During field testing of a logging-while-drilling (LWD) laterolog resistivity and imaging tool, formation resistivity differences were observed between the new laterolog and standard propagation resistivity. This paper compares the resistivity measurement acquired in the same borehole using different tools in both sand and shale formations. In addition, the high-resolution images acquired by the new tool are used for a detailed geolgical analysis of the sequence. The high-resolution images acquired by the tool are used to determine the sedimentary environments in this complex fan delta sequence. A wide range of facies types can be identified on the images and correlated to available core with detailed examples shown of the key reservoir facies (distibutary channels and mouth bars). The images also provide valuable structural, depositional trend and insitu stress information for this well. The laterolog resistivities were higher in the shales and lower in the sands than the propagation resistivity values. The data was acquired while drilling in a water-based mud, sub-vertical exploration well in the South China Sea. While the main objective of the data acquisition in the siliciclastic formations was high-definition resistivity borehole images for detailed geological description, the radial laterolog resistivity response was also of interest. An advanced wireline multi-frequency dielectric measurement was also acquired, and its response was used for comparison and validation. In this paper, we associate the differences in resistivity response for varying formation properties to the tool physics, vertical resolution, depth of investigation, and time after bit between the measurements. In the sands, a resistivity inversion was applied to correct the logs for invasion effects and forward modeling used to resolve the resolution differences. The inverted formation resistivity from the LWD laterolog matches the deeper reading LWD propagation resistivity. The shale response was initially found to be more difficult to explain. It is commonly and historically accepted that due to resistivity anisotropy laterolog reads higher than propagation resistivity in low angle wells with laminated formations. Advanced forward modeling was used to investigate the laminations observed on the high-definition images and high-resolution laterolog resistivity curves. Although a model could be created to match both sets of resistivity measurements, the level of anisotropy required was considerably higher than expected, and supplementary information was required to validate the model. The wireline multi-frequency dielectric measurements provided the additional information required to confirm the anisotropy contrast observed by the resistivity modeling and confirm the LWD tool responses. This paper will compare the tool responses, and to determine the correct sand and shale resistivity. It will show how by combining different measurements, additional insight can be obtained into the nature of the formation and its properties.

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Tight sandstone reservoirs characterization and evaluation is very difficult based on conventional well log data owing to the extremely low porosity and permeability, and strong heterogeneity. The main accumulation spaces of conventional reservoirs are intergranular pores, and the pore size is the main controlling factor of permeability. However, besides intergranular pores, fractures play much greater important role in accumulating hydrocarbon, improving the pore connectivity and pore structure in tight sandstone reservoirs. Hence, it should be accurately predicted the pore structure dredged by fractures to improve the characterization of tight sandstone reservoirs. Generally, nuclear magnetic resonance (NMR) logging is an effective method to evaluate formation pore structure. However, it cannot be well used in fractured reservoirs because the NMR T2 spectra has no any response for fractures with width <2mm. The borehole electrical image log is usable in characterizing fractured reservoirs. The pore spectrum, which is extracted from the borehole electrical image log, can be used to qualitatively reflect the pore size. Hence, it will play an important role in fractured reservoirs pore structure characterization. In this study, based on the comprehensive analysis of the pore spectra, the corresponding mercury injection capillary pressure (MICP) data and pore-throat radius distributions acquired from core samples, a relationship that connects the 1/POR and capillary pressure (Pc) is proposed. Established a model based on formation classification to transform porosity spectrum into pseudo capillary pressure curve. In addition, a Swanson parameter-based permeability prediction model is also developed to extract fractured formation permeability. Meanwhile, to verify the superiority and otherness of borehole electrical image and NMR log, the model that evaluated reservoirs pore structure from NMR log is also established. Based on the application of the proposed method and models in actual formations, the evaluated pore structure parameters and permeabilities from two types of well log data are compared. The results illustrates that in formations with relative good pore structure, the predicted pore structure parameters and permeabilities from these two types of well log data agree well with the drill stem testing data and core-derived result. However, in low permeability sandstones with relatively poor pore structure, the porosity spectra can be well used to evaluate the pore structure, whereas the characterized pore structure from NMR log is overestimated. With the comprehensive research of reservoirs pore structure and permeability, the fractured tight sandstone formations with development value are precisely identified. This proposed method has greatest advantages that the pore structure of fractured reservoirs can be characterized, and the contribution of fractures to the pore connectivity and permeability can be quantified. it is usable in tight sandstone reservoirs validity prediction.