The study presents an innovative cement spacer fluid based on microemulsion technology and an operationally simple cement design using a water-based multifunctional polymer. A case history is described where their combination was successfully applied on a deepwater exploration well in the South China Sea. Laboratory testing, modeling, and engineering design that preceded the field operation are outlined. The spacer's performance to clean the mud from contact surfaces was verified with the goniometer method. Mud/spacer and spacer/cement tests for optimum compatibility were conducted and a fluid friction pressure chart for the mud-spacer-cement train at different displacement rates was generated. The results show that the designed spacer is highly effective in displacing the mud and converting an oil-wet surface to a water-wet surface, and therefore to provide a clean and water-wet surface to which cement can strongly bond. A water-based multifunctional polymer in the designed cement slurry was tested to validate its ability to adjust slurry properties for deepwater challenges. The cement slurry was easy to mix at surface, stable under downhole conditions, and had a sufficient short transition time at low temperature, preventing water and gas intrusion. Furthermore the evaluated multifunctional polymer was found to work as a stabilizer and extender as well as provide very good fluid loss, free fluid, and gas control. As a consequence, the multifunctional polymer reduces the total number and amount of required chemicals, thereby simplifying logistics and operations for deepwater wells. The presented spacer and cementing technologies contribute to successful zonal isolation of deepwater wells and so minimize risks as well as expensive rig and nonproductive times due to remedial work.
Cementing is one of the most critical steps in the well construction phase. Qualified cement integrity is considered a barrier to inhibit fluid migration to surface. For conventional wells, cement in addition to barriers such as BOPs (Blow Out Preventers), fluid hydrostatic pressure, and mechanical methods are used to ensure fluid migration is inhibited. For top-hole sections of deepwater exploration wells however, cementing is your only barrier to mitigate uncontrolled fluid flow to the seabed. During the top-hole operations (typically 36-in. and 26-in. hole sections), the bore hole is drilled without a riser and returns are taken to seabed. This creates difficultly in controlling shallow hazards such as gas hydrates and shallow water flow because the well cannot be killed using conventional methods. To assure mitigation of shallow hazards, an emphasis is made on achieving short transition times for cement designs.For South China Sea operations, it is common practice to incorporate cenospheres (dry blended lightweight additive) into the cement design to ensure suitable properties are achieved. However, the use of cenospheres requires blending onshore and excess blends to be shipped offshore for contingency purposes. Although required slurry properties can be achieved with cenospheres; logistical issues, left over disposal concerns, costs, and low cenosphere pressure ratings create a complex operation. In addition, cement systems should be designed to incorporate loss of lightweight material during transfer offshore, and must account for higher down-hole densities due to crushing of lightweight cenospheres. All of these processes require great emphasis on Quality Assurance / Quality Control (QA/QC) and economic concessions.Other unique challenges that must be accounted for are low temperatures, commonly around 4°C (50° F) at seabed, low fracture gradients, enlarged hole sizes due to high rate of penetration (ROP) drilling, and environmental regulations due to returns at seabed. The cement system must be designed for all the above aspects, and still maintain excellent integrity to enable the BOP stack to be installed upon a firm foundation.This study will describe a new simplified cement system which exhibits excellent slurry properties necessary for a deepwater environment. Laboratory results and engineering procedures will be reviewed to demonstrate that all necessary qualities for mitigation of shallow hazards are met. Furthermore, logistical and HSE advantages will be highlighted, and two case histories will be discussed. TX 75083-3836, U.S.A., fax +1-972-952-9435
Capillary tubing has traditionally been used for various downhole chemical treatments applied to enhancing fluid loading, treating corrosion and scale buildup, and preventing paraffin and emulsion formation. Capillary tubing provides an advantage over coiled tubing due to its lighter weight, smaller footprint, mobile structure, faster running speeds, and more economical costs. One drawback however, is the increased friction pressures when pumping abrasive fluids. Typical capillary tubing is sized from ¼ to ¾ in. OD versus the more common coiled tubing, which ranges from 1 to 3 ½ in. OD. Therefore, the use of capillary tubing for cementing operations has not been considered until recently. This paper will feature a project in Australia where a capillary unit was employed to abandon a well with cement, while concurrently installing downhole pressure gauges to comply with local regulations. The cement design criteria along with two case histories will be described, and lessons learned will be evaluated. Data that has been collected through the various jobs will demonstrate that current simulation software will need to be modified to match pressure outputs witnessed in the field. A comparison of simulated versus actual job pressure data has shown as much as a 70% friction reduction in actual pressure readings. The witnessed pressure values are shown to be consistent over several operations; therefore a theoretical correlation can be drawn so more realistic values can be simulated in the future. Additionally, slurry designs which were proven successful and operational considerations for improved job quality will be discussed. This paper will discuss two case histories in which capillary tubing was used for the first time in Australia. Methodology, limitations, and future improvement possibilities will be discussed in detail throughout this paper.
Utilization of chemical treatment to isolate or shut off zone is not uncommon in this industry. Cement will normally be chosen as candidate to perform the job as it is more permanent and more economically effective. With recent advanced technologies, cement particles are now designed to be in smaller particles yet still be able to develop sufficient amount of compressive strength for effective zonal isolation and hydraulic seal. Magnesium based Ultrafine Cement System was chosen as chemical candidate to be used in Sarawak West Oil Field. The primary purpose of using this cement system is to penetrate through Wire Wrapped Screen with Mesh Size of 20/40 in the completion. The utilization of Ultrafine Cement in the operation was incorporated with Calcium Carbonate and Cement G slurries. Calcium Carbonate will act as the suspension fluid while Cement G slurry will be pumped to fill up the inside volume of Wire Wrapped Screen after Ultrafine Cement being pumped to occupy the outside volume of Wire Wrapped Screen. Compatibility test between Ultrafine Cement and the two slurries had been tested in the laboratory and it was reported that there was no significant change of viscosity value when they are mixed together. Application of Ultrafine Cement in Sarawak West Oil Field indicated that all Ultrafine Cement pumped during the operation was managed to pass through the 20/40 Mesh Size. Tubing Clearance Check (TCC) by Slickline showed high held up depth (HUD) but Coiled Tubing was used to run in hole to confirm on the HUD depth. It was reported that there was no significant weight loss when Coiled Tubing passing through Slickline HUD. Coiled Tubing stopped run in hole at Top of Calcium Carbonate to avoid disturbing the suspension fluid. Based on this situation, it is also known that there was no presence of Ultrafine Cement settle on top of Calcium Carbonate at all due to its efficiency in penetrating the Wire Wrapped Screen.
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