Well Design PDF

WELL DESIGN CEMENT DESIGN SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT  CEMENT DESIGN- CEMENT FUNCTIONS Cement is used primary as an impermeable seal material in oil and gas well drilling, it is also used for remedial or repair work on producing wells. Functions of oil well cementing The m...

WELL DESIGN CEMENT DESIGN SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT  CEMENT DESIGN- CEMENT FUNCTIONS Cement is used primary as an impermeable seal material in oil and gas well drilling, it is also used for remedial or repair work on producing wells. Functions of oil well cementing The most important functions of cement sheath are.. 1. To prevent the movement of fluids from one formation to another or from the formations to surface through the annuals between casing and borehole, 2. To support the casing string (specifically surface casing), 3. To protect the casing from corrosive fluids in the formation. 4. Close an abandoned portion of the well. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 2  CEMENT DESIGN- TYPES OF CEMENT POWER SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 3  CEMENT DESIGN- TYPES OF CEMENT POWER SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 4  CEMENT DESIGN- COMPOSITION OF CEMENT POWER 2CaOSiO2 4CaOAl2O3Fe2O3 3CaOSiO2 3CaOAl2O3 Gypsum C3S early strength, after 28 days 70% will react, C2S late strength, after 28 days 30% will react, C3A provides early high heat generation in hydration(rapid hydration), C4AF= little contribution on strength, It gives the colour of cement, CaSO4 prevents Flash Setting & retards the setting time of cement. Allows a longer working time for mixing, transporting and placing. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 5  CEMENT DESIGN- TYPES OF CEMENT POWER There are other non-API cement powder, there include. ❖ Pozmix cement: this is formed by mixing Portland cement with pozzolan ( ground volcanic ash) and 2 % bentonite, this very lightweight but durable cement. Pozmix cement is less expensive than most other types of cement and due to its lightweight is used for shallow well casing cementation operation. ❖ Gypsum cement: this type of cement is formed by mixing Portland cement with gypsum. These cements develop a high early strength can be used for remedial work. ❖ Diesel oil cement: this a mixture of one of the basic cement classes ( A, D, G, H), diesel or kerosene and a surfactant, these cements have unlimited setting times and will only set in the presence of water, consequently they are used to seal off water producing zones. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 6  CEMENT DESIGN- MIX WATER The water used to make up the cement slurry is known as mix water, the amount of mix water is based on: The need to have a slurry is easily pumped, The need to hydrate all of the cement powder, so high quality hardened cement is produced. Ensure that all of the free water is utilized to hydrate the cement powder and no free water is present in the cement sheath. If too much mix water is used the cement will not set as strong impermeable barrier, if less amount is used: 1. Slurry density and viscosity will increase, 2. The pumpability will decrease, 3. Less volume of slurry will be obtained each sack of cement. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 7  CEMENT PROPERTIES & ADDITIVES In order to fulfillment the cement functions, many properties must be achieved.. 1. Compressive strength: the casing shoe must not be drilled until the cement sheath reach compressive strength about 500 psi. the operation must be delayed whilst waiting the cement to develop this strength this waiting time called Waiting On Cement (WOC). The development of compressive strength is a function of several variables such as: temperature, amount of mix water added, elapsed time since mixing. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 8  CEMENT PROPERTIES & ADDITIVES 2. Thickening time (pumpability): the thickening time of cement slurry is the time during which the slurry can be pumped and displaced into annulus, the slurry must have thickening time to allow: mixing, pump into casing, displaced until reach required place. Wellbore conditions have a significant effect on thickening time: an increase in temperature, pressure, or fluid loss will reduce the thickening time. The thickening time of a cement slurry can be controlled with accelerators and retarders. Accelerators Retarders Calcium lignosulphanate Saturated salt solutions Sea water SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 9  CEMENT PROPERTIES & ADDITIVES SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 10  CEMENT PROPERTIES & ADDITIVES Extenders weighting agents Bentonite (2- 16%) Barite Pozzolan Hematite Diatomaceous ( 10- 40 %) Sand SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 11  CEMENT PROPERTIES & ADDITIVES There are many additives used to enhance the other properties of cement slurry such as: ▪ Friction reducing additives (dispersants): dispersants are added to improve the flow properties of slurry (lower viscosity) the most common used are: Polymers , salt, Calcium lignosulphanate ▪ Lost circulation Control agent: Materials which control the loss of cement slurry to weak or fractured formations called LCM. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 12  CEMENT JOB EQUIPMENT'S ( DOWN HOLE) In order to carry out a conventional primary cement job some special equipment must be included in the casing string as it is run.. 1. Guide shoe: A guide shoe is run on the bottom of the first joint of casing, it has rounded nose to guide the casing past any ledges or other irregularities in the hole. A float valve may be included in the guide shoe then it’s called float shoe. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 13  CEMENT JOB EQUIPMENT'S ( DOWN HOLE) 2. Float collar: A float collar is positioned 1 or 2 joints above the guide shoe, its act as a seat for the cement plugs used in the pumping and displacement of the cement slurry. The float collar also contains a non-return valve so that the cement slurry in the annuals cannot flow back up the casing. Some times The guide shoe has a non-return valve as an extra precaution. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 14  CEMENT JOB EQUIPMENT'S ( DOWN HOLE) 3. centralizers: These are hinged metal ribs which are installed on the casing string as it is run, their function is to keep the casing away from the borehole, the proper distribution of centralizers help to.. ▪ Improve displacement efficiency, ▪ Prevent differential sticking, ▪ keep casing out of key-seats. The centralizer is prevented from moving up & down the casing by positioned it across a casing coupling or a collar known as a stop collar ( in deviated section). SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 15  CEMENT JOB EQUIPMENT'S ( DOWN HOLE) 4. Scratcher: These are devices run on the outside of the casing to remove mud cake and break up gelled mud, they are some times used through the pay zone. 5. Cement basket: Cement basket protect weak formation from excessive hydrostatic pressure that exerted by the long cement column, it is positioned above the weak formation (stop collar may used). SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 16  CEMENT JOB EQUIPMENT'S ( DOWN HOLE) 6. Cement plugs: There are two types of cement plugs: The first called wiper/ bottom plug is pumped down before the cement to wipe the inside of the casing, when the bottom plug reaches float collar its rubber diaphragm is ruptured allowing the cement slurry to flow the plug. Bottom plug The second plug called shut-off/ top plug its pumped after the cement slurry, when it reaches the float collar it lands on the bottom plug and stops the displacement process. Top plug SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 17  CEMENT JOB EQUIPMENT'S ( SURFACE) 7. Cement head: The cement head provides the connection between the discharge line from the cement unit and the top of casing, this piece of equipment is designed to hold the cement plugs used in conventional primary cement job, and release them in the appropriate phase in the cement job. The cement jobs will be unsuccessful if the cement plugs are installed incorrectly, or are not released from the cement head. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 18  CEMENT JOB EQUIPMENT'S ( SURFACE) SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 19  CEMENT PLACEMENT TECHNIQUES Conventional Single stage Reverse- cement circulation Cement techniques Cement casing string Multi-stage Primary cement Inner string Cement liner string Balanced plug Cement plug Secondary/ Dump bailer remedial Low pressure Squeeze squeeze cement High pressure squeeze SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 20  CEMENT PLACEMENT TECHNIQUES (PRIMARY) The objective of a primary cement job is to place the cement slurry in the annulus behind the casing, in most cases this can be done in a single operation; by pumping cement down the casing through the casing shoe and up the annulus. However in longer casing strings and in particular where the formations are weak and may not be able to support the hydrostatic pressure of cement column, the cement job may be carried out in two stages. In the first stage the lower portion of annulus is cemented, the rest of annulus will be cemented in the second stage which start after the cement of first stage is set. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 21  CEMENT PLACEMENT TECHNIQUES (PRIMARY) Single stage cement: » SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 22  CEMENT PLACEMENT TECHNIQUES (PRIMARY) Multi-stage cement: When cementing long cement string; The multi- stage cement reduce: ❑ Long pumping time, ❑ High pump pressure, ❑ Excessive hydrostatic pressure. Cement Basket can be used and Positioned under the multi-stage collar » SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 23  CEMENT PLACEMENT TECHNIQUES (PRIMARY) Inner string cement: For large diameter casing conventional cement placement result in: ❑ Large potential cement contamination during pumping and displacement, ❑ large cement plugs can be stuck, ❑ large displacement volumes, ❑ long pumping time, ❑ large cement left at shoe track. No plugs are used in this type, also a special type of float shoe is used rather than conventional float shoe and float collar. The cement string is generally tubing or drill pipe this job also called stinger. » SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 24  CEMENT PLACEMENT TECHNIQUES (PRIMARY) Liner cement: Liners are run on pipe and therefore the conventional cementing techniques cannot be used for cementing a liner, the liner string has a conventional float collar and float collar, in addition to special equipment must be used to carry out liner cement job. » Reverse-circulation cement: This method has been used when extremely low-strength formations were present near the bottom of the hole, A special type of float collar or shoe as well as special well head assembly is required, so cement plugs are not used. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 25  CEMENT PLACEMENT TECHNIQUES (PRIMARY) Top of cement: The height of the cement sheath, above the casing shoe, in the annulus depends on the particular objectives of the cement operation. In the case of conductor and surface casings the whole annulus is generally cemented so the casing is prevented from buckling under the axial loads produced by the weight of the well head and BOP. In the case of intermediate casing and production casing the top of cement ( TOC) is generally selected to be approximately 300 – 500 feet above any formation that could cause problems in the annulus of the casing string being cemented. For formations that contain gas which could migrate to surface in the annulus would be covered by the cement. Liners are generally cemented over their entire length. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 26  CEMENT PLACEMENT TECHNIQUES (SECONDARY) Remedial cementing is undertaken to correct issues with the primary cement job of a well. Remedial cementing requires as much technical, engineering, and operational experience. Squeeze cement: Squeeze cementing is the process by which hydraulic pressure is used to force cement slurry through holes in the casing and into the annulus and/or the formation, the main application of squeeze cementing are: ▪ to seal off gas or water producing zones, ▪ to repair casing failure, ▪ to seal off lost circulation zones, ▪ to carry out remedial work on poor primary cement job, ▪ to prevent fluids escaping from abandoned zones. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 27  CEMENT PLACEMENT TECHNIQUES (SECONDARY) During squeeze cement the pores in the rock rarely allow whole cement to enter the formation since a permeability of about 500 decries would be required. There are two process by which cement can be squeezed: A. High pressure Squeeze: in this type the formation is fractured which then allows the cement slurry to be pumped into the fractured zone, B. Low pressure squeeze: in this type the fracture pressure of formation is not exceeded. Cement slurry is placed against the formation, and when the pressure is applied the fluid content ( cement filtrate) is squeezed into the rock, while the solid content (filter cake) builds up. The squeeze cement can be conducted with packer for low and high pressure squeeze; the packer is applied in low pressure squeeze for more accurate positioning of cement, whereas in high pressure the packer is prevent pressurizing all casing string and wellhead, or without packer for low pressure squeeze and this techniques called Braden-head. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 28  CEMENT PLACEMENT TECHNIQUES (SECONDARY) Squeeze cement with packer Squeeze cement without packer SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 29  CEMENT PLACEMENT TECHNIQUES (SECONDARY) Cement plugs: A cement plug is designed to fill a length of casing or open hole to prevent fluid movement, cement plug is utilized for: ▪ Abandoning depleted zones, ▪ Providing a kick off point for directional drilling, ▪ Isolating a zone for formation testing, ▪ Abandoning entire well, ▪ seal of loss circulation zone ( thief zones) The major problem when setting cement plugs is avoiding mud contamination during placement operation. After the cement has hardened the final position of the plug should be checked by running in and tag the TOC. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 30  CEMENT PLACEMENT TECHNIQUES (SECONDARY) There are two techniques for placing cement plugs A. Balanced plug: this method is aimed to achieved an equal (balance) level of cement in the drill pipe and the annulus. B. Dump bailer: A dump bailer is an electrically operated device which is run on wire line. A permanent bridge plug is set below the required plug back depth. The advantages of this method are: ❖ High accuracy of depth control, ❖ Reduce the risk of contamination of the cement. The disadvantages are: ❖ Only small volume of cement slurry can be dumped at a time, ❖ Not suitable for deep wells, unless retarders used. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 31  CEMENT PLACEMENT TECHNIQUES (SECONDARY) Balanced cement Dump bailer SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 32  CEMENT CALCULATION The following calculations must be undertaken prior to cement operation: ❖ Slurry requirements, ❖ No. of sacks of cement, ❖ Volume of mix water, ❖ Additives requirements, ❖ Displacement volume, ❖ Duration of operation. The most important parameter is the slurry requirements, all calculations is depends on it. The slurry requirements concept is differ from cement techniques to another, in this course the conventional single stage requirement will only be covered. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 33  CEMENT CALCULATION Slurry requirements: The cement slurry volume must fill the shaded area In the figure: Therefore the volumetric capacity and length of various sections must be known. In addition to the calculated volumes an excess of slurry is added, the excess is added to accommodate any error may arise due to inaccurate size of open hole due to wash out, or some losses may countered. The excess is commonly 10 – 20 % of open hole volumes. For single conventional cement job: 𝒔𝒍𝒖𝒓𝒓𝒚 𝒗𝒐𝒍𝒖𝒎𝒆 = 𝒔𝒉𝒐𝒆 𝒕𝒓𝒂𝒄𝒌 + 𝒓𝒂𝒕𝒆𝒉𝒐𝒍𝒆 + 𝒄𝒔𝒈 𝒗𝒔 𝒉𝒐𝒍𝒆 + 𝒄𝒔𝒈 𝒗𝒔 𝒄𝒔𝒈 SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 34  CEMENT CALCULATION No. of Sacks (No. sxs.): 𝑇𝑜𝑡𝑎𝑙 𝑣𝑜𝑙. 𝑜𝑓 𝑠𝑙𝑢𝑟𝑟𝑦 𝑁𝑜. 𝑠𝑥𝑠 = 𝑌𝑖𝑒𝑙𝑑 𝑜𝑓 𝑐𝑒𝑚𝑒𝑛𝑡 × 94 The Yield of cement is amount of cement slurry that can be produced from a sack of cement Water requirement: 𝑀𝑖𝑥𝑤𝑎𝑡𝑒𝑟 𝑣𝑜𝑙. = 𝑚𝑖𝑥 𝑤𝑎𝑡𝑒𝑟 𝑝𝑒𝑟 𝑠𝑎𝑐𝑘 × 𝑁𝑜. 𝑠𝑥𝑠 Additives requirement: 𝑁𝑜. 𝑠𝑥𝑠. 𝑜𝑓 𝑎𝑑𝑑𝑖𝑡𝑖𝑣𝑒𝑠 = 𝑁𝑜. 𝑠𝑥𝑠. 𝑜𝑓 𝑐𝑒𝑚𝑒𝑛𝑡 × % 𝑎𝑑𝑑𝑖𝑡𝑖𝑣𝑒 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑎𝑑𝑑𝑖𝑡𝑖𝑣𝑒 = 𝑁𝑜. 𝑠𝑥𝑠. 𝑜𝑓 𝑎𝑑𝑑𝑖𝑡𝑖𝑣𝑒 × 94 𝑙𝑏Τ𝑠𝑘 SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 35  CEMENT CALCULATION SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 36  PRIMARY CEMENT EVALUATION A primary cement job can be considered a failure if the cement does not isolate undesirable zones, this may happen if: ▪ The cement does not fill the annulus to the required height. ▪ The cement does not provide good seal between casing and borehole. ▪ The cement does not provide good seal at the casing shoe. When any failures occur some remedial work must be carried out. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 37  PRIMARY CEMENT EVALUATION A number of methods can be used to assess the effectiveness of cement job: Detecting the top of cement: A. Temperature surveys: this involves running thermometer inside the casing after cement job, the thermometer responds to the heat generated by the cement hydration. B. Radioactive surveys: Radioactive tracers can be added to the cement slurry before it is pumped, the top of cement is detected by identifying where the radioactivity decreases to background natural ranges. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 38  PRIMARY CEMENT EVALUATION Detecting TOC and cement bond quality : A. Cement bond logs (CBL): the CBL tool detects TOC, along with indicating how good the cement bond is. The CBL tool is basically a sonic tool which is run on wire line, the logging tool must be centralized in the hole to give accurate results. Both the time taken for signal to reach the tool receiver and the amplitude of returning signal since the speed of sand is greater in casing than formation or mud the first received signals traveled through casing, if the amplitude is large (strong signal) this indicates that pipe is free (poor bond), when the cement is firmly bonded to the casing and formation the signal amplitude is decreased. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 39  PRIMARY CEMENT EVALUATION B. Variable Density Log (VDL): the CBL log gives an amplitude and provide an indication of the quality of the bond between casing and cement, A VDL provides the wave train of the received signal, and can indicate the quality of the cement bond casing/cementing and cementing/formation. Casing arrivals present as parallel lines. Formation arrivals present as wavey lines. Mud arrivals present as parallel lines. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 40  PRIMARY CEMENT EVALUATION SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 41  PRIMARY CEMENT EVALUATION SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 42  PRIMARY CEMENT EVALUATION VDL/CBL interpretation summary Condition CBL response VDL response Good bond to casing Low No casing arrivals, Strong formation arrivals and formation No cement / free pipe High Strong casing arrivals, No formation arrivals Poor bond to casing Medium to high Strong casing arrivals, No formation arrivals Micro annulus Medium to high Casing arrivals, formation arrivals Good bond to casing low No casing arrivals, No formation arrivals Not to formation Channelling Medium to high Casing arrivals, formation arrivals SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 43  SECONDARY CEMENT EVALUATION After the secondary cement has hardened it must be pressure tested, the tests should be include both positive and negative differential pressure as follow: A. A positive pressure test can be performed by closing BOPs and pressuring up on the casing. ( do not exceed formation strength). B. A negative pressure test (inflow test) can be performed by reducing the hydrostatic pressure inside the casing, this can be done using DST tool or by displacing the well fluid by lighter fluid ( e.g. Diesel), this test is more meaningful since mud filled perforations may hold pressure from the casing, but may become unblocked when pressure from the formation is applied. SUST | CPET | PETROLEUM ENGINEERING DEPARTMENT 44