide range of values has been found, from 0.5 to 5.
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waterfloodA method of secondary recovery in which water is injected into the reservoir formation to displace residual oil. The water from injection wells physically sweeps the displaced oil to adjacent production wells. Potential problems associated with waterflood techniques include inefficient recovery due to variable permeability, or similar conditions affecting fluid transport within the reservoir, and early water breakthrough that may cause production and surface processing problems.
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varimax rotationA method for rotating axes of a plot such that the eigenvectors remain orthogonal as they are rotated. These rotations are used in principal component analysis so that the axes are rotated to a position in which the sum of the variances of the loadings is the maximum possible.
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variable rateA condition that results when the flow rate varies appreciably during a test period. This can be contrasted to multirate conditions, which describe the step changes in rate demanded by certain test designs. The variable rates observed during drawdown can be measured by a flowmeter at the sandface level in the well. Elegant mathematical methods have been developed to analyze well tests conducted at variable rates. Although, from a practical standpoint, it is much more desirable to conduct constant-rate tests, in reality the only truly constant rate is zero. Sandface flow-rate measurements provide considerable information from drawdown data that cannot be learned from a buildup.
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vitrinite reflectanceA measurement of the maturity of organic matter with respect to whether it has generated hydrocarbons or could be an effective source rock.
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tieA comparison, or the location of a comparison, of data. Properly processed and interpreted seismic lines can show good ties, or correlations, at intersection points.
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threshold velocityIn a spinner flowmeter, the theoretical minimum fluid velocity required to initiate spinner rotation, assuming the spinner response is linear. The actual fluid velocity required to start spinner rotation is slightly higher because of additional viscous and mechanical effects. The threshold velocity is determined by extrapolating the spinner response at higher fluid velocities, where it is known to be nearly linear, back to the value that exists when spinner rotation is zero.
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separatorA cylindrical or spherical vessel used to separate oil, gas and water from the total fluid stream produced by a well. Separators can be either horizontal or vertical. Separators can be classified into two-phase and three-phase separators (commonly called free-water knockout). The two-phase type deals only with oil and gas, while the three-phase type handles oil, water and gas. Additionally, separators can be categorized according to their operating pressure. Low-pressure units handle pressures of 10 to 180 psi [69 to 1241 kPa]. Medium-pressure separators operate from 230 to 700 psi [1586 to 4826 kPa]. High-pressure units handle pressures of 975 to 1500 psi [6722 to 10,342 kPa]. Gravity segregation is the main force that accomplishes the separation, which means the heaviest fluid settles to the bottom and the lightest fluid rises to the top. Additionally, inside the vessel, the degree of separation between gas and liquid will depend on the separator operating pressure, the residence time of the fluid mixture and the type of flow of the fluid. Turbulent flow allows more bubbles to escape than laminar flow.
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spottingPlacing a small volume or pill of fluid in a wellbore annulus to free differentially stuck pipe. Oil-base mud is the traditional stuck-pipe spotting fluid. Speed in mixing and placing the spot is of primary importance to successfully freeing pipe. Because of concern about mud disposal, spots used offshore are either synthetic-based emulsions or benign water-base formulations. Each type is supplied as prepackaged concentrate designed for rapid access and mixing at the rig. A spot frees pipe by covering the stuck region. It presumably breaks up the filter cake, allowing the spot to migrate into cracks in the cake and between the pipe and the cake, reducing the stuck area and allowing pipe to be pulled free.
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