- Settore: Oil & gas
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The depth of a well or features within the wellbore as measured while drilling. The measured length of each joint of drillpipe or tubing is added to provide a total depth or measurement to the point of interest. Drillers depth is the first depth measurement of a wellbore and is taken from the rotary table level on the rig floor. In most cases, subsequent depth measurements, such as those made during the well completion phase, are corrected to the wellhead datum that is based on drillers depth.
Industry:Oil & gas
The cross section of a material to photoelectric absorption, in barns/cm<sup>3</sup>. The volumetric cross section, U, is from the product of the photoelectric factor, PEF or P<sub>e</sub> , and the electron density. In practice, U is usually calculated using the bulk density instead of the electron density. U is a volumetric quantity, whereas P<sub>e</sub> is not. U is more useful in log interpretation since it can be used in a linear mixing law in terms of the volumes of the formation components.
Industry:Oil & gas
The costs associated with abandoning a well or production facility. Such costs are specified in the authority for expenditure (AFE), and typically cover the plugging of wells; removal of well equipment, production tanks and associated installations; and surface remediation.
Industry:Oil & gas
The electromagnetic force generated across an ion-selective membrane when solutions on either side of the membrane have different salinities. Shales and clays are cationic membranes, since they allow the passage of cations, such as Na<sup>+</sup>, but not anions, such as Cl<sup>-</sup>. When the drilling mud in the borehole and the formation water have different salinities, a membrane potential is generated at the boundary between a shale and a permeable formation. This potential is one component of the electrochemical potential, from which the spontaneous potential (SP) log is derived. The other, much smaller component is the liquid-junction potential. The membrane potential is reduced if the shale is not a good cationic membrane, or in other words has a low cation-exchange capacity. <br><br>A membrane potential may also be generated across the mudcake if there is no flushed zone; for example if the mud filtrate has moved vertically since invasion took place, and by clay within a shaly sand, but with the opposite polarity to the normal SP potentials. <br><br>The membrane potential is also used in core analysis to determine the cation-exchange capacity of a sample. In this case, the clay within the sample is the ion-selective membrane, and the potential generated across it is related to the cation-exchange capacity per unit pore volume, Q<sub>v</sub>. As a method of measuring Q<sub>v</sub>, the technique is faster than the multiple salinity method, and more representative of the in-situ value than destructive methods such as conductometric titration. However, care is needed in making the measurement and deriving the appropriate Q<sub>v</sub>.
Industry:Oil & gas
The data observed before the start of radial flow (middle-time transient data). When not dominated by wellbore storage, these data may reveal near-wellbore reservoir features including limited entry, hydraulic fracture and dual-porosity or layering effects. Downhole shut-in greatly improves the quality of the early-time transient data.
Industry:Oil & gas
The electromagnetic force created by two different metals in contact with each other. If two such metals are in contact in a logging tool, and also communicate along a conductive borehole, then a potential drop is generated in the borehole. This potential drop will appear on the spontaneous potential (SP) log, where it can be confused with the electrochemical potential. Since the magnitude of the drop depends on the formation resistivity, the effect of bimetallism is often seen as a resistivity log superimposed on the normal SP. Under usual circumstances, the effect of bimetallism on the SP is small, and care is taken to avoid it.
Industry:Oil & gas
The degree to which a distribution has lost the bilateral symmetry of a normal distribution. Skewness is usually expressed qualitatively rather than quantitatively.
Industry:Oil & gas
The degree to which a medium resists the flow of electric charge divided by the degree to which free space resists such charge. The degree, or dielectric permittivity, is defined as the ratio of the electric displacement to the electric field strength. The term is also known as the relative dielectric constant. However, at high frequencies, it is no longer constant and decreases with frequency. Relative dielectric permittivities, which are unitless, vary from about 4 to 400 in rock, but in rare cases may reach several thousand.
Industry:Oil & gas
The degree of heating of a source rock in the process of transforming kerogen into hydrocarbon. Thermal maturity is commonly evaluated by measuring vitrinite reflectance or by pyrolysis.
Industry:Oil & gas
