Question

Q1. Explain the working of magnetometer in petroleum industry with suitable diagram                             

Q2. What strategies are used to be adopted for exploration in stratigraphic traps?

Q5. Discuss composition of crude oil with reference to different sulfur and nitrogen and their effects in crude oil.                       

Answer 1

1.

Magnetometer:

Magnetometers are extensively used in various applications like geographical surveys, archeological surveys, metal detector, space explorations, etc. to detect the mineralization and geological structures. In oil and gas industry these meters play an important role for a directional drilling process. These meters are available based on the type of applications like land, airborne, marine and micro-fabricated atomic magnetometers.

Working principal of Magnetometer:

Magnetometers are used to measure the strength of the magnetic field and in some cases direction of the field. A sensor which is attached to this device measures the flux density of the surrounded magnetic field around it. Since the magnetic flux density is proportional to the magnetic field strength so the output directly gives the intensity or strength of the magnetic lines.

Earth is surrounded by the lines of flux which vibrate at the different frequencies depending on the locations. Any object or anomaly which distorts this magnetic field is detected by magnetometer.

Oil exploration

Magnetometers are also used in oil exploration to show locations of geologic features that make drilling impractical, and other features that give geophysicists a more complete picture of stratigraphy.Magnetometers are used in directional drilling for oil or gas to detect the azimuth of the drilling tools near the drill. They are most often paired with accelerometers in drilling tools so that both the inclination and azimuth of the drill can be found.

Figure showing working principal :

2.

Stratigraphic Traps

Stratigraphic traps are formed as a result of lateral and vertical variations in the thickness, texture, porosity or lithology of the reservoir rock. Examples of this type of trap are an unconformity trap, a lens trap and a reef trap.

Stratigrapijc studies in mature hydrocarbon basins offer a systematic approach toward the discovery and exploitation of subtle stratigraphic reservoirs and hydrocarbon reserves. The exploration for such traps involves detailed regional facies mapping of the palaeoenvironmental (depositional) and diagenetic attributes of the potential reservoir facies. Such studies are most effectively used in combination with conventional subsurface mapping and geophysical exploration techniques. Programs designed to exploit or enhance reservoir productivity, whether at the primary or secondary stages of field development, can be most effectively developed by prior analysis of the petrophysical framework of carbonate or siliciclastic reservoirs.

strategies

Perhaps the most important aspect of the stratigraphic approach is the education of young geologists, and those already in the industry who may be reluctant to accept a philosophy that leads to the generation of prospects that do not necessarily involve coexistent structures.
Most importantly, they must realize that existing stratigraphic-trap fields represent only a portion of the spectrum of depositional and/or diagenetic environments and undiscovered reservoirs that may exist in a given subsurface area. Because of complexities related to timing of trap formation versus hydrocarbon migration, porosity history, and structural evolution, these other environments may not all represent high-potential exploration objectives. However, complete stratigraphic studies do indeed involve a systematic approach toward reservoir exploration, certainly not unlike conventional approaches, in which the total geologic system is analysed and reservoir potentials evaluated.

In order to explore for stratigraphic traps, the geologist must first determine the lithologic nature and types of stratigraphic traps that are expected through the study of individual existing fields in an area of interest. Such reference information can then be integrated with regional stratigraphic-sedimentological (facies) studies so as to determine: (1) geologic controls on field-reservoir occurrence; and (2) likely areas where similar geologic conditions may have effected the deposition of potential reservoir facies of similar or different character; it is at this point that the predictive aspect of exploration relies heavily on a geologic imagination that derives from a study of Holocene and ancient depositional models.

3.

Sulfur Content

Sulfur content of crude oils is the second most important property of crude oils next to API gravity. Sulfur content is expressed as weight percent of sulfur in oil and typically varies in the range from 0.1 to 5.0%wt. The standard methods that are use to measure the sulfur content are ASTM D129, D1552, and D2622, depending on the sulfur level. Crude oils with more than 0.5%wt sulfur need to be treated extensively during petroleum refining. Using the sulfur content, crude oils can be classified as sweet (<0.5%wt S) and sour (>0.5% %wt S). The distillation process segregates sulfur species in higher concentrations into the higher-boiling fractions and distillation residua. Removing sulfur from petroleum products is one of the most important processes in a refinery to produce fuels compliant with environmental regulations.

Nitrogen Content

Nitrogen content of crude oils is also expressed as weight percent of oil. Basic nitrogen compounds are particularly undesirable in crude oil fractions as they deactivate the acidic sites on catalysts used in conversion processes. Some nitrogen compounds are also corrosive. Crude oils with nitrogen contents greater than 0.25%wt need treatment in refineries for nitrogen removal.

Effect of Sulfur on Crude oil:

These contaminants not only contribute to environmental pollution resulting from the combustion of petroleum, but also interfere with the processing of petroleum by poisoning catalysts and contributing to corrosion.

Sulfur (S) species (H2S, RSH, RSSR…) are poisonous for all catalytic processes employing reduced metals as the primary active phase. They are generally considered temporary, although their effect can be permanent depending on the process conditions, ease of regeneration, etc. Pgm catalyst(s) react readily with H2S to form sulfides, which may or may not be stoichiometric. Sulfur may cause significant deactivation even at very low concentrations, due to the formation of strong metal-S bonds. Sulfur chemisorbs onto and reacts with the active catalyst sites, preventing reactant access. Furthermore, the stable metal-adsorbate bonds can lead to non-selective side reactions, which modify the surface chemistry

Effect of nitrogen on crude:

In catalytic processes, nitrogen-containing compounds competitively adsorb with other compounds. Such competitive adsorption limits the access of other compounds to the catalyst surface, thereby reducing the rate of conversion of such compounds. For example, nitrogen-containing compounds compete with sulfurcontaining compounds for active sites during hydrotreating,

Table shows nitrogen composition: