For a producing field, oil-water contact movement, gas cap expansion/shrinkage and residual oil saturation (thus the sweep efficiency) are key reservoir dynamic properties for resource estimation and proper reservoir management. Jasmine field in the Gulf of Thailand first began oil production in June 2005. Light oil & gas has been produced from multiple high permeability fluvial sandstones of Miocene-Oligocene age. After more than seven years of development and production, reservoir monitoring becomes even more critical in decision making for well recompletion, drilling of new infill wells and overall fluids management. To understand fluid movement, pulsed neutron logging, including inelastic spectrum (carbon-oxygen ratio, C/O), thermal decay time (Sigma) and cased formation resistivity have been widely employed to evaluate formations through casing. However, each technology has its advantage and limitations. There are three major challenges for formation evaluation through casing in Jasmine field: Formation water is relatively fresh so it is very difficult to distinguish oil from fresh water with pulsed neutron capture (PNC) Sigma.In undertaking hydraulic workover operations, sea water has to be used to kill producing wells before logging, and therefore deep invasion is experienced in perforated zones with high permeability (multi Darcy) sandstone reservoirs. This can result in high uncertainty in oil saturations derived from C/O and partially to cased hole resistivity.In the deeper Oligocene reservoir section, massive shaly sands with low resistivity low contrast (LRLC) pay with high water saturation are present. Fluid typing in such strata is problematic even with open hole resistivity data. To address these various challenges, a combination of cased hole resistivity and pulsed neutron inelastic spectrum, thermal decay porosity & Sigma data have been employed used to reduce water saturation uncertainty and achieve multiple reservoir monitoring and formation evaluation objectives. Results from several logging campaigns since 2009 demonstrate the advantages of using these technologies in-parallel. Utilizing case studies, this paper summarizes the technical challenges and reservoir monitoring solutions as applied in the Jasmine field, including: Gas cap dynamics & OWC movementUnproduced perforated zones in commingled completionsUnswept portions of perforated zonesLow resistivity, low contrast shaly sand evaluation through casingReducing uncertainty in saturation estimation on sands killed by sea waterInputs to resource estimation, reservoir simulation and production optimization
The paper discusses an application of advanced wireline Formation Testing (FT) technology on an appraisal stage in order to improve an understanding of reservoir characteristics and to assist a field development plan. The advanced FT technology includes a focused sampling probe, a new 3D radial probe, and a new fluid analyser. Further information on tool functionality, real-time data interpretation, and acquisition result is described. Fit-for-purpose wireline FT modules were deployed. The focused sampling probe delivered quicker clean-up for downhole fluid extraction. The new fluid analyser with improved algorithm and more sensors measured fluid properties at downhole condition and also quantified a contamination level prior to capturing a fluid sample. The new 3D radial probe (Saturn Probe), which has the largest flowing area among probe family, enabled fluid pumping and sampling at low mobility zones. An Interval Pressure Transient Test (IPTT) to obtain permeability and skin was also conducted with this new probe. The data acquisition was closely monitored and discussed on real-time. Several wells have been drilled and data was successfully acquired at reasonable operation time. The focused sampling probe, with its unique design, met an objective of providing fast clean-up during pumping formation oil. This was indicated by a sudden change on the fluid analyser's Gas-Oil Ratio (GOR) and other parameters when the probe was in "split the flow" mode and focused. The sudden change was then followed by stable measurements of acquired properties indicating practically minimum contamination level has been achieved. Besides quantifying a contamination level, the new fluid analyser was also able to validate the fluid type which was derived from the pressure points. In addition, its viscosity sensor helped to understand viscosity variation among reservoirs which could not be done with a conventional fluid analyser. The new 3D radial probe maintained pressure drawdown while pumping at low mobility zones. Hence, sand failure that potentially deteriorates tool performance could be avoided. It also had shorter operation time than a conventional packer while conducting IPTT due to less inflating volume and tool storage. The IPTT results showed radial flow regime which was further analysed for permeability and open-hole skin. In an appraisal stage, data acquisition is critical for field development plan and final investment decision. It definitely requires robust and advanced technology that is able to deliver conclusive answer in challenging environment. A case explained here shows how the advanced technology revealed a hydrocarbon potential and confirmed reservoir continuity.
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 viscous oil can add another complication for fluid sampling operations. An unsuccessful logging program could have a major impact on the field development plan (FDP) and further field investment decision (FID). In the Gulf of Thailand (GoT), high temperature Pattani basin discovery wells, reservoir fluids are mainly gas and condensate. There are numbers of waxy oil reservoirs1–5 in certain area in the GoT, notably in the cooler peripheral Tertiary basins. However, the subject field is the first one that was identified as having productive heavy oil reservoirs. The viscosity variation ranges between 1 and 100 cp2–6. It was observed that there was a depth related variation with deeper reservoirs having higher viscosities, and therefore, reservoir fluid information is crucial for the FDP and FID resulting from a field extension drilling campaign in early 2018. This paper will discuss step by step (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 finer particulates towards the probe and into the flowline, causing plugging issues in other probe types even though a modified sand filter was added. In the end, the 3D Radial probe was proven in making this exploration campaign a success story for acquiring the heaviest oil samples to date in the GoT. The 3D Radial probe equipped with mesh filter plays an important role to restrict ingress of small sand particles, thereby allowing both sustainable pumping speed and flowing pressure. The single packer design also helps to support the formation preventing drawdown collapse. Coupled with larger flow area of the probe itself, the 3D Radial Probe has ability to control flowing pressure to stay above the sand break-away pressure even as more viscous formation oil enters. However, job objectives were achieved, 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 discusses the comparison between Downhole Fluid Analysis results and PVT lab analyses. Limitation and challenges for downhole measurements for this heavy oil environment. Advantages and disadvantages for different testing methods for this heavy oil reservoir will also be discussed.
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 viscous oil can add another complication for fluid sampling operations. An unsuccessful logging program could have a major impact on the field development plan (FDP) and further field investment decision (FID). In the Gulf of Thailand (GoT), high temperature Pattani basin discovery wells, reservoir fluids are mainly gas and condensate. There are numbers of waxy oil reservoirs1–5 in certain area in the GoT, notably in the cooler peripheral Tertiary basins. However, the subject field is the first one that was identified as having productive heavy oil reservoirs. The viscosity variation ranges between 1 and 100 cp2–6. It was observed that there was a depth related variation with deeper reservoirs having higher viscosities, and therefore, reservoir fluid information is crucial for the FDP and FID resulting from a field extension drilling campaign in early 2018. This paper will discuss step by step (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 finer particulates towards the probe and into the flowline, causing plugging issues in other probe types even though a modified sand filter was added. In the end, the 3D Radial probe was proven in making this exploration campaign a success story for acquiring the heaviest oil samples to date in the GoT. The 3D Radial probe equipped with mesh filter plays an important role to restrict ingress of small sand particles, thereby allowing both sustainable pumping speed and flowing pressure. The single packer design also helps to support the formation preventing drawdown collapse. Coupled with larger flow area of the probe itself, the 3D Radial Probe has ability to control flowing pressure to stay above the sand break-away pressure even as more viscous formation oil enters. However, job objectives were achieved, 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 discusses the comparison between Downhole Fluid Analysis results and PVT lab analyses. Limitation and challenges for downhole measurements for this heavy oil environment. Advantages and disadvantages for different testing methods for this heavy oil reservoir will also be discussed.
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