Standard -175
August, 1999
CEMENTING OPERATIONS
Prepared by
Committee on Cementing Operations
Oil Industry Safety Directorate,
2nd Floor Kailash,
26, Kasturba Gandhi Marg,
New Delhi - 110001
FOREWORD
The Oil Industry in India is 100 years old. Because of various collaboration agreements a variety of international codes, standards and practices have been in vogue. Standardization in design philosophies and operating and maintenance practices at a national level was hardly in existence. This coupled with feed back from serious problems that occurred in the recent past in India and abroad , emphasized the need for the industry to review the existing state of art in designing, operating and carrying out the cementing operations in an Oil well.
With this in view , the Ministry of Petroleum and Natural Gas in 1986 constituted a Safety Council assisted by the Oil Industry Safety Directorate (OISD) staffed from within the industry in formulating and implementing a series of self regulatory measures aimed at removing obsolesce , standardizing and upgrading the existing standards to ensure safe operations. Accordingly, OISD constituted a number of functional committees of experts nominated from the industry to draw up the standards and guidelines on various subjects.
The present standard on “Cementing Operations” was prepared by the Functional Committee on “Cementing Operations”. This document is based on the accumulated knowledge and experience of industry members and the various national and international codes.
The standard is meant to be used as supplement and not as a replacement for existing codes and practices.
It is hoped that provisions of the standard if implemented objectively, may go a long way to improve the safety and reduce accidents in Oil Industry. Users are cautioned that no standard can be a substitute for the judgment of responsible and experienced engineer.
Suggestions are invited from the users after it is put into practice to improve the document further. Suggestions for amendments to this document should be addressed to the Coordinator, Committee on “Cementing Operations”, Oil Industry Safety Directorate, Kailash Building, 26- KG Marg, , New Delhi-110001.
This standard in no way supersedes the statutory requirements of bodies like DGMS, CCE or any other Government Body which must be followed as applicable.
COMMITTEE FOR
PREPARING STANDARD ON
CEMENTING OPERATIONS
------Name Position in Committee
------
1. Shri A.K. Hazarika Leader
2. Shri A.K. MehraMember
3. Shri N.K.TyagiMember
4. Shri T.H. MazumdarMember
5. Shri D.K. RajkhowaMember
6. Shri T.SinghCoordinator
------
CONTENTS
PAGE NO.
1.INTRODUCTION1
2.SCOPE1
3.OIL WELL CEMENT SELECTION CRITERIA 1
4.CEMENT EQUIPMENT 3
5.PRIMARY & SECONDARY CEMENTING PRACTICES5
6.WELL ABANDONMENT PROCEDURE 17
7.CEMENTING SAFETY GUIDE LINES19
8.CHECK LIST OF CEMENTATION JOB22
9.TRAINING25
10.REFERENCES27
1
1.0INTRODUCTION:
Cementing is one of the most critical phases of well completion. It is difficult to imagine the drilling and completion of a well without the successful cementation jobs. Cementing of an oil/gas well is highly precise and complex job. So, from the safety and economic point of view the best available technical development should be applied directly to the operational areas with practical approach.
One of the objectives of this cementing operational standard is the formulation of concrete practical & implementable recommendation. Success or failure of primary cementing operation is normally influenced by safe planning and its execution. Therefore, it is expected that this recommendation based on standard safe practices of cementation both onshore as well as offshore wells will provide a valid support to the managers, supervisors and operators in further improving the planning, execution and evaluation stages of cementing operations.
Utilising the practical observations of cementing specialist and making liberal use of recent published literature, this is an attempt to frame specification for the safe cementing practices and procedures which are widely accepted standards in oil industry. A positive cementing philosophy, attitude, commitment, dedicated job involvement, vigilant supervision, quality control and team efforts must be developed and executed to get good quality and safe cementation job.
2.0SCOPE
Presenting a general overview of the fundamental cementing technique, these articles are designed to provide the oil field people with a basic knowledge of many things that influence quality and safety aspect of cementing operations. Systemisation, micro-planning, proper supervision, engineered concept and related safety measures applied religiously during the job execution may give positive effect on the success of cementing.
The important consideration associated with cementing are covered under seven articles. The opening article discusses physical and chemical properties of oil well
cement, packaging, handling and storage tips of cement and additives. The functional concepts and application engineering of various cementing equipment are also explained in brief. Basic fundamental practices for primary and secondary cementing are presented with various factors which contribute to cementation failure or success. Topics like recommended well abandonment procedure of onshore and offshore fields, cementing safety guidelines and checklist can help in the effort to eliminate accidents and failures during cementing jobs. Training needs at all levels are also highlighted to keep pace with technical progress and to create safe working culture.
It is believed that greater attention should be given to the planning, supervising and developing more efficient and safe cementing technique. The best results may be obtained by the basic fundamentals and using sound judgement in the execution of the job without trying short cuts.
3.0.0OIL WELL CEMENT SELECTION CRITERIA
OIL WELL CEMENT:
Oil Well Cement is equivalent and conforming to API - 10 specification for "Material and Testing of Oil Well Cement" 3rd Edition July 01,1986.
3.1.0 DEFINITION:
Oil well cement must conform to all chemical, physical and mandatory specifications laid down by API which are as under:
3.2.0 PHYSICAL REQUIREMENTS:
a)Water requirement for making slurry, water % by weight of cement. - 44%
b)Soundness (autoclave expansion)), - 0.8% maximum
c)Free water content percent by volume - 1.4%(max)
d)Compressive strength after 8 hours curing time at Atmospheric pressure and Curing temperature
I. At 38C 300psi (min)
II. At 60C 1500psi (min)
e)High pressure, High temperature Thickening Time test: Thickening Time at temperature 52C and pressure 5160 PSI raised in 28 min. (Scheme No.5 of API spec. 10) - 90-120 Minutes.
Maximum Consistency 15-30 Minutes stirring - 20 BC (Max.)
Consistency Initial and after 20 Minutes stirring -20 BC (Max.)
f)Maximum Consistency at temperature 27oC Initial and after 20 Minutes stirring in Atmospheric Consistometer - 20 BC (Max.)
3.3 CHEMICAL REQUIREMENT : HSR - TYPE CEMENT.
a)Magnesium Oxide (MgO) % by mass - 6.0 (max.)
b)Sulphur Tri-Oxide (SO3) % by mass - 3.0 (max.)
c)Loss on ignition, % by mass - 3.0 (max.)
d)Insoluble residue % by mass - 0.75 (max.)
e)Tricalcium Silicate (3CaO.SiO2) % by mass- 48 - 65
f)Tricalcium Aluminate (3CaO.Al2O3) % by mass - 3.0 ( max. )
g)Tetra Calcium Alumino Ferrite (4CaO.Al2O3.Fe2O3) plus twice the Tri-Calcium Aluminate (3CaO.Al2O3) % by mass - 24.0( max. )
h)Total Alkali contents expressed as Sodium Oxide ( Na2O ) equivalent percent by mass - 0.75(max)
i)Free lime content percent by mass - 1.0 ( max. )
3.4.0 MANDATORY SAMPLING AND TEST REQUIREMENTS:
Class 'G' cement manufacturer under this specifications shall comply with mandatory test requirements as indicated in Table 2.3 of API specification 10: Specification for Material and Testing.
a)Sampling procedure :- as per section 3 of API - Spec 10.
b) Test for:-
i. Free water - as per Section 7 of API Specification 10
ii. Compressive strength - as per Section 7 of API Specification - 10
iii.Soundness - as per Section 4 of API Specification 10
iv. Thickening Time as per Section 8 of API Specification - 10
3.5.0PREPARATION OF SLURRY:
As per Section 5 of API Specification-10
3.6.0MARKING
Each bag shall have clearly legible marking as given below:
a) Name of the product either with MSR or HSR.
b) Name of supplier
c) Date/ month /year of manufacture
d) Supply order No. against which supplies are made.
e) Weight only in Kilograms to be mentioned
3.7.0PACKAGING, HANDLING AND STORAGE OF CEMENT AND ITS ADDITIVES
3.7.1PACKAGING
a)Cement/ chemical bags should be packed in moisture proof bags and should be resistant to misuse during handling. Cement/ additive bag should be multi-layered paper bags consisting of six paper-layers with up to 2 polyethylene layers included between first and fifth paper layers. Up to two asphalt and bitumen layers may be included to further improve handling resistance.
b)Cement/Additives can also be packed in HDPE bags which should have two loops in the corners on one edge of the bags for easy handling and to avoid application of hooks.
c)Each cement bag should be of 50 kg. wt. (net) and each cement additive bag should be of 25 kg. wt. (net)
3.7.2HANDLING
a)Care must be taken during handling and transportation of cement/ additive bags so as not to allow introduction of moisture.
b)Use of iron hooks be avoided as it will puncture the bags and expose the material to moisture.
c)Possible contamination of bulk cement by other cement brands or bulk materials should be avoided in offshore operations.
d)Suitable moisture scrubbing equipment should be added in the cooler air lines between compressor and tanks. Particular care should be taken in offshore bulk cement handling operations to avoid transfer lines becoming wet.
e)One type of cement additive should be kept together.
f)For offshore use, cement additive should be sent to installation in sealed containers and if sent on pallets, then it should be properly covered with water-proof tarpaulin.
3.7.3STORAGE
a)Cement chemicals should be kept separately from other chemicals to avoid any intermixing of bags.
b)Storage of cement / chemicals should be such that oldest stock will be issued first.
c)It is advisable to store cement chemical bags on a platform with approximately 6 inches air space and tarpaulin should be spread on the base of stacking in order to form a moisture proof seal.
d)When stored on pallets, cement and additives should be stored from initial stage of receipt of material and on a pallet not more than 20 bags of additives and 30 bags of cement should be placed.
e)While storing cement for a long time in silo, either on site or in bulk handling plants, cement should be transferred from one silo to another, at least once in a month.
f)Air dryer must be used for moisture free air in handling cement when storing in silos.
g)Staggered delivery schedule should be maintained.
4.0.0 CEMENTING EQUIPMENT
Some of the offshore cementing equipment are different from the onshore cementing equipment, because in the case of onshore rigs such equipment is mobile whereas in case of offshore rigs the same is stationary.
4.1.0 CEMENTING UNIT
a)It should consist of two triplex pumps which are horizontal plunger type developing high pressures, driven by either Diesel engine or electric motor and mounted on single skid or on truck chassis. One pump should be able to develop pressure up to 15,000 psi and the other pump should be able to give maximum discharge up to 10 BPM at low pumping pressure.
b)Pressure release safety valve should be placed in discharge line so as to avoid sudden rise in pressure in the unit.
c)Recirculating system should be a part of cementing unit with a booster pump of 50 HP or otherwise batch mixer should be used.
d)The unit should have a Densometer to monitor slurry density.
e)The unit should have two centrifugal pumps for mixing water, one directly coupled with the main transmission and other with independent drive with 50 HP motor in case of offshore rigs.
f)Apart from recirculating system, unit should also have a ground mixing system using rotary jet, hopper goose neck pipe, slurry tub etc.
g)It should also have high pressure mixing system lines so that in case of failure of both the mixing units, high pressure mixing can be carried out by isolating one triplex pump from the other.
h)All high pressure lines should be of 2 inches nominal diameter and 15,000 psi rating.
i)All cementing units should have two displacement tanks with minimum 10 barrels or 1.6M3 capacity each with measuring scale calibrated either in barrel or cubic meter.
j)The onshore cementing unit is generally of mobile type and mounted either on 6x4 or 6x6 truck chassis.
4.1.1 CEMENT SILOS
The silos are used for storing of blended / neat cement for cementation jobs at sites or at bulk plant.
a]All offshore rigs should have at least 3 silos for cement storing purpose out of which two should be of 1,500 sacks (75 MT) and one around of 1,000 sacks (50 MT) capacity.
b)These silos should be equipped with suitable safety valves & weight indicators.
c)All the inlet, outlet and vent lines from these silos should always be kept clean to avoid any blocking / choking.
d)In line filters should be installed on the inlet and outlet ports of silos to avoid any cement stones entering into the system and choking lines. These filters should be periodically cleaned.
f)Compressed air used for transfer of cement from silos to surge tank should be free of moisture. Compressor should be equipped with suitable air dryer unit.
4.1.2 CEMENT SURGE TANK
a)The surge tank should be equipped for controlled discharge of cement to the mixing hopper. Surge tank is with a capacity of minimum 100-150 sacks (5 to 7.5 MT).
b)It should be equipped with safety valves and weight indicators and glass windows.
c)Surge tank should be kept empty after each cement job.
d)Provision may be kept to back load excess cement from surge tank to silo if required.
4.1.3 CEMENTING HEAD
Cementing heads are used in cementing jobs in order to facilitate connection between casing and pumping unit and has arrangement to load and release the cementing plugs at the proper time. Cementing heads are of single plug container type or double plug container type.
a)The cementing head should be cleaned, serviced, greased before and after every cement job.
b)Cementing head should be equipped with positive lever type indicator for plug release. Plug release indicator and assembly should be serviced regularly for its function at the time of job.
c)The cementing head should be of 15,000psi rating.
d)The cementing head should have at least 2 circulating connections with 15,000psi rating nipples with hammer unions.
e)All 'O' ring should be checked for any cuts or damages before putting in for cementing operation.
4.1.4 ADDITIVE MIXING TANK / SLUG PIT
a)In all rigs preferably a separate tank be provided for mixing of cement additives with suction facility from bottom by centrifugal pump and with delivery line to cementing unit displacement tank.
b)Stirrers/jet-guns should be provided for proper mixing of chemicals in tank.
c)Tanks should be provided with proper facility for cleaning.
4.1.5 HIGH PRESSURE LINES AND MANIFOLDS
a)All high pressure lines and manifold should be of 15,000psi CWP, pressure rating.
b)Pipe line layout on offshore rig should have minimum bends to avoid excessive pressure loss.
c)Two numbers of high pressure lines should be there from the cementing unit to derrick floor, one from each triplex pumps with interconnections for offshore rigs.
4.1.6 MOBILE PNEUMATIC BULK CARRIER:
The mobile pneumatic bulk carrier ( truck mounted ) consists of a horizontal silo of 20 MT capacity, surge tank, one air compressor of capacity 250 cubic feet per minute, a working pressure 4 kg/cm2 and one air drier along with pipe lines, victaulic couplings and butterfly valves mounted on a truck chassis. The mobile pneumatic bulk carrier should have load carrying capacity of 10 MT and stationary capacity of 20 MT. The air compressor should be rotary / screw type driven by Diesel engine and mounted on same chassis of truck.
4.1.7 LOADING POD:
Loading pod is required when cement is transported by trucks to site. Onshore rigs require provision of loading pod at site for loading cement to main silos. Loading pod is of 5 to 10 MT capacity depending upon requirement with provision of hopper, cutting pod for loading cement and then transfer to main silos. Suitable ladder should be equipped with the loading pod or otherwise a screw conveyor with a hopper placed at the ground be used for loading.
4.1.8 BATCH MIXER:
The purpose of a batch mixer is to prepare homogeneous cement slurry of desired gravity, and when this is properly accomplished, the end result is a cement slurry of predictable properties. The batch mixer may be skid type or movable powered by diesel engine or electric motor.
5.0PRIMARY AND SECONDARY CEMENTING PRACTICES
The success of cementing operations can be improved significantly by following the standards developed below. Major factors requiring detailed attention are:
A.Slurry design / job planning
B.Blending of cement and additives in bulk handling plant.
C.Casing lowering, hook up, pre-job arrangement.
D.Slurry mixing on location, pumping and job execution
E.Displacement of cement slurry
F.Job evaluation
5.1.0CEMENT SLURRY DESIGN / PLANNING OF CEMENT JOB
1.Gather the data, obtain and assess all the necessary information prior to preparing any cement job design and operation programme. The information should include the following points:
-Rig, Well No., Field location
-Type of job - casing or liner - conventional or sub-sea operation.
-Casing sizes, grades, weights and threads.
-Casing depths, deviation, hole size, caliper (if available), drilled depth.
-Type of mud to be used, mud parameters and rheology.
-Bottom Hole Circulating Temperature(BHCT) & Bottom Hole static Temperature (BHST), expected pore pressures and fracturing pressures.
-Interested zone intervals with Oil Water Contact (OWC) or Gas Oil Contact (GOC)
-Any special well problems (high pressure gas, Lost circulation etc.)
-Cement rise needed
-Specific requirement on cementing or hermetic testing of casing.
2.At job planning stage, the availability of equipment and additives for the job execution should be assessed.
3.Calculate the cementing parameters which include the quantity of cement, total mix water, pump rate, well head and bottom hole pressure during displacement, mixing time, mud displacement volume, surface pressure and other related information. This will assure that well will remain under control during the cementing operation.
4.Design maximum allowable down hole slurry density to prevent fracturing. Slurry density should be preferably 2-3 ppg heavier than that of drilling mud.
5.Determine bottom hole circulating temperature (BHCT) from logs and using API Temperature data. Temperature logged approximately 24 hrs. after the last circulation ceased can be used as BHST for API table.