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Xin, Haipeng (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Wang, Jianyao (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Wang, Xiangyu (No. 2 Cementing Branch Company, CNPC Bohai Drilling Engineering Co., Ltd.) | Yang, Kunpeng (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Zeng, Jianguo (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Zou, Jianlong (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology) | Sun, Fuquan (CNPC Tianjin Boxing Engineering Science & Technology Co., Ltd., Laboratory of Cementing Technology, CNPC Key Laboratory of Drilling Engineering, Laboratory of Cementing Technology, National Engineering Laboratory of Petroleum Drilling Technology)
ABSTRACT One of the main factors affecting the quality of salt layer cementing is the poor rheology of high-density saline cement slurry, which limits the implementation of improvement measures for improving cementing displacement efficiency. The high temperature in summer in Iraq accelerates cement hydration, which further leads to the reduction of cement slurry rheology. Affected by the continuous high ground temperature which could reach 60 °C in summer in Iraq, cement slurry was severely hydrated during the mixing process, resulting in poor fluidity, strong thixotropy and high initial consistency and this leads to difficulty in pumping and unstable density which seriously impact on on-site construction safety and cementing quality. Comb-type polycarboxylate dispersant synthesized via radical polymerization could solve dispersive problems such as poor dispersion and compression used in high pressure saline aquifers, large section of gypsum salt bed and offshore operations. After adding this dispersant, slurry prepared using saturation saline water and substitute ocean water exhibited strong dispersion ability, saturation salt resistance, and good performance without strength damage. Using a high-density saline cement slurry with a density 2.28 g cm resulted in 54 ml fluid loss, 16.5 MPa strength (24 h) as well as good stability and rheological property as flow behavior index n=0.72 and consistency factor K=1.03 Pa.s. The slurry was prepared at an ambient temperature of 60 °C. A comb-type polycarboxylate dispersant was applied to the high-density (2.28g cm) slurry and this was used for a 244.5 mm salt paste layer casing at 55–58 °Cambient temperature for 5 wells in Halfaya and Missan Oilfeild in Iraq. More than 85 % of the cementing job was excellent. INTRODUCTION During the drilling process, complex formations such as high-pressure saline formations, large salt paste formations, or water-sensitive formations were encountered (Chang, 2013; Da, 2012; Gao, 2014; Hou, 2013; Wei, 2014) both in China and overseas in Iraq, Kazakhstan, Uzbekistan, Indonesia and other countries (Chen, 2015; Gai, 2011; Zhou, 2011; Zou, 2015). In addition, in sea and beach operations, it is often attempted to directly prepare cement slurry with seawater (Chen, 2013; Lu, 2014). Due to the high solid content and high salt content, salt/seawater cement slurry exhibits poor fluidity, strong thixotropy and high initial consistency.
Reddy, B. R. (Aramco Services Company: Aramco Research Center-Houston) | Contreras, Elizabeth Q. (Aramco Services Company: Aramco Research Center-Houston) | Boul, Peter J. (Aramco Services Company: Aramco Research Center-Houston)
Abstract Achieving quality cement performance in deep water wells with large amounts of salt present requires fundamental understanding of the salt effects on the interactions of cement additives with cement on the slurry performance. Many problems encountered later in the life of the well can be traced to slurry performance issues during placement and the initial setting process. Cement slurry designs for an oilwell can range from simple to highly complex depending on the geology, lithology, placement logistics, wellbore conditions and long-term performance. Logically designed cement slurry formulations and dependable additive behavior are critical to meeting cement performance requirements. Formulations can include mineral admixtures added in substantial quantities and additives in smaller (<2% by weight of cement) quantities. The performance of the additives in cement slurries depends strongly on competitive adsorption on cement and mineral surfaces. Adsorption interactions are directly influenced by downhole temperature, the nature of the formation, and the mix water composition. These aspects underline the need for understanding additive interactions with cement under wellbore conditions. Of particular relevance to deep water cementing is the performance of additives in sea water containing monovalent and divalent salts with chloride and various other anions present in amounts close to 4% by weight. The problem of additive performance becomes even more of a concern when cement is placed against salt formations. High ionic strength of sea water or of a sea/fresh water slurry placed against a salt formation, can compress the electrical double layer of cement clinker particles, alter chain conformations of ionically charged or hydrophobically modified polymeric additives, or change the solubility of additives. Additives may perform extremely well in fresh water slurries, but may perform poorly in slurries with high salt content. Additionally, the salt itself can affect cement performance. For example, sodium chloride is a set accelerator in small quantities (≤13% by weight of cement) while it functions as a retarder in large quantities. The objective of this presentation is to gain molecular level understanding of relationships among additives based on chemical structures, adsorption onto cement surfaces, and the mix water ionic strength. In this study, typical additives for dispersion and retardation are contacted with Portland cement in deionized water, synthetic sea water, water containing 2% to saturation level of NaCl or divalent salts in a formation brine. The reactions were analyzed by isothermal calorimetry, UV/Visible spectroscopy and rheology. The interpretation and implications of laboratory results are presented.
The cement mixing procedure can be split into (1) a mechanical process thatincludes the wetting of the powder and the defloccuration and process thatincludes the wetting of the powder and the defloccuration and homogenization ofthe resulting suspension and (2) a physicochemical process that includes thedissolution of some cement phases, the formation process that includes thedissolution of some cement phases, the formation of supersaturated solutions,and the precipitation of cement hydrates. The mechanical process has beenvalidated by inert suspensions of silica and barite and by cement slurries ofvarious reactivities and physical characteristics (particle size distribution).The physicochemical process was investigated systematically by looking at theprecipitation kinetics, inert suspensions, and finally cement slurries. Therelevant mixing parameters were found to be the residence time of the slurry inthe mixer parameters were found to be the residence time of the slurry in themixer and the rotational speed. Physical properties, such as plastic viscosityand fluid loss, are related to these two parameters by the mixing energy.Properties related to cement reactivities, like the yield value, are Propertiesrelated to cement reactivities, like the yield value, are affected very littleby the rotational speed but are highly dependent on the residence time in themixer. The influence of these two parameters on the response to differentadditives (dispersants, retarders, and fluid-loss agents) is presented and acomprehensive physicochemical mixing is proposed. proposed. Introduction
Mixing conditions are known to affect the consistency of fresh concretecement paste. But very few studies have paste. But very few studies havethoroughly investigated the chemical and physical phenomena that occur duringthe physical phenomena that occur during the mixing of oilwell cement and theirlong-term effect on cement slurry properties. For laboratory mixing, the APIrecommends the use of a precise procedure to mix an oilwell cement slurry. Butlittle attention has been devoted to determining whether the slurry obtainedwith this method is well mixed and the effects of changing some parameters inthis procedure.
In this paper, cement is first considered as a powder and the differentphysical processes that occur during mixing are processes that occur duringmixing are presented. Next, the cement hydraulicity is presented. Next, thecement hydraulicity is taken into account and integrated into the wholeprocess. From this research, parameters critical to obtaining a well-mixedpowder in the laboratory are identified and discussed. A physicochemical modelof cement mixing is also presented. The second part of the study investigatesthe influence of these parameters on some key slurry properties. parameters onsome key slurry properties. Experimental Procedures
The cement slurries were prepared by mixing Class G cement and tap waterwith a propeller-type mixer. The volume of mixed propeller-type mixer. Thevolume of mixed slurry was kept constant at 600 mL for all tests. The mixerblades were weighed after every 10 tests and changed when weight loss exceeded5 %. The mixing energy (see the next section) was changed by varying either therotational speed of the blade (500 to 12,000 rev/min) and/or the duration ofmixing (15 to 50 seconds). After mixing, the rheological properties weresometimes measured or the properties were sometimes measured or the slurry wasconditioned in an atmospheric consistometer rotating at 150 rev/min for 20minutes at different temperatures. All physical tests following cement slurrymixing and conditioning were performed according to API Spec. 10. A sieve testwas performed to check for the presence of performed to check for the presenceof aggregates in the slurry. Immediately after mixing, the slurry was pouredthrough a sieve. The choice of sieve size can be based on the postulation thatthe slurry is deflocculated after API mixingi.e., that each particle isisolated from the others. Therefore, a 450-um sieve was selected to allownothing to remain on the sieve after API mixing. The percentage of the slurryremaining on the sieve indicates the amount of aggregates in the slurry.
A dependable method for converting fluid into a cementitiuos slurry has been sought for many years. Recent advancements in copolymer technology have made it possible to introduce Portland cement directly into drilling fluid while maintaining control over the rheology of the resultant slurry. For purposes of brevity, converted drilling fluid as described herein will be referred to as mud-to-cement, or MTC.
Conversion of drilling mud into a cement slurry has several unique advantages. As examples, conversion of spent drilling mud reduces disposal costs. Secondly, the superior compatibility into MTC significantly improves annular displacement efficiency by controlling the flocculation that normally results when drilling mud and cement contact. Thirdly, MTC makes the most benefit of manpower, equipment, time and materials by consolidating services at the rig site.
Consolidation of drilling mud and cementing technologies to cut costs while improving the quality of completions is the underlying topic of discourse in this paper. In addition to presentation of the slurry design paper. In addition to presentation of the slurry design process, laboratory data, mixing and handling concepts process, laboratory data, mixing and handling concepts and case histories are discussed. Also, several important avenues of potential savings are suggested. Applications in a variety of locations using different types of completions have all been successful both operationally and from the standpoint of results.
The basic purpose of cementing a wellbore is to return the annulus to as near the original state as possible. In general, this means removal of all drilling mud from the annulus and replacement with a contiguous cement sheath. Cement should provide at least four basic functions: (1) zone isolation, (2) casing support, (3) formation support, and (4) casing corrosion protection. The more complete the removal and replacement process, the more complete will be the provision of process, the more complete will be the provision of these four required functions. It is in this critical removal replacement process, however, that convention all cementing practice has often failed. The reason for that failure can be best explained as follows. Drilling mud and cement slurry are incompatible and formed a gelled mass when intermixed. Therefore, conventional cementing practice usually calls for a preflush or spacer fluid to separate mud and cement. preflush or spacer fluid to separate mud and cement. However, some spacer fluids available on today's market are incompatible with either mud or cement. Many spacer fluids are overwhelmed when all three slurries are commingled. A good spacer should have the dispersion power necessary to reduce the viscosity of such mixtures back to a level near that of the original fluids involved. Otherwise, large quantities of clabbered or severely gelled mixture will remain in the annulus. As a result, expensive remedial cementing is often required to correct inferior primary cementing applications.
To reduce the problems associated with mud and cement incompatibility into a cementitiuus slurry has been developed. Converting drilling fluid into a cement slurry has been a topic of research for many years. IN 1970, a Portland cement based formulation was introduced by Wyant et al., but it had a complex formulation, was very sensitive to temperature, and did not incorporate an adequate dispersant. Even so some field applications were done. Another formulation employing a magnesium based drilling fluid was introduced by Miller et al. in 1975.