Aker BP (Norway)

Abstract Many wells around the world suffer from compromised integrity in the form of leaking annular cement sheaths. Fixing leaking annular cement barriers is generally a labor intensive and costly proposition, particularly in offshore environments. If the leaking cement sheath is opposite a creeping shale or salt formation, there is a possibility of such a mobile formation "healing" the voids, cracks and annuli in the cement sheath and re-establishing annular barrier integrity. Such "healing" can be relatively easily achieved using heaters deployed in the wellbore without the need to create annular access. Large scale "shale-as-a-barrier (SAAB)" rock mechanics tests were carried out in the investigation reported here using a custom-built temperature-controlled triaxial frame to test shale core samples with an inner borehole. This borehole contained a simulated casing string and an annular cement sheath, which could be compromised either by using rubble-ized cement in the annulus or using repeated pressure cycles in the wellbore to attempt to create a micro-annulus at the casing-to-cement interface. The integrity of the annular barrier (or lack thereof) was probed throughout the test using pressure pulse decay experiments, and at the end of the test by breakthrough testing. The creep rate in the North Sea Lark shale was beneficially manipulated using elevated shale sample temperature. In the experiments with rubble-ized cement, it was found that thermally stimulated shale creep can plug the cracks, fractures and voids present within the cement material effectively to form a barrier. In the experiments with intact cement subjected to casing pressure cycles, evidence was obtained that thermally stimulated creep can support the annular cement barrier. The effect of elevated temperature, representing the effect of the deployment of a heater in an actual well setting, proved crucial to magnify and accelerate the creep phenomenon responsible for plugging the flow paths in the compromised cement. With many hundreds of thousands of wells around the work already leaking (or potentially leaking at some point in the future) and/or showing casing pressure at surface because of compromised annular cement barriers, it is important to find (cost-)effective long term remedial solutions. For wells intersection shale or salt formations that either creep at in-situ stress and temperature conditions, or can be induced to creep through thermal stimulation, the remediation using such creep to restore and improve the cement barrier is simple, practical (can be deployed with existing downhole heaters), cost-effective, and is expected to last for an indefinite timeframe. It thereby has the potential to revolutionize P&A operations on wells with compromised integrity.

Efficient and high-quality processing and visualization of Distributed Acoustic Sensing (DAS) data are essential for human and computer interpretation. Due to the large volume of data in its raw format, the information contained within DAS data are often extracted in predefined data features for practical analysis. Spectral features, those computed from data after a Discrete Fourier Transform (DFT), such as Frequency Band Energy (FBE), are commonly used in interpretation. Harmonizing feature data from different interrogator units (IUs) while maintaining information content is key for machine-learning applications and end-user interpretation. This work demonstrates that this can be achieved by using textbook time-series signal processing for spectral features - along with a novel data-driven method for estimating depth and time-varying noise in DAS data. Several data examples from the in-well environment are presented to illustrate how good practice impacts the result. It is shown that DAS data contains additive noise which have quasi-static Gaussian properties when looking at data in terms of strain (not strain rate). When subtracting the predicted noise from the power spectral densities (PSD) prior to estimating spectral features, we remove the variations in energy level over depth typically observed. We correlate these variations in noise to changes in temperature and mechanical strain of the fiber as observed in low-frequency (LF) DAS, and speculate that this is due to effectively changing the back scattering intensity pattern and thus the fiber as seen by the IU. Data from two different commercial DAS interrogators are compared, and it is shown that feature data from these two boxes are comparable after the suggested processing flow.

<strong class="journal-contentHeaderColor">Abstract.</strong> In marine environments, small hydrocarbon (HC) fluxes through organic-poor sediments are often fully degraded by microorganisms before reaching the seabed. Yet, these fluxes influence sediment geochemistry by stimulating microbial activity. We analyzed 50 gravity cores from the southwestern Barents Sea, covering zones affected by inconspicuous HC seepage and unaffected reference zones. Using various organic and inorganic geochemical analyses of the sediment along with pore water geochemistry, we assess the effects of low-intensity seepage and identify potential geochemical signatures. While analysis of the organic geochemical analyses provided limited insights, inorganic geochemical analyses revealed formation of minerals such as carbonates and sulfides, linked to microbial reductive processes. Element concentrations suggested that HC degradation leaves distinct signatures, particularly in redox-sensitive minerals. Pore water profiles in HC-affected zones showed significant variation, indicating carbonate precipitation. In contrast, sediments not affected by HC seepage displayed more uniform pore water profiles. Estimated fluxes of sulfate, calcium, and alkalinity varied notably between cores, particularly in HC-affected zones, suggesting local and potentially transient differences in seepage intensity. While microbial HC degradation likely occurs deeper than our sampling interval, high-resolution geochemical analysis of both sediment fractions and pore water revealed a clear imprint of HC seepage. This imprint, reflected in authigenic minerals and pore water gradients, allows identification of past and present seepage activity, with authigenic minerals providing evidence for past seepage, and pore water profiles informing about ongoing seepage.

Abstract Energy is critical for the global population, and natural gas is a reliable, affordable and transportable source. Water breakthroughs in gas wells can reduce productivity and recovery, leading to early well shut in. A new Autonomous Inflow Control Technology for gas wells (gas AICT) has been developed to autonomously detect and choke unwanted water production while allowing gas and condensate production, improving both economic and sustainability measures of gas wells. This novel AICT leverages the Hagen-Poiseuille equation and Bernoulli's principle to differentiate between gas, condensate, and unwanted water. The gas AICT autonomously chokes zones with water production. Extensive flow performance tests have been conducted as part of the qualification program, initially in a multiphase flow loop with model fluids and subsequently with hydrocarbon gas, condensate, and formation water under downhole conditions. A reservoir and well simulation model, based on a Norwegian gas discovery, was constructed to evaluate the impact of the gas AICT. This model also aids in understanding future development directions for the technology. The experimental results demonstrate that the gas AICT effectively chokes water while remaining open for gas and partially open for light condensate. The valve exhibits an acceptable flow rate for gas, which can potentially be further enhanced in the future. Reservoir simulation modelling predicts the performance of the gas AICT under downhole conditions and explores various scenarios for the lower completion. For the long horizontal gas wells in this study, the impact of annulus phase segregation is quantified. Potential solutions for the clean-up of heavier completion fluids are also briefly discussed. To our knowledge, this is the first published flow performance test of an AICT that autonomously detects and chokes water while allowing gas and light condensate at downhole conditions. This technology has the potential to extend well life and increase gas recovery, with estimates in the range 13-37% in the field case studied. Additionally, water production is significantly reduced. The reduction in water production and the improvement in gas recovery (reducing the need for new wells by enhancing recovery from existing ones) provide clear environmental benefits. In summary, the gas AICT studied here shows clear potential to enhance both economic and sustainability outcomes for new gas wells at risk of water production.

Model-based control and optimisation strategies can play a key role in improving energy efficiency and reducing emissions into produced water re-injection facilities. However, building a model that adequately describes the plant is challenging and can also be used in online decision-making procedures. This work proposes a simple model based on a real water re-injection facility operating on the Norwegian continental shelf. The results demonstrate the model's flexibility, which could be fitted to different plant operating points while being fast to solve when embedded in optimisation problems. The developed model is expected to aid the implementation of strategies like self-optimising control and real-time optimisation on produced water re-injection facilities.

Abstract Walk-to-work (W2W) concepts are widely used in the offshore wind farms as means of access to offshore wind turbine platforms. This is typically achieved using a Service Operation Vessel (SOV) equipped with a suitable W2W gangway. This system has also been explored in the Oil and Gas industry for temporary access to offshore platforms. However, the use of this system as a primary means of access to operating offshore oil and gas platforms remains limited. When it comes to selecting height of a W2W landing, from basic Naval Architectural hydrodynamic principles one can expect height of a W2W landing from sea level to have an inverse relationship with operability of the SOV gangway [1]. As such, the lower the W2W landing, the higher the SOV gangway operability. However, lowering the W2W landing, potentially exposes the W2W landing structure to extreme design wave loads (e.g. 10,000-year return period design waves). Loss of W2W landing to an extreme wave event could jeopardize further accessibility of the W2W landing and expose any subsea infrastructure to risk of dropped objects. This paper is intended to summarise results of an assessment where height of the “Munin” fixed offshore platform W2W landings with regards to SOV gangway operability is optimised. In this study effect of W2W landing elevation from mean sea level in relation to SOV gangway operability is quantified for the Munin Platform site specific conditions. Further, a qualitative evaluation is presented to show how benefits of raising W2W landings outside of the extreme wave load envelop outweighs the marginal SOV operability improvement due to lowering W2W landings elevation.

Summary Distributed acoustic sensing (DAS) is being deployed to enhance the monitoring of production and injection wells. While not yet the industry standard, the increasing number of examples and use cases of in-well DAS has demonstrated the potential to provide insights and influence the decision-making process in real time. In most cases, the installation of fiber is seen as a helpful addition, not a required tool for this purpose. Here, we present an interpretation story from the startup of a subsea production well where the Annulus B pressure gauge failed. We show that the presence of fiber made it possible to start up the well based on interpretation experience with fiber-optic data linked to the Annulus B pressure release system (APRS) opening. Real-time, continuous streaming of low-frequency (LF)-DAS data enabled informed decisions to be made by tracking standard operational events, such as valve testing, unloading, and cycling the glass plug, as well as monitoring more infrequent events, such as the liquid level inside Annulus A, and monitoring the APRS opening during the start of production. As our understanding of this data continues to improve, we expect to see more cases of value realization based on fiber-optic data.

Abstract This study explores a specialized spacer fluid based on geopolymerization, designed to set and develop mechanical strength while maintaining a low slurry density. This innovative spacer can act as a supplementary barrier to cement, reducing the risk of sustained casing pressure and preventing fluid leakage. This work examines the spacer's mechanical properties at elevated temperatures to evaluate its potential for enhancing well-cementing operations and improving well integrity. Key properties, including rheology, density, and thickening time, are measured at 50°C bottomhole circulating temperature (BHCT) to assess the fluid-state properties of the spacer. Furthermore, its compatibility with Class G cement is assessed, focusing on the effects on rheological and mechanical characteristics. The effect of two different dosages of Na2CO3 in the spacer design as strength booster on mentioned properties is also examined. The results show that the spacer has a low slurry density (1.3–1.5 s.g.), enabling safe placement in weak formations. Its density can be increased by incorporating barite or granite to create a greater contrast with the drilling fluid. The spacer's thickening time offers a pumpability window of at least 7 hours at 50°C BHCT, aligning with typical cementing schedules. The compatibility results indicate that the hardening spacer is rheologically compatible, as evidenced by the measured R-index. When the cement was contaminated with 10% spacer, its compressive strength showed a 29% reduction after one day at 70°C BHST. While additional testing and refinement are necessary for the spacer to function as an independent barrier material, it shows potential as a complementary component to primary barriers like cement in its current stage of development.

The presence of faults in reservoirs can directly affect reservoir energy and feasibility in hydrocarbon bearing formations as well as repository potential for subsurface storage. Subsurface fault characterisation is an important but challenging workflow because a geoscientist is limited to the resolution of seismic data and sparse well data. The Barents Sea is renowned for exhumation generated gas seepage allowing preferential retainment of oil. In this study, observations in the fault zones of the Wisting field show reductions of acoustic impedance (A imp ) on seismic images. We characterise five intersecting E–W and N–S normal faults in the Wisting Central blocks using a novel approach, whereby low A imp is mapped onto modelled fault surfaces and compared to parameters such as fault throw and shale gouge ratio. Low A imp dominates E–W faults which exhibit more brittle response when compared to two N–S faults, where low A imp values are sparse and the faults tip-out below a monocline. Two potential mechanisms causing the reduction of A imp are proposed: 1) gas saturation, which can be as little as 2% to significantly reduce A imp ; 2) fault damage, which can decrease wave velocities and A imp . The E–W faults in Wisting Central show higher reductions of A imp than their N–S counterparts, indicating that they are either saturated with gas or have undergone higher damage. • N-S and E-W faults dominate the Wisting field, Barents Sea. • Reduced acoustic impedance (A imp ) of 5 faults in Wisting Central is quantified. • A imp reduction is higher in E-W faults than in N-S faults. • E-W faults show more brittle deformation than N-S faults. • Causes of reduced A imp may be gas saturation or damage zone intensity.