No abstract

No abstract

As an important type of unconventional hydrocarbon, tight sandstone oil has great present and future resource potential. Reservoir quality evaluation is the basis of tight sandstone oil development. A comprehensive evaluation approach based on the gray correlation algorithm is established to effectively assess tight sandstone reservoir quality. Seven tight sandstone samples from the Chang 6 reservoir in the W area of the AS oilfield in the Ordos Basin are employed. First, the petrological and physical characteristics of the study area reservoir are briefly discussed through thin section observations, electron microscopy analysis, core physical property tests, and whole-rock and clay mineral content experiments. Second, the pore type, throat type and pore and throat combination characteristics are described from casting thin sections and scanning electron microscopy. Third, high-pressure mercury injection and nitrogen adsorption experiments are optimized to evaluate the characteristic parameters of pore throat distribution, micro- and nanopore throat frequency, permeability contribution and volume continuous distribution characteristics to quantitatively characterize the reservoir micro- and nanopores and throats. Then, the effective pore throat frequency specific gravity parameter of movable oil and the irreducible oil pore throat volume specific gravity parameter are introduced and combined with the reservoir physical properties, multipoint Brunauer-Emmett-Teller (BET) specific surface area, displacement pressure, maximum mercury saturation and mercury withdrawal efficiency parameters as the basic parameters for evaluation of tight sandstone reservoir quality. Finally, the weight coefficient of each parameter is calculated by the gray correlation method, and a reservoir comprehensive evaluation indicator (RCEI) is designed. The results show that the study area is dominated by types II and III tight sandstone reservoirs. In addition, the research method in this paper can be further extended to the evaluation of shale gas and other unconventional reservoirs after appropriate modification.

No abstract

No abstract

The characterization of artificial fracture propagation law in the fracturing process of shale reservoirs is the basis for evaluating the fracture conductivity and a key indicator of the reservoir stimulated effect. In order to improve the fracture stimulated volume of shale reservoirs, this paper systematically discusses the current status of research on artificial fracture propagation law from the research methods and main control factors and provides an outlook on its future development direction. The analysis finds that the study of fracture propagation law by using indoor physical simulation experiments has the advantages of simple operation and intuitive image, and the introduction of auxiliary technologies such as acoustic emission monitoring and CT scanning into indoor physical model experiments can correct the experimental results so as to better reveal the propagation mechanism of artificial fractures. At present, the numerical simulation methods commonly used to study the propagation law of artificial fractures include the finite element method, extended finite element method, discrete element method, boundary element method and phase field method, etc. The models established based on these numerical simulation methods have their own advantages and applicability, so the numerical algorithms can be integrated and the numerical methods selected to model and solve the different characteristics of the propagation law of artificial fractures in different regions at different times can greatly improve the accuracy of the model solution and better characterize the propagation law of artificial fractures. The propagation law of artificial fracture in the fracturing process is mainly influenced by geological factors and engineering factors, so when conducting research, geological factors should be taken as the basis, and through detailed study of geological factors, the selection of the fracturing process can be guided and engineering influencing factors can be optimized.

As an emerging unconventional energy resource, shale gas has great resource potential and developmental prospects. The effective evaluation of geological sweet spots (GSS), engineering sweet spots (ESS) and comprehensive sweet spots (CSS) is one of the main factors for a high-yield scale and economic production of shale gas. Sweet spot evaluation involves a comprehensive analysis based on multiple parameters. Conventional evaluation methods consider relatively simple or single factors. Although the main influencing factors are understood, the influence of different factors is as of yet unknown, and a comprehensive consideration may strongly affect the evaluation results. In this paper, the fuzzy mathematics method is introduced for shale gas sweet spot evaluation. With the help of fuzzy mathematics tools, such as membership function, the objective of comprehensive sweet spots evaluation based on multiple parameters is realized. Additionally, the reliability of the evaluation of sweet spots is improved. Firstly, previous research results are used for reference, and the evaluation factor system of geological and engineering sweet spots of shale gas is systematically analyzed and established. Then, the basic principle of the fuzzy comprehensive evaluation method is briefly introduced, and a geological engineering integrated shale gas sweet spots evaluation method, based on the fuzzy comprehensive evaluation method, is designed and implemented. Finally, the data from HB blocks in the Z shale gas field in China are adopted. According to the evaluation results, the modified method is tested. The results show that the method proposed in this paper can synthesize a number of evaluation indices, quickly and effectively evaluate the GSS, ESS and CSS in the target area, and the results have high rationality and accuracy, which can effectively assist in well-pattern deployment and fracture design.

As the northwestern area of the Junggar Basin is a key area for oil and gas exploration, the sedimentary facies of the Jurassic formations in the Wuerhe area has long been a focus of research. The target strata are Jurassic strata, including five formations: the Lower Jurassic Badaowan and Sangonghe, the Middle Jurassic Xishanyao and Toutunhe and the Upper Jurassic Qigu. Disputes over the are sedimentary facies division exist in this area. Considering the W105 well region in this area as an example, the overall sedimentary facies of single-well logging facies is analyzed and then expanded to two cross-sections and characterized. Based on previous studies, a detailed overview of the regional stratigraphy is obtained by well logs and other data. Then, two cross-sections are selected and analyzed. The single-well and continuous-well facies of 10 wells in the sections are analyzed to grasp the sand bodies’ spatial distribution. Finally, a planar contour map of the net to gross ratio is mapped to analyze the sources and the distribution of the sand bodies in each period. The sedimentary facies map is also mapped to predict the sedimentary evolution. The results show that the sedimentary facies of the Badaowan Formation in the study area was an underwater distributary channel of the fan-delta front, and the sand body spread continuously from northwest to southeast. The Sangonghe Formation entered a lake transgression period with a rising water level, at which time shore–shallow lacustrine deposits were widespread throughout the region. The period of the Xishanyao Formation entered a regression period, the northwest region was tectonically uplifted, and the central and southeastern regions facies were dominated by the fan-delta front and shallow lacustrine. During the Toutunhe Formation period, the northwest region continued to uplift and was dominated by delta plain facies. During the period of the Qigu Formation, the thickness of stratigraphic erosion reached its maximum, and the non-erosion area of the study area was mainly deposited by the fan-delta plain. Overall, the Jurassic system in the W105 well area is a fan delta–lacustrine–fan delta sedimentary system.