Low Permeability Gas-Bearing Sandstone Reservoirs Characterization from Geophysical Well Logging Data: A Case Study of Pinghu Formation in KQT Region, East China Sea

Abstract

The Pinghu Formation is a low permeability sandstone reservoir in the KQT Region, East China Sea. Its porosity ranges from 3.6 to 18.0%, and permeability is distributed from 0.5 to 251.19 mD. The relationship between porosity and permeability was poor due to strong heterogeneity. This led to the difficulty of quantitatively evaluating effective reservoirs and identifying pore fluids by using common methods. In this study, to effectively evaluate low permeability sandstones in the Pinghu Formation of KQT Region, pore structure was first characterized from nuclear magnetic resonance (NMR) logging based on piecewise function calibration (PFC) method. Effective formation classification criteria were established to indicate the “sweet spot”. Afterwards, several effective methods were proposed to calculate formation of petrophysical parameters, e.g., porosity, permeability, water saturation (Sw), irreducible water saturation (Swirr). Finally, two techniques, established based on the crossplots of mean value of apparent formation water resistivity (Rwam) versus variance of apparent formation water resistivity (Rwav)—Sw versus Swirr—were adopted to distinguish hydrocarbon-bearing formations from water saturated layers. Field applications in two different regions illustrated that the established methods and techniques were widely applicable. Computed petrophysical parameters matched well with core-derived results, and pore fluids were obviously identified. These methods were valuable in improving low permeability sandstone reservoirs characterization.

Formation Characterization and Type Prediction Based on Geophysical Well Log Data in Horizontal Well: A Case Study of Triassic Chang 8 Formation in Shunning Region, Central Ordos Basin

“…This theoretical relation can be well-used to express the variation between pore structure and cementation exponent, especially for tight rocks with porosities lower than 8%. The theoretical relation raised by has been verified to be widely usable in different types of tight reservoirs [40]. In this study, using the resistivity experimental data that are displayed in Figures 16 and 17, we also analyze the effect of pore structure to cementation exponent in Chang 8 Formation of Shunning Region and determine that the cementation exponent is heavily affected by porosity.…”

Fluid Identification Method of Nuclear Magnetic Resonance and Array Acoustic Logging for Complex Oil and Water Layers in Tight Sandstone Reservoir

“…The K s can be obtained by using Equation (6). In order to calculate K fa , K d and K m also need to be determined.…”

“…However, the complex interplay between depositional and post-depositional "diagenetic" attributes obliterates the petrophysical characteristics of sandstone reservoirs resulting in a tight pore. Combined with the influence of logging conditions and reservoir factors, the sensitivity of the logging response to pore fluid is reduced and complex oil and water layers, such as high-resistivity water layers and low-resistivity oil layers, are often misjudged or missed, which seriously restricts the economic benefits of the oilfield [4][5][6]. Nowadays, the research on the fluid identification method of complex oil and water layers in tight sandstone reservoirs has become an important topic in oilfield exploration and development [7][8][9][10].…”

Estimation of water saturation based on optimized models in tight gas sandstone reservoirs: A case study of Triassic Xujiahe Formation in northwestern Sichuan Basin

“…Meanwhile, also raised a statistical model to predict various saturation exponent from NMR logging to optimize the Archie's equation. These proposed models had been verified to be usable in certain reservoirs (Gao et al, 2023;Li et al, 2023). However, the widely applicability was questionable.…”