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There are many gas fields associated with large amount of CO2 concentrations (>50 mol%) in offshore Malaysia. Development of the contaminated gas fields is only possible if a geologically safe storage site is identified for the storage of produced CO2. The critical component of CCS project field development plan is monitoring of the storage site for the long-term containment and conformance security. 4D time-lapse seismic is key in monitoring, measurement, and verification (MMV) plan. The time-lapse 4D seismic has been traditionally used to identify the potential threats associated with reservoirs with enhanced oil recovery plan. The application of 4D seismic would benefits CCS project for monitoring CO2 plume migration along existing or induced fractures. The study was conducted on identified CO2 storage sites in both depleted carbonate gas reservoir and clastic saline aquifer. It highlights two methods applied in the 4D AVO analysis, that quantifies the changes in CO2 saturation within reservoir during injection. The Aki and Richards’ approximation were analyzed for the effect of changes in gas saturations on the seismic amplitudes and the Smith and Gidlow's approximation for the reflection coefficient relationship between the AVO gradient/intercept attributes and reservoir fluid/properties. The application of 4D seismic would benefits CCS project for monitoring CO2 plume migration along existing or induced fractures. The study was conducted on identified CO2 storage sites in both depleted carbonate gas reservoir and clastic saline aquifer. It highlights two methods applied in the 4D AVO analysis, that quantifies the changes in CO2 saturation within reservoir during injection. The Aki and Richards’ approximation were analyzed for the effect of changes in gas saturations on the seismic amplitudes and the Smith and Gidlow's approximation for the reflection coefficient relationship between the AVO gradient/intercept attributes and reservoir fluid/properties. This study focuses on the different characteristics on 4D seismic attributes for carbonate and clastic reservoirs and discusses to effectively utilize for MMV.

Carbon Capture & Storage (CCS) has globally been recognized as the way forward to manage & reduce Green House Gas (GHG) emissions. However, for every geological CO2 storage project there are two inherent yet independent storage risks: loss of containment and loss of conformance. For early detection and mitigation of these risks, a robust Monitoring, Measurement and Verification (MMV) plan is of supreme importance. While several matured, newly developed and under trial monitoring technologies addressing various aspects of MMV are currently available but it's crucial to evaluate them in terms of applicability, durability, ease of operation & maintenance, and cost to the project. This study focuses on the screening and selection monitoring technologies to achieve a site-specific, adaptive, and cost-effective MMV plan and design. Identification of critical containment & conformance risks were achieved through integrating information from various elements viz. CO2 plume migration forward modeling, 3-way coupled modeling, well integrity analysis, overburden risk analysis, CO2 marine dispersion modeling, environmental impact assessment (EIA), regulatory requirements, etc. Based on identified risks, the specific MMV elements were selected along with designing of their scheduling and frequency. Subsequently, an inventory of all available technologies addressing explicit MMV needs was prepared. These technologies were put through rigorous analysis on their capability of detection, operability, tool/technology longevity, availability, and associated costs. High-ranking technologies were then knitted for the final MMV planning & design. As a part of the arduous screening, permanent ocean bottom (OB) monitoring technologies were analyzed and some of the alternate low-cost technologies surfaced that can cater to continuous and long- term data acquisition needs. Knitting of 3D Distributed Acoustic Sensor – Vertical Seismic Profile (DAS- VSP) hybrid with 3D seismic surveys would help optimizing the logistic requirements and reducing cost of monitoring survey acquisition over the project lifecycle. During the entire screening and selection process, Multi-Fiber Optic Sensor System (M-FOSS) technology emerged as the leading monitoring technology, which is cost-effective, easy to operate and has the flexibility to be deployed at well and/or on seabed. An exhaustive inventory of available/emerging MMV technologies and the cost versus benefit matrix was developed that can be used for MMV planning and design across CCS projects. The study focuses to streamline the long-term sustainability of the adapted MMV planning to enhance the project economics by ensuring the optimum value propositions of implemented technologies.

Depleted hydrocarbon reservoirs are considered inherently safe for carbon sequestration, but high well density penetrating the CO2 storage reservoir could compromise the containment performance in a carbon, capture & sequestration (CCS) project. Based on the available well data, it is crucial to understand the age of the well, materials used for wellbore construction, cement quality, barriers performance, and well integrity. A risk management methodology can be incorporated to evaluate primary and secondary barriers in existing plugged and abandoned (P&A) and development wells to ensure long-term fate of CO2 sequestration project. Existing P&A wells and development wells in a depleted field were drilled 3–5 decades ago. The wellbore construction utilized non-corrosive resistant materials. Health of all wells that ever penetrated the CO2 storage reservoir need to be analyzed from long term perspective of storing CO2. Throughout the lifespan of wells, subsurface barriers should maintain hydraulic isolation to prevent leakage happening from subsurface to environment of reservoir fluids and injected CO2. Deterioration of strength of wellbore construction material due to corrosion, induced by downhole pressure and temperature conditions, should be considered. This study investigated 3 exploration and 21 development wells. Risk register was developed for each well describing causes and CO2 leakage risks, impacts and consequences. Metrics were defined for parameters such as well age, well head materials, wellhead functional test and leak test, sustained casing pressures for risk determination. Wells were risk rated individually based on the assessment. Wells with low risk can be utilized for well conversion. While for high-risk wells, an opportunity risk matrix was developed to mitigate risks in all the wells. This study evaluates the well integrity and CO2 leakage risk along the wells that penetrated the CO2 storage reservoir. The improved rigorous risk assessment exercise evaluates well barrier failure causes and impacts along with estimating the risk number per well. The well risk assessment score calculated was between 9.24 and 13.35 for 21 development wells. Out of these 21 wells, 4 wells with risk score

The Malay Basin is located at the southern part of the Gulf of Thailand between Vietnam and Peninsular Malaysia. The produced gases in the basin contain varying amounts of CO2. High CO2 concentrations (>50 mol%) are, in typical of reservoirs, mainly derived from inorganic sources. In order to develop these fields with reduced or zero greenhouse gas emissions for sustainability development, some geological storage sites were screened to store the future CO2 production. One of the important geological storage sites is the saline aquifer. There are many elements to assess the quality of the CO2 storage sites, such as caprock integrity and storage capacity. This study focused on one of the caprock characteristics, i.e., caprock velocity characteristic, and its significance for CO2 storage in a saline aquifer. The studied saline aquifer is one of a numerous grabens or sub-basins at the southern part of Malay Basin. There is one abandoned exploration well with 2D and 3D seismic surveys and there are several types of velocity data, including sonic log, checkshot and seismic stacking velocity. The formations are composited of multiple thick sandstones and shales. Based on velocity analysis, including average velocity and inter-val velocity analysis. the interval velocity in caprock zone is related to the lithology, normally expressed by the sandstone percentage in the caprock zone. The lithology variation will affect the geomechanics characteristics, so, the velocity in caprock zone presents the caprock quality. The caprock is confined within the sub-basin and sandstone percentage is less than 40%, which shows a good seal capacity, com-bined with the caprock thickness distribution. The velocity in shale zone (caprock) is higher than overlying and overlain sandstones. There is strong positive reflection (peak) at the top of shale zone (caprock) and negative reflection (trough) at the bottom of caprock, i.e., top of sandstone aquifer. There would be strong class III AVO feature at the top of sand-stone aquifer on time-lapse 4D seismic reflection once CO2 is injected. These features (negative reflection with bright spots) and class III AVO at the top of aquifer) are useful for MMV to monitor the CO2 plume migration.

CO2 sequestration is a process for eternity with a possibility of zero-degree failure. One of the key components of the CO2 Sequestration Project is to have a site-specific, risk-based and adaptive Monitoring, Measurement and Verification (MMV) plan. The storage site has been studied thoroughly and is understood to be inherently safe for CO2 sequestration. However, it is incumbent on operator to manage and minimize storage risks. MMV planning is critical along with geological site selection, transportation and storage process. Geological evaluation study of the storage site suggests the containment capacity of identified large depleted gas reservoirs as well as long term conformance due to thick interval. The fault-seal analysis and reservoir integrity study contemplate long-term security of the CO2 storage. An integrated 3D reservoir dynamic simulation model coupled with geomechanical and geochemical models were performed. This helps in understanding storage capacity, trapping mechanisms, reservoir integrity, plume migration path, and injectivity. To demonstrate that CO2 plume migration can be mapped from the seismic, a 4D Seismic feasibility study was carried out using well and fluid data. Gassmann fluid substitution was performed in carbonate reservoir at well, and seismic response of several combination of fluid saturation scenarios on synthetic gathers were analyzed. The CO2 dispersion study, which incorporate integration of subsurface, geomatic and metocean & environment data along with leakage character information, was carried out to understand the potential leakage pathway along existing wells and faults which enable to design a monitoring plan accordingly. The monitoring of wells & reservoir integrity, overburden integrity will be carried out by Fiber Optic System to be installed in injection wells. Significant difference in seismic amplitude observed at the reservoir top during 4D seismic feasibility study for varying CO2 saturation suggests that monitoring of CO2 plume migration from seismic is possible. CO2 plume front with as low as 25% saturation can be discriminated provided seismic data has high signal noise ratio (SNR). 3D DAS-VSP acquisition modeling results show that a subsurface coverage of approximately 3 km2 per well is achievable. Laboratory injectivity studies and three-way coupled modelling simulations established that three injection wells will be required to achieve the target injection rate. As planned injection wells are field centric and storage site area is large, DAS-VSP find limited coverage to monitor the CO2 plume front. Hence, surface seismic acquisition will be an integral component of full field monitoring and time-lapsed evaluations for integrated MMV planning to monitor CO2 plume migration. The integrated MMV planning is designed to ensure that injected CO2 in the reservoir is intact and safely stored for hundreds of years after injection. Field specific MMV technologies for CO2 plume migration with proactive approach were identified after exercising pre-defined screening criteria.

Maximizing drilling performance by pushing the limits of drilling tools is the key to reduce overall drilling cost. The interplay of complex parameters such as lithology, drilling parameters, drilling experience, downhole tool reliability, and the operational process help us to identify the limiting factors. Drilling dysfunction could deteriorate the reliability of downhole drilling tools including the overall drilling performance by causing damaged bits, failure of downhole electronic components, torsional fatigue of drillstring, over-torqued connections, etc. Precise modeling of dynamic responses of a bottomhole assembly in a given formation can help to identify operating limitations as well as post job analysis. The wellbore-drillstring interaction and well face-drill bit interaction are the sources of excitation of torsional oscillations. Stick-slip is one of the common and well-known torsional oscillation that usually occurs at low frequencies 10Hz to 500 Hz. This paper summarizes the HFTO phenomenon that causes high tangential accelerations and torsional loads within the bottomhole assembly (BHA) during drilling in critical formations. HFTO modeling that is validated with high-speed measurements helps to identify tangential accelerations and torsional loads across the BHA components. This paper highlights the benefits of modeling the rotary steerable system (RSS) BHA for HFTO in order to identify the point in the BHA that is subjected to the highest tangential acceleration and torsional loads. Real time monitoring for drilling optimization of RSS BHA shows that the HFTO modeling and post-job data analysis of high-frequency data confirms the distribution of tangential acceleration and torsional loads along the BHA. The paper also highlights the accuracy of the HFTO modeling based on results of pre-job modeling and post-job high-speed data analysis from drilling runs. Based on the analysis and the study, recommendations for optimal BHA design and operational parameters are provided to yield maximum footage per run and improved BHA performance. High-frequency torsional oscillations in the BHA can be mitigated if adequate BHA design, drilling parameters, and procedures are implemented. The in-depth analysis of HFTO with accurate modeling and high-frequency measurements can be used to develop a knowledge base to further optimize the drilling process, reduce non-productive time, realize fewer trips for failures, extend the on-bottom drilling time, reduce maintenance costs, and increase the drilling efficiency and performance.

Monitoring of CO2 plume migration in a depleted carbonate reservoir is challenging and demand comprehensive and trailblazing monitoring technologies. 4D time-lapse seismic exhibits the migration of CO2 plume within geological storage but in the area affected by gas chimney due to poor signal-to-noise ratio (SNR), uncertainty in identifying and interpretation of CO2 plume gets exaggerated. High resolution 3D vertical seismic profile (VSP) survey using distributed acoustic sensor (DAS) technology fulfil the objective of obtaining the detailed subsurface image which include CO2 plume migration, reservoir architecture, sub-seismic faults and fracture networks as well as the caprock. Integration of quantitative geophysics and dynamic simulation with illumination modelling dignify the capabilities of 3D DAS-VSP for CO2 plume migration monitoring. The storage site has been studied in detailed and an integrated coupled dynamic simulation were performed and results were integrated with seismic forward modeling to demonstrate the CO2 plume migration with in reservoir and its impact on seismic amplitude. 3D VSP illumination modelling was carried out by integrating reservoir and overburden interpretations, acoustic logs and seismic velocity to illustrate the subsurface coverage area at top of reservoir. Several acquisition survey geometries were simulated based on different source carpet size for effective surface source contribution for subsurface illumination and results were analyzed to design the 3D VSP survey for early CO2 plume migration monitoring. The illumination simulation was integrated with dynamic simulation for fullfield CO2 plume migration monitoring with 3D DAS-VSP by incorporating Pseudo wells illumination analysis. Results of integrated coupled dynamic simulation and 4D seismic feasibility were analyzed for selection of best well location to deploy the multi fiber optic sensor system (M-FOSS) technology. Amplitude response of synthetic AVO (amplitude vs offsets) gathers at the top of carbonate reservoir were analyzed for near, mid and far angle stacks with respect to pre-production as well as pre-injection reservoir conditions. Observed promising results of distinguishable 25-30% of CO2 saturation in depleted reservoir from 4D time-lapse seismic envisage the application of 3D DAS-VSP acquisition. The source patch analysis of 3D VSP illumination modelling results indicate that a source carpet of 6km×6km would be cos-effectively sufficient to produce a maximum of approximately 2km in diameter subsurface illumination at the top of the reservoir. The Pseudo wells illumination analysis results show that current planned injection wells would probably able to monitor early CO2 injection but for the fullfield monitoring additional monitoring wells or a hybrid survey of VSP and surface seismic would be required. The integrated modeling approach ensures that 4D Seismic in subsurface CO2 plume monitoring is robust. Monitoring pressure build-ups from 3D DAS-VSP will reduce the associated risks.