查看更多>>摘要：Heavy oil reservoirs are faced with many problems in the development process,such as complex technology,unsatisfactory productivity,and difficult evaluation.Huff and puff as a common method for improving the heavy oil reservoir is popularized.In this work,a brand new evaluation method for residual oil distribution is proposed to evaluate the sweep efficiency of heavy oil under different huff-puff patterns in a sand-packed model.The sand saturated by oil is sequentially taken out from the sand-pack model by using a hand gong drill,and the width of oil stain at every interval of 1 cm along the axis on the oil absorbing paper is measured with a ruler.Based on this innovative laboratory evaluation method,a single pipe model with different oil viscosity and a double pipe model with different permeability levels were designed for three different huff-puff patterns,including nitrogen huff-puff,nitrogen + foam huff-puff and nitrogen + viscosity reducer huff-puff.The results showed that the remaining oil distribution was mainly concentrated in the far well section of 15-60 cm in the sand-packed model.For μo>10000 mPa s,the overall peak width of the remaining oil by using nitrogen and viscosity reducer huff-puff method was relatively small,which had a better effect on heavy oil development.The experimental results for different permeability differences showed that the peak width at the end of the high permeability pipe was higher(W>15 cm)because of the terminal crude oil carried by the nitrogen gas in the low permeability pipe constantly coming into the high permeability pipe with low resistance.Compared with the distribution results of the remaining oil in the low permeability pipe with three different huff-puff methods under the same permeability difference,the width peak of the remaining oil generated by using the nitrogen and viscosity reducer huff-puff method was relatively low(w<13 cm).With the increase of the permeability differences,the peak width difference of the remaining oil at the end of the high/low permeability pipes gradually increased because of the low resistance in the high permeability pipe.Therefore,the remaining oil distribution is intuitively characterized by the application of this new evaluation method and this method reveal the significant reduction of the oil viscosity by using the nitrogen and viscosity reducer huff-puff method to improve the evolution effect of heavy oil.
查看更多>>摘要：A sufficient number of choices are available when it conies to injection gas for enhanced oil recovery(EOR)application in unconventional reservoirs,such as CO2 and field gas to name a few.Most likely,these gases have various degrees of compatibility with the in situ reservoir fluid from the oil recovery increase standpoint.In some cases,they might not even be compatible at all with each other.Instead of creating a better oil extraction,the introduction of the gases could diminish the oil recovery.It has been observed that some gases have exceptional ability in increasing the oil production by decreasing the oil viscosity while moving towards completely vaporizing the oil phase as the gases'molar fractions increase in the mixture.The optimum injection gas composition is the one that returns the lowest oil and gas viscosity while continuously vaporizes the oil phase at the same time.For instance,pure C2 is the optimum injection gas composition for the in-situ reservoir fluid used in this study.The significant increase in oil recovery given by the optimum injection gas justifies such injection fluid composition optimization attempt proposed by this study.Furthermore,the injection fluid composition should be among the first to be optimized,before other operational parameters such as huff-n-puff cycle durations.
查看更多>>摘要：Well logging data are the main support of petrophysical information in petroleum engineering,and as many natural signals,they have deterministic component and noisy component.Conventional denoising methods depend on various filtering parameters,which increase the possibility of error and losing useful information in the signal.This research provides a well-controlled method to reduce noise,based on empirical mode decomposition(EMD)and regularity analysis indexed by the Holder exponent(in short,EMD-Holder).First,well velocity logs are handled as noisy signals,and decomposed into intrinsic mode functions(IMFs)for fast oscillations to slow oscillations via EMD,then regularity exponent is computed for each IMFs using wavelet leaders(WL)algorithm.The Holder exponent(h)is one of the best metrics to quantify the singularity.The value of the Holder exponent h = 0.5 characterizes the white noise of the analyzed signal,and any value h calculated from an intrinsic modal function IMF less than or equal to a predefined specific threshold,this IMF function is considered as noise,to be discarded while the reconstruction of the new denoised signal.To determine the multifractal properties of P-and S-wave velocities denoted Vp and Vs,respectively,a multifractal analysis was performed using the wavelet leaders(WL).The estimated multifractal parameters:scaling exponent x(q),multifractal spectrum D(h),singularity strength h,and Hausdorff dimension D are used to quantify the non-stationarity and non-linearity of velocity,followed by an application of unsupervised statistical methods(a hierarchical clustering analysis,HCA,and principal component analysis,PGA)to establish a possible relationship between multifractal parameters and type of lithology(sandstone and clay).It is shown that the width of the multifractal spectra(Ah)estimated from well logs can be used as a lithological indicator of the studied geological formations.
查看更多>>摘要：Permeability prediction of porous media from numerical approaches is an important supplement for experimental measurements with the benefits of being more economical and efficient.However,the accuracy and reliability of traditional numerical approaches are strongly dependent on the high-resolution images of porous media,which greatly limits their implementation for engineering applications.Herein,a semi-supervised machine learning approach is proposed to predict the permeability of porous media from low-resolution images.This approach consists of an autoencoder(AE)module trained with unlabeled data to assist the backbone convolutional neural network(CNN)in the prediction by providing a mapping of the low-resolution porous media to high-resolution features.The low-resolution information from CNN trained with small amount of labeled data and high-resolution information from AE trained with larger amount of unlabeled data are comprehensively considered in this approach.The prediction performance of AE-CNN from low-resolution images is examined against the results from traditional approaches of CNN and lattice Boltzmann method(LBM)by the mean-square errors(MSE)and R-Squared(R2)calculations.Using 5-fold cross-validation method,the average value of R2 is 0.896 on the test dataset by AE-CNN,compared to 0.869 for the traditional CNN without the AE.The MSEs for AE-CNN are 0.022 and 0.064 on the training and test datasets respectively in the best-performance fold,while without AE,the MSEs for only CNN are 0.034 and 0.083 on the training and test datasets respectively in the best-performance fold,implying that AE modules can substantially improve the prediction performance from low-resolution images of porous media.As for the simulation results of LBM approach,its prediction reliability(average R2:0.42;MSE:0.37 and 0.36 in the best-performance fold)is extremely lower than that of CNN-based machine learning algorithms owing to huge numerical error at the blurred boundaries of low-resolution images.
查看更多>>摘要：In digital rock physics,the study of physical parameters and flow characteristics of reservoirs requires a wealth of three-dimension digital rock samples.However,traditional physical methods of obtaining digital rock are expensive,and numerical reconstruction method cannot obtain a reasonable pore structure for complex rock.Recently,generative adversarial networks(GANs)have proven to be a successful method for reconstructing pore-scale models,but the reconstructed large-size digital rocks look unreasonable due to the lack of sufficient consideration of multi-scale information fusion and it takes a lot of computational resources and time to build the model.Hence,we proposed a combination of InfoGAN and style-based GAN guided by prior information(CIS-GAN)to reconstruct more controllable and reasonable digital rock models using small set of samples.Porosity distribution as prior information is added into latent space to control pore distribution,and a classifier Q is set in discriminator to ensure the porosity is limited to reasonable range.Multi-scale information is applied each layer by style transfer and used to optimize the background information,pore structure,and micro information of model for multi-scale fusion to produce more reasonable and natural digital rock.Simple-structure sandstone and complex-structure carbonate are implemented to test the reconstruction ability of network.The result shows that synthetic sample has high consistency on pore-throat geometry and connectivity,and the CISGAN can produce natural and user-specified digital rock samples.And the CISGAN will provide more reasonable and various type samples for intelligent parameter prediction of digital rock.
查看更多>>摘要：To understand the interlayer change characteristics during coalbed methane(CBM)production from a multilayer superimposed gas-bearing system(MSGS),a large-scale coupled CBM production test device involving multiple fields was developed in the present study and a four-layer superimposed gas-bearing system was simulated.Based on the response characteristics of the deformation and pressure fields during CBM production,the interlayer change characteristics were analyzed.Results show that the reservoir pressure change involves multiple stages,and these changes decrease the pressure in production layers significantly.Changes in other layers are enhanced with proximity to the production layer,and the decrease in reservoir pressure causes shrinking and deformation of the coal body.Owing to the Poisson effect,the adjacent layer deforms by expansion,and this gradually decreases pressure in the layer.A sensitivity coefficient k and a deformation rate X are used to analyze the sensitivity of the other layers to changes in the production layer and the associated damage.The k increases linearly with production time,and both κ and λ increase with proximity to the production layer.The present study demonstrates that for CBM production from an MSGS,the deformation and reservoir pressure evolution data are suitable for determining the production effect characteristics of a coal seam.Targeted protection measures can thus be introduced in adjacent layers to ensure safe and efficient CBM production.
查看更多>>摘要：In this research,a 3D bonded block model(BBM)is applied to numerically quantify the strength and permeability of fractured rock mass.The reliability of the BBM is initially verified through comparisons between conceptual models and theoretical and laboratory results.A series of rock mass models incorporating complex fracture networks is then constructed,and the strengths are quantified accordingly.The rock mass is weakened when low fracture stiffness and friction angle are assigned,and steep fractures are simulated.In both cases the low strength is attributed to the decreasing frictional resistance of the initial fractures.The rock mass is further weakened when more persistent fractures are simulated,in which the weakening effects of the fractures are amplified.The numerical models are compared with the widely used Hoek-Brown strength criterion.The strengths resulting from the two methods converge only when steep and less persistent fractures are simulated.Numerical simulations also suggest that in general,the permeability is positively related to the strength for rock masses that are impermeable in the pre-peak loading stage.In such cases additional flow paths are formed and attributed to failed rock bridges.The research works provide new options to quantify the strength and permeability of fractured rock mass,and offer opportunities to examine relations between these parameters.
查看更多>>摘要：A quantitative model is proposed to predict hydraulic fracture propagating across cemented natural fracture based on the numerical simulation and statistical regression.The cohesive zone method is employed to capture fracture initiation and growth,and the model combining rock deformation and fluid flow is established to simulate hydraulic fracture propagation with pre-existing natural fracture.The numerical model is solved by using finite element method,and verified against the analytical solution on the classical fracture problem.The investigation of influencing factors on hydraulic fracture propagation shows that the horizontal principal stress difference,approaching angle,cementing strength of natural fracture,injection rate and fluid viscosity code-termine whether hydraulic fracture propagates across natural fracture.After identification of these influencing factors,a series of numerical cases are conducted based on different combination of factor levels.Then the logistic regression method is employed to get the quantitative relationship between the crossing result and the factors,and the accuracy of regression equation is above 99%.The crossing curves are drawn to give the threshold of injection rate for varying other influencing factors.The potential applications include the usage of crossing criterion in the numerical modeling of fracture network propagation and the optimization of injection rate in the real field.
查看更多>>摘要：The efficiency of the hydraulic fracturing processes is measured through its success rate in opening fracture space,fracturing fluid injectivity,and recovery rates of flowback fluid.This paper applies the volumetric ratio(Rff/fw)between recovered hydraulic fracturing fluid(FF)and formation water(FW)-besides gas production(GP)and flowback efficiency(FE)-as a third criterion and novel classification tool to quantify the loss of fracturing fluids,the inflow of formation water,and to define the type of involved fractures during hydraulic fracturing.Eight scenarios were designed to assess the performance and success rate of hydraulic fracking operations.For model calibration,geochemical time trends of flowback fluids from two horizontal wells were compared with the known composition of injected FF and local FW to quantify mixing ratios(Rff/fw)between both fluid types in produced water.The use of Na and Cl concentrations as nonreactive elements resulted in the most precise solution for endmember calculations.For the cased-hole scenario(C-1),low values of most operational parameters(gas recovery,injected fracturing fluid,recovered flowback volume,and FE of 0.37)reflect tight reservoir conditions with limited conductive capacity of induced fractures in the target zone.The elevated R_(ff/fw)ratio(2.65)and dominant FF return during the first day of flowback suggest that injected fracturing fluids either remained close to the sealed borehole and returned immediately to surface during post-fracture production or were lost to the formation due to unconnected hydraulic fractures.In contrast,a complex fracture system at the open-hole completion(0-1)allowed the release of gas from micropores,reflected by relatively elevated ratios of 0.5 for FE and low Rff/fw ratios of 1.09.The interconnectivity between natural and induced fractures permitted the injection of larger volumes of FF with an elevated flowback of both fracturing fluid and formation water.A portion of 26% of the injected FF was recovered from well 0-1 during a flowback period of 41 days,while an identical percentage was reached at well C-l during 10 days.It is of practical importance for fracking operations that geochemical fingerprinting of flowback water can provide strategic decisions to optimize fracturing project performance beyond the capabilities of petrophysical data from well logging.In the present case,similar permeability and porosity characteristics for both targeted clastic intervals could not explain the contrasting performance of both frac jobs.Geochemical assessment can lead to avoiding water-pay zones to minimize the volume of required fracturing fluids for injection purposes,and to economize the recycling process for recoverable flowback fluids.An improved understanding of the functionality of the structural network of natural and induced fractures by the present classification is applicable to predict the success rate for upcoming frac jobs.
查看更多>>摘要：The Upper Permian siliceous shale reservoir,which was less studied before,is considered to be a successor target of marine Wufeng-Longmaxi shale gas in Sichuan Basin.To deeply explore pore characteristics,evolution process,formation mechanism and their influences on shale gas capacity,we performed a comprehensive multiscale characterization on siliceous shales with different maturities from Dalong and Wujiaping Formations using low-pressure N2 adsorption(N2GAX mercury injection pressure(MIP),field emission scanning electron microscopy(FE-SEM),and methane sorption capacity.Results indicate that shale pore development,especially OM pore development,and physical property are strictly controlled by thermal maturation levels.OM pores are seldom in low-mature shales but are well-developed in high-to over-mature shales.Pore structures in shales with different maturities are determined by different factors.The high TOC content is conducive to developing OM micropores for high-to over-mature shales.High content of brittle minerals is conducive to developing interparticle(interP)pores and dissolved mesopores at high-mature stage.In terms of the data and published articles,we established a general pore evolution model in siliceous shales to illustrate shale pore development process and formation mechanism.Similar to OM pore development,methane sorption capacity is controlled firstly by thermal maturation and secondly by TOC content.It's pointed out that over-mature shales have smaller-sized OM pores compared with high-mature shales,and therefore they have higher specific surface areas and methane sorption capacities normalized to TOC.This indicates that siliceous shales with extremely high maturity still have good shale gas potential,which further expand shale gas exploration in over-mature shale gas reservoir,as well as provide exploration suggestion for the siliceous shale gas reservoirs in south China.
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