LWD logs are becoming increasingly reliable for the primary (and often the only) source of downhole log data. The standard and advanced mud logs in conjunction with LWD logs are used to conclude on the reservoir fluid typing (gas, oil, water) in real time. However, there are examples where the mentioned logs can equally misguide the log interpreter. An incorrect fluid interpretation can result in huge financial implications. There could be decisions associated with laying new pipelines, upgrading surface facilities (separators, compressors) and/or installing new platforms. In addition, the fluid fill would have a direct impact on the company reserves and reporting. Historically, a number of exploration and development wells were drilled in the SE Asia region where minimal LWD log data was acquired. This data is often considered sufficient for evaluation of reservoir properties. However, for fluid fill, the data was insufficient for various valid reasons and the initial interpretation from the LWD logs could have led one astray. This paper highlights examples where an integrated effort from the subsurface disciplines provided insights into the misbehaviour of the LWD logs and mud log data. The examples shown in this paper demonstrate that similar looking reservoir log responses could lead to an uncertain fluid fill. In such circumstances, the requirement for additional log data needs to be highlighted at an early stage of the project and should also be reflected in the well and field economics. The uncertainties in the reservoir fluid fill needs to be reflected in the project risk register and in the field development plan (FDP). This paper provides alarming signals to the log interpreters that extra caution needs to be taken in log data acquisition, processing and interpretation stages. The paper also highlights the importance of integration between subsurface disciplines and the criticality for the log interpreters to be familiar with the depositional environments. It has also been demonstrated that a limited set of log data could equally mean having no information unless additional evidence is available to address the uncertainties.

Since the advancement of Focused Sampling techniques, wireline formation fluid sampling has undergone a dramatic change. This has primarily been due to the promise of acquiring representative formation fluid samples with minimal mud filtrate contamination and large sample volumes, thereby adding value to the PVT laboratory studies as well as reducing the fluid sampling time, thus aiding significantly to the cost savings. This paper demonstrates the contribution of focused sampling technology for reservoir fluid mapping in numerous exploration and development wells in South East (SE) Asia, by optimized selection of different packer types based on varying reservoir properties. For the exploration wells, the primary objective was to determine the non-hydrocarbon (non-HC) content (CO2 and H2S in this case) of the single-phase reservoir fluid samples, which were expected to be close to the saturation pressures. Following the 3D near-wellbore simulations, an elongated and an extra-elongated focused packer were selected due to expected low permeabilities, reservoir thickness and wellbore conditions. The wells were drilled in managed pressure drilling (MPD) conditions, with overbalance ranging from 900 to 4,300 psi. The development campaign consisted of five producers with key objectives of determining fluid type and the non-HC (CO2 in this case) content along with assessing the reservoir/block connectivity. The concentration and uncertainty in CO2 distribution would have a major impact in developing the production strategy of the area. A standard focused packer was selected for the sampling jobs which were carried out on pipe due to high overbalance conditions (~2,400 psi). In the exploration wells, 30+ samples (gas, oil and water) were collected with the time-on-wall ranging between 1.5 and 7 hours. In the development campaign, 50+ samples (gas and oil) were collected with the time-on-wall ranging between 45 minutes and 2.5 hours. Given the depths and low permeabilities of the reservoirs with high overbalance, this resulted in significant time savings. The larger flow area of the elongated and extra-elongated focused packers ensured minimal contamination in the collected samples given the challenging sampling conditions, where restrictions to pressure drawdown existed. The PVT laboratory results showed ‘insignificant’ oil-based mud filtrate contamination in the samples. In addition, the large sample volumes provided flexibility for additional PVT studies and improved resource assessment. The focused sampling technology was successfully applied in both exploration and development campaigns in the SE Asia region. The pre-job simulations ensured optimal packer selection between the three focused packer types. The comparison between the actual sampling results and the 3D near-wellbore simulation would help optimize future sampling operations in the area. In addition, the two campaigns have reiterated a clear value of information in saving cost, reducing contamination in the samples and technology success in the given environments.