- Industry: Oil & gas
- Number of terms: 8814
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A representation of the measured diameter of a borehole along its depth. Caliper logs are usually measured mechanically, with only a few using sonic devices. The tools measure diameter at a specific chord across the well. Since wellbores are usually irregular (rugose), it is important to have a tool that measures diameter at several different locations simultaneously. Such a tool is called a multifinger caliper. Drilling engineers or rigsite personnel use caliper measurement as a qualitative indication of both the condition of the wellbore and the degree to which the mud system has maintained hole stability. Caliper data are integrated to determine the volume of the openhole, which is then used in planning cementing operations.
Industry:Oil & gas
A relatively thin cable used with other equipment to move small rig and drillstring components and to provide tension on the tongs for tightening or loosening threaded connections.
Industry:Oil & gas
A representation of the integrity of the cement job, especially whether the cement is adhering solidly to the outside of the casing. The log is typically obtained from one of a variety of sonic-type tools. The newer versions, called cement evaluation logs, along with their processing software, can give detailed, 360-degree representations of the integrity of the cement job, whereas older versions may display a single line representing the integrated integrity around the casing.
Industry:Oil & gas
A reaction by-product. In sandstone acidizing, the reaction between hydrofluoric acids (HF) or spent HF acids with formation minerals can precipitate nondamaging products, such as silica, borosilicates or fluoborates. However, other insoluble or difficult to remove by-products can create formation damage. <br><br>Ferric iron (Fe<sup>+3</sup>) and ferrous iron (Fe<sup>+2</sup>) are potential sources for precipitates. Ferric iron present in some formation minerals, including chlorite and glauconite clays, and in tubing rust (iron oxide) can precipitate as ferric hydroxide (Fe(OH)<sub>3</sub>), which is a gelatinous, highly insoluble mass that can plug pore channels and reduce permeability. The precipitation of ferric hydroxide or ferrous hydroxide (Fe(OH)<sub>2</sub>) depends on the pH of the spent acid. The former needs a pH higher than 2. 2, while the latter requires a pH higher than 7. 7. Since the maximum pH for a spent acid is approximately 5. 3, the precipitation of ferric hydroxide is more common. Iron-sequestering or iron-reducing agents can be used in acid to maintain the ferric iron in solution. <br><br>Calcium fluoride (CaF<sub>2</sub>) precipitates when HF contacts calcite or any other calcium source, and alkali-fluosilicates or iron sulfide form crystal-like by-products that can bridge pore throats. Additionally, some sequestering agents, corrosion inhibitors or friction reducers can also form residues that may plug formation pores. <br><br>The formation of precipitates can be avoided or reduced by using a preflush, which dissolves calcareous material, iron rust or iron scales, and displaces formation brines (K, Na, Ca ions) away from the wellbore, thereby reducing the formation of CaF<sub>2</sub>, ferric hydroxide and alkali-fluosilicates.
Industry:Oil & gas
A quantitative analytical procedure for water-mud filtrate and for calcium in a oil mud.
Industry:Oil & gas
A qualitative pilot test used to determine whether water-wet solids (for example, barite) exist in an oil-base mud. An oil mud is put into a clean, round, glass quart jar filled about 1/3 full. The mud is stirred on a commercial-grade mixer or blender for 15 minutes. The mud is poured out and the jar, drained and examined. Solids strongly adhering to the glass are indicative of the presence of water-wet solids in the mud. The test has been correlated with inside plugging of drillpipe, which occurs when an oil mud becomes under-treated with oil-wetting agent. The electrical stability test cam be used to evaluate wettability and emulsion quality along with evidence of free water in high-pressure, high-temperature filtrate.
Industry:Oil & gas
A pulley. In oilfield usage, the term usually refers to either the pulleys permanently mounted on the top of the rig (the crown blocks), or the pulleys used for running wireline tools into the wellbore. In the case of the crown blocks, the drilling line, a heavy wire rope, is threaded between the crown blocks and the traveling blocks in a block and tackle arrangement to gain mechanical advantage. A relatively weak drilling line, with a breaking strength of perhaps 100,000 pounds (45,400 kg), may be used to lift much larger loads, perhaps in excess of one million pounds (454,000 kg). During wireline operations, two sheaves are temporarily hung in the derrick, and the wireline is run from the logging truck through the sheaves and then down to the logging tool in the wellbore.
Industry:Oil & gas
A property of fluids and slurries that indicates their resistance to flow, defined as the ratio of shear stress to shear rate. Viscosity can be expressed mathematically as follows: <br><center><img src="files/OGL99118. Gif" alt="Viscosity" border="0" vspace="8" /></center><br>Poise is the unit for viscosity, equivalent to dyne-sec/cm<sup>2</sup>. Because one poise represents a high viscosity, 1/100 poise, or one centipoise (cp), is used for mud measurements. One centipoise equals one millipascal-second. Viscosity must have a stated or an understood shear rate in order to be meaningful. Measurement temperature also must be stated or understood.
Industry:Oil & gas
A product that enhances dispersion of a substance (such as clay) into colloidal form. Peptizing agents for drilling-mud clays are sodium carbonate, sodium metaphosphates, sodium polyacrylates, sodium hydroxide and other water-soluble sodium compounds, even common table salt, NaCl, if added at low concentration. The divalent cations on a clay are replaced by the sodium cations, aiding clay hydration and dispersion. Greater benefit is attained by an agent that contributes an anion (for example, carbonate, phosphate or polyacrylate) that precipitates divalent cations and removes them from solution. This process is successful only when the water first contacted is free of hardness ions, otherwise the anion in the peptizing salt (or polymer) will be precipitated by the hard water and make the peptizing agent much less effective.
Industry:Oil & gas
A product similar to mixed-metal hydroxide, but based on silicate chemistry.
Industry:Oil & gas
