PETROLEUM resources in finding out the same details.

PETROLEUM EXPLORATION ASSIGNMENT (CPM 4.1)

 

By: VIJAYA BASKAR B (31926360) (ISP/HPCL/CPM4/Direct
Sales/13)

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SECTION A

 

Question 1:  Define NDR.

 

Answer:  

 

The expansion of NDR is National Data
Repository. National Data Repository (NDR) is an integrated data bank on
exploration and production details of all the Indian sedimentary basins.

 

NDR is a distinctive platform run by
Govt. of India for the benefit of all E&P Operators, E&P Service provider
Companies, E&P Investors, Academic world, Universities to search inside the
diverse E&P database of Indian sedimentary basins.

 

The main objective of NDR is to provide
and set up high quality, reliable information about the exploration and
production data of all Indian sedimentary basins with choices for seamless
access and on-line data management. NDR will store and maintain all the
information and data regarding hydrocarbon exploration & production in a
safe and reusable manner and basic research work done on any sedimentary basin
is not repeated by other individual bodies wasting time, money and other
valuable resources in finding out the same details.

 

Specific goals of NDR:

 

Ø  To validate, store, maintain and reproduce high
quality and reliable information of all geo-scientific data.

 

Ø  To help in effective reporting, exchange and trading
of data among existing players including all geo-scientific agencies involved
in hydrocarbon exploration and production.

 

Ø  To encourage and motivate new E & P activities
by providing high quality and reliable data

 

Ø  To support and strengthen overall geo-scientific
activities in India.

 

The
different data classes of NDR are seismic data of the region, well & log
data of exploration wells, spatial data, other data like drilling, reservoir,
production, geological, gravity & magnetic and also other reports and
documents of the exploration wells.

 

Question 2: Describe the challenges linked to Shale Gas production.

Answer

Shale Gas contains 70-90% methane and smaller
amounts of other lighter hydrocarbons, and gases. The Shale gas is found deep
inside, around 2 to 3 Km below the earth’s surface.

 

Hydro Fracturing or Fracking is the
method by which shale gas is extracted from earth’s surface. In this process, a
fracking fluid is used which mainly consists of water and sand along with some
chemicals. This fracking fluid is injected deep underground at high pressure to
extract the natural gas from the shale rocks. Some of this fracking fluid comes
back to the surface of the earth as flow back water.

 

There
are some environmental risks and challenges associated with the production of
Shale Gas. These are as follows.

 

Contamination of Ground Water:
The production of shale gas poses risk to contamination of ground water. There are
lots of chances of contamination of groundwater by the methane gas present in
shale gas, fracking fluid chemicals and dissolved contaminants in flowback
water of fracking fluid.

 

Increased fresh Water consumption:
During production of Shale gas, each well needs about 10-20 million liters of
water, 500 tons of sand and 50 tons of chemicals and about 60-80 % of this
mixtures returns back to the surface as flowback water. Already India is facing
shortfall of fresh water supplies for regular consumption and removing huge
amounts of water from the water table below the earth for production of shale
gas will further aggravate the supplies of fresh water for regular consumption.

 

Disposal
of Flow back Water: Disposal of this flowback water is
another big challenge. The flowback water contain fracture fluid additives and
chemicals which will contaminate the surface and subsurface water resources.
Hence special treatment is required to remove any chemicals present in it
before disposing the same on the earth surface. They also contain trace amounts
of naturally occurring radioactive materials which needs to be safely removed
before disposal of the flowback water.

 

Induced Seismicity:
During the hydro fracking process, the fracking fluid is injected at very high
pressure in to the earth’s crust and this may trigger earthquakes in that
region.

 

Local
Impacts: Volume of truck traffic in the production regions,
noise problems, dust particles and land disturbances in the production regions
are some of the local issues associated with production of shale gas.

 

 

Question 4: Describe why does the drilling
operation uses drilling fluids?

 

Answer:

Drilling
fluids, also known as drilling mud
is a fluid used in drilling operation and is very important as it performs the
following functions:

 

Ø  It
removes the freshly drilled cuttings from the bit and carries them to the
surface thru the annular space between the drill pipe and the hole.

 

Ø  It
acts as a lubricant and cools the drill bit during drilling operation.

 

Ø  It
helps in maintaining an effective hydrostatic head to control the formation
pressures.

 

Ø  It
holds the cuttings and weight material in suspension, when the circulation of
drilling fluid is stopped.

 

Ø  It
builds a wall around inside of the hole due to which caving in of the hole is
prevented.

 

Ø  It
does act as a medium for electrical well logging devices.

 

Ø  It
gives maximum information about the wellbore and formations penetrated.

 

Ø  It
also supports a part of the weight of drill pipes and casings.

 

 

SECTION B

 

Question 6: What is meant by GTO? What
details do we get from GTO?

Answer:

GTO – GEOTECHNICAL ORDER:

GTO is basically a chart or document
jointly prepared by all technicians like geologist, geophysicists, drilling
engineer, chemist, mud engineer, reservoir and production engineer and has all
the details of geological and technical data available before the start of any
drilling activity and includes the plan of activities to be carried out during
drilling activity. This can also be called as well programming. And it helps
geologists, chemists, production engineers, geophysists, drillers and others
involved in drilling of the well as a ready guide in the process to continue a
long way.

The GTO has different columns in it
showing the different categories of information in each column. The different
categories of information in GTO includes general data of the well, geological
properties of the well, information on mud properties and drilling data of the
well to be drilled.

1.    General Data:

This part of the GTO includes the general details like well name, Well
number, Area and geographical location of the well, Water depth and Elevation
in the well, type of well, coordinates of the well, etc.

2.    Geological Data:

This column of the GTO has all the informations collected from
geological, survey, Geophysical and geochemical surveys and includes the following
parameters.

Ø 
Expected
depth of the well

Ø 
The lithological
sequence and stratigraphy expected during drilling

Ø 
Proposed
coring intervals to analyse the nature of rocks while drilling

Ø 
Geophysical
survey informations like Logging, RFT, etc.,

Ø 
Policy
on collection of drill cuttings to analyse the same in getting desired
hydrocarbon information

Ø 
Probable
zones of caving and mud loss,

Ø 
Expected
oil and gas shows,

Ø 
Expected
formation temperature and pressure at different depths of the well required to
maintain the density of the mud to be used.

Ø 
Recommended
mud programme where in the details of mud parameters to be maintained at
different intervals is mentioned

Ø 
Casing
policy to be followed

Ø 
Drilling
policy as specified by drilling engineers

 

3.    Mud Parameters:

Based on the above data, the mud parameters
are studied by the mud engineer and the drafted in the GTO as a separate
column.

The mud details include the specific gravity
/ density of the mud to be maintained while drilling to counterbalance the
formation pressure in the well, correct viscosity of the drilling fluid or mud
to be used based on the depth of the well and cuttings obtained from drilling
of the well, pH and sand percentage in the mud to be used at different depth of
the well, etc.

4.    Drilling Data:

Based on the geological data and mud
parameters decided abo, the Drilling engineer designs the drilling data of GTO.

It includes the details like casing
policy for the well to be drilled, type of drilling to be carried out either
vertical or directional drilling, type and size of the bit to be used for
drilling, Number of bits expected, details of meterage per bit, weight on the
bit, RPM of rotary table, drilling time and pump discharge rate for the
drilling fluid and other details.

Below is a typical diagram of how does a GTO report looks
like.

Finally approval is sought from concerned sectional
heads to use the same as a guide while drilling and after the approval is
granted by all the sectional heads,  the GTO
is issued to all the concerned parties for following as a guide lines while
drilling.

The GTO also helps in augmenting the
production from the well.

Although GTO serves as a guideline and
work plan for drilling activity, it can also be modified as and when needed, by
the concerned persons as per the actual details of the well conditions obtained
during drilling.

 

7. (a). Define the term logging. Describe Natural Gamma Ray Logging.

Answer:

Logging:

Logging or Well logging is a technique
used in the Oil and Gas Industry for recording the properties of the rocks and
their fluids in the well to find the potential hydrocarbon zones in the
geological formations within the earth’s crust.

It is a technique of making petro
physical measurements in the sub-surface formations through the drilled bore
hole to determine both the physical and chemical properties of the rocks and
the fluids they contain. It is also called as Formation Evaluation.

These physico-chemical measurements
are then interpreted to locate and quantify the potential depth zones where oil
and gas can be found.

There are different LOGGING TOOLS used
to measure the electrical, acoustic, radioactive, electromagnetic, and other properties
of the rocks and fluids containing the rock cuttings.

Well Logging is very useful as it
provides more detailed geological information on drilled holes in a cost
effective manner.

Logging or Formation Evaluation is carried out by:

1.   
Mud
Logging

2.   
Core
Logging

3.   
Electro
Logging

1.   
Mud Logging:

Here the rock cuttings, brought to the
surface by the circulating drilling fluid / mud, are examined thoroughly to find out any
traces of subsurface hydrocarbon gases & oil when the well is being drilled.

2.   
Core Logging:

Here a cylindrical shaped rock sample
(core) is taken out from a particular depth and examined for various properties
like porosity, permeability, fluid saturation, etc and recorded in the well
log.

This activity of core logging is carried out in between the drilling
operations by pulling out the drilling assembly and inserting a special
assembly which comprises a core bit & a core barrel to remove a core sample
for analysis. Here the drilling operation is stopped to remove the core. So
this core logging involves extra rig time and hence core logging increases the
exploration cost.

      

The cores removed at different depths are numbered and kept
in  a sequential way as per the depth
from where they have been removed and can be used in case of any future
analysis if required.

3.   
Electro logging
or Wire Line Logging:

Here a logging tool called as
“Sonde” is attached at the end of a cable or wireline & lowered
into a well to measure the rock and fluid properties like electrical,
electromagnetic, acoustic, radioactive properties of the formation. The
measured data is then transferred through the cable and recorded &
processed in a logging unit on the surface.

All the informations and measurements
obtained through different logging techniques are recorded and interpreted to locate the potential
depth zones where hydrocarbon oil and gas can be found out.

Description of Natural Gamma Ray
Logging:

It is one type of Electro Logging or
Wire line Logging method based on the principle that different types of rocks
emit different amounts and different spectra of natural gamma radiation.

Usually shales emit more gamma rays
than other sedimentary rocks, such as sandstones &
lime stones. This
is because of the presence of radioactive potassium in the clay content of
shales and the cation exchange capacity of the clay causes them to absorb uranium and thorium. This
difference in radioactivity between shales and sandstones/limestone rocks
allows the gamma ray logging tool to distinguish between shales and non-shales.

This gamma ray logging, like other
types of Electro Logging, is done by lowering the probe, called as Sonde, down
the drill hole and recording the variation in gamma radiation at different depths.
The gamma ray log is plotted in a graph with low radioactivity to the left and
high radioactivity to the right.

Accordingly, the shales kick to the
right showing maximum radioactivity while sandstones and limestones kick to the
left showing minimum radioactivity. Gamma radiation is usually recorded in API units.

A typical Gamma Ray response is as
below.

An advantage of the gamma log over
other types of well logs is that it works through the steel and cement walls of
cased boreholes where other logging methods do not respond properly.

Although concrete and steel absorb
some of the gamma radiation, enough travels through the steel and cement to
allow qualitative determinations of radioactivity. Typical application of Gamma
Ray Logging includes Indication of lithology, determination of reservoir
thickness, correlation between wells and estimation of Shale volume in the well
being drilled.

7. (b). Describe the methods by which the deviation is done in
directional drilling.           

Answer:

Drilling of non-vertical oil wells is
done by controlled directional drilling. It is the technique of directing a bore
well along a previously determined path to a target located at a given distance
from the vertical.

It is useful when the area above the
target reservoir is inaccessible or where the rig cannot be set up due to
various obvious reasons like reservoir found below mountains or river beds,
etc,.

Most common applications are

Ø 
Off
shore drilling, where an optimum number of wells can be drilled from a single
platform, thereby minimizing the cost of operation.

Ø 
Fault
Drilling where it eliminates the hazard of drilling vertical thru a inclined
fault plane

Ø 
Reaching
inaccessible target reservoirs

Ø 
Avoiding
Salt dome during drilling

Ø 
Drilling
of Relief wells, where the mud and water can be pumped into the uncontrolled
well and thereby kill the blow out.

Ø 
Sidetracking
and Straightening etc.

Most directional wells begin as
vertical wellbores. At a designated depth, known as the kickoff point, the
directional driller deviates the well path by increasing the inclination to
begin the build section. The direction of the bit and the tool face or the
orientation of the measurement sensors in the well are decided based on the
surveys taken during the drilling process. The directional driller constantly observers
these measurements and fine-tune the trajectory of the wellbore as needed to
intercept the next target along the well path.

The deviation in directional drilling is achieved by the
following techniques:

 I) Downhole Hydraulic Motors (Mud Motors)
with a “Bent sub”:

In this technique, the wellbore
direction is controlled by using a bent motor housing, which is oriented to
point the drill bit in the desired direction. Downhole hydraulic motors, also
called as Mud motors, are powered by drilling mud flowing through the motor to
rotate the bit without rotating the drill string from the surface. These allow
for the drill bit to continue rotating at the cutting face at the bottom of the
hole, while most of the drill pipe was held immobile.

A piece of ‘bent sub’ between the top
of the motor and the stationary drill pipe allow the direction of the wellbore
to be changed without needing to pull all the drill pipe out. The bit and the bend
are first oriented in the desired direction, then the downhole mud motor alone
drives the bit leaving the drill string above the bit stationary.

By alternating intervals of rotating
mode, where the complete drill string rotates from the surface) and sliding
mode, where the drill string is stationary, the directional driller can govern
the wellbore trajectory and navigate it in the desired direction.

 

A whipstock  is a wedge shaped,
long inverted concave steel tool with heavy steel collars (through  which the drillstem fits) deployed
downhole to mechanically alter the path of the well.
The whipstock is  positioned to
deflect the bit from the original borehole at a slight angle and in the
desired direction for the sidetrack
This tool deflect  the rotating
drillstem to the side of the hole and is then removed once proper deviation
is achieved. This technique can be used in cased or open holes.

II) Using Whipstock :

This technique is used where subsurface formations are relatively
soft and the borehole can be deflected using the hydraulic energy of the drilling
mud through a jet bit.
Here bits are conventional tricone bits with one of their three
nozzles opened up and the other two openings are closed or reduced in size.
In soft formations, drilling mud can be circulated at high velocity to wash
out the side of the hole.
The washed out section is a path of least resistance and hence
becomes the path which the bit and drill string will follow.
 

III) Using Jet Bits:

 

IV) RSS
(Rotary Steering System):

Directional drilling with a downhole motor needs occasionally stopping the
drill pipe rotation and sliding the pipe through the channel as the motor cuts
a curved path. Sliding can be difficult at times in some hard formations, and
it is always a slow process almost and hence more expensive than drilling while
the pipe is rotating. So the ability to steer the bit while the drill pipe is
rotating is most desired to speed up the process. Several companies have
developed various tools that allow  directional
control while rotating. These tools are referred to as Rotary Steering Systems (RSS).

There are two steering concepts in the RSS—”point the bit” and “push the
bit”. The “point the bit” system uses the
same principle employed in the bent-housing motor systems. In RSSs, the bent
housing is contained inside the collar, so it can be oriented to the desired
direction during drill string rotation. “Point the bit” systems  allow the use of a long-gauge bit to reduce
hole spiraling and drill a straighter wellbore. The “push the bit” system uses
the principle of applying side force to the bit, pushing it against the
borehole wall to achieve the desired trajectory. The force can be either
hydraulic pressure or by way of mechanical forces.

RSS designs
characterized by their steady-state behavior:
In “point the
bit” systems (left side in the picture), the bit is tilted relative to the
rest of the tool to achieve the desired trajectory.
“Push the bit”
systems (right side in the picture) apply force against the borehole to
achieve the desired trajectory.