Primary cementing practices and compliance in Queensland’s petroleum wells

Cementing production and intermediate casing designs required cement to extend at least 50 m inside the previous casing shoe

Free water content in cement was specified as less than 2%, following API RP 10B-2 (API 2024) guidelines

Pressures during cementing operations, particularly before plug bump, were recorded to assess cement column height and potential downhole problems

Wiper plug assemblies were mandated to ensure plug bump and pressure testing before cement curing.

Formal safety assessment: some operators lacked a formal safety assessment and instead relied on embedded controls within the technical standards, engineering designs and programs. Where risk assessments were present, they were either included in high-level risk registers or attached as addendums to generic programs. For operators who incorporated risk assessments within programs, the depth and quality of cementing risk identification varied significantly between programs. Where risk assessments were found, not all cementing risks were thoroughly considered.

Cement design: operators typically delegated cement slurry design to cementing contractors, adopting an outcome-based approach. Operators provided functional specifications and expected contractors to develop compliant cement recipes verified through laboratory testing. However, the audits indicated a strong emphasis by operators on overseeing the contractors’ workplace health and safety compliance, with a gap in overseeing their technical compliance. To assess contractors’ technical capabilities, more work is required to ensure that cement slurries are optimally designed for well conditions, aligning with industry best practices and regulatory expectations.

Laboratory testing: most laboratory reports lacked direct comparisons between test results and design requirements. Fluid compatibility between cement, mix water, and spacers was often unrecorded. Water sources were often vaguely identified, creating uncertainty about whether the wells were cemented using the same water source used during testing. This issue was particularly relevant in programs covering multiple wells. Furthermore, contrary to legislative requirements, laboratory tests were not consistently included in WCRs.

Verification procedures: even though the code mandates verification procedures for primary cementing jobs, only half of the operators included cement verification as well acceptance criteria (WAC) in their drilling programs. However, it appears that cement verification WACs – where present – were not fully aligned with table 3 of the code (Table 1), possibly because table 3 is only mentioned in the FTMCO reporting requirements. Only one operator explicitly required the production of resulting records to demonstrate the success of WACs in their program. Another operator referenced the need for verification per table 3 in their cementing standard, but the specific verification steps were not outlined in their programs.

Losses: cement losses, particularly in the depleted coal seams, were identified as a significant risk, especially for frac wells. Losses primarily occurred due to depleted zones, high permeability or when formation fracture pressure was exceeded. The audits revealed that most operators mitigated these losses by adding lost circulation materials (LCMs) into spacers and cement blends. Other mitigation practices varied between operators. One effective mitigation approach observed was addressing drilling losses before commencing cementing operations. One operator implemented a no-go loss rate threshold of 10 bbl/h, ensuring that losses were controlled before proceeding with cementing. The operator also used cement with thixotropic properties to reduce losses and slumping. Additional methods to mitigate cement losses included light slurries, two-stage cementing, and secondary Annular Casing Packers deployment.

Bulk shrinkage: most operators used shrinkage-limited slurry, but only one mandated expansion ring test for all lab tests. The same operator required zero bulk shrinkage for gas-tight slurries. Another operator only performed expansion ring tests when trying new slurries. Quality assurance deficiencies are suspected because of lack of systematic bulk shrinkage investigations.

Washouts: wireline logs suggested minimal risk of overgauging and washouts in the Surat Basin. Washouts did not significantly contribute to cementing failures.

Cement excess: most operators could not consistently justify the cement excess requirements stipulated in their documentation, due to a loss of corporate memory regarding the original reasoning behind these standards. Excesses are calculated on field experience.