Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. A parameter that defines the amplitude of the wave that reflects from an interface. The magnitude of a reflection coefficient at an interface is linearly proportional to the difference in seismic impedance across that interface. The algebraic sign of a reflection coefficient defines the polarity of the reflection event.
Demulsification is the breaking of a crude oil emulsion into oil and water phases. A fast rate of separation, a low value of residual water in the crude oil, and a low value of oil in the disposal water are obviously desirable. Produced oil generally has to meet company and pipeline specifications. For example, the oil shipped from wet-crude handling facilities must not contain more than 0.2% basic sediment and water (BS&W) and 10 pounds of salt per thousand barrels of crude oil. This standard depends on company and pipeline specifications. The salt is insoluble in oil and associated with residual water in the treated crude. Low BS&W and salt content is required to reduce corrosion and deposition of salts. The primary concern in refineries is to remove inorganic salts from the crude oil before they cause corrosion or other detrimental effects in refinery equipment. The salts are removed by washing or desalting the crude oil with relatively fresh water. Oilfield emulsions possess some kinetic stability. This stability arises from the formation of interfacial films that encapsulate the water droplets.
Spacers and flushes are effective displacement aids, because they separate incompatible fluids such as cement and drilling fluid. A spacer is a fluid used to separate drilling fluids and cementing slurries. A spacer can be designed for use with either water-based or oil-based drilling fluids, and prepares both pipe and formation for the cementing operation. Spacers are typically densified with insoluble-solid weighting agents. For example, a spacer is a volume of fluid injected ahead of the cement, but behind the drilling fluid.
From a purely thermodynamic point of view, an emulsion is an unstable system because there is a natural tendency for a liquid/liquid system to separate and reduce its interfacial area and, hence, its interfacial energy. However, most emulsions demonstrate kinetic stability (i.e., they are stable over a period of time). Produced oilfield emulsions are classified on the basis of their degree of kinetic stability. Water-in-oil emulsions are considered to be special liquid-in-liquid colloidal dispersions.
Assuming that the amplitudes are accurately rendered, a host of additional features can be derived and used in interpretation. Collectively, these features are referred to as seismic attributes. The simplest attribute, and the one most widely used, is seismic amplitude, and it is usually reported as the maximum (positive or negative) amplitude value at each sample along a horizon picked from a 3D volume. It is fortunate that, in many cases, the amplitude of reflection corresponds directly to the porosity or to the saturation of the underlying formation. Attributes can be obtained from typical post-stack seismic data volumes, and these are the most common types.
A variety of seismic sources exist that can apply vertical impulse forces to the surface of the ground. These devices are viable energy sources for onshore seismic work. Included in this source category are gravity-driven weight droppers and other devices that use explosive gases or compressed air to drive a heavy pad vertically downward. Multiple references describe these types of sources. Chemical explosives are no longer used as marine energy sources for environmental and ecological reasons. First, it should be determined whether the selected impulsive source creates adequate energy input to provide data with an appropriate signal-to-noise ratio and a satisfactory signal bandwidth at appropriate offset distances. Second, it is important to determine whether an impulsive source causes unwanted reverberations in shallow strata. Vibroseis energy sources are some of the more popular seismic source options for onshore hydrocarbon exploration. Vibrators have several features that make them attractive for seismic data acquisition.
Noise logging is an inexpensive way to investigate whether there is channeling in injection or production wells. The noise-logging tool "listens" passively to downhole noise, for example, from gas bubbling up through liquid in the wellbore. Behind pipe, a channeling flow often passes through cramped spaces and constrictions. These "tight spots" cause high velocities, sudden pressure reductions, and significant flow turbulence. The noise tool listens to the noise associated with the turbulence.
Unfocused gamma-ray density logging is also sometimes called gravel-pack density logging. While focused density logs assess wellbore fluids, the unfocused density logs look at the fluid below the screen or in the gravel pack. The unfocused gamma ray density logger incorporates a compacted slug of Cesium-137 near the bottom of the device. A gamma-ray detector, located approximately 20 in. A counter determines the counts/min (intensity) of the gamma rays; this information is transmitted through the logging cable to the surface, where the count rate is plotted against depth.
Principles for Polycrystalline Diamond Compact (PDC) bit design are discussed here. During design, all factors are considered simultaneously. Cutting structures must provide adequate bottomhole coverage to address formation hardness, abrasiveness, and potential vibrations and to satisfy productive needs. Early (1970s) PDC bits incorporated elementary designs without waterways or carefully engineered provisions for cleaning and cooling. By the late 1980s, PDC technology advanced rapidly as the result of new understanding of bit vibrations and their influence on productivity.
The full elastic seismic wavefield that propagates through an isotropic Earth consists of a P-wave component and two shear (SV and SH) wave components. Marine air guns and vertical onshore sources produce reflected wavefields that are dominated by P and SV modes. Much of the SV energy in these wavefields is created by P-to-SV-mode conversions when the downgoing P wavefield arrives at stratal interfaces at nonnormal angles of incidence (Figure 1). Horizontal-dipole sources can create strong SH modes in onshore programs. No effective seismic horizontal-dipole sources exist for marine applications.