Petroleum- Interesting FACTS #1

Refining a 42-gallon barrel of crude oil yields 20 gallons of gasoline, 7 gallons of diesel, and 17 gallons of petroleum byproducts such as propane, ammonia and plastic material, totaling 44 gallons; a net gain of 2 gallons.

More than a dozen other petroleum products are also produced in refineries. Petroleum refineries produce liquids the petrochemical industry uses to make a variety of chemicals and plastics.

In simple words, every 159 liters barrel of Crude oil produces the following:

* 73 liters Petrol
* 36 liters Diesel
* 20 liters Jet fuel & heavy fuel oil
* 6 liters Propene
&
* 34 liters of other products (Butane, Asphalt & Sulphur)

This is of course done by mixing other additives to derive the desired products.

Refineries operate 24/7

A refinery runs 24 hours a day, 365 days a year and requires a large number of employees. A refinery can occupy as much land as several hundred football fields.

Petroleum - Upstream - Basic Concept

Upstream is a term used in the oil industry which refers to the searching for, the recovery and production of crude oil and natural gas.

The upstream sector includes

• Exploration – the searching for potential onshore or offshore oil and gas reservoirs, and the drilling of exploratory wells
• Production and maintenance of wells and facilities to recover and bring the crude oil and/or raw natural gas to the surface plant and to process the produced hydrocarbons.

The upstream sector in the context of the petroleum industry cycle

Within the upstream sector, a typical oil and gas operating cycle sees several and different phases that aim to target varied goals using specialized technologies.

A schematic representation of the field cycle and the activities generally carried out in each phase is shown in the figure below:

The oil and gas operating cycle and activities

The term “Petroleum” refers to both crude oil and natural gas.

These are mixtures of hydrocarbons which are molecules, in various shapes and sizes, of hydrogen and carbon atoms, and different mixtures of hydrocarbons have different uses and different economic values.

Basic hydrocarbon structures

Crude oil refers to hydrocarbon mixtures produced from underground reservoirs that are liquid at normal atmospheric pressure and temperature.

Natural gas refers to hydrocarbon mixtures that are gaseous, at normal atmospheric pressure and temperature – the gas mixtures consist largely of methane – the smallest natural hydrocarbon molecule (CH4).

The extremely variable compositional complexity of petroleum reveals the joint effects of all processes involved in the origin of petroleum accumulations and their history during the geological time.

The process of origin of oil and gas

Hydrocarbon reservoirs (porous and permeable host rocks) are thousands of feet below the surface, and oil and gas accumulations form in sedimentary basins if some geological conditions (Petroleum System) are met:

• Existence of source rocks which generate petroleum under particular subsurface temperature conditions
• Expulsion of petroleum from the source and subsequent migration
• The occurrence of reservoir rocks of sufficient porosity and permeability allowing the flow of petroleum through the pore system
• Configurations and arrangement of rock layers to form traps
• Presence of impermeable layers (cap rocks) to confine petroleum accumulations in place
• Correct timing with respect to the sequence by which all the above processes have occurred during the history of a sedimentary basin
• Advantageous conditions for the preservation of petroleum accumulation during the geologic time

Common types of petroleum traps

Credits: Oil and Gas portal

Oil and Gas- Offshore Drilling Rigs

Modern and advanced drilling techniques and methods have increased Companies’ ability to find hydrocarbons and the speed at which their projects are developed.

There are technology advances for exploration and development, better control of environmental impacts, increased efficiency, and improved understanding of the marine environment.

The techniques and equipment for drilling offshore wells (offshore drilling) are very similar to those used for onshore drilling.

The main differences consist in the arrangement of the drilling rig and of the equipment and in certain particular methods of carrying out the operations, which have to be adapted to the requirements dictated by far more difficult and often extreme environmental conditions.

This entails considerably higher costs, which must also be added considerable investments to provide the facilities and plants for subsequent field development.

An offshore drilling rig has to create the same working conditions as for onshore rigs which can move from one point to another without any difficulty, and they have several additional features to adapt them to the marine environment, including:

Heliport

• a large deck area that is placed high and to the side of offshore rigs;
• It is an important feature since helicopters are often the primary means of transportation.

Living quarters

• usually comprise bedrooms, a dining hall, a recreation room, office space, and an infirmary.

Cranes

• used to move equipment and material from workboats onto the rig and to shift the loads around on the rig.

Risers

• used to extend the wellhead from the mudline to the surface.

These conditions increase the complexity of the offshore rigs and justify their higher daily rate compared with an onshore drilling rig of the same capacity.

From an operational point of view, offshore drilling may be subdivided into two main categories, depending on the water depth.

1.  Bottom supported drilling rigs

• The safety equipment, i.e. ordinary Blow-Out Preventers (BOPs) located permanently above sea level and accessible from the supporting structure;
• drilling operations are identical to those carried out in onshore drilling.

2.  Floating drilling rigs

• The wellhead and the subsea BOPs are placed on the seabed and are not therefore directly accessible from the supporting structure.
• Drilling operations differ from onshore ones, as the rig floats, subjected to the action of the wind, currents, and waves, which cause it to make small horizontal and vertical movements.

The use of floating rigs is necessary for exploratory drilling in water depths of more than 100 m (this refers solely to exploratory drilling operations, and not to the subsequent development drilling).

Exploration Drilling Rigs

1.  Bottom supported rigs

Barges

• They are designed to work in shallow water (less than20 ft deep).
• The rig is floated to the drill site, and the lower hull is sunk to rest on the sea bottom.
• The large surface area of the lower hull keeps the rig from sinking into the soft mud and provides a stable drilling platform.

Drilling Barge

Submersibles

• They are barge that is designed to work in deeper water (to 50 ft deep);
• They have extensions that allow it to raise its upper hull above the water level.

Submersible Drilling Rig

Platforms

• Platforms use a jacket (a steel tubular framework anchored to the ocean bottom) to support the surface production equipment, living quarters, and drilling rig.
• Multiple directional wells are drilled from the platform by using a rig with a movable substructure.

Offshore Drilling Platform

Jackups

• Backups are similar to platforms except that the support legs are not permanently attached to the seafloor – The weight of the rig is sufficient to keep it on location.

Jack Up Drilling Rig

2. Floating drilling rigs

They are not attached or resting on the ocean bottom and have special features to facilitate this:

                    (i)  They are held on location by anchors or dynamic positioning
                    (ii)  The drill string and riser are isolated from wave motion by motion compensators.

There are two categories of drilling floating rigs

Semi-submersible rigs

• They consist of a large triangular, rectangular or pentangular platform, connected with submerged hulls by means of large columns which vary in number from 3 to 8, according to the shape of the vessel
• They are kept vertical over the site by means of mooring or dynamic positioning systems
• Semis are subjected to wave motion, their drilling apparatus is located in the center where wave motion is minimal.

Drill ships

• Drilling ships are used for operating in deep waters, often under extreme environmental conditions, such as drilling in arctic areas
• Drilling ships represent an optimal solution of drilling exploratory wells in remote areas, far removed from supply points, as it can carry all the material necessary for drilling even a particularly difficult well.
• Drilling ships are kept in a vertical position over the well by means of mooring or dynamic positioning systems

Drilling Ship

Offshore drilling operations

• Drilling starts after the rig has been positioned vertically over the well, by means of mooring or dynamic positioning systems.

Subsea BOPs

• In offshore drilling, BOPs have the same function as those used in onshore wells but are connected in a single complex (the BOP stack) before being mounted on the wellhead, so as to reduce assembly times at the sea bottom.
• They are lodged in a square-section cage structure with female columns at the apexes, into which the male tubular columns of the permanent guide structure fit.
• The BOP stack is lowered and fastened to the wellhead by means of a hydraulically controlled connection, ensuring hydraulic sealing.

A drilling ship and a subsea BOP stack

A semisub drilling rig and a subsea BOP Stack

                        

Credits: Oil and Gas portal

Oil & Gas- Drilling Technologies

Oil well drilling is a complex operation and the drilling industry engages the services of personnel and a complicated array of machinery and materials to drill an oil/gas well to depths greater than 6000 meters, The drilling industry has seen technological progress, however, these advances have not changed the fact that, besides the use of complicated machinery, successful drilling is a result of tremendous team effort. Numerous personnel from the operating company and several service companies work together to drill and complete an oil/gas well. A drilling rig is used to drill a hole, and this requires qualified personnel, different types of equipment the application of a great variety of techniques.

When a drilling project is commenced, two goals must be achieved:

• To drill and finish the well in a safe manner (personal injuries, technical problems) and according to its purpose;
• To complete the project with minimum cost.

The overall costs of the well must be optimized and this optimization may influence where the well is drilled (onshore – extended reach or offshore above reservoir), the drilling technology applied (conventional or slim-hole drilling), as well as the evaluation procedures, run to gather subsurface information for future drilling projects. Rotary drilling is the most efficient technology applied in the oil and gas industry. It is a drilling technology that relies on the continuous circular rotation of the bit to break rocks, while drilling fluids circulate through the bit and up the wellbore to the surface, making it possible to drill safely and efficiently the well.

Rotary drilling rig

The drilling rig consists of a set of equipment and machinery located on the so-called drilling site and normally the rig is not owned by the oil company but by drilling service companies, which hire out the rig complete with operators and which construct the well according to the client’s specifications.

Drilling Rig Systems

A drilling rig is composed of different systems:

1. The hosting system

• It the set of equipment necessary for handling any material inside the well(drill string and the casing);
• It consists of a structural part (Derrick/mast and substructure), the complex of the crown and traveling block, the draw works (hoist) and the drilling line;
• The substructure is the supporting base for the derrick, the draw works, and the rotary table, and constitutes the working floor for operations, or drilling floor.

The Hosting System

2. The rotating system

• The rotating system allows the rotation of the drill string, and it consists of the rotary table, the Kelly, and the swivel;
• In modern rigs, top drive groups together the functions of the above three items of equipment.

   

                                                  

The Kelly System                                                               The Top Drive System

3. The circulation system

• The circulation system consists of mud pumps, distribution lines, and the mud cleaning and accumulation system;
• It is the closed hydraulic circuit which allows the mud to flow from the surface to the bottom of the hole, inside the drill string, and subsequently back to the surface, in the drill string borehole annulus;
• The mud from the hole has to have the cuttings removed before being reinjected to the bottom of the hole and the mud pumps supply the energy necessary for circulation;

Drilling fluids are subdivided into three major classes:

1. Water-based muds;
2. Oil-based muds;
3. Air-based muds (used to reduce bottom hole pressure, to avoid circulation losses in surface layers, or to limit damage to productive formations).

The Circulating System

4.  The power generation system

• A power generation system is needed to run the machines driving the main components of the rig and it is provided by diesel engines, diesel-electric engines;
• Power is transferred from the engines to the different rig systems by belts, chains, and driveshafts on a mechanical rig, or by generated DC electrical power on an electric rig and it is distributed to the rotary table and mud pumps and to the draw works.

Drilling Rig Power Generation System

5.  The drill string

The drill string is an assemblage of hollow pipes of circular section, extending from the surface to the bottom of the hole.

It has three functions:

• it takes the drilling bit to the bottom of the hole while transmitting its rotation and its vertical load to it;
• it permits the circulation of the drilling fluid to the bottom of the hole;
• it guides and controls the trajectory of the hole.

                    

 Drill String                                   An Insert Tricone                                           Bit A PDC Bit

6.  Casing

• The casing is a steel tube that starts from the surface and goes down to the bottom of the hole and is rigidly connected to the rocky formation using cement slurry, which also guarantees hydraulic insulation.
• The casing supports the walls of the hole and prevents the migration of fluids from layers at high pressure to ones at low pressure.

Casing Strings

7.  Cementing

Cementing is the operation of pumping a cement slurry between the casing and the formation, and can be performed by injection into the annulus from inside the casing.

The cementing (primary cementing) serves to rigidly connect the casing to the formation and to guarantee the hydraulic insulation of the various formations, preventing the migration of the fluids from layers at high pore pressure to those at low pressure.

The centralization of the casing is particularly important, as the geometry of the well is seldom regular, but tortuous and with a variable diameter.

Primary cementing

Credits: Oil and Gas portal

INTRODUCTION TO OIL & GAS WELL DRILLING

The term drilling indicates the whole complex of operations necessary to construct wells of the circular section applying excavation techniques.

To drill a well it is necessary to carry out simultaneously the following actions (drilling process):

• to overcome the resistance of the rock, crushing it into small particles measuring just a few mm;
• to remove the rock particles, while still acting on fresh material;
• to maintain the stability of the walls of the hole;
• to prevent the fluids contained in the drilled formations from entering the well.

This can be achieved by using rotary drilling rigs which are the ones operating today in the field of hydrocarbons exploration and production.

The drilling rigs are complexes of mobile equipment which can be moved (onshore and offshore) from one drill site to another, drilling a series of wells.

In rotary drilling, the rock is bored using a cutting tool called the bit, which is rotated and simultaneously forced against the rock at the bottom of the hole by a drill string consisting of hollow steel pipes of circular section screwed together.

                      Land Drilling Rig

        

After having drilled a certain length of the hole, in order to guarantee its stability it has to be cased with steel pipes, called casings, joined together by threaded sleeves.

The space between the casing and the hole is then filled with a cement slurry to ensure a hydraulic and mechanical seal.

The final depth of the well is accomplished by drilling holes of decreasing diameter, successively protected by casings, likewise of decreasing diameter, producing a structure made up of concentric tubular elements.

The Drilling Process

Planning the drilling of a well

The planning of a well is a fundamental part of the drilling process – it is the basis for making all the important technical choices, for assessing the costs and organizing the actual construction of the well in the most efficient way.

The well planning starts the moment when the interpretation of the seismic data and the reconstruction of the geology of the area reveal the presence of a structure favorable to the accumulation of hydrocarbons.

Overview of the well planning process

Choice of the rig, wellhead, and BOP

The casing levels, the diameters, and weight of the strings, the pressures and temperatures concerned, and the volumes of drilling mud to be used, are all aspects participating in determining the choice of rig type, blowout prevention systems (BOP, choke manifold, hydraulic circuit) and wellheads.

The choice of the rig is closely bound up with the depth it is wished to reach and with the weight of the strings concerned.

According to the weights of the strings to be handled, rigs are used that have different characteristics, and what is of basic importance is the strength of the whole assembly, (traveling block, crown block, hook and derrick floor) from which the string hangs while being lowered into the well.

In the offshore activity, the choice of the rig is determined, not only by the weight of the strings but also by the depth of the water in the area of operations.

Drilling rigs installed on offshore vessels or platforms are built to reach the maximum possible depths and have all the material and equipment necessary for drilling on board.

The composition of the wellhead depends on the pressures that can be reached during the various working phases – both drilling and production – and on the diameters of the strings to be lowered into the well.

Well abandonment

If, when drilling has been completed, the well is productive hydrocarbons, a start is made on all those operations that will ensure its economically advantageous working, whereas if, on the contrary, it should prove to be barren or in any case not economically exploitable, it will be shut down.

Well shutdown entails the restoring of the initial conditions of the section of the well not lined and possibly also the lined part if the separation of the permeable levels of different pressure is not assured.

The purpose of these measures is to prevent the transfer of fluids from one level to the other.

The final shutdown of a well must satisfy not only the requirements set out in the engineering best practices fixed by the operator but must also respond to all the requisites of law aimed at safeguarding the environment and the safety of the people living in the vicinity of abandoned wells.

Well Plug & Abandonment

ENVIRONMENTAL IMPACT OF PETROLEUM AND NATURAL GAS

The secret to fossil fuels ability to produce energy is that they contain a large amount of carbon. This carbon is left over from living matter — primarily plants — that lived millions of years ago. Oil and natural gas are usually the results of lots of biological matter that settles to the seafloor, where the hydrocarbons(molecules of hydrogen and carbon), including methane gas, become trapped in rocks.

Petroleum sources are usually small pockets of liquid or gas trapped within rock layers deep underground (often under the seafloor). Extracted crude oil is refined and used to manufacture gasoline (used in transportation) and petrochemicals (used in the production of plastics, pharmaceuticals, and cleaning products).

1. THE ENVIRONMENTAL IMPACT OF DRILLING FOR OIL

Oil companies pump liquid oil out of the ground by using drilling rigs and wells that access the pockets of oil resources. The oil fills the rock layers the way water fills a sponge — spreading throughout open spaces — instead of existing as a giant pool of liquid.

This arrangement means that to pump out all the oil, drillers have to extend or relocate the wells after the immediate area has been emptied. Oil drilling rigs set on platforms in the ocean to access oil reserves below the seafloor must, therefore, employ a series of more technically complex drill rigs built to access oil reserves in deeper water.

The below figure illustrates some of the most commonly used ocean drilling rigs and platforms and the water depths they’re most suited for.

2. THE ENVIRONMENTAL IMPACT OF FRACKING FOR NATURAL GAS

Natural gas is a relatively clean-burning fuel source — it produces approximately half the CO2 emissions that coal burning produces — so the demand for natural gas has increased in the last few decades as concerns grow about carbon emissions and global warming.

Now fuel producers are exploring natural gas in reservoirs separate from petroleum as sources of this fuel. To release the gas from the rocks and capture it for use as fuel, companies use a method of hydraulic fracturing or fracking.


The sand and chemicals are left behind in the rock fractures, leading to groundwater pollution and potentially less stable bedrock. Currently, scientists are concerned that earthquakes in regions of the Midwestern United States that have never experienced earthquakes before are the result of wastewater from natural gas fracking operations.

Credits: Dummies.com

Fundamental of Reservoir Simulation

Reservoir simulation is an area of reservoir engineering that, combining physics, mathematics, and computer programming to a reservoir model that allows the analysis and prediction of the fluid behavior in the reservoir over time.

It can be simply considered as the process of mimicking the behavior of fluid flow in a

petroleum reservoir system ( including reservoir rock and fluids, aquifer, surface, and subsurface facilities) through the use of either physical or mathematical models.

It’s a valuable tool to understand the oil and gas reservoir performance under various operating strategies.

Basically, reservoir simulation consists of:

1.   a geological model in the form of a volumetric grid with cell/face properties that describe the given porous rock formation

2.   a flow model that describes how fluids flow in a porous medium, typically given as a set of partial differential equations expressing conservation of mass or volumes together with appropriate closure relations

3.   a well model that describes the flow in and out of the reservoir, including a model for flow within the well bore and any coupling to flow control devices or surface facilities

 Steps to undertake during a Simulation study

Reservoir simulation is used for two main purposes:

• to optimize development plans for new fields
• to assist with operational and investment decisions.

To carry out reservoir simulation, it is necessary to perform several and complex studies that are normally made by teams of specialists from different disciplines – due to a large amount of data required for the preparation of the simulation input data set.

The main elements of a simulation study include

• matching field history
• making predictions (including a forecast based on the existing operating strategy)
• evaluating alternative operating scenarios

Numerical techniques and approaches

Traditional finite difference simulators dominate both theoretical and practical work in reservoir simulation. Conventional Fluid Dynamics (FD) simulation is underpinned by three physical concepts: conservation of mass, isothermal fluid phase behavior, and the Darcy approximation of fluid flow through porous media. Thermal simulators (most commonly used for heavy crude oil applications) add conservation of energy to this list, allowing temperatures to change within the reservoir.

Numerical techniques and approaches that are common in modern simulators:

• Most modern FD simulation programs allow for the construction of 3-D representations for use in either full-field or single-well models.2-D approximations are also used in various conceptual models, such as cross-sections and 2-D radial grid models.

• Theoretically, finite difference models permit discretization of the reservoir using both structured and more complex unstructured grids to accurately represent the geometry of the reservoir. Local grid refinements are also a feature provided by many simulators to more accurately represent the near wellbore multi-phase flow effects. This “refined meshing” near wellbores is extremely important when analyzing issues such as water and gas coming in reservoirs.

• Representation of faults and their transmissibilities are advanced features provided in many simulators. In these models, inter-cell flow transmissibilities must be computed for non-adjacent layers outside of conventional neighbor-to-neighbor connections.

• Natural fracture simulation (known as dual-porosity and dual-permeability) is an advanced feature that model hydrocarbons in tight matrix blocks. Flow occurs from the tight matrix blocks to the more permeable fracture networks that surround the blocks, and to the wells.

• A black oil simulator does not consider changes in the composition of the hydrocarbons as the field is produced. The compositional model is a more complex model, where the PVT properties of oil and gas phases have been fitted to an equation of state (EOS), as a mixture of components. The simulator then uses the fitted EOS equation to dynamically track the movement of both phases and components in the field.

The simulation model computes the saturation change of three phases (oil, water, and gas) and the pressure of each phase in each cell at each time step. As a result of declining pressure as in a reservoir depletion study, gas will be liberated from the oil. If pressures increase as a result of water or gas injection, the gas is re-dissolved into the oil phase.

A simulation project of a developed field usually requires “history matching” where historical field production and pressures are compared to calculated values. The model’s parameters are adjusted until a reasonable match is achieved on a field basis and usually for all wells. Commonly, producing water cuts or water-oil ratios and gas-oil ratios are matched.

Credits: Oil and Gas portal

Petroleum Production Optimization Innovations- Through Tubing Drilling and Completion

Through-tubing drilling and completion is a cost-effective technology for increasing production and recovery. TTDC is a generic term for drilling sidetracks in existing producers and injectors and covers both coiled tubing drilling (CTD) and through-tubing rotational drilling (TTRD), including installing the associated lower completion, typically liners or screens.

The main advantage of the technology is that new reservoir sections can be reached without having to remove the existing, the completion of the production casing, thereby reducing operational time significantly compared to a “standard” slot recovery or side-track. TTDC- wells are particularly useful for accessing pockets of isolated oil and gas in mature fields. Due to the deep side-tracks achieved with this technique, it is possible to minimize borehole lengths and avoid drilling problems in overlying formations.

Through tubing rotary drilling

WELL MATRIX STIMULATION WITHOUT HCl

Well acidizing is a common practices in the oil industry and hydrochloric acid (HCl) has been used as the main acid for limestone stimulation purposes There are several concerns with the use of HCl acids: health and safety of the field crew, corrosive nature of the acids for the flow lines and equipment, and environmental effects of the produced HCl.

A new product called FF-01 is an environmentally-friendly and equipment-friendly product. It is a conversion to an organic base to maintain very low pH as a vehicle for aggressiveness, along with the creation of buffers and surface tension relievers. Low pH, slower reaction rates with limestone, a small amount of residue after a reaction, safety, minimum damage to equipment, and longevity are the properties of this product. 

Tests have been conducted to develop this new product and study possible improvements in this blend. It has been observed that FF-01 dissolves limestone rock samples with smaller reaction constants compared to HCl However, it will dissolve the same mass of rock if enough time is given, and it lasts longer during the course of reaction while leaving fewer residues. 

HCl performs better in cleaning the near-wellbore rock while FF-01 performs better in generating long wormholes and higher effective permeability compared to the cores that were treated using HCl.

UNCONVENTIONAL STIMULATION

The acoustic stimulation technology has the potential to provide a low-cost procedure for enhancing oil recovery in mature fields. Low-frequency shock waves produced downhole can increase the oil production and are currently producing well with high WC mobilizing immobile oil in ¾ mile range. Application of this technology well suits well/field having the following properties:

• Oil Viscosity less than 10 cP

• High water cut, ideally greater than 80%

• Low GOR, ~10 m3 per m3 of fluid produced is ideal

• Minimum spacing of 400 m between source wells with production wells spaced within 300 m radius “stimulation zone”, if multiple tools are run.

Credits: Oil and Gas portal