As part of plug and abandonment (P&A) operations, several acceptance criteria need to be considered by operators to qualify barrier elements. In casing annuli, highly bonded material is occasionally found far above the theoretical top of cement. This paper aims to describe how the highly bonded material can be identified using a combination of ultrasonic logging data, validated with measurements in lab experiments using reference cells and how this, in combination with data from the well construction records. can contribute to lowering the costly toll of P&A operations. Ultrasonic and sonic log data was acquired in several wells to assess the bond quality behind multiple casing sizes in an abandonment campaign. Data obtained from pulse-echo and flexural sensors was interactively analyzed with a cross-plotting technique to distinguish gas, liquid, barite, cement, and formation in the annular space. Within the methodology used, historical data on each well was considered as an integral part of the analysis. During the original well construction, either water-based or synthetic oil-based mud was used for drilling and cementing operations, and some formation intervals consistently showed high bonding signature under specific conditions, giving clear evidence of formation creep. Log data from multiple wells confirms formation behavior is influenced by the type of mud used during well construction. The log data provided information of annulus material with a detailed map of the axial and azimuthal variations of the annulus contents. In some cases, log response showed a clear indication of formation creep, evidenced by a high bond quality around the production casing where cement cannot be present. Based on observations from multiple fields in the Norwegian continental shelf, a crossplot workflow has been designed to distinguish formation from cement as the potential barrier element. NORSOK D-010 has initial verification acceptance criteria both for annulus cement and creeping formation as a well barrier element, both involving bond logs; however, in the case of creeping formation it is more stringent stating that "two independent logging measurements/tools shall be applied." This paper aims to demonstrate how this can be done with confidence utilizing ultrasonic and sonic log data, validated against reference barrier cells (SPE-199578). Logging responses like those gathered during full-scale experiment of reference barrier cells with known defects were observed in multiple wells in the field. Understanding the phenomenon of formation creep and its associated casing bond signature could have a massive impact on P&A operations. With a successful qualification of formation as an annulus barrier, significant cost and time savings can be achieved.

Summary As part of plug and abandonment (P&A) operations, several acceptance criteria need to be considered by operators to qualify barrier elements. In casing annuli, highly bonded material is occasionally found far above the theoretical top of cement. This paper aims to describe how the highly bonded material can be identified using a combination of ultrasonic logging data, validated with measurements in laboratory experiments using reference cells and how this, in combination with data from the well construction records, can contribute to lowering the costly toll of P&A operations. Ultrasonic and sonic log data were acquired in several wells to assess the bond quality behind multiple casing sizes in an abandonment campaign. Data obtained from pulse-echo and flexural sensors were interactively analyzed with a crossplotting technique to distinguish gas, liquid, barite, cement, and formation in the annular space. Within the methodology used, historical data on each well were considered as an integral part of the analysis. During the original well construction, either water-based mud (WBM) or synthetic oil-based mud (OBM) was used for drilling and cementing operations, and some formation intervals consistently showed high bonding signatures under specific conditions, giving clear evidence of formation creep. Log data from multiple wells confirm that formation behavior is influenced by the type of mud used during well construction. The log data provided information of annulus material with a detailed map of the axial and azimuthal variations of the annulus contents. In some cases, log response showed a clear indication of formation creep, evidenced by a high bond quality around the production casing where cement cannot be present. Based on observations from multiple fields in the Norwegian continental shelf, a crossplot workflow has been designed to distinguish formation from cement as the potential barrier element. NORSOK Standard D-010 (2013) has initial verification acceptance criteria both for annulus cement and creeping formation as a well barrier element, both involving bond logs; however, in the case of creeping formation, it is more stringent stating that “two independent logging measurements/tools shall be applied.” This paper aims to demonstrate how this can be done with confidence using ultrasonic and sonic log data, validated against reference barrier cells (Govil et al. 2020). Logging responses like those gathered during full-scale experiments of reference barrier cells with known defects were observed in multiple wells in the field. Understanding the phenomenon of formation creep and its associated casing bond signature could have a massive impact on P&A operations. With a successful qualification of formation as an annulus barrier, significant cost and time savings can be achieved.

Jet-type perforate-wash-cement (P/W/C) is a relatively new well plugging technique that is more cost effective than the traditional casing milling method. ConocoPhillips has extensively used this technique in the Greater Ekofisk Area (GEA) over the last 10 years. In this method, Tubing Conveyed Perforating (TCP) guns perforate casing in the target interval before the zone is washed and a cross-sectional cement plug is installed using a specialized Bottom Hole Assembly (BHA). The BHA has nozzles in respective zones to separately spray wash fluid and cement during the operation. Tool translational (up and down movement) and rotational speeds, nozzle diameter, number of nozzles, nozzle angle, mud and cement properties, flow rates and nozzle pressure drop are the key governing parameters. In 2014, ConocoPhillips Norway launched a project to improve quality of wash and cement processes and since 2016 utilized Computational Fluid Dynamics (CFD) for parametric optimization. The analysis significantly enhanced understanding of the fundamental processes involved, enabling improvement of the existing tool and processes. The focus of this paper is on how BHA rotational speed, nozzle diameter, and nozzle angle influence wash process efficiency. Deeper insight from CFD analysis on the influence of these parameters on the wash process is discussed in more detail in this paper. Updated wash and cement procedures and parameter values were introduced in 2017 based on CFD modeling and detailed in a best practice document. To date approximately 200 successful operations have been performed as per the best practice.

Perforate-Wash-Cement (P/W/C) is a well plugging technique extensively used by ConocoPhillips in the Greater Ekofisk Area over the last ten years. In Jet-type P/W/C, Tubing Conveyed Perforating (TCP) guns perforate casing in the target interval before the zone is washed and a cross-sectional cement plug is installed using a specialized Bottom Hole Assembly (BHA). The goal is to maximize the cement plug quality through optimizing the BHA and operational process parameters within constraints imposed by the operating conditions. This paper describes application of Computational Fluid Dynamics (CFD) to achieve this objective. CFD is well suited for modeling wash and cement processes including the associated non-Newtonian fluids. A CFD model of these processes employs unsteady multiphase Reynolds Averaged Navier Stokes (RANS) based Volume of Fluid (VOF) approach with a Shear Stress Transport (SST) K-omega turbulence model. BHA translation and rotation are simulated using moving deforming-layering mesh with interface approach. Physical properties of non-Newtonian fluids selected are based on in-situ conditions and derived via lab tests. CFD-specific considerations such as domain size, turbulence model, mesh type and size, and computational timestep are discussed in this paper. The magnitude and duration of the jet-induced "pressure pulse" in the annular space between the formation wall and the casing are a key to efficient displacement during the wash and cementing processes. Displacement efficiency, in terms of the percentage of mud or cement in a control volume as a function of time, depends on perforation size and density, nozzle size/number, flow rate, fluid properties, as the ROP/BHA pulling speed and tool RPM. Key findings from a parametric study to optimize these parameters are presented. To validate CFD nozzle flow predictions and to rule out potential for false results due to cavitation, laboratory tests were performed under pressurized conditions. A comparison of results from CFD simulations using traditional versus optimized parameters are presented, demonstrating significant efficiency improvement achieved. The study initially focused on North Sea application. Encouraged by substantial improvement in process efficiency through parametric optimization, the technique was extended to UK operations and is planned for the Bayu-Undan field. Cementing simulation results for Bayu-Undan specific well configurations are presented, showing how CFD modeling helped reveal less than ideal cementing efficiency. Ultimately, this work provides significant time savings and quality improvement for P&A projects while maintaining a high safety standard.

In 2014 ConocoPhillips (CoP) decided to focus on the Jet-type perforate, wash and cement (P/W/C) technique as its primary permanent well abandonment method for setting a full cross-sectional cement/steel barrier. Following this decision, a quality improvement project was launched to prepare for a transition from Cup-type to Jet-type P/W/C to improve barrier plug quality. The initiative was presented during the Stavanger P&A Forum (PAF) conference October 2014 for information and to indicate for specific vendors that there were opportunities for participation. The perforate, wash and cement method is complex and as with any cementing operation there is operational risk involved. This paper is written to share ConocoPhillips experience and learning from the improvement project which is still ongoing. It is specifically written for drilling engineers planning Jet-type P/W/C operation to help identifying key parameters to achieve a top-quality operation as well as managing the operational risk inherent to the operation. Quality requirement in P&A operations? It can be a hard sell to argue for costly fluids, BHAs (bottom hole assembly) and TCP (tubing conveyed perforation) guns to plug off a depleted reservoir where the test of time is hundreds of years from now as the reservoir gets pressurized again. The latter is not the case in the Greater Ekofisk Area (GEA) where active water injection increases the average reservoir pressure quickly and the established production strategy is dependent on good isolation of abandoned wellbores. To get a ‘’good’’ P&A plug you need to understand how to prioritize and control the variables such as cement properties, drilling fluid properties, drill pipe and BHA design, hole cleaning, ECD, displacement, TCP performance, operational sequence and many more. ConocoPhillips have made a structured approach to build a process which captures the basics of getting a high quality well abandonment plug. The displacement process itself has been modelled with computational fluids dynamics (CFD) software to understand key drivers for the placement of a cross-sectional P&A plug. This understanding has been mated with the practical limitations from a standard drilling unit to get a robust operational plan. To ensure the quality is maintained from operation to operation, the process have been accurately described in a Best Practice document. The operation itself is checked against a QA form to verify that execution was performed according to plan. The QA form is then filed as part of the P&A documentation, similar as a casing test during well construction. In the GEA experience a good P/W/C P&A plug is one set as per the Best Practice document where the operation is quality assured with an "all green" QA (quality assurance) sheet. A more tangible description is offered: After the operation the offshore cement sample which is contaminated with 10% mud will set up in the UCA (ultrasonic cement analyser) cell per programmed setting time plus no more than 3 hrs. The cement plug itself will be tagged at planned TOC (top of cement) +/- 20 ft. It will hold the positive pressure test to fracture gradient + 1000 psi. From time to time the plug will be drilled out. If that is the case, we expect to see an average weight on bit larger than 15,000 lbs for a 9 5/8’’ casing plug. The external well barrier element may be logged using a CBL/USIT (cement bond log) string or similar. In that event we expect to see "bond quality", which is a weighted interpretation of CBL, VDL (variable density log), flexural attenuation and pulse echo measurements as "good" to "very good" throughout the perforated section. This paper is one of many discussing the P/W/C technique (1) and is written to help you prioritize focus areas and optimize those. We think a high focus on QA will be your fundament, not only for a "good" P&A plug but also for a flawless execution of the complex offshore operation. Our results can be reviewed in Appendix B. Performance approach technical limit.