Formation water content is one of the key petrophysical quantities provided by dielectric logging. However, to determine water content from formation permittivity measurements the rock matrix permittivity must be known. Uncertainty in the rock matrix permittivity values translates into uncertainty in the water content estimate, which is especially important in low-porosity formations or complex lithologies. Matrix permittivity values are not well known for a number of minerals and can also vary for the same type of mineral in different formations. Thus, a laboratory methodology for the accurate determination of matrix permittivity at dielectric logging frequencies is required to facilitate accurate log interpretation. Matrix permittivity values can be measured on solid plugs (Seleznev et al., 2011). However, the plug-based methodology can be challenging in very low-permeability or unconventional reservoirs because of difficulties with plug drying. In addition, it is not readily applicable to unconsolidated formations. Finally, it may be impossible to cut solid plugs due to limited availability of rock material. Matrix permittivity measurements made on rock powders are capable of addressing all of these issues. We introduce a methodology for laboratory measurements of matrix permittivity on rock powders at 1 GHz. The methodology is based on conducting dielectric measurements on mixtures of rock powders and liquids with variable permittivities in a dielectric resonator. The permittivity of the rock matrix is inverted from a series of measurements obtained on pure liquids and powder-liquid mixtures. The methodology was benchmarked on a collection of samples representing common oilfield lithologies with matrix permittivity values between 4.6 and 8.6. The reference matrix permittivity values were first measured on solid plugs. Then the plugs were crushed into powders and the matrix permittivity values were determined on powders following the proposed methodology. The values obtained on powders matched the ones measured on solid plugs within 0.2 dielectric units resulting in accuracies better than 1% for the water-filled porosity and better than 1000 ppm for water salinity. This new methodology was applied to a number of core samples from a carbonate reservoir, offshore Sarawak where dielectric logging had been performed along with conventional core analysis. The resulting measured matrix permittivity values were then used to interpret the dielectric log measurement. Results showed a better estimation of water filled porosity and of the textural MN parameter than would have resulted from using ‘chartbook’ values of matrix permittivity. A consistent and optimized interpretation was obtained in porosities ranging from 5% to more than 30%.

Thinly laminated and silty deep-water reservoirs of offshore Malaysia have historically posed difficulties in formation evaluation due to complex log responses causing uncertainties in key petrophysical properties like porosity, water saturation, net pay and productivity. Moreover, compartmentalization of the reservoirs due to extensive faulting in this area increases the evaluation challenges. Generally, thinly laminated reservoirs are evaluated either by high-resolution methods, including borehole imaging and whole core analysis; or bulk volumetric approaches, which utilize nuclear magnetic resonance (NMR) and suitable shaly sand saturation equations. Adding silt as an additional component requires a cautious combination of these two approaches. Furthermore, linking the petrophysical evaluation with depositional processes and structural settings using borehole image, acoustic log and formation pressure is key to the future development of the field. Lastly, securing clean formation fluid samples is crucial to design the production strategy. Aforesaid complete dataset was acquired in a deep-water well of offshore Malaysia to assess hydrocarbon potential. While relatively higher resistivity distinguished potential hydrocarbon bearing zones, NMR-based irreducible water saturation was a crucial indicator of possible water-free hydrocarbon production from the silty zones with high water content. Net sand was accurately calculated from the high-resolution borehole image and compared with the standard petrophysical approach. Then, a detail analysis of formation dip, facies and paleo-current direction was performed on borehole image to recognize different depositional processes and structural settings. Formation pressure data was collected extensively to understand reservoir compartmentalization. While the testing zones were selected based on higher free fluid and higher resistivity anisotropy; the precise testing depths on sand laminae were guided by high-resolution borehole image. Later, low contamination downhole fluid samples were collected using focused sampling technique. 2D NMR method and real-time downhole analysis of optical absorbance, refractive indices, fluorescence, density, viscosity and sound speed were used to differentiate formation fluid from the OBM filtrate. The reservoirs were then evaluated integrating the petrophysical properties with the depositional process and structural settings to understand their long-term production potential. This paper represented a case study of an integrated workflow of optimum data acquisition and evaluation of the thinly laminated sand-silt-clay sequence of deep-water reservoirs of offshore Malaysia. Effective and optimum integration of NMR, high-resolution borehole images, formation testing and sampling data provides the robust framework of this formation evaluation workflow to solve the complex petrophysical and geological uncertainties of these reservoirs.

Summary Formation water content is one of the key petrophysical quantities provided by dielectric logging. However, to determine water content from formation permittivity measurements, the rock matrix permittivity must be known. Uncertainty in the rock matrix permittivity values translates into uncertainty in the water-content estimate, which is especially important in low-porosity formations or complex lithologies. Matrix permittivity values are not well-known for a number of minerals and can also vary for the same type of mineral in different formations. Thus, a laboratory methodology for the accurate determination of matrix permittivity at dielectric logging frequencies is required to facilitate accurate log interpretation. One can measure matrix permittivity values on solid plugs (Seleznev et al. 2011). However, the plug-based methodology can be challenging in very-low-permeability or unconventional reservoirs because of difficulties with plug drying. In addition, it is not readily applicable to unconsolidated formations. Finally, it may be impossible to cut solid plugs because of limited availability of rock material. Matrix permittivity measurements made on rock powders are capable of addressing all these issues. We introduce a methodology for laboratory measurements of matrix permittivity on rock powders at 1 GHz. The methodology is based on conducting dielectric measurements on mixtures of rock powders and liquids with variable permittivities in a dielectric resonator. The permittivity of the rock matrix is inverted from a series of measurements obtained on pure liquids and powder/liquid mixtures. The methodology was benchmarked on a collection of samples representing common oilfield lithologies with matrix-permittivity values between 4.6 and 8.6. The reference matrix-permittivity values were first measured on solid plugs. Then, the plugs were crushed into powders, and the matrix permittivity values were determined on powders following the proposed methodology. The values obtained on powders matched the ones measured on solid plugs within 0.2 dielectric units, resulting in accuracies better than 1% for the water-filled porosity and better than 1,000 ppm for water salinity. This new methodology was applied to a number of core samples from a carbonate reservoir offshore Sarawak, where dielectric logging was performed along with conventional core analysis. The resulting measured matrix permittivity values were then used to interpret the dielectric log measurement. Results showed a better estimation of water-filled porosity and of the textural MN parameter, equivalent to the Archie's cementation exponent in a water-bearing zone, than would have resulted from using “chartbook” values of matrix permittivity. A consistent and optimized interpretation was obtained in porosities ranging from 5% to more than 30%.

Operators, regulators, industry experts and service providers had lately landed onto a common ground on the needs for a strategic late field life management focusing on well abandonment planning and execution. With increased number of depleted well strings after exhaustive attempts to unlock the remaining well potential, this topic is gaining a spotlight day by day which triggers the industry to spare their attention to find the best solutions in getting the most out of the campaign. This paper will highlight the practical experiences and capture the lessons learned obtained while executing well abandonment campaign in Peninsular Malaysia waters demonstrating a quick learning curve and agile workflow in achieving a safe and world class project execution. Some best practices will be also proposed to strengthen the technical assurance, project governance as well as enhancing the safety features. Lessons learned gained are categorized under seven lenses namely cap rock identification and subsurface study, governance model, well and equipment preparation, perforation and cementing operation, cement bond logging and casing integrity evaluation, HSE related matters and also special topics where few examples and case studies will be presented for each. New insights, interpretation and efforts to improve the operational efficiency have led to the birth of new technology deployment, increased industrial networking for knowledge sharing and also integrated project management for cost optimization. As each abandonment campaign is unique in terms of threats and challenges, different approaches will be required to abandon the wells safely which steer the operators to be high on the learning curve and subsequently promote greater industrial collaboration. In essence, the lessons learned and insights gained throughout abandonment campaigns will keep accumulating with time to feed into the knowledge and experience vault. With proper project documentation, many success cases and best practices can be emulated both from technical and commercial point of view.

Majority of producing reservoirs in Malaysia come from sandstone accumulation with varying properties, rock fabrics and qualities. Being one of the major culprits in development and production spectrum, failure to take proactive measures for early prevention and detection of sanding issue has proved to be an expensive lesson learned especially during the mature production stage and late field life. High cost, increasing risk and intervention complexity and massive revenue loss are among the consequences due to this failure. This paper will highlight the challenges faced in sand prediction and monitoring and the proposed solutions at various field stages incorporating subsurface analysis, technology and brilliance at basics. The same approach will be used in rock strength evaluation for field subsidence analysis. Subsurface data such as logs, cores, drill cuttings and downhole well configuration can offer a tremendous insight at early stage of sanding issue. During field exploration and appraisal phase, information on reservoir compaction, barrier and heterogeneity, grain size, clay types and fines accumulation are usually investigated to give the overall reservoir potential and productivity overview. More comprehensive study could be conducted if core is available such as compressive strength, pore volume compressibility, elastic properties and even flooding test to simulate formation damage and factors affecting sand production. In area where limited core data is available, logs can be used to predict and generate sanding parameters such as grain size and other rock strength properties, hence driving the completion optimisation efforts and sand production preventive measures. Once production commences, sand count and particle size mapping should be updated frequently to complement the monitoring program. Leveraging on technology and collaboration, downhole logging acquisition to locate sand producing interval, chemical based sand consolidation treatment and core-driven sand screen selection and gravel size design are among the common scenarios taking place to help with production revival. Results generated from subsurface study will be input to the early formulation of field development plan and production strategy especially for downhole as well as surface sand control mechanism. In addition, integrated grain size and rock strength prediction workflow had been formulated based on logs to provide a competitive framework for time and cost optimization. Case studies presented in this paper will demonstrate a holistic and integrated approach at each stage of field life to win over the sand production hurdle as well as minimizing threat to production sustainability. Banishing the emerging threat through comprehensive subsurface study, strategic planning, execution and monitoring become the main agenda to protect well integrity as well as safeguarding the production.