Abstract Slickwater fracturing with high injection rate and large volume has been widely used in the development of shale reservoirs, while the proppants cannot distribute uniformly in fracture networks, usually in the forms of sand-bed, separated pillars and local displacement. Thus, there are still some key issues need to be figured out for better fracturing design, such as the proppant placement status in complex fractures, and how to achieve effectively propped fractures, etc. In this paper, a three-dimensional proppant transport model is established by Dense Discrete Phase Model (DDPM). The flow field and concentration distribution of the proppants were analyzed, by tracking the trajectory of proppants in different types of complex fractures. Besides, the placement status of particles in the primary and secondary fractures was analyzed. In addition, we also conducted the research on proppant transportations in perf clusters. Finally, according to actual fracturing treatment schedule, three different sizes of proppants were gradually injected and the distribution law of the proppants was studied. Based on the concentration distribution of proppants in the complex fractures, fractures can be divided into four zones: pure fluid zone, critical suspension zone, flowing slurry zone and settling bed zone, while the critical suspension zone and flowing slurry zone of secondary fracture are smaller than primary fracture. Besides, the proppants concentration entering into the fractures far from the entrance is more than that entering the fractures near the entrance. The ratio of proppant concentration into each perf cluster (3 clusters per stage) is about 1:1.5:2, while that concentration ratio is 1:1.25:1.6:2 in four clusters per stage scenario, while the proppant concentration is inversely proportional to the amount of proppant and liquid injected. The proppants of 100 mesh injected in the early stage migrates to the far end of the fracture, and some enters into the branch fractures, while most of them settled in the sand bed of the main fracture. Meanwhile, the following 40/70 mesh proppant injected is mainly distributed in the main fracture at flowing slurry zone. The 30/50 mesh proppant injected in the later stage is mostly located at the fracture entrance and at the top of the sand bed. Finally, it was found that high injection rate, small particle size, and low-density proppant could improve proppants preferentially entering branch fractures. This paper provides a clear insight of proppant distribution law in complex fractures under field fracturing treatment schedule. And our model can be used to optimize the fracturing treatment design.
Abstract The karst caves and fractures are widely developed in carbonate reservoirs, which results in strong spatial heterogeneity. So the parameters obtained from its cores and numerical simulation are limited to reflect its production situation of the entire reservoir, which causes that the traditional economic prediction method for carbonate reservoirs has a high risk. To solve these problems, this paper proposes a new method to accomplish the economic prediction based on expert library and oilfield database, named Delphi-AHP-TOPSIS-MLS-FNPV complex algorithm (DATMF). DATMF method can take account of geological factors, such as sedimentary facies, reservoir types, the characteristics and heterogeneity of caves and fractures. It also considered the impact of production factors on the economic prediction, such as oil production, annual decline rate of production, well spacing density. The process of the DATMF method is as follows: First, establishing a set of hierarchical structure to describe the carbonate reservoirs in the database; Secondly, optimizing the database and analyzing the data based on the expert library; Thirdly, predicting the key development parameters of the new reservoir according to its geological data; Finally, substituting these parameters into the future net present value (FNPV) method to complete the economic prediction of the new carbonate reservoir. Through the calculation example of T7-444CH reservoir, it is found that DATMF method can predict oil production, investment recovery period, and the future net present value, etc. quickly and accurately. On the one hand, it greatly reduces the time and money cost of using traditional economic prediction methods. On the other hand, comparing with the popular big data analysis method, it improves the data's quality and increases the result's professionalism and practicality by using experts’ experience to constraint data, which makes the DATMF method can work on the smaller database. It is very suitable for the DATMF method to be applied in the early or middle stage of oilfield information construction.
Summary The tight-fracture reservoir is an important reservoir type of Triassic Xujiahe Formation in Sichuan basin. Since the reservoir has low porosity, low permeability and strong heterogeneity characteristics, the accurate prediction of properties of Xujiahe Formation is the key and difficult point of oil and gas exploration and development. Facing with these problems, We propose a theoretical workflow of reservoir prediction. The main idea of our workflow is to define sand in face and define fracture in sand. Firstly, the distribution of favorable sand is predicted by seismic attributes and seismic inversion on the basis of facies-controlled techniques; then using pre-stack and post-stack technology to predict multi-scale fractures, at the same time, based on the fault-fracture evaluation system and reservoir-cap evaluation system to assess the effective of fault-fracture system. Finally, Considering the prediction result of sand and fractures point out the favorable exploration target area. The reliability of our method has been testified by comparing with drilling data, and we believe our method can be used to predict others tight sandy reservoir.
The obvious method of achieving simultaneous transcription of speech would be by using a speech recogniser. Unfortunately, the difficulties involved in the recognition of unconstrained, unlimited vocabulary connected speech are daunting and will not be solved for many years. Therefore, alternative methods have been investigated which require a human intermediary to carry out the computationally difficult tasks of isolating the speakers voice from other background sounds, separating words in the speech, ignoring the redundant speech utterances and simultaneously encoding the essential speech components of each word via some other medium such as keyboard or handwriting. The authors describe an approach for the segmentation and classification of the consonant part of a vocalised Pitman outline into its phonetic features involves three stages. Each segment is examined to determine whether it is long enough to be a primitive. Once the segmentation has been completed the features are classified using a fuzzy technique which classifies each feature into categories in terms of the degree of membership. Finally, decision making is achieved using the maximum likelihood principle. >
The distribution of the geostress field in reservoirs holds significant implications for the precise exploration and efficient development and utilization of oil and gas resources, especially in deep strata regions where faults are prevalent. Geological structural movements in these deep strata regions exacerbate the complexity of geostress field distributions. To elucidate the perturbation of the geostress field in deep reservoirs caused by faults, this study initially conducted a series of physical model tests on single fault dislocation, employing digital image correlation techniques to capture the displacement fields of various types of fault dislocations. Subsequently, a numerical model of the fault interface element was established, and fault element parameters were determined through sensitivity analysis and trial calculation. This study further analyzed the perturbation of the geostress field using this numerical model. Finally, a multi-fault numerical simulation model was constructed to clarify the perturbations in the regional geostress field under the influence of multiple faults. The results indicate that the geostress perturbation range under the action of multiple faults spans from 183.06 to 310.06 m.
Coronary slow flow phenomenon (CSFP) is an important, angiographic clinical entity but is lacking non-invasive detecting techniques. This study aimed to elucidate the value of transthoracic Doppler echocardiography (TTDE) in the diagnosis and monitoring of coronary slow flow in left anterior descending (LAD) coronary artery.We consecutively enrolled 27 patients with CSFP in LAD detected by coronary arteriography from August 2009 to April 2010. Thirty-eight patients with angiographically normal coronary flow served as control. Corrected thrombolysis in myocardial infarction (TIMI) frame count (CTFC) was used to document coronary flow velocities. All subjects underwent TTDE within 24 hours after coronary angiography. LAD flow was detected and the coronary diastolic peak velocities (DPV) and diastolic mean velocities (DMV) were calculated.Sixty of 65 (92.3%) subjects successfully underwent TTDE. Baseline clinical characteristics were similar between the two groups. Coronary DPV and DMV of LAD were significantly lower in the CSFP group than in the control group ((0.228 ± 0.029) m/s vs. (0.302 ± 0.065) m/s, P = 0.000; (0.176 ± 0.028) m/s vs. (0.226 ± 0.052) m/s, P = 0.000, respectively). There was a high inverse correlation between CTFC and coronary DPV and DMV (r = -0.727, P = 0.000; r = -0.671, P = 0.000, respectively). Receiver operating characteristic (ROC) curve showed that the area under the curve (AUC) was less than one half for coronary DPV (AUC = 0.104) and DMV (AUC = 0.204), respectively.In patients with CSFP, there is a high inverse correlation between CTFC and coronary diastolic flow velocities in the LAD coronary artery, as measured by TTDE. The value of TTDE in the monitoring and evaluation of coronary flow in patients with CSFP deserves further investigation.
Virtual simulation technology plays an important role in educational engineering. The limitation of enough Chinese herbal medicines and instrument obscured the better understanding of Traditional Chinese Medicine (TCM). In this paper, the concept of virtual simulation technology and its application was outlined in the teaching of TCM theory and experiments. The superiority and insufficiency of this technology was also approached. The basic idea on building a virtual teaching and simulation platform for TCM was discussed, which may provide referred methods in the innovation of Chinese medicine teaching.
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