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

Fundamentals of Petroleum Production Optimization

Production Optimization refers to the various activities of measuring, analyzing, modeling, prioritizing and implementing actions to enhance the productivity of a field: reservoir/well/surface. Production Optimization is a fundamental practice to ensure the recovery of developed reserves while maximizing returns. Production Optimization activities include:

• Near-wellbore profile management

              gas–water coning and fingering
              near-wellbore conformance management

• Removal of near-wellbore damage 

              matrix stimulation or acidizing

• Maximize the productivity index

              hydraulic fracturing
              maximum-reservoir-contact well with multilateral completion

• Prevention of organic and inorganic solid deposition in the near-wellbore/completion/pipeline

• Well integrity

              prevention and remediation of casing and cement failure

• Design of Well completion

              optimization of artificial lift performance at field and well level
              sand control management

• The efficiency of oil and gas transport

• Design of surface facilities and fluid handling capacity

• Production system debottlenecking

Production Optimization, along with Reservoir Management, is a central part of a company’s field development and deliverability strategy. The key factor in production optimization is the capability to mitigate formation damage during well construction and production routine operations. Formation damage mitigation can be accomplished assuring that operational details are achieved before reaching the pay zone to the last production parameters recorded.

Credits: Oil and gas portal

Offshore Drilling and ROVS(Remotly Operated Vehicle)

As the oil and gas industry moves to a more subsea environment, ROVs will become an even more important tool in drilling, development, and repair offshore. In fact, some ROVs are being built to work on specific subsea developments, with manipulators and tools designed for work on equipment in a precise field. In this case, as the subsea architecture is being designed, the ROV that will handle the subsea work is taken into account, as well, ensuring that all tasks at hand can be managed by the ROV.

One of the technologies that spurred the development of offshore drilling was ROV (Remotely Operated Vehicle). In the 1970 Oil industry adapted ROV for drilling. Diving in deep water is dangerous for people. So the Military is using this ROV technology to retrieve the lost equipment underwater.