Holding the core in the core barrel for as long as required

Many varieties of core catchers are offered. The standard core catcher is a split spring housed on a tapered shoe. As the relative motion of the core occurs, the spring slides down the taper and closes, thereby reducing its ID and tightening on the core. It is too large to pass through the bottom of the housing and the continued upward movement starts to pull on the core which eventually breaks. A variation of this is the slip catcher. This operates on the same principle, but instead of a...

Faults

Faults can determine whether or not a potential reservoir could hold hydrocarbons. Normal faults tend to be open and are caused by a system of extension in the horizontal plane. Often they are effective drains and provide links between reservoirs for fluid and gas flow, however they are not always open. A fault plane can become, due to localised pressure decrease, a site for premature or syntectonic crystallisation of minerals such as quartz, anhydrite, dolomite or c a kite, none of which are...

Caliper logs

Caliper tools use arms which extend out from the body of the tool to determine the hole diameter. They range from two-arm to four-arm calipers and clearly, the more arms that you have on the tool, the closer to the actual hole configuration the results will be. The commonly used tool today is the borehole geometry tool which utilises four-arms. Modern logs such as this will not only plot hole diameters but will totalise hole volume against depth and even print out cement volume requirements,...

Carbonates

There are two main types of carbonate (CaC03 and CaMg (CO,)3 limestone dolomite). Although clastic limestones do occur (derived from the erosion of preexisting carbonates) most limestones are of chemical or biochemical origin 1. As a bi-product of the life process of animals or plants. 2. Direct chemical precipitation from sea water. Precipitation of CaCO occurs in warm, clear, shallow water away from silicate detrial deposition. Limestone is deposited under limiting temperature and depth...

Casing and cementing

Identification of suitable rock types and depths for setting casing is necessary in the planning stage so that the appropriate amount of casing is on rig site. Good geological interpretation can reduce the stock of casing needed and provide a better seat. Fracture gradients of formation types are needed to plan the casing programme, identifying where and how many strings of casing to set. Identifying good strong casing shoe formation is a priority for well control. Knowledge of fault types and...

Checking Procedure

The checking procedure falls into four main groups 2. Repair and maintenance programmes 4. Physical check-list for acceptance Time should be taken to talk to rig personnel to determine their length of service with their present company An overall impression should be gained as to ambience of the rig, by considering the following questions Is there pride in the rig Is the rig running smoothly How much line-supervision is evident What is supervisor-subordinate relationship A chaotic rig is...

Chloride stress corrosion cracking

This is corrosion in a high chloride environment and usually takes the form of highly localised anodic dissolution of the metal under tensile stress. The strength of the material has little or no effect on the susceptibility of materials to this form of attack. It is important to know that chloride can and does promote sulphide stress cracking in corrosion resistant alloys. Here the chloride reduces the effectiveness of the alloy's passive film and thus encourages corrosion. This increases the...

Classification And Origin Of Emergencies

Emergencies can be subdivided into three main groups 1. Major the operator is unable to restore the situation to normality without external assistance. 2. Serious - there is significant risk to life, equipment or the environment. 3. Minor - there is no danger to life and only minimal risk to equipment or the environment. The causes for the occurrence of emergencies can be divided into three main groups 1, Emergencies caused by operational failures resulting in fire and explosion well control...

Coal

Coal is formed from dense forest close to the coastline, building up a layer of plant material faster than decomposition can occur. This is followed by a change in sea level, which brings an influx of salt water killing off the root zone. Continued subsidence allows sediments to bury the un-decomposed plant material, sealing it from the atmosphere and gradually compacting it. If subsidence stops, erosion takes place followed by the growth of a new layer of plant material. Subsidence is then...

Combination logs

As most wells require several logs to be run to fully evaluate their reserves, much thought is given to combining logs into single run tools. In chapter 3, (F. 27), we state that radioactive logs should never be the first logs run in a sequence. Apart from that restriction, we can combine the logs up to the limit of the tools' capabilities, A typical combination of logs would be as follows Run 1 sonic, laterolog, gamma ray, SP, caliper Run 2 density, neutron, gamma ray, caliper Run 4 etc....

Contract Tendering

Having established our rig requirements for a given Drilling Programme, we then approach drilling contractors with this type of rig and ask if they wish to be included in the tendering exercise. From this information, a list of contractors to tender is drawn up and at this time a short-list can be made of the contractors that we feel can perform well. Filling in tenders is a laborious and time-consuming exercise for the drilling contractor and also creates a lot of work for us in analysing the...

Corehead failure

Corehead failures occur for two basic reasons 1. Hard material such as junk, pyrite or chert gets caught between the bit and the formation. This rolls around under the bit causing chips or scars which can then extend and become a 'ring'. The indications of this are initially low penetration rates and irregular torque followed by an increase in pump pressure and progress going to zero. 2. Soft material such as clay, LCM clogs the waterways on the bit. Indications of this are higher than normal...

Coring

In petroleum drilling, geologists are asked to determine models of reservoirs. This is to determine both the size of the reservoir, as well as how much hydrocarbons the reservoir contains. Part of this modelling requires determining how various fluids will flow through the reservoir. The economics of development and the manner of development should reflect the nature of the reservoir and mistakes in the accepted reservoir model can be very costly, out weighing the cost of the odd well or two by...

Coring hardware

The following is a suggested list of hardware which should be available on site Overshot (for fishing the core barrel) Cross over (core barrel to drill collar) It would be advisable to have the following available as backup, ready for immediate dispatch should this become necessary additional spares additional core heads specialised equipment for difficult formations, i.e., soft formation catchers, vented assembly etc.

Daily costs

Daily costs are related to the time spent on the operation. On offshore rigs, they are usually the largest items of expenses and are listed below payments to drilling contractors (rig time) tool rental drilling consumables rope, soap and dope) transport of materials The Drilling Supervisor on site, the Drilling Manager and Drilling Engineers can all have an effect on daily costs.

Development

Once the information has been gained from the exploration and evaluation phases and the reservoir has been modelled to identify the amount of hydrocarbons which can be recovered, the reservoir development will be designed and the economics evaluated. At this stage, it is important to realise that limited information may be available but if the economics permit, ie development will proceed and a number of development wells will be drilled and completed. During the drilling of the development...

Disposalremoval equipment

Disposal equipment requirements will vary depending on the location of the rig and local environmental regulations. Normally, the oil and gas is flared off through burners. Some offshore locations do not permit oil burning due to environmental constraints and so the oil is flowed to a tank or barge to be transported ashore. In production tests it is becoming common for the hydrocarbons produced to be pumped to a storage tanker for transport ashore and so as to recoup some of the initial...

Drilling

The Drilling Department is responsible for the safe and efficient drilling of the well to defined targets and locations identified by Exploration and Petroleum Engineering. They are further charged with the responsibility of ensuring that all evaluation work is conducted safely and in accordance with the requirements of the other departments. In this context, there will generally be two specific functions within drilling, namely, Operations, which are responsible for the day-to-day supervision...

Drilling Operations Policies

To carry out safe and efficient drilling operations, everyone involved must be aware of the overall game plan and rules. No programme can be effectively written or carried out until these rules and objectives have been clearly stated in a Drilling Operations Policy Document. From this Drilling Operations Policy Document, the Drilling Contract, Drilling Operations Manual and the Emergency Contingency Manual can be constructed for specific operations and from these the Drilling Programme can be...

Drilling well

Having determined the rig requirement and received official approval for the well, it is now time to go to the market to select a suitable rig. As for the rig, third party services now need to be tied down contractually. At this stage, the bids received from the contractors are assessed financially and technically to establish the most suitable choice to meet the well's objectives safely, efficiently and economically. In the event that there is no obvious choice of rig, it will be necessary to...

Emergencies caused by third party acts

Deliberate acts of sabotage by determined individuals are difficult or impossible to prevent in most cases. The role of the Emergency Contingency Plan is to minimise damage and confusion should such an event take place. To create a meaningful reaction the Emergency Contingency Plan must consider and address the following points 3. Potential support from Police and Army 4. Site security and access arrangements Tc be prepared for bomb threats, the following organisation should be in place 2....

Emergency Contingency Planning

In this chapter, we look at the function and operation of emergency contigency planning. Until recently, operators would prepare these plans solely for their own use. However, more and more governmental authories are insisting on having such plans In place prior to issuing drilling permission. As managers of the drilling operation, we must be involved in the construction of the Emergency Contingency Plan. We know more than anyone about the technical problems and downhole pressures that the well...

Evaluation

The process of prospect evaluation is both expensive and will require considerable technical resources to effectively evaluate interesting reservoir prospects. The information required from an evaluation process consists of the following 1. Identification of the depositional sequence within the reservoir and information relating to the thickness and minerology of the various sediment layers. 2. Information relating to the pore space in terms of the porosity and the fluid saturations within the...

Exploration

The Exploration Department will be responsible for identifying structures for consideration for development and providing a substructure map of the prospect. The responsibility of exploration would be to further update, refine and modify the substructure map and reservoir modelling in accordance with the increased amount of data which becomes available during the development programme. The Exploration Department will further be required to provide guidance on the selection of final well...

External electrochemical corrosion

Electrochemical corrosion of casing strings occurs on casing strings set in formation with low or no electrical resistance, and in salt or salt water bearing formations. This type of corrosion requires electrical current to flow from the casing to the formation and may be very difficult to detect. Buckling is a stability failure and can occur at stress levels well below the yield stress of the material. Buckling does not occur where the casing is supported by cement. Factors responsible for...

Extracting the core

Only coventional coring will be dealt with in this section as other techniques have specialised handling methods. The details of the operation are available in any coring manual. The salient point regarding the core is to ensure that it is placed the right-way-up in the core catching trays, with the minimum of breakage or spillage. Pieces of core should be raked up using a hammer or shovel. The line of vision between the Driller and the Coring Engineer should be uninterrupted at all .times to...

Faulting folding and fracturing

In general, deformation is due to changes in tectonic stress, which can manifest themselves in a number of ways. The modification of a rock can be represented by the Bingham plastic model in terms of stress and strain, (Figure 2). Depending on individual properties of rocks and the external forces upon them, folding (ductile deformation) or faulting (brittle fracture) will result. The yield point is the point at which elasticity of the rock is overcome and permanent deformation results. The...

Folding

A Drilling Engineer must be aware of folding structures for a number of reasons. First of all, before proceeding, the terms dip and strike off a bed should be explained, see Figure 14. Dip is the maximum inclination from the horizontal of the plane. Strike is the horizontal direction at right angles to dip, 1, Hole stability problems arise if the angle of dip of beds being intercepted by the well is high. Loose formations such as shales tend to cave or slide causing holes to be unstable. The...

Overburden effect

Normally when a sediment is compacted by deep burial, fluid content and porosity is reduced. With normal sedimentation rates, expelling of fluid keeps an equilibrium with burial pressure, however, in areas of fast sedimentation, expelling of fluid may not keep up with sedimentation compression forces, causing an overpressured zone. A reduction in porosity is accompanied by an increase in bulk density. If you enter a higher pressure zone, bulk density of clays will decrease, despite consistent...

Generation Of Hydrocarbons From Organic Matter

After the initial burial of organic matter at shallow depth, it is broken down by the action of bacteria generating biogenic methane. With increasing depth, bacterial activity decreases gradually, giving way to chemical cracking. Cracking is the process in which heavy products (large hydrocarbon molecules) are transformed to light products (small hydrocarbon molecules). Under the influence of temperature, hydrocarbons are created from organic matter. Thermochemicai generation of light...

Geological Time

The idea of geological time is perhaps the first concept to master. In every drilling programme, there is at least the framework of a stratigraphical column. To the non-geologist, often this does not mean much, but in fact it is a fairly simple concept. The earth has existed for 4600 million years, which spans the entire geological time as we know it, however, hydrocarbons are rarely found on any rocks older than Cambrian, which is 500-600 million years old. This time span 0-4600 million years...

Gravity surveys

This technique, along with the magnetic technique, is generally used for regional rather than detailed geophysical assessment. Minute variations in the force of gravity are measured at surface by a gravimeter. These variations are caused by different densities of subsurface rock. Crystalline basement, generally, has higher densities than overlying sediments, therefore gravity surveys can be used to outline sedimentary basins. Older, dense rocks can also be identified by this method. For...

Testing

H.l The Drilling Supervisor has overall responsibility for the testing operation and will check all safety and gas detection equipment prior to commencing testing operations. H.2 A detailed programme for testing must be prepared and approved by the Drilling Manager. Any amendments or alterations to the testing programme must be approved in writing by the Drilling Manager. H.3 A pre-test meeting must be held on site with all the relevant company and service company personnel present. H.4 After...

Hole condition

The Drilling Supervisor should discuss any potential hole problems with the Coring Engineer prior to making up the core barrel on the rig. Any tight spots or dog-legs should be considered as potential trouble spots, especially if previous runs have been with Tricone bits on limber BHAs. Note Core barrels should be considered a stiff packed hole assembly and if there are tight spots or dog legs present, then a core barrel is much more likely to hold up than any other drilling assembly. Water...

Contingency Plan Objectives

The primary objective of an Emergency Contingency Plan is to protect life and prevent injuries. To establish the best timing for a specific drilling project. To specify the potential emergencies which can be anticipated during a specific To provide a clearly understandable list of all actions which must be taken in an emergency. To create a working organisational framework that will guarantee a rapid and effective response to an emergency. To designate the persons responsible for taking action...

Problemsolving Mechanics

Drilling problem-solving can be considered analogous to fire-fighting. Whilst there are many ways to put fires out, it is always better to prevent the fire from starting in the first place. Just as with fire-fighting, fires can be prevented by separating combustible materials from ignition sources, so drilling problems can be avoided by fore-thought and awarement of potential problems. This chapter looks at problemsolving mechanics in general and then discusses the means at our disposal to...

Suspension and abandonment

I.l All wells permanently abandoned or suspended must be left such that legislative requirements are satisfied, and potential leakage of formation fluid to surface and between reservoirs has been stopped. 1.2 All cement plugs sealing off hydrocarbons must be tested both by weight and pressure. 1.3 Before leaving an offshore location, a seabed survey must be carried out and the seabed left clear of debris. 1.4 Abandoned land sites must be restored to original condition with all top soil replaced...

Igneous rocks

These can also be described as primary rocks. They are formed from molten rock (magma) and crystallise from this melt as combinations of minerals. These combinations of minerals are related to the initial melts chemical composition and the crystallisation pressure temperature regime. Common igneous rocks are granite and basalt. The names given to igneous rocks relate to their (crystallised) constituent minerals, crystallised mineral grain size and texture. Igneous rocks are often intruded or...

Safety policies

J.l The Chief Executive of the company is responsible to the Board of Directors for the safety of all company operations. J.2 Every person employed on the rig should be provided with a copy of instructions to be followed in the event of an emergency. Such instructions should also be prominently displayed so as to be easily and frequently seen by all employees. J.3 The Drilling Supervisor must keep a log of all arrivals and departures and the purpose of any visit by non-crewmembers. J.4...

Jamming

Jamming is indicated by a sharp change in pump pressure and or torque and or rate of penetration. Any situation in which there are rapid changes in pump pressure and or torque must be watched very closely and, if there is any doubt as to the source of the fluctuation, then the core should be pulled since the recovery of core is the prime aim of the whole operation. Sometimes a core can jam with very little or no indication and what looks like the characteristic torque and pressure fluctuations...

Job planning

The following list is normally requested the equipment required by the coring service company to evaluate 2. Minimum acceptable core size 7. Expected method of core point identification 9. Special coring techniques, e.g. core orientation 10. Rig limitations - derrick height, top drive or rotary table etc. 11. Offset data - preferably core logs but bit records will do From this information, a detailed programme can be established selecting equipment to meet the job requirements. If the well is...

Security policies

K.l No information gained by or for the company before, during or after drilling operations shall be divulged to any person or persons outside the company unless it is essential for these to have this information to safely and effectively provide services for the company. K.2 No unauthorised personnel will be allowed on the rig at any time. K.3 All holes will be treated as 'tight hole' unless specified otherwise in the Drilling Programme. K.4 Only authorised personnel will be permitted in the...

Magnetic surveys

Igneous and metamorphic rocks tend to form the basement below sedimentary basins. These rocks contain ferro-magnesium minerals and so show distictions or anomalies in the earth's magnetic field. The magnitude of the anomaly is related to the distance from the source. This can be used to deduce the thickness of sediment overlying the basement. Measurement is done from aircraft which is flown in a grid pattern similar to a gravity survey. Compensation for different types of tectonic structures...

Makeup

Make-up should always follow the manufacturers guidelines. 2. Points to watch out for at this stage are the general appearance of the barrel, the ease with which joints make up. Without tearing the barrel apart, it is extremely difficult to make further inspections. 3. Before running in the hole, it is prudent to check that the safety joint has not been 'cracked' when making-up the first collar. It is not advisable to reverse in collars as this can lead to the loss of the outer barrel. Tripping...

Manual Preparation

An Emergency Contingency Manual should be prepared well in advance of operations, containing all the information required for those involved to understand their roles and functions in any anticipated emergency. In most drilling operations, this can all be contained within one manual, however, where drilling is being carried on in areas of knock-on effect, such as platforms, several manuals may be required to cover all eventualities. To be effective, the manuals must contain the following...

Natural emergencies

As with all emergencies our priorities for action are 1. The safety of personnel in the affected area or onboard the installation 2. Minimising damage to equipment 3. Minimising loss in production For all natural emergencies, the Emergency Contingency Manual should detail the following 1. The influence each emergency can have on the operations 2. How weather movements and changes will be effectively monitored 3. An effective means of evacuating installation personnel to safety In all cases, the...

Operations

The Operations Section within Petroleum Engineering provides the necessary link between operational groups within Drilling, who will be responsible for the drilling of the exploration and development wells and the evaluation and technical specialists within Petroleum Engineering for whom the well is being drilled to yield the necessary information for the reservoir modelling. The Operations Section, therefore, requires a detailed understanding of the role of drilling and also of the various...

Osmosis

This is defined as the spontaneous movement of water through a semi-permeable membrane, separating two solutions of different concentrations until the concentration of each solution becomes equal, or until the development of osmotic pressure prevents further movement from the solution of a lower concentration to that of the higher concentration. The clay layer would act as a membrane between different salinities of fluid bodies. This method, however, is thought to be restricted to a few limited...

Permeability

Permeability can be described as the relationship of the ease of fluid movement between interconnecting pore spaces. This is dependent on a number of factors, such as size and geometry of pores, density of fluid, viscosity, pressure and temperature conditions. The permeability of a rock can be reduced if more than one fluid is present. It should be noted that good porosity does not automatically have good permeability associated with it, A rock may have good porosity but poor permeability,...

Production

The production phase of a development will be intended to allow oil and gas production to proceed as follows 1. At the maximum rate and for the maximum period possible. 2. The production phase must at all times ensure maximum safety in view of personnel, capital costs and the environment. 3. There must be a continuous assessment of the production process to maximise the efficiency with which it is conducted and to ensure that minimum production costs ensue. The production phase is therefore one...

Protection Prevention And Preparation

It is essential that prior to embarking on a drilling project the following review of operations is made 1. Potential emergencies that could be encountered during the drilling project. 2. Protection requirements to limit the consequences of emergencies. 3, Preparedness for dealing effectively with emergencies, 4. Whether well timing could be altered to reduce exposure to emergencies. In many cases, natural and man-made barriers can give passive protection against the effects of emergencies, for...

Reservoir engineering

Reservoir engineering is a broad discipline and as such Reservoir Engineers will be responsible for the following areas of technology 1. The properties and performance of reservoir fluids. 2. The response of the reservoir rock to the production process. 3. Assessment of the response of a reservoir to the production or depletion process. 4. To identify and recommend the means by which oil recovery can be enhanced or improved e.g., pressure maintenance or by the use of enhanced oil recovery. In...

Sandstones

These are formed from rock fragments measuring 0.06-2 mm. Their most common constituent is quartz Si03 followed by silicates of Al, K, Na, Ca etc. Sandstones are generated in a wide variety of environments fluvial environments (rivers, streams etc.) delta fronts or channels coastal plains, barrier island, tidal channels desert and coastal aeolian plains shallow and deep marine environments About half of the world's total recoverable reserves of oil and gas occur in sandstone reservoirs.

Seafloor stability

In many areas of the world, seafloor stability can be a problem for the positioning of rigs. Knowing the depth and type of recent sediments can help give a framework to plan and overcome problems. Geological interpretation may give an indication of the depths to which it is necessary to drive a conductor for drilling in unstable sediments. Shallow gas can also be identified by bright spots on shallow seismic survey. Initial rig selection will be influenced in some areas by seafloor conditions.

Section Site Plan

A site plan should be included in each programme showing the following features For all wells The licence area in which the well is being drilled. The position of the well relative to other outstep wells. For land wells Access roads and instructions on how to reach the site. For offshore wells Details of any sea bed obstructions, pipelines etc, in the area In practice, to satisfy the above requirements, two plans will need to be included in most Drilling Programmes. Some operators like to...

Sedimentary rock type and structure

Due to the fact that most hydrocarbons produced in the world today are reservoired and generated in sedimentary rocks, it is perhaps a good idea to study them in more detail. Most sedimentary rocks are stratified or bedded i.e., occur in laid down layers. Each layer is separated from one another by a bedding plane. The attitude of this layer i.e., its dip and strike, is fundamental to interpretation of structures that may be present in rocks. Each type of sedimentary rock is formed in a set...

Sedimentary rocks

Sedimentary rocks can be described as secondary rocks and there are two basic sources jt, Deposits which are made up from the remnants of pre-existing rocks. Sedimentary rocks of this type are made of the remnants of pre-existing rocks through erosion of rocks by chemical and mechanical systems e.g., freeze-thaw, river complexes, hydraulic fracturing, sand blasting, chemical solution etc. This breakdown means that components of the existing rocks are broken from an existing body of rock and...

Seismic surveys

The most common method of exploration is seismic survey. In basic terms, it employs a source that directs acoustic energy at the rock and geophones which detect the energy waves when they reach surface. There are two types, depending on the wave path taken refraction and reflection. Reflection and refraction take place at the interface between rocks of different acoustic properties. The time taken for a seismic impulse to pass from source or shot point to the detector via the reflecting or...

Separator and metering equipment

A separator is used to separate oil, water and gas from the stream flow so that they can be individually measured and sampled. The separator should be sized according to the flow rates expected. All separators must be equipped with two relief valves and should be properly vented. Incorporated with the separator is the metering equipment for measuring the oil, water and gas. A range of orifice plates should be available on each test for measuring gas. Positive displacement or rotary meters are...

Shales

A shale is a fine grained detrital rock composed of silt and clay particles less than 1 16 mm in diameter. The most important components of shales are fine crystalline silicates of Al, Na, K and Ca with quartz, calcite and dolomite making up most of the remainder. Organic rich shales deposited under anoxic conditions can act as source rocks under favourable conditions. Due to their very low permeability, and semi-plastic nature shales also function as cap rocks or seals to oil and gas...

Side wall sampler SWS

The sidewall sampler tool is equipped with small steel cups mounted on a frame from which they are propelled by an explosive charge. The cups are forced into the formation at the shooting point and then pulled out by the tool as it is pulled clear by means of a steel wire which attaches the sample cup to the tool. The sidewall sample tool can, theoretically, be of any length, however, a typical tool will have 30 cups, all of which can be selectively shot into the formation. Clearly, the value...

Solid composition

Solids control planning will relate to the formation type being drilled. High sand content in drilling fluids from drilling may result in erosion of pump lines and circulating equipment. Proper selection of shaker screens, de-si Iters, de-sanders and centrifuges can significantly reduce use of equipment, as well as improve mud qualities. Pre-planning equipment requirements and configuration is important to cover the range of formation types expected to maximum effect. Limestones structure can...

Sticky hole

Sticky hole problems are usually restricted to tripping. If severe, they must be treated by running a bit and conditioning the hole before attempting to core. Between core runs it may be necessary to condition the hole. If the core barre is run in these circumstances, there is a likelihood of sticking and of burning the gauge of the corehead. The main problem caused by sticky formation while coring is torque on the collars or stabilisers which interrupts the smooth flow of power to the corehead...

Structural Geology

Structural geology is the result of tectonic stress. Structures vary in size from regional (hundreds of kilometers) to micro fractures (millimetres). Each type of structure is significant in structural geology as the same basic structures occur throughout a tectonic area, but on different scales. Almost all structural interpretation is based on combinations of a few basic concepts. Faulting, folding, fracturing, thrusting, are all terms used in structural geology. These terms are used to...

Treatment equipmentSolids removed in microns

De-sanders and De-silters 60- E5 + Shale shakers These are the single most important component in the system since they are the initial cuttings removal system and remove the major portion of drilled solids circulated out of the well. Double-deck shakers are fairly standard these days and they allow a course upper and fine lower screen to increase cutting removal efficiency. Mud cleaners By employing both de-silting hydrocyclones and fine mesh vibrating screens, mud cleaners effectively remove...

Use of fibre glass inner barrels

Fibre glass coring is sometimes used when coring in soft, unconsolidated formations and although fibre glass inner barrels were originally introduced to cut 30 ft sections of soft formations, they are increasingly being used in longer sections. This means that systems must be utilised to break and layout each 30 ft section safely without breaking the fibre glass or dropping pieces of core during the operation. The essential points of handling fibre glass inner barrels are 1. The section of tube...

Washouts

In the case of suspected washouts in the core barrel or drillstring, the core barrel should be lifted off bottom and the off bottom pressure recorded at the start of coring, compared with the new pressure. If this is significantly lower, and the pump rate has remained constant or has increased, the drillstring and core barrel should be pulled out of the hole and checked. Note The difference between on and off bottom pressures for surface set diamond coreheads will be much greater than for PDC...

Working With Drilling Contractors

To get the best value from a drilling contract, the operator's representative, who approves the contractor's invoices, cannot be too familiar with the contract. As mentioned earlier, the drilling contractor for all his faults, will know the contract in detail. Liberties may be taken if the operator's representative does not monitor the exact time breakdown of operations and its contractual implications. On the rig, the operator's Drilling Supervisor should go through each day's IADC report and...

Porosity

Porosity can be defined as the voids within a rock matrix expressed as a percentage of the total rock volume. There are two main porosity types primary porosity and secondary porosity. Primary porosity can be defined as the porosity when the sediment was deposited. This can further be divided into intergranular and interparticle porosity. Secondary porosity develops after the deposition of sediments. The main processes of formation being solution, fracturing and dolomitisation, A generalisation...

Neutron logs SNPCNL

These tools emit neutrons and measure how much these neutrons are slowed down by the nuclei of the formation material. Hydrogen is the most effective element in slowing down these nuclei and has the most effect on the log, regardless of what compound it is present in. Liquid hydrocarbons and water possess similar concentrations of hydrogen. Consequently, if the rock itself has minimal quanities of hydrogen in its construction and its porosity is totally filled with oil, condensate, or water,...

Metamorphic rocks

Metamorphic rocks can be formed from sedimentary, igneous or previously existing metamorphic rocks. Metamorphism is the change from one state to another. Rocks that have been metamorphosed have undergone at least one of two processes. These are change in temperature and change in pressure. The pre-existing rock's chemistry may change due to partial melting and either loss or gain of chemical components. The gain of components usually involves the addition of water, i.e. mineral hydration,...

Establishment of formation fracture gradients

As with formation pressures, prediction can be based on anticipated geology and outstep well records. Most rocks of a certain type will exhibit typical characteristics. This can be used to assist in fracture gradient estimation. It is vital to have an accurate assessment of this so that the casing design can be done in an effective manner. Once a leak-off test has been carried out in the well, equations such as 'Daines' are used by employing values of Poissons Ratio for given formations to...

Gas analysis

The Chromatograph will give an indication of the make up of the gas being tested by subdividing it into methane ethane propane butane pentanes The device does have limits to the percentages of each component that it can handle so, in some cases, it is necessary to dilute the gas sample with air prior to testing. If it is vital to know the chemical composition of the gas accurately, then it is worth stipulating flame ionisation gas detection systems. For most wells, though, the Chromatograph...

Mud Logging

Mud logging is probably the most under-utilised form of evaluation service in use today. Most rigs have Mud Loggers on board but in the author's opinion, use them to about 10 per cent of their capability. A modern mud logging unit, staffed with experienced graduate geologists, is a 'real time' database for the operator to use. They record every parameter which indicates formation, drillability, hydrocarbon presence and pressure trends. Despite this, they are still treated as the poor relation...

Coring technology

Coring is the technique of cutting a cylinder of rock and bringing it to the surface where it can be examined. The types of core barrel are many but fall into two main categories, 1. Conventional, where the entire core barrel is withdrawn to surface to recover core. 2. Wireline, where only the inner tube is brought to surface to recover the core. This is done by means of a wireline. In the petroleum industry, wireline systems are rarely utilised. This is predominately because the drillstrings...

Free point indicator FPI

This is a tool which is usually run inside drillpipe to detect the point at which it is stuck. It has a set of pads mounted at each end of the tool and a means of measuring stretch and torque between these pads once they are set against the inside wall of the drill pipe. Stretch and torque applied to the drillstring at surface will register on the tool unless the tool is positioned below the stuck point. Thus, by moving the tool progressively down this hole and applying stretch and torque, the...

Laterolog

This logging tool has a current emitting electrode positioned inbetween two long guard electrodes. A constant current of electricity is supplied to the emitting electrode and an auxilliary current of similar polarity is supplied to the two long guard electrodes. These currents are maintained so that there is no potential difference between the current emitting electrode and the long guard electrodes. Because of this, the emitted current flows directly into the formation. This current is picked...

Getting the core into the core barrel

Originally core barrels were single tube items and the advent of a double tube system, where the inner barrel was independent of the outer rotation, improved core run lengths and recovery rates dramatically. In bearing assemblies, it is generally accepted that the lower the torsional connection between inner and outer the better. Most core barrels have the inner tube hanging from a simple roller ball thrust bearing located in the top of the core barrel. The bottom of the inner tube is kept...

Production testing PT

A production test is flowing a well through tubing and surface equipment in a temporarily completed well. Its primary purpose is to collect information to predict well and reserve oil performance under future operational conditions. The well is produced according to a schedule of predetermined rates, during which bottom hole and tubing head pressures are recorded and produced fluid quantities are measured. In the course of the test, wire line formation tests (WLFT) can also be taken. Depending...

Tiedback liner

For a high pressure well, the intermediate string may simply be unable to withstand the tubing leak at surface pressures, acting in the burst mode. The solution to this problem is to run a full string of pipe to surface. Within the full string choice are two options. Firstly, to run a full string of casing, and secondly, to run a liner and tie it back. The following facts should be considered 1. Running a full string is easier, faster and hardware can be cheaper. 2. If, when running a full...

Establishment of subsurface pressure regimes

In order to proceed with well planning, the subsurface pressure regime must be established. Most sediments will naturally have a pressure profile similar to that of seawater since they were laid down in a marine environment. These formations are said to have hydrostatic pressures. Higher pressures can be encountered for several reasons such as sediment compression mineralisation surcharged formations formations can also be sub hydrostatic due to Formation pressures can be estimated from...

Contract Negotiation

Negotiation techniques are the same whether you are renting a rig or buying fruit in an Indian market. To negotiate successfully, you must know exactly what your own resources are and what you need. Furthermore, you must also try to know as much about the contractor as you possibly can. This section looks at getting the best deal from a contract by both sides. To do this, it is important to consider what both sides want from the contract. Since only one item, quiet life, is desired by both...

Contract Format And Management

The contractor rig contract on most wells represents 30-40 per cent of the overall well costs. To ensure that the operator's interests are best protected, the drilling contract is drawn up by the operator and issued complete to drilling contractors. Drilling contractors submit their bids for the work, based on the issued contract. Upon signing by both partners, the contract then forms the basis of the working relationship between operator and drilling contractor. Both partners are bound by the...

Induction log

These resistivity logs are used when drilling with either air, foam, freshwater-based muds or oil-based muds, since the induction system does not need to transmit current through the drilling fluid in use. Induction logging tools have transmitter coils which produce eddy currents by electromagnetic induction. These currents exhibit a magnetic field which induces measurable voltages in the receiver coils which are mounted elsewhere on the tool. The voltages measured by the receiver coils are...

Organisational Structure

The means by which exploration, drilling, petroleum engineering and production interface within an oil company varies between companies. In some cases, these specialisms form distinct departments within the organisation, whereas in others, the structure evolves from a limited number of departments and therefore would involve some combination of specialisms, such as exploration and petroleum engineering or well services and production. A typical structure is indicated in Figure 2 which shows the...

Drilling Economics

To optimise drilling operations, we have to specify the yardstick by which performance is measured. The most relevant yardstick is cost per metre or foot drilled. Overall cost must be looked at since individual costs can be misleading. The rig operating rate represents only a fraction of the overall cost, therefore a cheap rig day rate does not always coincide with a cheap well. Holes are drilled in the ground to provide information in the form of cores or logs or test information , to provide...

Surface flowline

A 3 inch nominal , usually 10 000 p.s.i. working pressure, steel line connects the Christmas tree to the fixed flowline. This size steel line is available for low temperature and sour service with Weco 1502 unions fitted. On floating rigs, care should be taken to ensure that the barge heave movements are accommodated by the steel line. A flexible hose is often preferred to the flexible steel line on floating vessels, because of vessel movement. Hoses with 3 inch ID, standard lengths of 30 ft or...

Land Drilling Project Management

Anyone who thinks that drilling on land is easier than drilling offshore, has probably never tried it. The planning and operational challenges in land drilling are different from those in offshore drilling bnt no less significant. Offshore rigs tend to be totally self-contained units with proven working systems and logistic support networks. Land rigs have to start from scratch on most locations and each new location presents its own particular environmental service or logistic problem....

Stuck pipe

Mechanical stuck pipe can be a problem in certain areas, particularly in thinly bedded alternative soft and hard formations. Identification of problems such as this, in certain formations, may affect the BHA choice. For directional wells, the kick-off point can be selected to avoid this problem if it is identified early enough. Differential sticking problems tend to occur in porous permeable formations particularly sands. Selection of drilling assemblies, particularly slick ones, must therefore...

Well control operations

G.l All drilling completion and workover operations will be performed with drilling fluid of such a gradient that primary control is maintained and a 'trip margin' of minimum 8 bar is incorporated. G.2 The Drilling Supervisor must ensure that the rig crew is fully briefed on all potential well control problems. G.3 The Drilling Supervisor is responsible for ensuring that all well control equipment on the rig is fully operational, tested to company standards and to those specified in the...

Contractors expenditure

Before looking at how the contractor can make money from a contract, his expenses should be understood. These costs can be broken down into 11 groups. If the contractor can, by manipulating the contract, get the operator to assist in any of the above expenses, then the contractor's profitability will increase. This concept must be fully understood by the operator to ensure that he is aware that what seems a small concession by the operator, could increase the contractor's profitability...

Auditing Effectiveness

Having established an Emergency Contingency Plan, the next step is to check its effectiveness. In practice, training has to be carried out for all personnel involved until they are fully conversant with the workings of the plan and efficient in carrying out its procedures. Training should be carried out in three formats Training sessions should be used to familiarise staff with emergency equipment and procedures and their individual role in each type of emergency. Drills should be used to check...

During the process of drilling

The primary geological information during drilling comes from the mud logging company. Maximising the use of their geological information can enhance drilling. Description of cuttings can be very important as it often shows trends in the formation sequence. It may also give an indication of a fault being crossed or of sudden changes in formation. Bulk density can be used to predict pore pressure as density decreases with increasing pressure. The shape and size of cuttings also gives an...

Preface

This book discusses all the technologies involved in managing drilling operations. Whilst looking at the obvious operational aspects of drilling oil and gas wells, it also tackles the less obvious but equally important fields of Contingency Planning, Contracts Economics, Optimisation and Problem-solving. A chapter is devoted to the creation of a Drilling Policy Document which can be used by the operating company as the back bone for its operations. Rig Selection and Acceptance is discussed in...

Oil show detection and analysis

Mud Loggers detect oil shows at two stages. Firstly, in the microscope, and secondly in the ultra violet light box. Under the microscope, some cuttings can be readily seen to be oil stained. By placing cuttings under an ultra violet light in a UV light box, oil shows can be seen between fluorescence caused by external sources such as pipe dope and that caused by hydrocarbons from downhole. From the appearance and colour of the fluorescence, an estimate of the grade of oil present can be made....

Chemical composition

The chemical composition of the rock types being drilled can have implications for Drilling Engineers. Limestones have few problems associated with them, however, calcium carbonate dissolves in water-based muds and can lead to high levels of dissolved drilling solids. Sandstones also have few chemical problems associated with them as they are largely insoluble. Shales the composition of shales is very important for Drilling Engineers. Different mineral compositions can have a marked affect on...

Of Drilling Operations

At present, as the oil industry is coming out of recession, the costs for individual types of rig is varying considerably. The table below illustrates the average cost comparisons between rig types at time of writing These figures are general and should only be used as a guide. Even though jack-up costs have been traditionally cheaper than those of semis, demand for deep water jackups has pushed their day rates above most semis. 2.1 Specific cost breakdown - offshore exploration wells To...

Reciprocation

The cement bond is of prime importance to provide isolation of different horizons within the hydrocarbon bearing formations. To give the best possible chance, the operator may want to reciprocate or rotate the liner. With reciprocation, the rig personnel must be aware of the maximum overpull permissible. Tension calculations should be reconsidered for this situation. On a heaving floating rig, reciprocation is unavoidable until the casing is landed. The likely position of the production test...

Logistic policies

C.l Only twin engined helicopters will be used over water or jungle areas. C.2 Effective communication links between Rig Site and Base Office must be maintained. A minimum of two separate means is required for offshore or remote areas. C.3 On offshore locations, a standby boat will be used at all times. This vessel should have direct communication links with the operations base, rig, helicopters, supply boats and emergency services coastguard . The vessel crew must be efficient in the picking...

Evaporite deposits

Evaporites have two roles in pressure generation 1. A passive role as a reservoir seal. 2. An active role in which sealed, pressured units can be transferred upward due to salt dipairism i.e., the upward movement of plastic salt under the force of gravity. In conclusion, the identification of abnormal pressure has an important role to play in safe drilling practices. Knowing local geology, the history of deposition of an area and the criteria under which high pressure zones form, all help to...