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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.
Ahmed, Al Salmi (Petroleum Development Oman LCC) | Younes, Al Haji (Petroleum Development Oman LCC) | Saif, Al-Hamhami (Petroleum Development Oman LCC) | Isehaq, Sabhi (Petroleum Development Oman LCC) | Abduallah, Al Fadhli (Halliburton)
Abstract In a north Oman field, it is common practice to cement vertical pilot holes up to the kickoff point. A cement plug is then used to initiate the sidetrack through extremely hard formations. Previously, it has taken several attempts to sidetrack these holes and, in some cases, a mechanical whipstock had to be used. There are challenges when trying to initiate the sidetrack because the formation hardness far exceeds that of the kickoff cement plug. As a result, the sidetracking assembly is repeatedly directed back into the relatively softer cement plug (i.e., vertically). Gravity also plays a role to some extent in bringing the sidetracking assembly back into the vertical hole, increasing the challenge. This paper documents successful implementation of modifications to the slurry design and cementing procedure, as well as the successful use of a side-tracking method/technique in North Oman. The compressive strength of cement has been increased from 5,000 to around 9,000 psi for standard, 17-lbm/gal, Class G cement. The effect of oil-based mud (OBM) contamination has been examined and spacer designs have been improved to help ensure good mud displacement while performing cementing operations. The sidetracking method and tools have also been improved with impressive results. This includes proper selection of the kickoff point based on the drill-speed log of the vertical pilot hole, selecting the correct combination and configuration (e.g., outside diameters of components and angle setting) for the bottomhole assembly (BHA), and using the correct application parameters and techniques while initiating the sidetrack, which is also called "time-drilling." This paper investigates the new techniques applied in detail and clearly illustrates their development. Some case histories are also presented.
Abstract Water-soluble acrylamide tert-butylsulfonic acid (ATBS)-based copolymers are commonly used to provide fluid loss control for oil well cement slurries. In our study, we investigated the behavior of a CaATBS-NNDMA copolymer synthesized by aqueous radical polymerization with respect to its fluid loss performance in presence of sulfate, chloride and Welan gum and at high temperature (80°C). First, we found that CaATBS-co-NNDMA adsorbs in high amounts on both cement and silica flour. Its effectiveness relies exclusively on high adsorption onto these mineral surfaces. FLA adsorption may, however, be perturbed by several physico-chemical effects. Inorganic anions present in high concentrations such as e.g. chloride, as well as organic anionic admixture molecules such as Welan gum, can negatively impact the effectiveness of CaATBS-co-NNDMA. They were found to compete with the polymer for adsorption sites on the surfaces of cement and silica. This way, they reduced the adsorbed amount of the ATBS copolymer. Their impact on the ATBS copolymer generally depends on their anionic charge density, the quality of their anchor group to the cement/silica surface and their concentration. Elevated temperature (80°C) causes a significant increase in the concentration of solved sulfate present in cement pore solution. As a result of the higher ionic strength, the ATBS copolymer changes its solved conformation from stretched to coiled. Coiling of the macromolecule, however, results in lower adsorption. Through this mechanism, higher temperature reduces effectiveness of the FLA.
- - Section II Paper 10 PD 5 GERMANY BOND OF CEMENT COMPOSITIONS FOR CEMENTING WELLS H. Becker * - G. Peterson ** Abstract. For a casing cementation the space between the Résumé. En cémentant un sondage on remplit l`espace borehole and the casing must be filled with cement slurry. entre la paroi du trou et le tubage avec du «cement The cured cement has to shut-off water and gas and to slurry)). Le ciment durci doit fermer l'espace annulaire et support the casing at the desired location. It was tried to ancrer le tubage dans la position prévue. On a cherché à evaluate the necessary bond of the cement and to define trouver l'adhérence nécessaire du ciment et les paramètres the influencing variables. qui l'influencent. During preliminary tests, methods and models were Au commencement des expériences on choisit des métho- chosen which allow ,a transfer of the experimental results des et des modèles d`essai qui permettraient l'application to the conditions and the dimensions of a borehole. The des résultats obtenus aux proportions d'un sondage. Les investigations showed that the strength of cement bond expériences effectuées montraient que l'adhérence du between either the casing and the cement or the cement ciment au tubage et à la paroi du trou dépend de la con- and the formation depends on the nature of the contact dition de la surface au contact et de l'hydratation du surfaces and the hydratation characteristics of the cement. ciment. The necessary bond to shut-off water and gas and to sup- L'adhérence nécessaire pour la fermeture de l'espace annu- port the casing could be determined. An analysis of these laire et pour l'ancrage du tubage fut définie. L'analyse de results showed that the bond cannot be indicated exactly ces résultats montrait que l`emploi d'une méthode de dia- by acoustic logging techniques. graphie acoustique pour I'évalution de l'adhérence est de valeur limitée. Introduction success of cementing jobs was not adiieved in prac- tical operations as inspections of examined cemen- Up till now compressive and tensile strength of tations show')'). Many of the defects are correlated the cured cement are the major criteria for cement- b y the authors with no bond or insufficient bond of ing boreholes. To control these physical properties the cement. The paper deals with the following standardized testing methods Werge developed to problems: estimate the quality of the cement used for cement- ing operations. It was assumed that a material of 1. Experimental investigation of bond between satisfying compressive and tensile strength also cement, casing and formation. develops an adequate bond. But often the desired 2. Causes of bond between cement, casing and * formation. Becùer, Hubert, Germany, Engineer, Professor, Dr.-Ing., Director of Institute of Drilling and Oil Production at Bergakademie (School of 3* Of different conditions in boreholes Mines) Clausthal
Abstract Directional drilling makes it possible to drill multilateral wells into different parts of a reservoir from a single wellbore. Many directional wells are drilled to reach reservoirs inaccessible from a point directly above because of surface obstacles or geologic obstruction. Wellbore sidetrack drilling operations with hard cement plugs have been used for years. Placing cement plug in the borehole and allowing the cement to develop high compressive strength perform sidetracking technique. The hardened cement plug when drilled deflects the bit away from the current borehole, starting another open hole section. Conventional cement formulations for sidetrack kickoffs usually fail when the ROP (rate of Penetration) for the cement plugs is much more than the ROP in the formation Sidetracking failures, in building up kickoff angles, results in operation delays and cost overrun. High compressive strength cement system with slow ROP should be designed and developed specifically for side tracking operations. A rate of penetration device helped optimizing cement formulations to determine the ROP through cement plugs. This is done by controlled circulation of drilling fluid through the drill bit and rotating the bit at a fixed load and speed. Different chemicals for buildingup compressive strength were evaluated. Special types of cements were designed and evaluated for possible use for sidetrack kick off plugs. Addition of inert particles to cement and their effect on the compressive strength and ROP were investigated. In this paper, a new system was developed and results in a slow ROP for the use in sidetrack drilling. The performance of this system outstand any known existing cement formulations for side track drilling and has great potential to improve sidetrack angle builds up. Introduction A previous study has been done to improve placement methods of cement formulations for sidetracks. Others focused on studying the effect of hole size, geometry and mud properties on cement plugs. It is an easy way out to blame placement methods in case of sidetracks failures. Still with proper placement methods, failure in sidetracks cements can occur. Currently, conventional cement formulations are used for kick off plugs in sidetrack drilling. Many hours of rig time are lost to set plugs just to build up the angel in sidetrack drilling. Some times it is extremely difficult to sidetrack in some areas because the cement rate of penetration is much faster than that of the adjacent formation. The compressive strength of regular cement is much lower than the formation leading to this extremrly fast cement ROP compared to formations. To solve this problem, the difference in the rate of penetration between the cement plug and the adjacent formation must be minimized by increasing the compressive strength of the cement. The maximum compressive strength for cement is 5,000 to 9,000 psi. The compressive strength of the formation can reach up to 22,500 psi. The required compressive strength for cement to provide good isolation is 100 psi, However, for kick off plugs, a much greater compressive strength is required. Cement compressive strength is the result of the growth of hydrated calcium silicate crystalline structures. As these structures grow, they gain more strength and interlock with each other. Bond strength of these crystals will be weaken as the water to cement ratio increases, thus decreasing the cement compressive strength. A previous study suggested that the use of metal particles can reduce the penetration in sidetrack drilling. This system was evaluated and compared to other systems including the system developed in the present study. The objectives of this study are to:Find a reference ROP from selected cores, Study the effect of density and different chemicals on the rate of penetration of cement, and Develop a new cement system and evaluate its performance for sidetrack drilling.