Well Logging

Introduction

Logging began with straightforward electric logs estimating the electrical conductivity of rocks, yet it is currently a high-level and refined technique utilized regularly in various periods of hydrocarbon investigation, field advancement, and checking. It gives us a consistent downhole record that gives an itemized subsurface image of both steady and sudden changes in actual properties starting with one bed then onto the next. By contrast, just chose portions of the supply rocks are cored, and tests of cuttings from the remainder of the well give something like an overall thought of the lithology. None of the logs measure the boundaries that are of most interest to us, like how much oil or gas is in the subsurface, or how much is being delivered. Such significant information must be inferred, from the deliberate properties, for example, gamma radiation, thickness, speed, and resistivity, utilizing various presumptions which, if valid, will give sensible assessments of hydrocarbons. To play out a logging procedure on wireline, the estimating instrument is brought down into the borehole on the finish of a protected electrical link after the penetrating apparatus is pulled up. The actual link is utilized as the profundity estimating gadget, so properties estimated by the instruments can be connected with specific profundities in the borehole. 

Well, logs are generally recorded while the logging gadget is being winched vertically through the well. The estimations from the instruments housed in the logging apparatus are recorded carefully at timespans somewhere in the range of 3 and 15 cm and the information are handled close to the well ashore, or on the stage on account of seaward. Recording the well log includes various steps, starting with detecting and pre-handling the estimation in the logging instrument itself, the transmission of this data to the surface more than a few kilometres of wireline, further handling in the logging truck PC, information capacity on a circle or attractive tape, lastly show of the information on film or paper. A deliberate log shows numerous varieties from top to base, and each squirm has importance. Most logs are reliant upon direct contact with the stone through the dividers of the well and must be pursued progressive time frames boring before each phase of the steel packaging is introduced in the well.

Well Logging

Well logging is a method for recording the physical, acoustic, and electrical properties of the stones entered by a well. It is completed by administration organizations, which work under an agreement with the oil organizations. Logging enjoys the benefit that it measures in situ rock properties which can’t be estimated in a research facility from either centre examples or cuttings.

Types of Logging

1.Spontaneous Potential Log

The estimation of normal electrical flow (voltage) created by the collaboration of development connate water, conductive penetrating liquid, and shale in the borehole. The SP bend mirrors a distinction in the electrical potential between a mobile terminal in the borehole and a decent reference terminal at the surface.

  2.Resistivity Log

It is the stone property on which the whole study of logging was previously created. Various materials have various capacities to oppose the progression of power. Resistivity is estimated by electric logs. The equal resistivity is conductivity. Resistivity is an essential estimation of a supply’s liquid immersion. In log translation, hydrocarbons, rocks, and freshwater all go about as separators and are, in this manner, non-conductive and profoundly resistive to electric streams. Concerning salt water, is a guide and has a low resistivity. Resistivity logs are plotted on a logarithmic scale.

   3.Nuclear Logs

Atomic logs (additionally called radioactivity logs) record regular and instigated radioactivity. Atomic logs enjoy an essential upper hand over most different logs-they can be made in by the same token cased or open openings loaded up with a liquid ( Since numerous radiation beams can go through steel packaging). Three sorts of logs: Gamma Ray Log, Neutron Ray Log, and Density Log.

4.Sonic or Acoustic Logs

The acoustic or sonic log estimates the movement season of a flexible wave (sound) through the arrangement. Give a nonstop record of the time (Δt) taken in microsecond/foot by sound wave to travel from the transmitter (Tx) (above) to the collector (Rx) (underneath) the sonde. The beat estimated is a pressure P-wave followed by shear and stonily waves.

 5.Calliper Log

The Calliper Log is a tool for measuring the diameter and shape of a borehole. – It uses a tool that has 2, 4, or more extendable arms. – The arms can move in and out as the tool is withdrawn from the borehole. – The arms are linked to a potentiometer and the movement is converted into an electrical signal by the potentiometer.

Importance of Well Logging

It is the most cost-effective means of gathering and analysing data on a well’s geophysical features. Obtaining wireline logs with high-tech logging equipment is far more cost-effective than digging wells with specialised coring instruments. The cores must be transported to the surface for comprehensive investigation during the coring process. This can be time-consuming since the well’s pressure might harm the core’s softer sediments. Logging data, in this case, provides more information about the natural features of sediments or rocks while inflicting no harm to them.

Second, well logging allows for a real-time assessment of formation properties. This data may be put to good use in revising borehole drilling schedules. Well logs, for example, can be used to identify a defect and take remedial action in real-time if the depth of the target formation differs from the predicted depth. When compared to the coring procedure, the creation of well logs requires far fewer resources. They take much less storage space than core samples. For storage, the latter requires climate-controlled facilities. Once the data has been collected, it may be analysed for future research of the same site for more natural resources.

Conclusion

Geological sampling during drilling (cuttings) provides a very imprecise record of the formations encountered. Entire formation samples can be brought to the surface by mechanical coring, but this is both slow and very expensive. In the narrowest sense, well logging supplements the analysis of cores, side-wall samples, and cuttings. Logs are used for a variety of purposes depending on the nature of the data recorded. Correlation from well to well is one of the oldest and probably the most common use of logs. Connection is normally founded on the states of the recorded bends versus profundity. It permits the subsurface geologist to plan arrangement profundities, sidelong conveyances, and thicknesses, and afterward to recognize conditions that could trap hydrocarbons. Distinguishing proof of the lithology of the stone succession is another significant use. After gaining experience in a space it is feasible for a log investigator to make a reasonable deduction as to lithology by looking at the log from another well. A bunch of logs running in a well will generally mean various things to various experts.