Sustained casing pressure, otherwise known as casing-casing annulus (CCA) pressure, is a common problem encountered in the deep, high pressure, high temperature (HPHT) gas fields of Saudi Arabia, and in many other locations globally. Although many solutions have been tried in these fields over the years, none of the existing solutions have proven to be 100% effective. A new solution has recently been implemented in Saudi Arabian gas fields that features a combination of heavy-weight cement blends greater than 21ppg and a polymer resin to improve the mechanical properties of the cement, especially the shear bond, to prevent the CCA pressure. Polymer resin is also resistant to hydrocarbons, acids, and salts, enabling the cement-resin system to be placed in harsh environments. This resistance will help to maintain a dependable barrier throughout the life of the well. This paper presents a case history of the application of this heavy-weight cement-resin (HWCR) system in the Saudi Arabia Harradh field where the failure of a differential valve (DV)packer meant that there would be no redundancy backup should the cement fail to provide a full barrier in the annulus. The paper describes the process used to design the HWCR system and how its application is critical to the success of the job.
In certain regions of oil and gas operations, lost circulation is a common occurrence, especially when a majority of the openhole exposed during primary cementing is carbonate-based formations. This can lead to lost circulation risks in most applications. To overcome lost circulation risks during primary cementing, a new tailored spacer system shows to improve the cement placement success. The manuscript discusses the quality assurance and performance testing with field cases demonstrating the value contributions of the spacer for achieving zonal isolation requirements as well as the top of cement objectives. The work efforts presented shows a spacer meeting and sometimes showing incremental wellbore strengthening in comparison to the published literature for existing available spacers used to overcome similar lost circulation risks.
The high-pressure/high-temperature (HPHT) environment poses different challenges for a cement design. In addition, there are challenges with the tight annular clearances across the liner overlap with the previous casing, and then finally achieving the desired top of cement. Engineering solutions and best practices can be implemented to overcome the challenges encountered while cementing under these conditions. A heavyweight engineered spacer with loss circulation material and an expandable-rotatable liner hanger were key components of the success. Thoughtful analysis of the equivalent circulating density (ECD) resulted in the design of the train of fluids with a density difference of no more than 0.5 ppg. However, to overcome the risk of losses, an engineered spacer with a tailored load of its main component based on extensive lab testing was used. The weighting agent was carefully selected to ensure stability and rheological hierarchy. The cement job was performed with backside pressure applied with Managed Pressure Cementing (MPC) to keep a constant downhole pressure. To improve displacement efficiency and enhance cement bonding, an expandable liner hanger was rotated throughout the entire job and set afterwards. The best practices implemented to cement the 9 5/8in liner resulted in performing the cement job without losses or flow. The ECD was kept within 5% from the mud weight density, based on the pressure match simulation. No abnormal pressures were observed while pumping and displacing indicating no settling issues were endured with the engineered spacer. Additionally, the liner hanger's unrestricted bypass area assisted in reducing the ECD's as no slips were required to keep it in place. The liner hanger was successfully rotated at 15 rpm throughout the job providing good cement placement. After the cementing job, the Liner hanger expanded successfully which confirmed the liner top integrity with a metal-to-metal seal. The expandable liner hanger also allows for less leak paths in the system along with providing high sealing and loading capability in high temperatures with a gas tight seal rating. After the wait on cement (WOC) time, the positive and negative tests were performed successfully meaning that a sustainable barrier was achieved. This paper describes a success story while cementing under HPHT conditions with very narrow margins between pore pressure and fracture gradient and depicts the best practices that contributed to the success of the job, such as using a heavyweight engineered spacer with LCM and an expandable/rotatable liner.
A cleaning system that effectively displaces movable and immovable mud from the wellbore prior to cementing is key for a successful cementing job and for long term zonal isolation. If in addition, the cleaning system can help in minimizing losses while showing proper compatibilities with mud and cement both, this will provide another assurance for a competent cement sheath in the wellbore. This new spacer system was tailored as per the actual wellbore conditions for Saudi operations. To analyze the behavior of the new spacer system under different conditions, fluid compatibilities were performed with diverse drilling fluids and cement slurries. The stability of the new spacer was also verified under static and dynamic conditions. Furthermore, this spacer was tested with and without Lost Circulation Material (LCM) through different slot sizes ranging from 500-5000 microns along with a Particle Plugging Apparatus (PPA). This test was used in determining the spacer's capability to plug the slots under different pressure and temperature ranges. In this study, spacer design was optimized to maintain the rheological and density hierarchy requirement between three fluids - drilling fluid, spacer, and cement slurry. Spacer design was tailored to maintain the above-mentioned hierarchies at both surface and downhole temperatures. It was found that the new spacer system has improved compatibility results with different drilling muds and cement slurry systems even without adding any additional viscosifier agents. The tailored spacer proved its stability under high pressure high temperature (HPHT) conditions using a consistometer with no settling and zero free fluid. In addition, it shows to effectively plug a 500-micron slot disk and was able to seal up to 5000 microns when LCM was added across different pressure ranges (100, 500 and 1000 psi). In addition, field trials for wells encountering dynamic and static losses were performed where spacer with LCM was pumped after considering critical flow path and minimum flow area restrictions. As a result, the new spacer proved to be compatible at multiple densities, demonstrated its ability to bring cement to desired depths, and helped in improving Cement Bond Logs (CBLs). The application of this engineered spacer system is extremely valuable for the fields having low fracture density formations. Pumping this spacer, will not only help in the effectively cleaning of wellbores prior to receiving the cement but also in forming a seal to reduce any loss circulation issues. This will help in bringing the top of cement (TOC) to the desired depth and ensuring placement of a dependable barrier throughout the life of the well.
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