Question

How is oil and gas in an offshore setting is explored and produced

Answer 1

Ive areas, which are Exploration The following Scientific methods are generally employed for locating the prospeel likely to be petroleums bearing 1. Giravimetric method This method is based on the fact thail the magnitude of gravitational pull of underground rock varies directly with il's density. although the actual Variations are extremely small. Compared to the igneous rockss elsewhere, the Sedimentary rocks at oil reserves exert a relatively lower gravitational attraction. Thus near petroleurs fields, the gravity meters show a reduced reading of gravity. So by maleing a gravity Survey, and correlating with the normal values, a geoglogist can get indications of Sub Surface structural formations 2. Magnetic melbod. oil tend to be found in layers of Sedimentary rock, which le on top or basement rock : This Is mueb denser than the Sedimentary layers and contains bigher concentration of iron and other magnetic materials. A magnetometer, fundamentally Specially designed magnetic compass, detects minute differences in the magnetic properties of various rock formations, thus helping to find structures which might contain oil. Magnetometer Surveys are now made by air. This method not only perasit rapid and large scale Surveys, but is also accurate and permits Surveys. Over regions where groundwork is impossible or costly. 3. Seismic lo Survey. This method is based on the Science of Seismology developed for Studying earthquakes. In this method, the geophysicist creates his own By earthquake by exploding a small and controlled charge of explosive buried at the bottom of a shallow hole in the ground. The Seismograph is then made to measure the shock Waves from the explosion. The Velocity of travel of a disturbance through the ground is in mathematical relationsh- of igneous

to the elasticity and density of the ground and it's components. Some of the accoustic Waves which travel outward in all directions from the site of explosion get reflected back to the ground Surface by the densey rock formation below. The Wave Velocity varies with the type of rock. A Series of detectors arranged in a predetermined pattem Surrounding the location of the explosion Yecieves the reflected Waves. The time elapsed between the explosion and detection of the reflected wave at the surface provide data about the nature and situation of underground formations. 4. Borebole logging This isethod involves drilling a well and then using instruments to log or make measurements at various levels in the hole. Changes in electrical Yesistivity radioactivity, acoustics density can be employed as given below for the purpose. OY a) Electrical logging. a rock layev. This method is based on the fact that the resistivity of is a function of it's fluid content oil filled sand has a very high resistivity

6) Radioactive logging This method is based on the fact that certain types of in particular, black sbale contain Reactio- elements. llenie mary constituents of rock exhibit natural radicactive properties. Two commonly used methods of dochoactive logging gamma-ray and [essing. Sediment and neutron hole when warsy enter elections in 1124 of rock and a portion The gamma-ray log helps to define shale. Here a strong radioactive source is lowered down a gamni says will pass through the mad and casing and The Suvicce:ading fork. There they will collide with mineral aloms will be sealt med back towards a delector in the hole. The despree of lack sealtering is proportional to the number of dections in canet volume of The Rock and is closely aclated to Rock clinsily, Carama-ray logging helps to estimate the porosity of the Formations In neutron logging, 2 artificial Paclioactive soule lowered borc hole. High energy 'Frest' neutrons Produced energy mainly by cellision with bychrozen nuclei and become theynalised to energies appropriate to the temperature of the surrounding medicus. These Thermal Deutrons Jer rapteed bg sense of ganoma days or may simply be back scattered loa neutron detector in the hole. hydrogen content of the wall locks may tus be estimated by measuring either Jamnya reys or the neutrons. The measure of porosity both water and hydrocarbons condain ng drogers. into the menclei resulting in the eneission Tise hydrogey concentration Single

Here The instreament is moves down on of pulses that treovel through the instrument transmitted which the instrument recorded al designed in such a way that it permits automatic is absorbed is a function of the density of the c) Accoustic logging an electrically operated acoustic pulse Jenerator is made use of Selection and recording of the travel times of the audeats on sets the lack wall of the hole as up. The signals care Through Special cable on is Sensipreret Suspended and continously at the surface. The velocity log Thas obtained can help to define beds and to avaluate For mortion porosities d) Density logging The instrument used here consists of Fachoactwe anal cobalt source of gamanna. Trys Crager Counter which is sheldal from this source. as detector. Arecioactive cobalt The Janona - Rays from the to bombard the rock formations mach Source ale the Genger Couragter detector from the some of them being scalieved back Formaton and enter The degree to which The orginal Racliation Nock.

e) Core Sampling can coves, which Much information work Rogeaching Farther exploration be provided by the nell data Obtured by the examinations of formaton samsplos taken from various depths in the borehole. These samples can be have been takon from the hole bej a specind coring device or chill cuttings screened from the circulating This type of sample examination helps strata in the bore-hole and to various to identify the with the their standard Strontigraphic Compare Sequence. drilling muda positions

a Petroleum present in varying depth are extracted by drilling boles in the earth's crust and Sinking pipes till the drill reaches the oil Sand - Rotary drilling is the most common drilling method, it works on rotary grinding action. They can be operated - sbore or o off shore. Rotary drilling consist of power plant, drilling column, rotating and boisting mechanismos, ancillary equipments, blow out preventers and la fluid circulation systems, The drilling action is caused by rotating columos, contains bollow steel pipes with drilling bits. These drilling bits a carves, grinds or chisels, depending on the type of bit. The cuttings from the bottoms are returned to the Surface via pipe/bore annulus , they are allowed to circulate through the bit and pipe. The drill pipe and casings weigh about 200 tons, they are. lowered or raised using boisting mechanisms. The drill column is rotated using rotary table. The drill collars are 6-9 m long thick steel cylinders, to which the drilling bits are connected, Various drilling bits are available, each with different number of blades, cutting shape and the Iselal used.

Crown Block Crown Safety Platforro Safety platforma Rotary Table Traveling Block Kelly Draw works Med Tanks Power unit junetion of Kelly and Tep section of - Ingoing Muda Returning Machi Drill pepe it •Drill collar Incing Returring mud Bit Drilling Method of drilling using Rotary Drill systers