HPHT well subjects zonal isolation and long term cement integrity into critical factor to achieve long term production life. Repeated cycles of high differential pressure and temperature tend to break bonding between cement, casing and formation. Microannulus as consequence of debonding will provide space. At gas wells, it will provide space for gas migration which may lead to sustained casing pressure. Providing zonal isolation is also important to ensure there will be no communication between two different formations or reservoirs This paper discusses the design, execution and evaluation of cement technology implemented at 9 5/8-in HPHT intermediate liner. Special softwares were used to simulate gas migration risk and stress analysis to cement sheath. High risk gas migration and microannulus were expected based on sofware results. An expandable cement system was identified as a solution and deployed successfully. In order to achieve better understanding of behaviour of cement slurry at field application, laboratory experiments were performed. To achieve long term cement integrity, it is not only about design of cement slurry, mud removal is one of the key factor need to be considered. Best practices were perfomed to achieve the highest mud removal efficiency. Expansion test was perfomed by using pressure curing chamber at 247°F. Expansion was detected for six days simulation which was considered as enough based on stress analysis simulation of compression, traction and microannulus cement sheath performed. It was indicated that expandable cement managed to eliminate microannulus which was created by pressure and temperature changes. Evaluation was performed by locating pressure sensor at the A annulus of 9 5/8-in liner and 13 3/8-in casing. The sensor indicated zero pressure at the annulus while drilling next two more section and during the production life of the well
Aluminum composite reinforced ceramic particles can be created through stirring process (Stir Casting) so that the molten aluminum to form a vortex as a space for the reinforced of Al2O3 particles well distributed on the aluminum melt. Engineering ceramic particles and vortex formation process will determine the distribution of particles in molten aluminum metal. Mg was added during the melting and argon was flushed to improve wetting system and protect oxidation. In this study, billet Al.6061 was combined with various percentage of Al2O3 from 5Vf % to 20Vf%. The results showed that the optimum tensile strength obtained at 10Vf % Al2O3 with the value of 190 MPa.
A flowing or pressure-sustained annulus is a live threat to the environment, population, vegetation, and natural habitat. In the current oilfield environment under strengthened regulations from regulatory authorities, zonal isolation must be assured before completely abandoning a well. In the west region of Sumatra, Indonesia, a large number of shallow injector wells are drilled; after passing a certain age and productive life, they are abandoned. Most of these wells have lost circulation and therefore need a cost- and time-efficient cement placement method that can demonstrate zonal isolation by means of cement bond logs. The conventional cement placement method across the perforations requires several steps: placing cement, squeezing, leaving the cement on top of the perforations, waiting on cement, drilling the cement, and running the cement bond log. A novel squeeze method was deployed as a solution by combining a chemical contaminant and a squeeze technique. The objective was to perform the cement bond log directly after wait on cement without spending time to drill out the cement. In this technique, cement was placed using a coiled tubing pump-and-pull method: A squeeze was performed in the perforations; then coiled tubing was run into the well below 30 ft of perforations and an engineered contaminant fluid was pumped to contaminate the cement in the tubing. After the recommended wait- on-cement time, the cement bond log was run to confirm zonal isolation across the perforations. This technique eliminated the need to drill the set cement in the slim tubing, saving several days of work time. In most of the wells, the cement bond log showed less than 5 mV, which helped to determine the achievement of zonal isolation. Furthermore pressure tests were conducted to ensure the zonal isolation across the perforated intervals. Engineered cement and contaminant design is required to ensure cement will gain and maintain designed mechanical properties behind the tubing. This paper will discuss the case histories from six wells in the west region of Sumatra field, where the novel coiled tubing placement technique has been applied and proven successful and cost-effective.
Cementing is one of the sequences in the drilling operations to isolate different geological zones and provide integrity for the life of the well. As compared with oil and gas wells, geothermal wells have unique challenges for cementing operations. Robust cementing design and appropriate best practices during the cementing operations are needed to achieve cementing objectives in geothermal wells. Primary cementing in geothermal wells generally relies on a few conventional methods: long string, liner-tieback, and two-stage methods. Each has challenges for primary cementing that will be analyzed, compared, and discussed in detail. Geothermal wells pose challenges of low fracture gradients and massive lost circulation due to numerous fractures, which often lead to a need for remedial cementing jobs such as squeeze cementing and lost circulation plugs. Special considerations for remedial cementing in geothermal wells are also discussed here. Primary cement design is critical to ensure long-term integrity of a geothermal well. The cement sheath must be able to withstand pressure and temperature cycles when steam is produced and resist corrosive reservoir fluids due to the presence of H2S and CO2. Any fluid trapped within the casing-casing annulus poses a risk of casing collapse due to expansion under high temperatures encountered during the production phase. With the high heating rate of the geothermal well, temperature prediction plays an important part in cement design. Free fluid sensitivity test and centralizer selection also play an important role in avoiding mud channeling as well as preventing the development of fluid pockets. Analysis and comparison of every method is described in detail to enable readers to choose the best approach. Massive lost circulation is very common in surface and intermediate sections of geothermal wells. On numerous occasions, treatment with conventional lost-circulation material (LCM) was unable to cure the losses, resulting in the placement of multiple cement plugs. An improved lost circulation plug design and execution method are introduced to control massive losses in a geothermal environment. In addition, the paper will present operational best practices and lessons learned from the authors’ experience with cementing in geothermal wells in Indonesia. Geothermal wells can be constructed in different ways by different operators. In light of this, an analysis of different cementing approaches has been conducted to ensure robust cement design and a fit-for-purpose cementing method. This paper will discuss the cementing design, equipment, recommendations, and best available practices for excellence in operational execution to achieve optimal long-life zonal isolation for a geothermal well.
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