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Accelerators speed up or shorten the reaction time required for a cement slurry to become a hardened mass. In the case of oilfield cement slurries, this indicates a reduction in thickening time and/or an increase in the rate of compressive-strength development of the slurry. Acceleration is particularly beneficial in cases where a low-density (e.g., high-water-content) cement slurry is required or where low-temperature formations are encountered. Of the chloride salts, CaCl2 is the most widely used, and in most applications, it is also the most economical. The exception is when water-soluble polymers such as fluid-loss-control agents are used.
Summary To determine which salt-based cement system (potassium chloride or sodium chloride) was suitable for cementing across halite and anhydrite salt sections in West Africa, eight slurry recipes were tested to assess how formation salt contamination would affect slurry properties. The formation salt used for testing was sampled from a deepwater, presalt well in Angola. The recommendations developed from the laboratory study were implemented in 10 projects across West Africa over 5 years with 100% operational and well integrity success. A candidate deepwater well was selected in which the surface and intermediate strings penetrated salt formations. Four slurry designs (a lead and tail slurry used on each casing string) were programmed. Each slurry was designed and tested as two distinct systems using potassium chloride and sodium chloride salt, respectively, yielding a total of eight slurry designs. Using the methodology and data presented by Martins et al. (2002), the mass of dissolved formation salt that each slurry may receive during placement was estimated and duly incorporated into each slurry design. Subsequently, the salt-contaminated slurries were tested and compared with the properties of the initial uncontaminated slurries. On the basis of these results, conclusions were then made on which salt slurry system (potassium chloride or sodium chloride) exhibited better liquid and set properties after contamination with formation salt. Subsequently, this knowledge was applied to 10 projects across three countries in West Africa. This study showed that when the contact time of liquid cement slurry to salt formation was low—typically when the salt-formation interval across which the cement slurry flowed was less than 100 m thick—the level of formation salt dissolution entering the slurry during placement was limited. In this case, a potassium chloride salt-based slurry delivered improved liquid and set properties as compared with a sodium chloride salt-based slurry. In the field, this knowledge was applied in all oilfield projects cemented by an oilfield service company between 2015 and 2020. This included deepwater, shallow offshore, and onshore wells. All related salt-zone cement jobs, including sidetrack plugs, placed across the salt formations were successful on the first attempt. In an absence of industry consensus around salt-formation cement slurry design, this paper validates a guideline for West Africa, based on results from laboratory testing and 5 years of field application. In contrast to current literature that recommends only sodium chloride salt-based slurry designs across halite or anhydrite salt intervals, this work demonstrates that potassium chloride salt-based slurry systems can effectively be used to achieve well integrity where a halite or anhydrite salt interval is less than 100 m (328.1 ft) thick.
Abstract One of the last exploratory frontiers offshore, where some of the biggest reservoirs have been found in late days, are the ultra deepwater areas of the Gulf of Mexico, in the Mexican side. Several methods and lessons learnt have been produced during the Exploratory Campaign of these waters, becoming the massive salt formations, one of the major challenges faced, not only for drilling methods and techniques, but for zonal isolation in general terms, related to cementing operations. Cementing jobs executed in salt environments require cement slurries with specific concentrations of salt in order to avoid the acceleration/retarder effect of thickening time on the cement slurry due to formation salt incorporated during fluids placement in the annular space, and to avoid the dissolution of natural salt formation. Likewise compressive strength development must be capable of mitigating the effects of salt cuttings on the casing that isolates the zone to ensure the integrity of the section. Salt is commonly classified as: Magnesium salts – regular movement Halite – low movement Carbonates – without movement This paper includes lab tests to determine the physical and chemical properties of cement slurries with different concentrations of sodium chloride (NaCl) and potassium chloride (KCl). A deep analysis was performed with these slurries when in contact with salt formations, determining the dissolution effect of salt in cement slurries. Lab tests were performed with Halite samples from ultradeepwater wells in the Northern Region of the Gulf of Mexico.
Abstract A number of reservoirs around the globe are deep, and often it is necessary to drill and cement through salt zones to reach the reservoir section. Brazil offshore is one example where reservoirs are buried deep, and the salt zones there are quite challenging to drill through and cement. Many of these salt zones contain chemically reactive salts, such as magnesium and calcium chloride, and usually pose unique challenges during placement of the slurry and subsequent cement slurry hydration and compressive strength development. These salts, especially MgCl2, chemically interact with the cement slurry, thereby altering the mechanism and kinetics of cement hydration, leading to premature gelation and shorter thickening times. Mitigating these effects is a challenge and is important to successfully place the cement slurry in the annulus and for the slurry to develop the required mechanical properties, such as compressive strength. In the present study, slurries were formulated to overcome gelation issues with the required compressive strength for successful zonal isolation. The slurries were designed in such a way that they can take up to 12% contamination by weight of water (bwow) of the MgCl2-based salts known as carnalite and tachyhydrite. Pertinent data that characterize performance of these slurries are presented in this paper.
Abstract Cementing in front Salt Zones requires an appropriate cement slurry design to assure minimum dissolution of the formation by the cement slurry and also minimum deleterious impact on the properties of the cement. The influence of halite on the cement slurry properties is already well discussed in the literature, but there’s no much information regarding the influence of other salts like taquidrite, carnalite, which are much more soluble than halite and are found in Brazil Offshore Fields. The first stage of the work consisted in evaluating the influence of different levels and types of salt on the hydration process and its effects on the behavior of the main physical properties. It was produced fourteen cement pastes, five of them containing NaCl at the contents of 5, 10, 15, 20 and 36% by weight of water and eight containing KCl at contents of 1, 3, 5, 7, 10, 15, 20 and 34% by weight of water. It was also prepared a cement slurry with no salt added to be used as reference. The dissolution rate of the different salts core formation in these cement slurries was determined. The influence on the cement slurry properties, such as free fluid, thickening time, compressive strength and rheological parameters due to halite, carnalite and taquidrite incorporation were also determined. This paper presents the studies conducted to design cement slurries for cementing well through salt layers (halite, carnalite and taquihydryte) located in the Aguilhadas Field in Northeast, Brazil. Based on the results, about 500 m of salt were cemented with a semi-saturated cement slurry which provided an excellent quality of the cementing, proved by acoustic logs. Salt cores of halite, carnalite and taquihydryte were used to determine the dissolution rate of salt into the cement slurry. X-Ray tomography was used to visualize and to quantify the salt dissolution in the dynamic tests. The shear bond strength between halite core and hardened cement slurry with 15% NaCl was determined showing good results.
With the ever present emphasis on reducing exploration and production costs, oil and gas operators must continue to look at all aspects of drilling, completion, and production for new methods and/or technologies to help achieve enhanced performance while still improving economics. when focusing specifically on drilling, one area offering room for advancement is in wells with zones containing clays or shales (which are) sensitive to fresh water in general, and cement filtrate in particular.
Historically, either sodium chloride (salt) or potassium chloride (KCl) have been the primary materials of choice to yield a filtrate less damaging to these zones. However, the deleterious effects of salt on cement have been extensively documented, and recently published material has also detailed the negative impact KCl can impose on cements. This paper will address a new material for use as a cement clay control additive. Laboratory data is presented to detail the effectiveness of the material on sensitive clays and shales, as well as its effect on cement fluid loss, viscosity, thickening time, and compressive strength development. The material shows superior clay controlling properties without the undesirable side effects of either sodium or potassium chloride, and it exhibits this elevated level of performance while maintaining economic and environmental advantages as well.
Whenever the subject of clay control in cement is discussed, the most predominate area of concern, especially for production engineers, is normally centered around the possibility of damaging formation permeability with cement filtrate. While many may argue on either side regarding the legitimacy of this concern there still exists another area where untreated cement filtrate can cause significant problems. If the water in the cement slurry destabilizes sensitive sections of a hole (shales), extreme cases can result in a complete failure of the primary cement placement and the additional costs of remedial cementing. Many times, even if the remedial cementing is considered a success, it still does not deliver the zonal isolation/casing protection possible in a successful primary cement operation.
Given the serious implications of either situation, concerned operators and service companies have tried for years to combat both situations with varying degrees of success. Following the example of mud companies, various loadings of salt (sodium chloride) are used in cement formulations to protect against shale/clay problems. The concentrations of salt can be between 5% and 37.2% (salt saturated) by weight of mix water (BWOW) and the effects on cement performance differ depending on the exact concentration used.