Water base mud

Water base mud

Consists of:

1-Liquid water, continuous phase

2-Reactive solids, for viscosity and yield point

3-Inert solids, for density

4- Chemical additives, to control properties

Hydration of clays

•Clays with high cation exchange capacity exchange large amount of water into the exchangeable layer and adsorb water onto the outer surface of plates

•This effect gives high viscosity and high yield point

•Adsorption of water causes a very sticking expansion of clay

•Overall hydration transform clay from dry power to plastic slurry

•Clay yield depends on: purity, nature of atoms in exchangeable layers and salinity of water

Bentonite and attaplugite

•Bentonite consists primarily of montmorillonite

•Came from French town Montmorillon, where first mined 1874

•Basic structure is close to pyrophllite.

•There are a small number of exchangeable ions, sodium calcium and magnesium

•Most common bentonite are those with sodium and calcium as exchangeable ions

•Attapulgite belongs to a different family of clay minerals

•Instead crystallizing as platy crystals, it forms needle like crystals

•Have excellent viscosity and yield strength when mixed with salt water

•Disadvantage is suffering high water loss and poor sealing properties

Dispersion, flocculation and defloccullation

•Agitating of clay suspension in water gives three modes: edge to edge; face to edge; and face to face

•Dispersion occurs with no face or edge association

•It results in increase in viscosity and gel strength

•Aggregate occurs with face to face association

•Aggregate results in a decrease in viscosity and gel strength

•Flocculation occurs with face to edge association

•It causes excessive gelation

•Flocculation can be broken by chemical thinners

•The resulting suspension is called deflocculated

Inert solids

•Include low gravity and high gravity

•Low gravity include sand and chert

•High gravity are added to increase mud weight or density

• Referred to as weighting materials

•Mud named as weighted mud, they are:

                                1)Barite (barium sulphate, BaSO4) sp.gr. 4.2

                                   Used to prepare mud in excess of 10 ppg

                                  Refened to as weighting agent for low cost and high purity

2)Lead sulphides (galena) sp.gr. 6.5-7.0

• Allowing mud weight up to 35 ppg

•Iron ores, sp. gr. 5+ More erosive

• Contain toxic materials

 

 

 

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Drilling Fluids Functions

–They  

 

1-Cool the drill bit and lubricate its teeth
2-Lubricate and cool drill string
3-Control formation the pressure
4-Carry cutting to the surface
5-Stabilize the well bore
6-Help in the well logs
7-limitting corrosion

1-Cool bit and lubricate its teeth

  

•Drilling action requires mechanical energy in form of weight on bit, rotation and hydraulic energy

•Large part of energy dissipated as heat

•A Heat must be removed to allow drilling

•Mud helps remove heat

•Mud helps remove cutting between the teeth and prevent bit balling

2-Cool and lubricate drill string

•Rotating drill string generates heat

•Mud help dissipate heat from hole

•Mud absorbs heat by convection and release it by radiation

•Mud lubricate drill string and reduce friction

 

 3-Control formation pressure

•For safe drilling, high formation pressures must be contained within the hole to 

prevent damage and injury

•This achieved by hydrostatic pressure of mud

•Mud pressure should be higher than formation pressure

•An overbalance of 100-200 psi is used

•Pressure overbalance id referred as chip hold down pressure

    (CHDP)

•Penetration rate decreases as CHDP increases

•For abnormal pressure CHDP becomes negative and kick will happen

 

4-Carry cutting to surface

 

•Cutting generated by the bit must be removed

•Drilling mud carries cutting form bottom to surface

•A Carrying capacity depend on annular velocity, plastic viscosity and yield 

point of mud and slip velocity of generated cutting For power law fluid

 

 5- Stabilize the wellbore  

•Good mud cake stabilize the hole

•Differential pressure between mud and formation keep hole stable

•Reduce drilling time also help keep hole stable

 

 6-Help in the evaluation 

 
and interpretation of the well logs

•During logging mud fill the hole

•Logs used to detect hydrocarbon, measure porosity, formation ,pressure

•Mud should posses properties that help evaluate these properties

•Water base -mud  is  better  for  electric  logging  

7-Limiting corrosion

•The drilling  fluid in most cases  will have water which contain dissolved salts

•This serves as a medium for corrosion

•Precautions should be taken  to prevent  damage  of the  equipment

•Mud containing oil as the continuous phase may decrease

   or  prevent corrosion  completely

 

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Perforation (6)(SAFETY PROCEDURES)

2.7. GENERAL SAFETY PROCEDURES

The following comments are applicable to both TCP and wireline conveyed methods.

Additional comments are given in section specific to wireline conveyed perforating.
 

a) All perforating operations, since they involve the handling and use of explosives and possibly radioactive materials, require special safety procedures to be strictly observed at all times.

b) Perforating operations should be carried out strictly according to the safety policies of Eni-Agip and the perforating Contractor. In the event of any inconsistency between policies, the most conservative policy will apply.

a) Operations involving the use of explosives shall only be performed by

Contractor’s specialized personnel responsible for perforation and similar operations. The number of persons involved shall be as low as possible.

b) Only perforating Contractor’s personnel are allowed to remain in the hazardous area (gangway, rig floor etc.) during arming of guns. The number of personnel should be limited when the guns are within 500ft of surface when tripping in and out of the hole.

c) Any operation involving the use of explosives is not allowed in the presence of thunder, lighting and thick fog, as these are sources of electric potential.

d) Explosives shall be kept on site for the shortest possible time, any remaining at the end of the operation shall be removed from the installation.

e) Explosives shall be stored on site in proper containers, within a confined area on the rig. Detonators shall be stored in separate boxes, in the same area as explosives.

f) Warning signs must be placed around the hazardous area where explosives are used.

g) All radio transmitters, radio beacons included, within a radius of 500ft from the well, shall be turned off, (since they may detonate blasting caps), starting from gun arming until perforating guns are 500ft below the sea bottom (similarly, when pulling guns out of hole and guns above 500 ft). All portable transmitters (both Eni-Agip’s and Contractors) shall be placed inside the Eni-Agip office and turned off to avoid accidental transmission. Avoid critical periods of perforating coinciding with arrival and take-off of helicopters.

h) Cranes and welding machines shall be put out of service starting from gun arming till gun pulling out and unloading.

i) District Office shall be advised by the Well Operations Supervisor on the estimated time of radio silence two hours before starting operations. The Radio Operator shall communicate actual timing.

j) Casing perforating can be performed during daylight or at night. However, the first series of shots must be carried out in daylight hours. Before perforating casing, the acceptable cement job quality shall be ascertained by means of CBL/VDL and/or by squeeze jobs.

k) Explosives are to be transported unarmed and clearly labeled to the site in secure and protective containers. Extreme care must be applied during loading and off-loading.

l) At the rig it is the responsibility of the Installation Manager to ensure that these precautions are taken.
 

2.7.1.Firing Systems for TCP Operations

It is normal practice to run the TCP guns with two firing systems, whenever possible, to improve the chance of a successful operation especially when running the guns on the bottom of a completion. A common combination is to use a tubing pressure actuated system as the primary means of detonating the TCP guns with a mechanical system as the back up. There are four main types of firing mechanisms for TCP guns. Only top down firing mechanisms should be used for safety when arming the guns. The operation of each firing mechanism is:

2.7.2. Tubing Pressure Activated

The guns are fired by pressuring up the test string and then bleeding off the pressure immediately. A time delay device is incorporated to allow time to bleed off. This device can be either hydraulic or a slow burning fuse. Some of the firing heads for this system are wireline retrievable which gives another back up option. However, this would preclude the

use of the drop bar system as a back up. Although this technique could be expensive on nitrogen, it is well suited to the use of a nitrogen cushion but the time delay on the system will have to be increased to allow time for the nitrogen cushion to be bled off.

2.7.3. Mechanical Impact

The TCP guns are detonated by the mechanical impact of a firing bar, which for safety must be run on wireline. (This system is colloquially known as the drop bar system.) Since the system can be affected by debris in the tubing, the completion fluid must be kept clean. The system is preferred as a back up instead of the primary firing mechanism because of the need to use wireline.

2.7.4.Electrically Activated

With this system, the guns are fired with an electrically-initiated detonator which must be run on a logging cable. Therefore the pressure control system must be rigged up. Since an inductive or wet electrical connection must be made at the firing head, the system is also susceptible to debris. This system is rarely used on well tests as the only is that the firing heads for this system are wireline retrievable, hence the guns can be run unarmed and, in the case of a misfire, the firing head can be recovered on wireline to determine the cause of the misfire.

2.7.5. Retrievable Slick line Firing Head

This type of head was primarily designed to overcome the concerns over about the possibility of guns being denoted by stray pressure or tools/debris/unnamed articles which could fall down through the tubing string and force the detonating pin into the initiator. With this type of head, this possible problem has been completely eliminated due to the design of the system. The guns are run in the hole without the firing head. Then, when ready to arm the guns, the head is run to depth on slick line and latched on to the firing stem or stinger. This system

provides its own back-up in that if the firing head does not work, it can be retrieved and a replacement run.

Retrievable firing heads are available with mechanical, hydraulic or electric triggering.

Safety

Working with explosives is one of the most dangerous professions. While working with explosives you must concentrate on what you are doing. You must perform each step carefully and correctly. Because when shortcuts are taken, when concentration is broken, when communication fails, when respect for explosives is ignored, when instructions in the book are ignored, accidents can happen and they do happen.

Safe operating practices are critical to the long-term success of perforating.

Any deviation from these procedures can put lives and properties in danger. If precautions are not taken, the danger of premature detonation may occur!

Oil and gas are our main sources of energy and in all probability will be for a long time. The oil and gas industry is involved in finding and exploiting underground deposits of oil and gas in addition maintenance of the equipment used to provide a passage for hydrocarbon to flow from reservoir to the surface is also critical.

Due to the nature of work involved, hazards typical to the oil and gas industry operations exist. Therefore, in the oil and gas industry work and safety must go hand –In -hand.

Safety measurement includes:

Properly designed, constructed and tested equipment

Well-trained, highly qualified personnel

All perforating crew members receive training on the characteristics of the explosives they use and proper techniques for handling and transporting these explosives .perforating engineers and technicians also need to be proficient in the specialized process of gun arming and disarming. They should thoroughly understand procedures and applicable local regulations. In addition, only the engineer or technicians is permitted to arm or disarm the perforating guns on a perforating job.

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perforation (5)(WIRELINE DEPTH CONTROL)

WIRELINE DEPTH CONTROL

Depth control for perforating is almost universally obtained through radioactivity instruments run in the cased hole in conjunction with the Casing Collar Locator (CCL). The Gamma Ray Log is generally used (Figure B28) though, in some cases, the Neutron Log or both Gamma Ray and Neutron are run. Accurate correlation of radioactivity logs with open hole logs establishes the position of casing collars with respect to the formation to be perforated. A short sub in the casing string is highly desirable to eliminate ambiguities with CCL identification, particularly when all joints of casing are about the same length. If the depth control log is made on a separate trip in the well, the proper shooting depth is determined on the perforating run by recording a second collar log with the collar locator attached to the perforator.

2.6.1.1. Gun-Gamma Ray Tool

If the combination Gun-Gamma Ray Tool is used, the entire equipment for depth control and perforating is run on a single trip in the well. The Gun-Gamma Ray Tool includes a rugged, shock proof gamma ray detector. A casing collar locator and a perforating gun can all run together. This offers greater assurance of accuracy and considerable saving of rig time. Depth control should always be used to accurately position TCP guns. A reference radioactive collar is run in the work string and its distance from the top shot is measured. Once on bottom, a through-tubing GR/CCL log is run and compared to open hole logs to establish how guns should be moved for exact positioning opposite the target formation. A variation of this procedure has been used from floating vessels in sand control completions. A sump packer is positioned and set with a wireline and becomes the locating device. The TCP gun string then is run with a locator and collet assembly on bottom. The distance from bottom gun shot to the collet latch is selected to place guns on depth. A radioactive collar should still be run to allow adjustment by logging in case of pipe tally discrepancies or slippage of the sump packer downhole.

2.6.2.2. Precision Identified Perforations

P.I.P. tags are used to provide a record of the position of perforations with respect to casing collars and/or formation boundaries. Special shaped charges fired at top and bottom of the perforated section leave traces of radioactive material within the perforations. The top and bottom perforations are then identified by sharp peaks on a Gamma Ray curve after perforating. Small size, low activity and short half-life of radioactive material used in the special charges prevent significant contamination of produced fluid. When run with Gun-Gamma Ray tool and Hollow Carrier perforators, no additional rig time is required other than that needed to log through the perforated interval.

2.6.2.  TCP DEPTH CONTROL

Four main techniques are used to ensure that the guns are at the correct perforating depth:

- Running a through-tubing gamma ray collar locator to locate a reference point in the string and tie into openhole logs.

- Setting the packer on wireline at a known depth, and stinging through the guns and completion string.

- Setting the packer and guns on wireline at a known depth, and stabbing the completion string in the packer.

- Tagging a fixed and accurate reference point such as a bridge plug. The first method is the most accurate. It relies on a radioactive marker sub in the string, and the distance from the radioactive marker sub to the top shot being precisely measured at surface. The string is run in the hole to approximately the correct depth and a short section of GRCCL (Gamma Ray-Casing Collar Locator) log is run over the zone where the sub is located. The gamma ray log indicates the position of the sub (a short radioactive peak anomaly) relative to the formation gamma ray as shown in Figure B30. As the distance from the sub to the top shot is known, the position of the guns can be calculated, and corrected if necessary by spacing out the string at surface. After the packer is set, the gamma ray may be rerun to ensure that the guns are at the correct depth. Fig. B30: TCP Depth Control Log.

As the cased hole gamma ray log can be considerably attenuated, a low logging speed will achieve better correlation results between the cased hole and the open hole gamma ray logs. If the formation gamma ray curve does not show much activity, a radioactive pip tag may be placed

As the cased hole gamma ray log can be considerably attenuated, a low logging speed will achieve better correlation results between the cased hole and the open hole gamma ray logs. If the formation gamma ray curve does not show much activity, a radioactive pip tag may be placed in or below one casing joint. (Placement of the pip tag must be included in the casing setting program.) Alternatively, a TDT or a neutron log can be run in place of the gamma ray log.

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Perforation (3) (Explosives Classifications)

Explosives Classifications

Explosives were invented first by the Chinese in the 10th century, then independently by the Arabs in the 13th century. The low explosive, or black powder, was characterized by slow reaction rates, 500 to 1500 m/sec, and relatively low combustion pressure. Much later, in 1846, the first high explosive was discovered by an Italian, Ascanio Sobreto, and then made commercially by Alfred Nobel in 1867 with the development of dynamite, a combination of nitroglycerin and clayey earth. High explosives, unlike the earlier low explosives, detonate at very rapid rates of 5000 to 9000 m/sec and generate tremendous combustion pressures. The terms low and high explosive are still used to characterize chemical explosives.

2.4.1.Low explosives (propellants)

 Are used in modern oilfield applications as power charges for pressure setting assemblies, bullet perforators and sample taker guns as well as for stimulation (high-energy gas fracturing, perf wash, etc.). High explosives are found in shaped charges, the detonating cord and detonators, and blasting caps.

2.4.2.High explosives 

 are further classified by their sensitivity or ease of detonation. 

2.4.2.1. Primary high explosives 
 are very sensitive and easily detonated by shock, friction or heat. For safety reasons, primary high explosives, such as lead azide, are used only in electrical or percussion detonators in Schlumberger gun systems.

2.4.2.2. Secondary high explosives  

are less sensitive and require a high-energy shock wave to initiate detonation (usually provided by a primary high explosive). Secondary high explosives are used in all other elements of the ballistic chain (detonating cord, boosters and shaped charges). PETN, RDX, HMX and HNS are secondary high explosives used in oilwell perforating. The rate of reaction, combustion pressure and sensitivity of chemical explosives are affected by temperature. Consequently, maximum safe operating temperatures are defined for all explosives. Exceeding temperature ratings may result in autodetonation or reduced performance. The table below lists the 1- and 100-hr temperature ratings and uses for the various explosives in gun systems.
 

2.4.3. Effect of temperature

Temperature affects the rate of reaction, combustion pressure and sensitivity of chemical explosives. Consequently, maximum safe operating temperatures are defined for all explosives. Exceeding the optimum temperature rating may result in autodetonation or reduced performance.

The table lists the 1-hr and 100-hrtemperature ratings and uses for the various explosives in schlumberger gun systems.

 

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