Experimental Study of the Main Influencing Factors in Mechanical Properties of Conglomerate

In recent years,with the success of exploration and development of conglomerate reservoirs in Mahu Depression,Junggar Basin,China,it is urgent to study the mechanical properties and its influencing factors of conglomerate which is considered as a new oil and gas reservoir.Based on the investigations of petrologic characteristics,heterogeneity and mechanical properties of conglomerate in Baikouquan formation,the content and geometric characteristics of gravel in conglomerate,the main factors in heterogeneity and the mechanical behavior in the triaxial compression experiment of conglomerate are analyzed in this paper.The results show that the size and content of gravel in conglomerate varies greatly,and conglomerate has strong heterogeneity under the influence of gravel content and size.An analysis of mechanical properties of conglomerate shows that conglomerate is characterized by plasticity.Besides,the sphericity is negatively correlated to the gravel content,while the heterogeneity increases with the increase of conglomerate plasticity.Due to the existence of heterogeneous gravel,local stress may concentrate in conglomerate when the stress is loaded.Consequently,a large number of micro-cracks appear at the edge of gravel,demonstrating the strong plasticity of conglomerate.This paper is of referential significance to the study of rock mechanical properties and the evaluation of engineering properties in conglomerate development.

Imaging-Based Characterization of Perthite in the Upper Triassic Yanchang Formation Tight Sandstone of the Ordos Basin,China

This work investigated the element distribution of perthite from the Upper Triassic Yanchang Formation tight sandstone in the Ordos Basin of northern China by field emission scanning electron microscopy(FE-SEM) and energy dispersive spectrometer(EDS). FE-SEM results indicate significant differences in the morphology of Na-rich feldspar when K-rich feldspar is the main component of the perthite. EDS results show that different types of perthite have clearly defined differences on different element indexes. Additionally, indexes such as average-weight-K(K-rich)/Na(Na-rich), maximumweight-K(Na-rich)/Na(Na-rich) and average-atomic-K(K-rich)/Na(Na-rich) might be the most effective ones to identify perthite types. Perthite is divided into six main types, i.e., perthite with thick parallel stripe distribution, with thin parallel stripe distribution, with lumpy stripe distribution, with dendritic stripe distribution, with encircling stripe distribution, and with mixed stripe distribution.

Investigation of flue gas water-alternating gas (flue gas–WAG) injection for enhanced oil recovery and multicomponent flue gas storage in the post-waterflooding reservoir

Flue gas fooding is one of the important technologies to improve oil recovery and achieve greenhouse gas storage.In order to study multicomponent fue gas storage capacity and enhanced oil recovery(EOR)performance of fue gas water-alternating gas(fue gas-WAG)injection after continuous waterfooding in an oil reservoir,a long core fooding system was built.The experimental results showed that the oil recovery factor of fue gas-WAG fooding was increased by 21.25%after continuous waterfooding and fue gas-WAG fooding could further enhance oil recovery and reduce water cut signifcantly.A novel material balance model based on storage mechanism was developed to estimate the multicomponent fue gas storage capacity and storage capacity of each component of fue gas in reservoir oil,water and as free gas in the post-waterfooding reservoir.The ultimate storage ratio of fue gas is 16%in the fue gas-WAG fooding process.The calculation results of fue gas storage capacity showed that the injection gas storage capacity mainly consists of N_(2) and CO_(2),only N_(2) exists as free gas phase in cores,and other components of injection gas are dissolved in oil and water.Finally,injection strategies from three perspectives for fue gas storage,EOR,and combination of fue gas storage and EOR were proposed,respectively.

Reformation of deep clastic reservoirs with different diagenetic intensities by microfractures during late rapid deep burial: Implications from diagenetic physical simulation of Cretaceous Qingshuihe Formation in the southern margin of Junggar Basin, NW China

Constrained by the geological burial history of Cretaceous Qingshuihe Formation in the southern margin of Junggar Basin, the diagenetic physical simulation experiment was carried out with the low-mature sandstone samples taken from the outcrop area. Then, coupling with the regional geological data, the reformation of reservoirs with different diagenetic intensities by microfractures and the significance of microfractures for development of high-quality reservoirs were discussed. The results show that the large-scale microfractures were formed in the stage of late rapid deep burial, roughly equivalent to the period when organic acids were filled. The microfractures created good conditions for migration of oil and gas in deep and ultra-deep clastic rocks, and also enabled the transport of organic acids to the reservoirs for ensuing the late continuous dissolution of cements and particles. The existence of matrix pores and microfractures in the reservoirs before the rapid deep burial determined how the microfractures formed during rapid deep burial improved the reservoir quality. If matrix pores and microfractures were more developed and the cementation degree was lower before the rapid deep burial, the microfractures would be more developed and the dissolution degree would be higher during the late rapid deep burial, and so the reservoir quality would be improved more greatly, which can increase the reservoir permeability by up to 55%. If cementation was very strong, but matrix pores were not developed and microfractures existed locally before the rapid deep burial, the microfractures would also be more developed during the late rapid deep burial, which can increase the reservoir permeability by 43%. If cementation was strong, matrix pores were absent, and microfractures were not developed, limited microfractures would be formed during the late rapid deep burial, which can increase the reservoir permeability by only 16%. Formation of large-scale microfractures during late rapid deep burial and promotion of such microfractures to the dissolution of organic acids are considered as key diagenetic factors for the development of deep and ultra-deep high-quality reservoirs.

Influence of the Addition of Cotton Stalk during Co-pyrolysis with Sewage Sludge on the Properties, Surface Characteristics, and Ecological Risks of Biochars

Sewage sludge produced by municipal sewage treatment plants can potentially be used as a biomass energy source because of its high organic content.Presently,the conversion and utilization of rapidly growing amounts of sewage sludge represent an urgent challenge in China.Thermal conversion of sewage sludge to biochar through pyrolysis is a promising solution to this problem.However,biochar produced by pyrolysis of sewage sludge alone has a poor pore structure as a result of its low C content and high ash content.Furthermore,it is enriched in heavy metals that may pose high ecological risks.In this study,we addressed these issues through co-pyrolysis of sewage sludge and cotton stalks(1:1,wt./wt.)at different pyrolysis temperatures ranging from 350℃ to 750℃.The properties and surface characteristics of the biochars were investigated.Meanwhile,the transformation behavior of heavy metals during the co-pyrolysis process was studied,and the potential ecological risks of heavy metals in biochars were assessed.The results showed that elevated pyrolysis temperatures reduced the biochar yield and C content of the biochars,whereas such temperatures increased the pH value and ash content of the biochars.The biochars prepared at different pyrolysis temperatures were all mesoporous materials.The elevated temperatures promoted the transformation of heavy metals from mobile fractions to stable ones,thus resulting in a significant decrease in the ecological risks.In summary,co-pyrolysis of sewage sludge with cotton stalks proved to be a feasible method for the conversion and utilization of sewage sludge.