Overcoming the Heaviest Oil in Unconsolidated Environment in the Gulf of Thailand.
Exploration activity is always associated with many challenges such as uncertain pore pressure, and uncertain formation depths and characteristics. Unconsolidated formation could cause more serious troubles for drilling, formation evaluation, and production such as borehole washout, wellbore collapse, and sanding if proper planning is not in place. In addition, a viscose oil can add another complication for fluid sample operation. An unsuccessful logging could have a major impact on the field development plan. In the Gulf of Thailand (GoT), discovery reservoir fluids are mainly gas and condensate. There are numbers of waxy oil reservoirs in certain part in the GoT. However, this particular field is the first field that was identified as heavy oil reservoirs. The viscosity variation was originally ranges between 1 and 30 cp. Different reservoirs have different viscosity variation, and therefore, reservoir fluid information is crucial for the FDP. This paper will discuss step by step for (1) reservoir characterization challenges (2) proposed methods to obtain reservoir and fluid information, as well as the interval pressure transient test, (3) the actual field results, (4) recommendations and way forward for similar reservoirs. Different proposed options are also discussed with field examples to obtain high quality PVT samples. Pumping to clean up high viscous oil contaminated tends to attract more sand particles to come to the probe and into the flowline, causing plugging issues in other probe types though modified sand filter was added. At the end, a 3D Radial probe was proven to make this exploration campaign a success story for heaviest oil samples in the GoT. The 3D Radial probe equipped with mesh filter plays an important role to safeguard small sand particles, thereby allowing both sustainable pumping speed and flowing pressure. The single packer design also helps to support formation. Coupled with larger flow area of the probe itself, the 3D Radial Probe has ability to control flowing pressure to stay above the sand breaking away pressure though more viscous formation oil comes. However, we managed to complete job objectives which were formation pressure acquisition, high-quality fluid sampling, and Interval Pressure Transient Testing (IPTT) as well as Vertical Interference Testing (VIT). This paper also discuss comparison between Downhole Fluid Analysis results and PVT lab analyses. Limitation and challenges for downhole measurement for this heavy environment. Advantages and disadvantages for different testing methods for this heavy oil reservoir will also be discussed.
AAPG Datapages/Search and Discovery Article #90336 ©2018 AAPG Asia Pacific Region, The 4th AAPG/EAGE/MGS Myanmar Oil and Gas Conference, Myanmar: A Global Oil and Gas Hotspot: Unleashing the Petroleum Systems Potential, Yangon, Myanmar, November 13-15, 2018