The global oil and gas industry is being challenged to increase production to meet the rising world energy demand. One of the key areas now being explored and developed to meet this demand are reserves below massive salt formations.To reach these reserves, it is necessary to drill through and case off the salt. Casing and cementing operations in such salt zones can pose particular challenges, ranging from the effect of salt dissolution on cement-slurry properties, to the potential dangers presented by salt creep to the integrity of the well and the need to plan for contingencies for potential zones of overpressure or lost circulation. This paper examines and explores the challenges inherent with cementing across salt zones in the global arena.The current best practices for cementing casing strings across salt zones in some of the major subsalt basins of the world, including the North Sea and the Gulf of Mexico, are detailed and discussed.This work should help assist those tasked with the construction of wells that have to penetrate significant salt formations to achieve their objectives safely and reliably.

Summary Many wells that have been successfully cemented initially are showing annulus pressure buildup because of damaged cement- sheath integrity by post-cementing operations/conditions. This has been a concern by many operators where wellbores may be exposed to severe conditions and/or production regimes over a period of time. Sometimes this problem can be temporarily dealt with by releasing the annulus pressure, if environmental conditions and well type will allow. However, this method of annular gas production relief is not a long-term solution to the problem. In addition, it is not always possible to reduce the annulus pressure by releasing the trapped pressure into the environment on a regular basis, even if all other conditions permit this operation. An engineered cement-slurry system can save the operator from facing this situation by applying a lifetime zonal isolation remedy through the proper cement job design. Gas injection in specific areas in the UAE is performed to help maximize the production from these development fields. This paper will discuss the process of engineering a cementing system for these gas-injection wells and the development of a solution that has successfully protected wellbores in gas-injection areas where high pressures are applied to the wellbore. By treating the cement under defined wellbore conditions and studying the mechanical behavior of the cement sheath, it was possible to design a cement- slurry system that could withstand the high pressures applied through gas-injection operations. The mechanical behavior was evaluated using 3D finite element analysis (FEA) that considers mechanical properties such as Young's modulus, Poisson's ratio, and tensile strength in addition to confined compressive strength. The importance of complete zonal isolation is of high order. Elastic cement designs have provided a resilient nonfoamed, or conventional, system that successfully isolated the wellbores for more than a dozen gas-injection wells.

Proposal Conventional means of primary cement placement pump the cementing fluids down the casing and well returns are taken from the annulus. This is the most common way of cement placement for the industry and has been used for more than 80 years. Much less commonly used by the industry, but recently gaining in use is the Reverse Circulation of Cement (RCC) technique. When using the RCC technique, the cementing fluids are pumped into the annulus of the well and returns are taken through the casing. The recent acceptance of the RCC technique is mainly driven by economics and state-of-the-art technology bringing an alternative technique. Benefits of the RCC technique can include lowering bottom-hole placement pressure, reducing cement retarder concentration, lowering the time for cement placement, and increasing location safety. The main drawback to the technique is determining when uncontaminated cement is at and around the casing shoe. This paper discusses the benefits and shortcomings of the RCC technique in relation to fluid friction, cement slurry design, location safety, and zonal isolation. The paper illustrates, through a case history, how RCC technique's strengths are obtained while shortcomings are minimized. Field data from a recent job using the RCC technique on a 3100-m gas well in Alberta, Canada, as well as lessons learned from the job, are presented. Introduction One of the common concerns in the industry when it comes to cementing is the potential for lost circulation. While a few different approaches can be taken to address this problem, a viable alternative in reducing equivalent circulating density (ECD) is reverse cementing.1 RCC is a process in which spacer(s) and cement slurries are pumped down the annulus and returns are taken through to the surface casing string (Fig. 1). Cement slurry's location can be determined by two common methods:Utilizing a logging tool and radioactive tracersFluid markers Fluid markers have been the favorite system because no environmental issues are involved and it is more economical. Logging tools and radioactive tracers are more attractive when top of cement (TOC) inside the casing needs to be limited; i.e., when foamed cement systems are used in conjunction with RCC. However, not every well is a prime candidate for RCC. Certain conditions should be present to indicate the necessity of this method. RCC is not an entirely trouble free system. Some disadvantages exist in this system just like any other system that is in use. In the remainder of this paper, the advantages and disadvantages of RCC are discussed in detail. Also, a process is examined to aid with the decision-making when an operator is evaluating the options available to cement a string of casing. Evaluation The following sections detail important advantages, disadvantages, and challenges of using the RCC method. Advantages of RCC RCC can provide the following advantages in wells meeting the requirements for the method:Reduced EDCsImproved mud displacementShorter slurry thickening timesImproved compressive strength developmentImproved safety and environmental managementEasier cement slurry selectionImproved formation production due to less risk of cement invasion into the producing zone

The main purpose of the annular cement is to provide effective zonal isolation for the life of the well so that oil and gas can be produced safely and economically (1) . To achieve this objective, the drilling fluid should be removed from both the wide and narrow annulus and the entire annulus should be filled with competent cement. The cement should meet both the short-term and long-term requirements imposed by the operational regime of the well.Traditionally, the industry has concentrated on the short-term properties that are applicable when the cement is still in slurry form. This effort is necessary and important for effective cementslurry mixing and placement. However, the long-term integrity of cement depends on the material/mechanical properties of the cement sheath, such as the Young's modulus, the tensile strength and the resistance to downhole chemical attack. Considering properties of the cement sheath for long-term integrity is critical if the well is subjected to common changes in the pressure and temperature of the cased well.After cement is placed in the annulus, if no fluid immediately migrates to the surface, short-term properties such as density, rate of static gel strength development and fluid loss of the cement may have been designed satisfactorily. However, recent experience has shown that after well operations such as cement hydration, casing pressure testing, completions and production, the cement sheath could lose its zonal isolation capabilities to provide zonal Abstract Many successfully cemented wells begin to show annulus pressure buildup, which is often caused by damage to cement sheath integrity due to post-cementing operations. This problem may be temporarily dealt with by releasing the annulus pressure. However, this method of annular gas production is not a longterm solution to the problem. A finite element analysis (FEA) method has been developed to analyze the effects of various well events and operations such as cement hydration, casing pressure testing, completions and production on the integrity of the cement sheath during the life of the well. The three-dimensional FEA modelling considers the sheath's mechanical properties, such as Young's modulus, Poisson's ratio and tensile strength, in addition to confined compressive strength, and helps provide the user with a cement design that can maintain an annular seal over the life of the well.This paper discusses how a cementing design specialist can model the events upon and after cement placement to help provide a long-term seal of the annulus. The required input data is discussed and the output information is shown for example wells.isolation (1) . This failure can create a path for formation fluids to enter the annulus, which pressurizes the well's annulus, and could render the well unsafe to operate. The failure can also result in premature water production that can limit the economic life of the well.Failure of the cement sheath is most often caused by pressureor temperature-induced stresses inherent in well operations. Los...

IntroductionThe long-term integrity of a cement sheath throughout a well's life is the ultimate factor for determining whether the sealant will withstand the planned operations, production and injection that are planned for the well. In the case of heavy oil operations, the primary design considerations for a long-lasting sealant are the temperature and pressure regimes. The stresses caused by the extreme changes are exerted on casing, cement and the rock. It is important that all involved parameters are known and taken into consideration to formulate the final design of sealants. Also, at an earlier stage of the process, when the cement is pumped in the wellbore, proper best practices can help to ensure cement sheath integrity after the cement is set and hardened. Placing the cement slurry at the designed parameters is crucial to the success of the zonal isolation. The effectiveness of the slurry placement can significantly influence the cement sheath integrity and the future of the well. The hydration process, as well as the long-term compressive strength, tensile strength and permanent bonding capability of the cement system, are directly related to the density control and flow regime as the cement slurry is being pumped downhole (1,2) .A complementary component of a successful cement job is the use of cementing best practices (3) . Regardless of the fitness of the sealant, the wellbore may still exhibit steam breakthrough or annulus pressure buildup (APB) in SAGD or CSS operations caused by improper slurry placement. Of course, future damage to the cement sheath from post-cementing operations or from new, unanticipated conditions could also have the same effects.To examine each of the elements involved in heavy oil cementing separately, we begin by studying the design of the sealant systems. Cement Slurry Design and PlacementThe design stage and laboratory testing of the candidate systems of the cement slurry to be used in a thermal operation are the beginning stages of the process. This initial phase requires the drilling engineer and cementing specialist's highest level of coordination. A successful thermal cementing operation execution requires a clear understanding of the mechanical/physical aspects of the wellbore and selected sealant(s). Field development plans and delivery expectations from the cemented wellbores are the determining factors of the future life of the field. The objectives and operational details must be clearly understood by the cementing engineer, with the cooperation of the drilling engineer. Mechanical aspects of the design should cover two main areas: 1) the minimum mechanical property requirements of the set/cured cement needed to comply with regulatory directives and future planned operations; and 2) the hydraulic optimization of the slurry placement necessary to reduce or eliminate the chances of lost circulation and best-fit flow regime to effectively place the slurry. AbstractWith the high demand for oil and gas, operators are becoming increasingly interested in unconventional ...