Malaysia's oil and gas fields are often characterized by multiple stacked reservoirs. This complexity is due to the region's diverse geological history, which includes various sedimentary processes and tectonic activities. The reservoirs can vary significantly in terms of depth, pressure, and fluid characteristics, requiring advanced exploration and production techniques to effectively manage and extract hydrocarbons. To improve recovery in multi-stack reservoirs, secondary recovery is required. For efficient waterflooding and recovery management, multizone completions with isolated zones are necessary and it is imperative to know the injection profile along the wellbore. In such conditions, the flow events happen behind the point of measurement and standard approaches are blind to respond to them and usually provide limited value. Reliable flow diagnostics of such wells pose a great challenge in the industry. The most promising techniques for accessing the flow performance of multizone offshore injectors with complex completions are high-precision temperature and spectral acoustic logging with subsequent numerical modeling of hydrodynamics and thermal processes in a coupled fashion to access the performance of individual reservoir layers of injection wells.
The methodology addressing these complexities was developed and its feasibility and robustness were evaluated during the flow diagnostics surveys conducted in Field A of Sarawak Basin to evaluate the flow characteristics and flow geometry of two offshore injector wells. The processing of acquired data includes thermo-hydrodynamic modeling (Temperature modeling) that was carried out to quantify the injection flow profiles of target reservoir zones by matching the high-precision temperature logging data using an inverse modeling approach. The 2D numerical modeling with the integration of other borehole-measured data allowed us to assess and allocate injection distribution across the wellbore section and reservoir area in the near-wellbore vicinity. Modeling utilizes acquired temperature data under multiple regimes which sequences were comprehensively designed during the preliminary forward modeling phase enabling the relevant data acquisition for processing. Most of the published cases of high-precision temperature and spectral noise logging applications focus mainly on matching the recorded temperature profiles whereas in this study we included borehole pressure readings into the global optimization loop which allowed us to get insight into the reservoir parameters like bulk permeability, skin factor, reservoir pressure variation between zones, and effective reservoir working thickness.
Overall, the methodology showed good responsiveness and applicability, the main challenges and lessons learned are discussed in this paper as well. Novel integration of temperature and acoustic data, robust operation optimization, and advanced processing allowed us to define active flow units, evaluate injectivity, and differentiate between flows through the reservoir matrix, behind-casing channel, and wellbore completion components. The findings will provide insight for the Operator on the performance of individual zones to plan the reservoir management, future intervention activities, and remedial workovers to better manage waterflooding and hence maximize the production for Field A.
