In 2018, an operator in Malaysia completed a sidetrack campaign consisting of injector wells. These wells were planned for maximum productivity via sustainable wellbore zonal isolation. The presence of Carbon Dioxide (CO2) in these wells elevated concern about the zonal isolation of cement across the interval. Moreover, for an injector well, the cement must exhibit resilient properties by design of enhanced mechanical properties to provide long-term isolation based on a cyclic wellbore. An advanced slurry system was designed that enabled the set cement to manifest superior properties in three parameters—corrosion resistance against CO2, flexibility against wellbore stress changes, and expansion to mitigate microannuli. The design of the slag-based flexible cement system with expanding additive (slag-flex) considered all three parameters in the fit-for-purpose application of a resilient and flexible expansive cement system in a CO2-rich well. The system’s mechanical properties, such as Young’s Modulus, Poisson’s Ratio, and tensile strength, were verified with laboratory-scale testing and validation against stress analysis software to confirm on the resilient and flexible properties. The laboratory testing result demonstrated the improved properties of the system, including high tensile strength and low Young’s modulus. Furthermore, the reduced water content of the system decreases the permeability of set cement and thus increases resistance towards corrosive substance such as CO2. For certain cases in the past, two separate slurry systems had to be designed—a lead slurry with CO2-resistant properties and a tail slurry with flexible and resilient properties. Often, several issues arose from this practice, including complex logistics due to cement silo blend arrangement and complexity during job execution. Hence, this new system presents a novel idea and methodology that will deliver value to the oilfield industry by integrating CO2 resistance, flexibility and expansion properties in a single slurry system. The system was successfully pumped in wells in Malaysia; no sustained casing pressure has been recorded to date, and wells have been delivered to their intended zonal isolation requirements without compromising well design and overall integrity. This is an innovative application of this type of cement system in the region, and the long-term zonal isolation and well integrity assurance in these and future wells have the potential to save millions of dollars in remedial work. The cement system is currently recognized as the default technology for CO2-rich injector wells in Malaysia.
A seven-well drilling campaign was carried out in Malaysia brown field targeted for enhanced oil recovery (EOR) purpose. The targeted sands were heavily depleted with pore pressure as low as 4 ppg. Good hydraulic isolation in the annulus is critical to prevent the production of unwanted fluid, i.e. water behind casing. The cement evaluation logs performed in the first four wells revealed presence of microannulus response across the same sands in the field. This microannulus occurrence complicated the decision making on perforation intervals. There was a need to prevent or to minimize the microannulus occurrence in the subsequent three wells that planned to penetrate the same sands. A systematic approach had to be taken to integrate the multiple-domains raw datas and a platform was needed to analyze the data to resolve the problems. Integrated workflow was introduced for the first time in South East Asia region. Via integrated workflow, a thorough study integrating the data from multiple domains i.e. drilling data, well trajectory, petrophysical evaluation, pore pressure, cementing design and execution, effective mud removal, centralizers’ performance evaluation and cement evaluation logs, was performed on the first four wells, with the key objective to identify the root cause for the microannulus response. The root cause for the microannulus in these four wells was successfully identified, besides verifying the centralizers’ performance and mud rheology in slurry displacement process. The solution was able to be proposed and implemented in the subsequent three wells’ cementing recipe, which include the usage of lightweight cement, fluid loss optimization and formation netting using fiber. The efficiency of the proposed enhancement on the cementing recipe was verified through the obvious improvement in the cement evaluation logs in the wells that followed the integrated platform recommendations. The microannulus impact was greatly reduced in these wells which penetrated the same problematic sands as in first four wells. The hydraulic isolation evaluation in the planned perforations could be performed with less ambiguity and the confidence on the cement quality for long term well integrity assurance increased. This improvement further verified the key reason identified for the microannulus occurrence. Integrated workflow could increase the level of assurance on cement evaluation by integrating the data via robust workflow and access to the experts in multiple disciplines. The platform provided valuable information by correlating open-hole formation evaluation logs, surface measurements and cementing data using acoustic logs. A complete database was established for cementing planning in future EOR wells. The production data from these newly completed wells complement the study and confirm the efficiency of hydraulic isolation. This workflow has served as maiden approach to develop the cement evaluation integrated platform in South East Asia region.
Hollow-glass microspheres (beads) are widely used to generate light weight cement slurries for cementing across highly depleted zones and weaker formations; this paper discusses tailoring of a cement slurry and the execution of cementing operations for the successful deployment of an innovative liquid bead solution instead of the conventionally blended beads to achieve zonal isolation for a development well in Malaysia. Usage of dry bulk blended beads poses many challenges, such as rig and vessel silo management, quality control of beads, multiple blends on the rig and excess back-up blends. A new approach has been proposed using a liquid bead system to produce a light weight cement slurry by adding beads stabilized within a suspension fluid as another liquid additive to help eliminate the need of dry bulk blending of beads and at the same time accomplishing all the obligatory cement properties for a production casing section in depleted zones. A successful offshore application of liquid beads was executed in a production casing, meeting all the necessary property requirements for cementing in a depleted zone. The cement slurry was developed in a local field laboratory with standard laboratory testing techniques and equipment. Liquid beads can be added to the cement slurry using liquid additive pumps or batch mixed on the surface. Considering the slurry volume of the production section and the importance of a homogeneous cement slurry, liquid beads were injected into the recirculating line of the cement batch mixer. A yard trial was performed prior to the actual job which validated the easy transfer of liquid beads. Relative to the conventional dry-blended approach, this economically more efficient liquid bead cement system was easy to mix and achieved the required design density without any operational issues. The cementing operation was executed with full returns throughout the job at maximum planned displacement rates. To evaluate cement placement, a post job analysis was performed. The first application of this liquid bead technology in Malaysia was to generate a light-weight cement slurry and was successfully implemented for a 9-5/8" production casing where 167 bbl of the liquid bead base cement slurry was mixed, pumped & effectively placed.
Sustained casing pressure (SCP) is a very costly event for any operator either at production phase or at the end of a well’s lifecycle. SCP is a result of incomplete hydraulic isolation across hydrocarbon bearing zone. In one of the gas fields in Malaysia, notoriously known for shallow gas hazard, drilled development wells which have reportedly been suffering SCP. In the past, various improvements in cement slurry design and placement methods were deployed in order to provide complete zonal isolation, especially at the shallow gas sand, yet SCP issue was encountered occasionally. In the current development campaign, different strategy to providing annulus sealing was adopted. This paper discusses proactive steps taken in the slurry design, fit together with the dual stage cementing approach, as a primary means of placing cement above the shallow hazard interval. During the design phase, essential key parameters that would lead to successful placement of cement in the annulus as well as unique slurry design that suits for two stage cementing methods were studied. Risk involved in first stage cementing is one of the most important steps that should be analyzed in detail and put mitigation measures in place to ensure the second stage cement job can be performed as planned. In addition to the slurry properties, such as fluid-loss value, gas-tightness, etc., thickening time and top of cement (TOC) of the lead slurry in the first stage cement job has become enormously critical in designing dual stage cementing job in order to assure cement ports in the stage collar are not covered with hard cement forcing the termination of second stage job prematurely. Besides cementing design, careful selection of the stage collar location and casing annulus packer in the string is also of significant importance in leading to successful two stage cement job. Two development wells with above approached has been delivered and no sustained casing pressure has been experienced. This proactive approach to use two stage cementing as primary plan has proven to successfully eliminate the risk of SCP, which was a frequent struggle in their sister wells drilled with primary cementing in the past in the same field. The risk analysis combined with careful considerations of critical cementing design parameters and selection of stage tool location have become a novel approach to combat against SCP in this gas field.
This paper describes the application of key technique for splitter wellhead cementing of top-hole section in conductor-sharing wells in dozens of development wells in offshore Malaysia. Its objective is to elaborate on the challenges faced during the well planning phase, methodology of cementing technique, cementing slurry design as well as solutions outcome and lessons learnt. Limitations of current software in the industry to simulate the conductor-sharing well cementation and approaches to maneuver through these limitations are also discussed. During the well planning phase, cementing technique to address the risks associated with splitter wellhead cementing such as accidental cementation of dummy string, poor cement coverage in shared conductor, and losses uncertainties were analyzed. The cementing execution results of first batch of wells are examined, i.e. pressure profile, cement returns as well as opportunities for improvement were documented and translated into recommendations leading to eventual success for future well design. The cement slurry design for each casing in the splitter wellhead are also established based on its associated job objectives which is based on the unique approach in splitter wellhead cementing. The establishment of key cementing technique for such an unconventional well construction technology is important in order to ensure continuous success both in cement placement as well as cement slurry design. The best practices are currently being replicated by other major operators in Malaysia for all splitter wellhead cement design. The learnings from the technique are incorporated into the technical standard of Malaysia operator as well to serve as a specific mandated requirement for future operations. An integrated study of wellhead design, drilling practices and cementing technologies enabled a novel methodology to assure long term zonal isolation for the wells and innovation in the cementing approach enable cost savings for the operator as the wells can be drilled in a safe, efficient and cheaper way.
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