Search

Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Comprehensive the analysis of cores, thin section, physical properties, mercury injection, and X-CT, genesis of heterogeneity of conglomerate reservoirs in Baikouquan formation of Mahu sag is studied. The Baikouquan formation belongs to fan delta glutenite deposit, typical conglomerate reservoir is developed. The dissolution pores are the dominated reservoir space, and its development degree has strong heterogeneity among different intervals, sedimentary facies, and rock types. Seven lithofacies are divided according to composition, structure, and sedimentary characteristics, among these; underwater distributary channel lithofacies is the most favorable for reservoir development followed by braided dam lithofacies and braided branch channel lithofacies. The strong hydrodynamic underwater deposition is favorable for the formation of high-quality reservoirs. Sedimentation determined the original difference and the difference of diagenesis promotes the formation of conglomerate reservoir heterogeneity. [ABSTRACT FROM AUTHOR]

Zeolites are important diagenetic minerals in petroleum reservoirs and have complex impacts on reservoir quality. To highlight this critical and challenging issue, we conduct a case study in the Middle Permian Lower-Wuerhe Formation in the Mahu Sag, Junggar Basin, China. Formation mechanism of zeolites and their impacts on the reservoir quality. Our results show that there are five types of zeolite minerals (i.e. laumontite, heulandite, analcime, stilbite, and clinoptilolite) in the Lower-Wuerhe Formation reservoir, with laumontite and heulandite being the main types. Petrographic and geochemical data suggested that laumontites developed in the Lower-Wuerhe Formation were mainly precipitated from pore water, whereas heulandites were formed associated with alteration of volcanic materials. In addition, the distribution of different type of zeolite minerals is generally controlled by sedimentary facies. The heulandite–laumontite zone developed mainly in the front of fan-delta plain, and the laumontite zone developed mainly in fan-delta front. The distal part of fan-delta front is dominated by albite. The zeolite mineral assemblages are generally controlled by geochemical composition of volcanic lithic fragments. The high content of intermediate-basic volcanic lithic fragments in the eastern Mahu Slope sediments is responsible for authigenic minerals such as heulandite, chlorite, and laumontite. However, the content of intermediate-basic volcanic lithic fragments in the western Mahu Slope sediments is low which results in the cement in this region is dominated by laumontite and mixed-layer illite/smectite. In general, conglomerates deposited in fan-delta front are favorable for the formation of early laumontite and late dissolution of laumontite due to resistance to compaction by coarse fraction and accumulation of acidic fluids in structural highs, which resulted in the formation of a high-quality reservoir. Our results have general implications for hydrocarbon exploration of the zeolite-bearing conglomerate reservoirs in non-marine petroliferous basins. [ABSTRACT FROM AUTHOR]

The determination of high-quality intervals in oil reservoirs has always been challenging work while their petrophysical attributes are relatively low. To date, extensive reservoir evaluation studies have been undertaken to locate favorable zones for oil exploration and exploitation. However, without the geological constraint principles, the selected evaluation parameters depend heavily on experience or pure mathematical methods. Hence, we propose a reservoir evaluation method based on petrophysical facies to undertake the reservoir quality assessment for the conglomerate reservoirs of the Triassic Baikouquan Formation in the northern Mahu sag, Junggar Basin, western China. The lithofacies and diagenetic facies were first identified based on laboratory data. Subsequently, petrophysical facies types were recognized by the combination of lithofacies and diagenetic facies. Afterward, capillary pressure curves of different petrophysical facies were clustered to clarify the reservoir quality variation in distinct geological origins. Consequently, the evaluation standard was established and the reservoir quality distribution was analyzed and drawn out. These results indicate that there exist 4 rock types in the Baikouquan Formation (from RT1 to RT4). The distributional status of the optimal reservoir (RT1) and the worst reservoir (RT4) are primarily determined by grain size, while rock type 2 (RT2) and rock type 3 (RT3) are predominantly controlled by dissolution and compaction. Moreover, an evident positive association exists between the rock type and the single well production capacity, which reveals that the utilization of petrophysical facies to assess reservoir quality is reliable. It is concluded that reservoir evaluation based on petrophysical facies harbors the potential to be a pivotal tool for reservoir property assessment and prediction of favorable porosity and permeability zones. • Petrophysical facies is applied in reservoir evaluation of low permeability conglomerate reservoirs. • This method can reveal the geological genetic mechanism of distinct petrophysical characteristics. • The petrophysical facies applies well in prediction of profitable porosity and permeability zones. [ABSTRACT FROM AUTHOR]

Understanding reservoir heterogeneity and associated diagenesis, have a paramount importance for efficient petroleum exploration and development strategies. Diagenetic variations and factors that control these processes have, therefore, been investigated in this study using petrographic and geochemical methods, including cathodoluminescence, scanning electron microscopy, x-ray fluorescence, electron probe microanalyses and stable isotope analysis. Mechanical compaction and chemical diagenesis trends have obviously varied as a function of rock types and geological locations. The conglomerate reservoirs with high content of tuffaceous matrix and characterized by poor sorting showed stronger compaction. The tuffaceous matrix displays a large degree of dissolution during the progressive burial diagenesis due to its thermodynamic instability. The tuffaceous matrix in Na-rich conglomerate reservoir rocks mainly transformed into analcite, while it transformed into illite in K-rich conglomerate reservoir rocks. In most conglomerate reservoirs far away from deep-rooted faults, calcite cements are indicated to have been sourced from the decarboxylation of organic matter in the interbedded mudstones. Carbonate cements in conglomerate reservoirs near the deep-rooted faults possibly formed from hydrothermal fluids or thermochemical oxidation of pre-existing methane accumulations. This study can serve us an excellent example for the control of sediment composition and paleo-fluid evolution on diagenetic variations in fan-delta conglomerate reservoirs. • Compaction and dissolution in conglomerate reservoirs were controlled by sediment composition and texture. • Authigenic silicoaluminate minerals formation in conglomerate reservoirs were controlled by sediment composition. • Carbonate cements formation in conglomerate reservoirs were controlled by paleo-fluids evolution. [ABSTRACT FROM AUTHOR]