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A new technique has been developed for densified slurry cementing operations employing a new mix-water dispersible weighting agent. This approach has overcome many logistical, quality control and slurry design problems encountered with conventional dry-blended weighting agents.
Wells in the Po Valley of Northern Italy encounter bottom hole pressures over 150 MPa and temperatures to 190 degrees C. Such conditions dictate the use of weighted cement slurries with controlled thickening time, fluid loss, slurry stability and acceptable rheologies at both surface and downhole conditions.
Historically, weighting agents such as barite, or haematite, have been used to densify the slurries, the materials being dry-blended into the cement at the bulk plant. These blends, however, require considerable time and expense prior to the job for preparation, verification and transportation to rig site.
Despite such rigorous controls, some authors I have reported problems caused by density segregation of the weighting agent in the dry blend during transportation and storage.
Three additional factors must be considered when using dry blends. Firstly, any changes in slurry design after initial blending are time consuming and costly since they involve returning the material to the supply base for re-blending. Secondly, additional quantities of material must be blended and tested, if field logs indicate that the hole is larger than anticipated. Thirdly, excess blend causes complications for storage, and disposal poses environmental problems. In offshore or remote locations these three factors are of even greater concern.
All of these problems can be addressed by a new technique that uses a novel water dispersible weighting agent. This material allows great flexibility to accommodate last minute design changes as there is no pre-blending and the weighting agent is not added until the slurry mix water is prepared. Ibis is particularly beneficial in Italy since a proprietary blend of Class "G" cement plus 40% silica flour is supplied direct from the manufacturers. All the cementing additives can, therefore, be added to the mix water eliminating the need to dry blend cement for these wells.
This paper describes the new technique and its field application. It includes slurry properties and cost comparisons between the new weighting agent and traditional designs.
Barite was the original weighting agent used in this area. It has a moderate density (approximately 4.2 g/cm3) but requires significant amounts of water to wet the particle surfaces. Large quantities of barite must, therefore, be used in high density slurries, and this leads to poor rheologies and reduced compressive strength. From job experience the poor theological characteristics of barite slurries have resulted in surface mixing problems, high displacement pressures and loss of returns due to formation breakdown.
Haematite has a density of approximately 4.9 g/cm3 and was introduced to overcome many of the shortcomings of barite. It has become the most commonly used slurry weighting agent. Like barite, haematite is formed by the milling of mineral ore and is, therefore, subject to natural variations in the raw material and particle size distribution during the manufacturing process. This can lead to difficulties in designing an easily mixable slurry that is also stable under well conditions.
Abstract High-pressure and salt /anhydrite rocks at 1340-1950m Lower Fars formation present a lot of challenges in 244.5mm casing cementing in Halfaya oilfield due to existing the alternations of salt and anhydrite and clay, high pressure, high salinity(160000~220000ppm), low static temperature (30-70°C) and narrow safety margins (0.08g/cm), which all contribute to not only limit the achievement of high performance high density salt resistance slurry, but also lead to the low pump rates and bad displacement rates due to the only 0.03 g/cm density difference between the drilling fluids with density of 2.25 g/cm and the cement slurries with density of 2.28 g/cm during cementing operation, and long cementing job duration caused by the constraints of large annular clearance and long isolation interval, so poor slurry performance, severe lost circulation, hole instability and well kick is likely to occur simultaneously during drilling and cementing process, all result in unsuccessful cementing job and poor cement bond quality. In some cases, right after the wells were put on production, the 9 5/8" casing annulus would show an increase in casing head pressure. So a new high efficiency sealing spacer with density of 2.20 g/cm was developed to displace drilling fluids effectively, which is composed of weighting agent, suspending agent, dispersing agent, fluid loss agent and anti-leakage agent. At the same time, a new high performance salt resistance slurry system with density of 2.28-2.30g/cm has achieved with good stability, proper rheology, and high early strength development of set cement. the 10-15% optimal salt concentration (BWOW) has obtained by the evaluation of rheological property, fluid loss control ability, thickening time property and ultrasonic compressive strength development under the different salt concentration(0~30%); the optimal weighting agent component ratio ((ilmenite: Manganese powder =4:1) and dosage (83%) is determined by building mathematical model to calculate the packing density(φ) of the dry blend with different proportion and water demand, and evaluate slurry properties, introduce a new Carboxylic acid salt salt-resistance dispersant to maintain the good rheological properties. This new slurry technology not only simplify cementing job from the two-stage to one-stage but also improved the cementing bond quality and reduce costs. Extensive lab experiments and pilot tests prior to field application demonstrated the superior performance of this sealing spacer and new salt resistance slurry system; more than 45 wells onsite cementing jobs have been completed in the field with great success. This paper will systematically describe the details of lab development of high density salt resistance slurry system and present case histories to demonstrate its effectiveness in high-pressure and salt /anhydrite rocks casing cementing.
American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the 46th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, held in New Orleans, Oct. 3-6, 1971. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
In order to provide a reliable cementing composition and reduce variations noted with Portland type cement, silica-lime cements have Portland type cement, silica-lime cements have been developed to provide a new deep well cementing composition. Although Portland type cement has been used successfully for several decades as a well completion material, the complicated manufacturing process produces a cement that varies within limits from batch to batch. These variations are tolerable when cementing the shallow well, but the deep wells, with temperatures from 300 degrees F to 500 degrees F, present a different situation. At these temperatures, normal variations will be magnified to an extent that different batches often perform much the same as different cements.
The silica-lime system consists of a simple mixture of ground quartz sand and hydrated lime. At temperatures above 200 degrees F, lime will react with freshly broken faces of sand and with water to form calcium silicate hydrate. There are only two factors to be considered with this system. Since a surface reaction is involved, the surface area of the ground quartz will control the quantity of calcium silicate hydrate formed. The temperature at which the reaction takes place will dictate the ratio of calcium to silica and water to calcium silicate. This chemistry has been well documented by publications from the autoclaved calcium silicate building products industry in Europe and the United Kingdom. The utility of this system is demonstrated by the growth of the autoclaved calcium silicate products industry over the past few decades. products industry over the past few decades. This composition has been thoroughly tested for thickening time, permeability, compressive strength, shear bond, rheology, and compatibility with some drilling muds. Data are presented to show the concentration of retarder to give adequate thickening time and compressive strength throughout the temperature range of 260 degrees F to 400 degrees F. Strength retrogression data have been gathered up to 28 days. Shear bond and permeability is similar to that of Portland type permeability is similar to that of Portland type cement. This system can be mixed with 60 to 90 percent water as well as with a weighting agent to percent water as well as with a weighting agent to give any slurry density from 12 to 20 pounds per gallon. Because of the surface chemistry, this system can be used at any slurry weight without materially affecting the thickening time. This is a very simple but flexible system that offers more reliability for cementing deep hot wells.
The deep Anadarko basin of western satisfactory zonal isolation from the primary mixers so a separate batch mixer is Oklahoma and part of the Texas panhandle cement job. Treatment reports and postcement-bond not needed to prepare the spacer. The system contains deep, tight, gas wells. These wells logs indicated that many of the is dry blended at the bulk plant and have average depths of 12,000 to 18,000 ft. The most common target formations placement that resulted in channels behind weighting agents are used for densities up to are Pennsylvanian sands, specifically the the pipe with no cement or containing a approximately 13.5 lbm/gal, and barite is Granite Wash, Red Fork, Morrow, and mixture of cement and mud.