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
Tiung Biru field is a promising development field in East Java, It yielded many discoveries including the Kujung Reservoir containing both gas and oil zones. The operator is only focusing on producing oil zones thus requiring a good annular zonal isolation quality to be able to produce the oil zones without producing the gas zones. Once well construction was finished the cement bond quality behind casing appeared to be mediocre which was compromising the operator production objectives for a number of oil producing zones.Two producing wells in Tiung Biru (TBR) field which produced from Kujung Reservoir were inefficient because of a significant increase of gas production cross flow. A CBL showing high amplitude across the production zone is a strong indication there is communication between a gass bearing zone adjacent to the oil producing interval. Therefore, squeeze cementing was proposed. The success criterion for the squeeze job is the reduction of the GOR (gas oil ratio) by isolating the gas zone from the oil interval close by. The first squeeze cementing attempt was performed with a conventional cement slurry; post job logs showing mediocre cement quality log result and the squeeze was unable to isolate the cross flow. Conventional cement will hydrate and bridge off before it can achieve objective. This paper explains a solution for improving zonal isolation with an engineered and optimized microcement slurry with low fluid loss control, thin filter cake, low rheology resulting in a better stability and performance for the squeeze application. This paper also presents slurry design, execution procedure, pre and post job evaluation.On the execution, slurry can go through the narrow gap behind the casing and improve zonal isolation with evidence of perfect post cement log quality. The slurry penetrated the narrow gaps without dehydrating, and showing good mechanical properties with short setting times (Moulin et al, 1997) which is of prime importance to seal off gas zone and meet isolation objectives. Production test after squeeze also shows that the GOR had reduced drastically.
Zonal isolation is an important thing to acquire good cement integrity. One of many ways to evaluate this is by running Cement Bond Log (CBL). Well condition prior, during, and after cement placement contribute high impact on the result of CBL. Aside from that, temperature and pressure changes also give significant outcome to CBL result. In this paper, some improvements wereapplied and the logging results showed significant impact on zonal isolation compare to previous well. Objectives of this paper include improvement applied on case studies to obtain good zonal isolation and no remedial cementing required, emphasizing on applied cementing best practice recommendation, and introducing expanding agent in order to recover micro annulus. Well integrity is a vital element to have long well life cycle. The paper describes the enhancementfrom poor zone isolation in previous well to be better in next well and this became one of best practices of cementing design and execution for Operator. Improvement in mud removal was done by adding spacer volume with high concentration of turbulent spacer. Cement slurry had expanding agent in the system and smart retarder which provided better compressive strength. Improvements in cement system were seen in faster compressive strength build up and ability to recover micro annulus. Linear expansion result from expanding test is 80 μm in 7 days, which is sufficientto cover micro annulus that has happened before in previous well. The designed slurry was also supported by using more centralizers in execution. Quality check was done by measuring rheology of drilling mud and spacer. Cementing job was executed with no issues and following job program. Evaluation of cement job supported with the playback pressure data. Result of CBL result showed that good bonding was achieved on upper and lower side of interest zone.
The cement sheath of an oil or gas well is designed to prevent fluid communication between the drilled formations during the productive life of the well through post-abandonment. However, even when cement initially provides good hydraulic seal, zonal isolation can deteriorate after initial placement due to microannuli formation. In many cases, a microannulus can be formed because of wellbore temperature changes, wellbore pressure changes, or set cement bulk shrinkage.Microannuli are considered serious concern in gas wells because, unlike liquid, gas flows easily to surface through very narrow microannuli. Cementing operations which fail to provide adequate zonal isolation may result in loss of isolation which poses a hazard to both personnel and the environment. A cement that has ability to expand post set, can help prevent the formation of microannuli. The concept is that the expanding cement will fill microannuli and ensure good bonding either between the formation and the cement or between casing and the cement. This paper discusses the application of expanding cement in two large gas fields; located in South Sumatra. In those fields, wells are produced using 7-in production tubing, with 13 3/8-in casing and 9 5/8 in liner as production strings. Production strings are constantly exposed to changes in pressure and temperature, both during drilling and during production. These changes can create stresses on the cement sheath and may create microannuli. There is a particular focus on the isolation around 13 3/8-in production string: unlike the 9 5/8-in production liner string, the 13 3/8-in string relies only on cement to isolate the gas zones, without any packer. This string needs to provide isolation is critical to ensure that the well can perform as designed and pose no hazard to personnel and to the environment. The paper also discusses the design steps and considerations, as well as evaluation results.
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