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In its recent infill drilling campaign, an operator offshore Malaysia was facing challenges to isolate the shallowest hydrocarbon zone during the Production Liner and Casing cementing operations. This challenge is mainly caused by the severely depleted reservoir section resulting from existing wells production and a naturally weak formation. Cementing across this formation requires cement slurry optimization particularly in terms of Density and Rheology. The primary goal of the cement job is to ensure that the Top of Cement (TOC) reaches the minimum required height and provides a sustainable barrier for zonal isolation downhole. This can only be achieved by managing the Equivalent Circulating Density (ECD) effect to be below the fracture gradient which indirectly avoids losses during cementing operations. Based on the predicted fracture gradient and pore pressure, optimization on mud weight against borehole stability requirement, casing design, casing shoe depth and hole size was made and based on the engineering simulation and sensitivity analysis, it is important to consider the overall properties, pumping procedure, and effect of mud-spacer-cement to mitigate the risk of losses during cementing operations and achieve the desired TOC. From the desktop engineering simulation and lab analysis of few formulations’ options of normal G-cement, proprietary blend and spacers, the team has opted to include a loss-circulation spacer pill to be pumped ahead followed by a tailored high strength low density cement design. Throughout this article, the hollow light beads will be referred as high strength low density beads. This approach reduces the overall fluid (spacer & cement) downhole ECD, maintains the rheological hierarchy compliance among all fluids, improving mud displacement efficiency, encourages good cement bond with the formation, and helps to achieve the required minimum cement compressive strength for future well perforations scope. Post-cement job condition testing was also conducted in the laboratory including sedimentation test and survivability (%) between crushed (popped) density of cement slurry with high strength low density beads against increasing pressure exposure test to ensure no segregation of particles takes place after the cement sample hardens, by measuring the static stability density in several specimens, with multiple pressure exposures versus density performance conducted which aim to validate the survivability of high strength low density beads cement particles, simulating downhole conditions upon cement placement. The need to introduce high strength low density beads particles into the cement formulation option is driven purely due to lower Specific Gravity (SG) than that of fresh water. The beads type, size and usage are also designed specifically based on its pressure rating (ability to withstand up to the rated pressure before crushed and later causing the slurry density to be higher than the design intent). High strength low density beads bulk blend cement transfer requires extra handling precautions due to component size and material weight. Excessive pneumatic pressure during transfer operations may cause overproduction of dust through vent lines creating an inhomogeneous blend that could potentially impact transfer consequently leading to partial or full blockage of transfer lines. During cementing operations, when the cement slurry is mixed and pumped downhole and circulated up the annulus for the final slurry displacement, the high strength low density beads particles will exhibit higher rheology readings (more viscous) due to the particles inside the slurry. It is vital that the high strength low density beads’ crush point be verified against the maximum pressure exposure to keep the surface and downhole densities constant as well as hydrostatic pressure and ECD profile residing within the formation fracture gradient limit. The two 7" production liners and one 9-5/8" production casing cement jobs utilized 10.5ppg loss circulation spacer pills and 11.0 ppg gas tight properties of high strength low density beads cement design successfully and stably mixed and pumped ‘on the fly’ across severely depleted formation(s) and achieved good zonal isolation(s) above the shallowest hydrocarbon zone as verified with a Cement Bond Log run within 10 days after slurry placement. This success story has instilled the confidence for the operator to adopt similar technical concepts, basis of design, planning and execution for future wells having similar challenges of cementing across depleted formations.
In its recent infill drilling campaign, an operator offshore Malaysia was facing challenges to isolate the shallowest hydrocarbon zone during the Production Liner and Casing cementing operations. This challenge is mainly caused by the severely depleted reservoir section resulting from existing wells production and a naturally weak formation. Cementing across this formation requires cement slurry optimization particularly in terms of Density and Rheology. The primary goal of the cement job is to ensure that the Top of Cement (TOC) reaches the minimum required height and provides a sustainable barrier for zonal isolation downhole. This can only be achieved by managing the Equivalent Circulating Density (ECD) effect to be below the fracture gradient which indirectly avoids losses during cementing operations. Based on the predicted fracture gradient and pore pressure, optimization on mud weight against borehole stability requirement, casing design, casing shoe depth and hole size was made and based on the engineering simulation and sensitivity analysis, it is important to consider the overall properties, pumping procedure, and effect of mud-spacer-cement to mitigate the risk of losses during cementing operations and achieve the desired TOC. From the desktop engineering simulation and lab analysis of few formulations’ options of normal G-cement, proprietary blend and spacers, the team has opted to include a loss-circulation spacer pill to be pumped ahead followed by a tailored high strength low density cement design. Throughout this article, the hollow light beads will be referred as high strength low density beads. This approach reduces the overall fluid (spacer & cement) downhole ECD, maintains the rheological hierarchy compliance among all fluids, improving mud displacement efficiency, encourages good cement bond with the formation, and helps to achieve the required minimum cement compressive strength for future well perforations scope. Post-cement job condition testing was also conducted in the laboratory including sedimentation test and survivability (%) between crushed (popped) density of cement slurry with high strength low density beads against increasing pressure exposure test to ensure no segregation of particles takes place after the cement sample hardens, by measuring the static stability density in several specimens, with multiple pressure exposures versus density performance conducted which aim to validate the survivability of high strength low density beads cement particles, simulating downhole conditions upon cement placement. The need to introduce high strength low density beads particles into the cement formulation option is driven purely due to lower Specific Gravity (SG) than that of fresh water. The beads type, size and usage are also designed specifically based on its pressure rating (ability to withstand up to the rated pressure before crushed and later causing the slurry density to be higher than the design intent). High strength low density beads bulk blend cement transfer requires extra handling precautions due to component size and material weight. Excessive pneumatic pressure during transfer operations may cause overproduction of dust through vent lines creating an inhomogeneous blend that could potentially impact transfer consequently leading to partial or full blockage of transfer lines. During cementing operations, when the cement slurry is mixed and pumped downhole and circulated up the annulus for the final slurry displacement, the high strength low density beads particles will exhibit higher rheology readings (more viscous) due to the particles inside the slurry. It is vital that the high strength low density beads’ crush point be verified against the maximum pressure exposure to keep the surface and downhole densities constant as well as hydrostatic pressure and ECD profile residing within the formation fracture gradient limit. The two 7" production liners and one 9-5/8" production casing cement jobs utilized 10.5ppg loss circulation spacer pills and 11.0 ppg gas tight properties of high strength low density beads cement design successfully and stably mixed and pumped ‘on the fly’ across severely depleted formation(s) and achieved good zonal isolation(s) above the shallowest hydrocarbon zone as verified with a Cement Bond Log run within 10 days after slurry placement. This success story has instilled the confidence for the operator to adopt similar technical concepts, basis of design, planning and execution for future wells having similar challenges of cementing across depleted formations.
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.
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.
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