The global oil market remains uncertain in terms of the potential risk factors affecting the project deliverability targets. Therefore, the operators and service providers should continuously strive to enhance operational efficiency. The Tembikai field is a marginal field in shallow waters offshore Malaysia. Meeting the operational efficiency targets was paramount to develop and make the field economically viable. To achieve the aggressive targets, a fully offline cementing operation was introduced, which resulted in an average savings of 24 hours by offline cementing alone and 14% improved operational efficiency for each well. The five Tembikai Gas development wells were batch drilled using a jack-up rig. All wells consisted of 9 5/8 in. surface casings, 7 in. intermediate casings, and 3 1/2 in. cemented monobore completion tubing. Offline cementing for all three casing strings was planned. The offline cementing operation was performed after landing the casing at desired depth, then the rig is immediately skidded to the next well slot. While the casing is cemented offline, the rig drills the next well section, thus creating simultaneous operation efficiencies. After completing the surface section of each batch drilled well, the rig is positioned to the first well again to drill the intermediate section and the same process is repeated. Offline cementing eliminates wait on cement time (WOC) and enables the operator to perform other activities offline like running the gyro on the slickline to survey the inside of the previous casing, running cement bond logs etc. To perform the offline cementing, a separate high-pressure cementing line was rigged up to the platform. A custom-made offline cementing assembly was used. A special compact cement head, preloaded with cement plugs, was rigged up above the wellhead compact housing. This compact cement head is 33% shorter and lighter than conventional cement heads, which helped improve the safety aspects of this operation. Providing a dependable zonal isolation barrier is key for the success of an offline cementing operation. Tailored cement slurries for each section were designed to meet well requirements and advanced three-dimensional (3D) modeling software was used to simulate hole cleaning and cement slurry placement. All risks and mitigations for offline cementing such as shallow gas hazards, losses, gas kick etc. were covered in the cementing design of service (DOS) document. As a result of detailed planning and focused execution, 24 hours were saved per well by offline cementing alone, resulting in an average of seven days per well from drilling to completion of all wells in the campaign. The collaboration between the operator and cementing service provider for offline operations has proven to be a significant shift in operational efficiency in Malaysia, with time and cost savings achieved. These wells have achieved the lowest well cost per foot for current development wells in Malaysia.

One objective of well abandonment is to help prevent pollution to the environment from residual fluids left in the well post caprock restoration. These fluids may have been present in the annuli when well construction was commenced. They are normally removed when the casing(s) is retrieved from the well and capped with an environmental cement plug, or more recently, via perforating the casing(s) and circulating out the annuli contents prior to setting the environmental cement plug. Gaining access to the annuli is achieved via tubing conveyed perforation (TCP) guns and the charges are designed to penetrate the targeted casing(s) with sufficient entry hole diameter (EHD) without causing damage to the casing beyond. Fluid is then circulated into the annuli via the perforations with returns taken through the wellhead side outlet valves (SOVs). Cement is subsequently circulated into the annuli and a wellbore cement plug is placed above the cement retainer thereafter to form an environmental plug. This approach requires two trips, the first where the mechanical setting tool, cement retainer with TCP guns attached below is run into the well to perforate the casings and perform the cement circulation. The second trip is with a cement stinger to place a wellbore plug above the cement retainer after the Mechanical Setting Tool (MST) has been retrieved. The retrieval of the MST is required as the MST outside diameter (OD) is almost equal to the inside diameter (ID) of casing. This can cause cement swabbing and contamination if pulled through the cement plug after the placement. In this case, an alternative Bottomhole Assembly (BHA) was explored where the entire operation can be performed in a single trip. This involved the use of a hydraulically set cement retainer that comes with a slick tubing for placing the cement plug once the running tool is removed from the cement retainer. The cement slurry design was tailored to allow for additional thickening time to compensate for the single trip run. A successful trial was performed in Brunei's operations in the 3rd quarter of 2021, where the cement was placed immediately above the cement retainer after annuli fluids removal and cement circulation in the B and C annuli after perforations were completed. A single trip system with revised cement slurry design has also been trialed successfully to enable removal of residual fluids and cementing of the annuli and a wellbore cement plug to be placed in a single trip. This reduces HSE exposure to the crew and achieved significant time and cost savings.

Tailoring slurry designs using amorphous liquid silica base has been a success for Cementing Extended Reach Drilling (ERD) wells in Brunei in development fields. The use of this unconventional slurry density and design has helped to achieve the necessary top of cement and required zonal isolation for the production string of these wells. Cementing across depleted formations has been a challenge for the drilling sector within the oil industry. Isolation of production zones with competent cement slurries has become a necessity in fields, especially where a low Equivalent Circulating Density(ECD) during the cementing operation is required to achieve the desired top of cement in low fracture gradient formations. For Brunei offshore operations a novel approach has been proposed that uses an amorphous liquid silica-based slurry system to design a new 14 ppg lightweight cement slurry. The slurry properties were tailored to eliminate the need for a dual slurry system. Planning, execution, and post-operation evaluation methods have been developed for this new design. Extensive laboratory testing has been performed for the 14 ppg extended slurry which includes basic slurry testing as well as more advanced evaluations such as a full mechanical properties study and finite element analysis that was used compared to conventional slurry designs. Various optimizations were done for the slurry design to overcome mixability challenges and deployment using a conventional offshore liquid injection system or by premixing the water with liquid additives on a mixing tank or rig pits. To validate this technology, a field trial was performed at the rig site where a production liner for an extended reach well was cemented and subsequently evaluated using cement evaluation logging tools. The first Brunei offshore trial operation, executed in Q2 2020, was a 4.5-in. production liner where 16.5 m3 of a 14ppg novel slurry design was mixed, pumped and successfully placed within the annulus. Since the initial trial, a total of 8 jobs have been executed successfully in Brunei, with a few more wells identified as candidates for this solution. The paper provides laboratory testing details, hydraulic simulation validations along with job execution and post-operation cement evaluation.

Drilling and cementing across permeable, naturally fractured, and depleted formations have become some of the most common challenges across the world. A major operator in Offshore Brunei was facing similar challenges across such formations. The primary objective of the cementing job across this difficult formation was to isolate shallow hydrocarbon zones. Achieving desired top of cement (TOC) without inducing losses was the major design challenge. Drilling across such formation generally leads to loss circulation scenarios. This makes subsequent cementing operation more challenging. In order to minimize losses during the cement job, an innovative tailored spacer system was designed and pumped immediately before the cement slurry. This tailored spacer system not only helped in mud removal and wellbore cleaning but also helped to mitigate losses during cementing. Spacer and cement slurry density and rheology was optimized with the help of an advanced hydraulic simulator and industry leading computational fluid dynamics (CFD) software. To check the effectiveness of the spacer system, several laboratory tests were conducted to determine the spacer system's ability to plug a porous medium. Specialized particle suspension analysis was conducted to assure that the spacer design can maintain the fluid system's solid transport stability under both dynamic and shutdown periods. This helped to avoid plugging off restrictions such as critical flow paths in float equipment and the liner hanger. To validate the spacer design, several field jobs were executed for surface, intermediate and production casing scenarios. For each job the spacer design was tailored for the wellbore condition based on the severity of losses. For such jobs, initial purely hydraulic simulations predicted the possibility of losses. No losses or substantially reduced losses were noted for the cement jobs where this tailored spacer system was used. These results validated that the tailored spacer helped to mitigate the loss potential from the hydrostatic pressure. Top of cement was also validated based on fluids returns to surface and final displacement pressure. The first cement job using this innovative spacer system was executed for a 13-3/8inch surface casing job in Q3-2020. 100 bbls of an 11 ppg spacer was pumped across a permeable formation ahead of the cement slurry. Cement returns were observed at surface. Since the first job, 14 cement jobs using this innovative spacer system have been successfully executed in offshore Brunei for various casing sizes.