M. Reza Rezaee

Intelligent approaches for the synthesis of petrophysical logs

Log data are of prime importance in acquiring petrophysical data from hydrocarbon reservoirs. Reliable log analysis in a hydrocarbon reservoir requires a complete set of logs. For many reasons, such as incomplete logging in old wells, destruction of logs due to inappropriate data storage and measurement errors due to problems with logging apparatus or hole conditions, log suites are either incomplete or unreliable. In this study, fuzzy logic and artificial neural networks were used as intelligent tools to synthesize petrophysical logs including neutron, density, sonic and deep resistivity. The petrophysical data from two wells were used for constructing intelligent models in the Fahlian limestone reservoir, Southern Iran. A third well from the field was used to evaluate the reliability of the models. The results showed that fuzzy logic and artificial neural networks were successful in synthesizing wireline logs. The combination of the results obtained from fuzzy logic and neural networks in a simple averaging committee machine (CM) showed a significant improvement in the accuracy of the estimations. This committee machine performed better than fuzzy logic or the neural network model in the problem of estimating petrophysical properties from well logs.

Effect of Water Blocking Damage on Flow Efficiency and Productivity in Tight Gas Reservoirs

Tight gas reservoirs normally have production problems due to very low matrix permeability and significant damage during well drilling, completion, stimulation and production. Therefore, they might not flow gas at optimum rates without advanced production improvement techniques. The main damage mechanisms and the factors that have significant influence on total skin factor in tight gas reservoirs include mechanical damage to formation rock, water blocking, relative permeability reduction around wellbore as a result of filtrate invasion and liquid leak-off into the formation during fracturing operations. Drilling and fracturing fluids invasion mostly occurs through permeable zones or natural fractures and might also lead to serious permeability reduction in the rock matrix that surrounds the wellbore, natural fractures, or hydraulic fracture wings.

Lithofacies and Sequence stratigraphic Framework of the Kockatea Shale, Dandaragan Trough, Perth Basin

Initial studies affirm large-scale shale-gas potential for the Permo-Triassic intervals of the Perth Basin. The Dandaragan Trough, as a major depocentre in the basin and with the highest number of wells intersecting these intervals, has possibly the greatest shale-gas potential in the area. The primary self-contained shale-gas system proposed for the Dandaragan Trough is in the basal Kockatea Shale (Hovea Member), which was deposited during the Late Permian-Early Triassic. Seven lithofacies have been identified in a continuous 35 m core from the Hovea Member of the Kockatea Shale at Redback–2. Among recognised lithofacies, besides siliceous mudstone, which contains clastic particles, most are representative of deposition in a shallow marine environment with different energy levels. Bioturbated lithofacies reveal deposition in a higher-energy environment compared with the other lithofacies. The sequence stratigraphic framework of the Hovea Member is established based on diagnosis of the lithofacies, cyclical stacking patterns, transgressive surfaces of erosion (TSE), and condensed sections (CSs). The framework supports deposition mainly in an aqueous environment with rare regressions. Periodic tectonic activity can be revealed in high-frequency relative sea-level changes during Hovea Member deposition. Gamma ray (GR) log analysis indicates that the highest GR peak is related to black-shale lithofacies with 1.75% TOC content. The greatest amounts of TOC, however, exist in the fossiliferous mudstone and pyritic mudstone lithofacies. A north–south GR correlation of the Hovea Member shows nearly the same lithological distribution throughout the trough despite its thinning in various areas.

Measuring Ultrasonic Characterisation to Determine the Impact of Toc and the Stress Field on Shale Gas Anisotropy

ABSTRACT While the majority of natural gas is produced from con-ventional sources, there is significant growth from uncon-ventional sources, including shale-gas reservoirs. To produce gas economically, candidate shale typically requires a range of characteristics, including a relatively high total organic carbon (TOC) content, and it must be gas mature. Mechanical and dynamic elastic properties are also important shale char-acteristics that are not well understood as there have been a limited number of investigations of well-preserved samples. In this study, the elastic properties of shale samples are de-termined by measuring wave velocities. An array of ultrasonic transducers are used to measure five independent wave ve-locities, which are used to calculate the elastic properties of the shale. The results indicated that for the shale examined in this research, P- and S-wave velocities vary depending on the isotropic stress conditions with respect to the fabric and TOC content. It was shown that the isotropic stress signifi-cantly impacts velocity. In addition, S-wave anisotropy was significantly affected by increasing stress anisotropy. Stress orientation, with respect to fabric orientation, was found to be an important influence on the degree of anisotropy of the dynamic elastic properties in the shale. Furthermore, the relationship between acoustic impedance (AI) and TOC was established for all the samples.

Liquid loading in wellbores and its effect on cleanup period and well productivity in tight gas sand reservoirs

Tight gas reservoirs normally have production problems due to very low matrix permeability and significant damage during well drilling, completion, stimulation and production. Therefore they might not flow gas to surface at optimum rates without advanced production improvement techniques. After well stimulation and fracturing operations, invaded liquids such as filtrate will flow from the reservoir into the wellbore, as gas is produced during well cleanup. In addition, there might be production of condensate with gas. The produced liquids when loaded and re-circulated downhole in wellbores, can significantly reduce the gas pro-duction rate and well productivity in tight gas formations.