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This paper presents an investigation of several slurries using field and laboratory prepared drilling fluids solidified with Blast Furnace Slag. The data presented includes base mud properties, final slurry composition, and slurry properties. This investigation includes measurements of the common properties of thickening time, compressive strength, free water, etc. It also includes an evaluation of the bulk shrinkage ot the set material, shear bond, etc., as well as rheological compatibility studies of the finished slurries with the base muds. These additional tests are considered critical in the potential application of this process under field conditions. Results of large scale bond log tests are included.
One of the main benefits from any mud solidification process is the reduction in the environmental impact. The benefit is due solely to the reduction of the volume of mud disposal requirements. Due to the dilution requirements of the mud for the incorporation of the Blast Furnace Slag, the actual volume of mud that can be "saved" from disposal may be considerably less than that reported. This study evaluates the actual reductions in disposal volumes while accounting for the dilution volumes. Economic comparisons from field operations are included as well as a theoretical comparison for zero discharge areas like Mobile Bay. Operational considerations and the economics of required mud isolation and storage are reviewed.
From the laboratory data evaluated, environmental, and economic evaluations, it is apparent the use of Blast Furnace Slag slurries for oil field applications must be carefully evaluated on a per case basis. While the process may be a viable mud solidification process, the replacement of Portland cement by this material may compromise some properties considered essential in a cementing operation.
For this investigation, three typical field muds were chosen. The muds were taken from wells representing various parts of the drilling process. An 8.8 lb/gal lightweight spud mud typical of surface holes, a 12.6 lb/gal mud often seen at intermediate casing points and a 17.6 lb/gal mud representative of the final stages of a well were used as the base muds for this study. The mud properties for each mud are listed in Table 1.
Blast Furnace Slag (BFS) slurries were prepared for each of the muds. A temperature of l85°F BHST was chosen for the investigation as this is typical for a 10,000 ft well (with a 1.1 temperature gradient) in the Gulf of Mexico. The aim was to prepare a BFS slurry that would give three to five hours of thickening time at 150°F BHCT. The formulations used for preparing the BFS slurries are found in Table 2. Note that the BFS concentration is expressed in pounds of BFS per finished barrel of slurry. In earlier investigations1-3 it is not clear whether the BFS was added to a barrel of diluted mud or was expressed as pounds per finished barrel. If the concentration of BFS is expressed in pounds of BFS added to a barrel of mud, the apparent concentration is higher. This is due slmply to the additional volume taken up by the BFS. For example, in this study Mud 5 has 300 lb BFS per finished barrel or 428 lb added to a barrel of diluted mud.
New lightweight cement technology, based on increased cement fineness, has been developed in response to problems associated with cementing primary oilfield casings in cold environments. When low density slurries are required at low temperature conditions, adequate compressive strengths may be difficult to obtain. The new technology presented in this paper, called ultrafine cement, offers lightweight cement slurries paper, called ultrafine cement, offers lightweight cement slurries (10.0 lb/gal-13.0 lb/gal) which exhibit much higher early compressive strengths than conventional lightweight systems when cured in cold environments (40 deg. F - 80 deg. F).
By means of laboratory investigation, this paper introduces ultrafine cement as a unique lightweight primary cementing material. Performance properties of ultrafine slurries are discussed and comparisons to commonly used lightweight cements are presented.
Cementing oilfield casings in cold environments has been a challenge to field operators for many years. The in capability of cement slurries to gain early compressive strengths in these operations has led to increased research efforts and development of various types of accelerated cement compositions. Low temperature cement designs and proper cementing techniques, from the permafrost of the Alaskan North Slope to the cold waters of offshore exploration, have been documented extensively. Few papers, however, have been written on the performance of lightweight cement slurries in cold environments because very few lightweight cement slurries are available which can perform under low temperature conditions.
Recent advancements in particle size technology, however, have yielded a new ultrafine cement that performs with exceptional results at low temperatures. Tested in the laboratory from 40 deg. F to 80 deg. F, ultrafine cement slurries exhibit early compressive strengths more rapidly than conventional lightweight slurries of equal density.
Ultrafine cement technology was introduced initially to oilfield operations for remedial cementing. While use in this area continues to grow, refinement of the cement in both its physical and chemical properties has resulted in particle sizes physical and chemical properties has resulted in particle sizes that are 10 times smaller than standard oilfield cements. Increased surface area, requiring significantly more water, results in a low density mix, ideal for use in lightweight primary cementing applications.
The advantages of ultrafine cement for primary uses include less waiting-on-cement (WOC) time, a stronger cement sheath during drillout, simple slurry design - (cement and water), and other secondary benefits.
A detailed discussion of the properties and applications of ultrafine cement for primary cementing are presented in this paper. Also presented is a review of lightweight cement paper. Also presented is a review of lightweight cement compositions currently used in cold environments, including performance comparisons to ultrafine cement. performance comparisons to ultrafine cement.
Lightweight cements play a vital role in primary cementing operations. A prime reason for the use of lightweight cement is the reduction of hydrostatic pressure when cementing across a weak formation. Other uses for lightweight slurries include preventing lost circulation during pumping operations, preventing lost circulation during pumping operations, eliminating "fallback" after the cement is placed, cementing long annular columns, or as a "filler" cement to lower costs.
Abstract In deepwater Gulf of Mexico, the use of synthetic-based drilling fluids (SBM) is common practice in all types of wells drilled by different operators. These fluids have been under constant development in past years. However, even with the latest in SBM technology, cementing operations can be adversely affected when this type of fluid is used, which can compromise the quality of the cement jobs. One of the challenges faced is the rheological incompatibility between the cement slurry and the SBM. This may lead to issues such as induced losses during primary cementing operations, due to higher friction pressures, or stuck pipe during plug placement, among others. The higher friction pressures during cement placement in primary jobs can also lead to an inaccurate or inconclusive post-job evaluation when attempting to match software-simulated pressures with actual pressures acquired during the jobs. Despite the use of mechanical separation and spacers, the post-job analysis of several recent cement jobs suggests that contact between cement slurry and drilling fluid is often still occurring. As expected, this contact is most frequently occurring in the annular space wherein there is typically an absence of mechanical separation. In these jobs, laboratory test results using mixtures of slurry and SBM with various ratios have shown levels of incompatibility, which have been correlated to evidence of higher-than-expected friction pressures in the same jobs. The solution proposed for this scenario is to add surfactant or surfactant-based chemical additives at low concentrations to the cement slurry. The addition of surfactant to cement slurries has been proven to reduce rheological incompatibility between the slurry and SBM and the impact of contamination on set cement properties. This paper presents the laboratory test results, operational concerns, mitigation, and a case study showing the application and effectiveness of this technique comparing similar strings that were cemented in different wells.
This paper is presenting an overview of a refined methodology to secure optimal control of slurry properties for coiled tubing squeeze cementing. The basis is accurate specifications of critical slurry properties, specialized test procedures and slurry mixing procedures.
Special emphasis is placed on properties of filter cake generated during a squeeze. It was verified that slurries with copolymer type fluid loss additives as well as latex based fluid loss control additives produced firm, predictable filter cakes, while retaining other critical properties.
Shear energy imparted to the cement slurry proved to influence several slurry properties. Laboratory and field data verified that filter cake height, fluid loss, slurry consistency and thickening time stabilized when a certain level of shear energy was reached. Reproducibility of test data between laboratory and the field was within acceptable limits.
Specialized methods for preparation of cement slurries, in the laboratory as well as in the field, are described along with the supporting theory.
Quality assurance procedures throughout the process are described in detail.
Cement squeeze operations for profile modifications and zone abandonment, have been done on a routine basis in the Prudhoe Bay Field on the North Slope of Alaska for a number of years.
Rapid production declines led to initiation of an aggressive fracturing program in 1990. During fracturing operations extreme differential pressures were employed, often resulting in failures of squeezed perforations. In mid-1990 a coiled tubing squeeze program which increased final squeeze pressures from 1,500 psi to 3,500 psi was implemented. This resulted in stronger squeezed perforations and increased success ratio for CT squeezes.
The success of a coiled tubing squeeze operation also depends heavily on the performance of the cement slurries pumped. It should be noted that the performance criteria for a coiled tubing squeeze cement system are considerably more stringent than those for primary cementing. Therefore, predictable cement systems, and procedures, giving superior reproducibility had to be developed. Difficulties in achieving the desired slurry properties, both in the preparation for a job, and on location complicated the operations and increased the cost of the operations.
Abstract When constructing deepwater wells, incompatibility between synthetic-based mud (SBM) and Portland cements can lead to poor cementation and loss of cement integrity, which in turn may compromise zonal isolation. An alternative cementitious material based on geopolymers has been developed with improved SBM compatibility for primary and remedial cementing purposes as well as lost circulation control. Geopolymer benefits go beyond mere SBM compatibility: it is in fact possible to solidify non-aqueous fluids such as SBM and oil-based mud (OBM) using geopolymer formulations. This also means that non-aqueous fluids (SBM, OBM) can be disposed of in a cost-effective way, which presents a viable option for environmentally acceptable on-site or off-site disposal of drilling muds and cuttings. Geopolymer is a type of alkali activated material that forms when an aluminosilicate precursor powder (such as fly ash) is mixed with an alkaline activating solution (such as sodium hydroxide). A novel SBM solidification method was developed by blending varied amounts of geopolymer and SBM. This solidification method was tested with various sources of precursor powders, SBMs and OBMs. The rheology and strength of the geopolymer/SBM blends were measured under downhole conditions. Strength testing results showed that geopolymer cement lost only 30% of its strength when blended with 10% SBM, while a neat Portland slurry lost 70% strength. Geopolymer/SBM blends containing up to 40% SBM were found to have measurable strength when cured under downhole conditions. By changing the amount of geopolymer and SBM in the slurry, the geopolymer/SBM system can be developed into a lost circulation treatment with low compressive strength, or into a primary cementation material with higher compressive strength. The geopolymer/SBM blends at different mixing ratios have shown great improvement in rheology of the geopolymer cement, allowing for pumpability of the slurry for well cementation. For instance, 30% SBM blends have downhole rheology profiles that approach those of neat Portland slurries.