Test Interpretation Methods Research Articles

Well test inversion method for fractured horizontal wells based on deep neural network

Well-test interpretation is an important means to obtain reservoir parameters. However, the traditional well test interpretation method of fractured horizontal wells is limited due to the computational efficiency of the well test model. This paper proposes an automatic interpretation method for well-test curves based on neural networks. Considering the basic parameters of the reservoir, the dimensional pressure, pressure derivative, and time data are used as samples to train the network. The well test data are processed and input into the trained optimal network to automatically identify well test parameters such as reservoir permeability. Mini-batch gradient descent with a batch size of 32 was used to train the network. The results showed that the network training achieved a lower loss function value and the best performance. Adaptive learning rate decay and increased samples were adopted to improve the parameter inversion accuracy. In addition, the two-dimensional convolutional neural network was compared with the fully connected neural network. We validate the results that the two-dimensional convolutional neural network had better parameter inversion accuracy and noise resistance than the fully connected neural network. Finally, two cases were used to further verify the parameter inversion model.

Small-strain stiffness of selected anthropogenic aggregates from bender element tests

Abstract This article presents a study on the stiffness of mixtures of anthropogenic materials derived from construction or demolition waste, specifically fine recycled concrete aggregates (fRCAs) with different fine fraction (FF) contents. The study investigated small-strain shear moduli via various signal interpretation methods, examining, above all, the time domain approaches and considering the influence of FF content. However, the inconclusive results from the bender element (BE) tests highlight the complexity of factors affecting shear wave velocity, which requires further research to refine the methodology and assess long-term performance in geotechnical applications. Selecting the correct test frequency and interpretation method is crucial to obtain accurate results. The BE test method should consider all relevant factors. At low input frequencies (≤5 kHz), the near-field effect affected the received signal for fRCA mixtures. At higher frequencies (around 14 kHz), the noise levels increased, thereby interfering with the S-wave travel time determination. Intermediate input frequencies (10.0 and 12.5 kHz) provided the representative shear modulus (G) values. The small-strain shear modulus (G max) of the fRCA compounds from the resonant column and BE tests was found to be in good agreement, despite differences in the test procedures themselves.

Study on Flow Line Characteristics and Well Test Interpretation Methods of Multi Branch Fractured Wells in Dual Porous Media

Fractured reservoirs have developed fractures, strong heterogeneity, and complex seepage patterns. The analysis of core and imaging logging data in Bohai BZ Oilfield shows that there are a large number of fractures developed in the formation, with some wells having up to 6-8 fractures per meter. To study the impact of fractures on seepage, a multi fracture system seepage field simulation method was established, and the characteristic curves of flow lines under different fracture shapes were drawn. The fracture flow line morphology shows that there is a significant difference in the distribution of flow lines between the presence and absence of fractures, and the location of the fractures The size and shape of the reservoir have varying degrees of influence on the distribution of the streamline. The streamline around the well is distributed radially around it. When the fluid encounters an area with developed fractures, it first flows into the fractures and then flows from the fractures towards the wellbore. At the same time, based on the characteristics of fracture development in BZ oilfield and the theory of vertical fracture well testing, a dual medium multi fracture system oil well testing model was established. The model was numerically solved using Laplace transform, and a dual logarithmic curve chart for dual pore medium multi branch fracture well testing was obtained. The effects of fracture branching number, fracture length, conductivity coefficient ratio, and fracture conductivity on the shape of the testing curve were analyzed. The established well testing interpretation model can analyze oilfield stratigraphic information, reservoir fracture development, and boundary conditions. The research results have important guiding significance for evaluating the dynamic performance of oil wells in a dual pore medium multi fracture system and designing oilfield development plans.

Multi-deconvolution in non-stationary conditions applied to experimental thermal response test analysis to obtain short-term transfer functions

Thermal response test interpretation methods usually rely on the assumptions of constant operating conditions in time. However, through desired or undesired processes, these conditions often vary in time. Since interpretation is usually done with stationary methods, no current algorithm allows to account for non-stationarity in thermal response test, as encountered with varying flow rate. The goal of this article is to apply a multi-deconvolution algorithm to retrieve a set of short-term transfer functions during a thermal response test with changing operating conditions. The deconvolution algorithm uses an optimization-based technique as the inverse model, while considering non-stationarity in the forward model through a recent non-stationary convolution algorithm. By optimizing a set of nodes on each estimated short-term transfer function, precise reconstruction of the experimental temperatures is possible. Results show that temperature reconstruction is as precise as an error of 0.06 °C on numerical cases and 0.07 °C on field cases. The usable transfer function duration and an analysis of the objective function’s optimum are also demonstrated. With the proposed algorithm, only the dataset of a thermal response test is needed to obtain short-term transfer functions when operating conditions are changing.

Automatic Well Test Interpretation Method for Circular Reservoirs With Changing Wellbore Storage Using One-Dimensional Convolutional Neural Network

Abstract In order to develop reservoirs rationally, accurate reservoir parameters are usually obtained through well test analysis. However, a good deal of well test data with changing wellbore storage characteristics bring difficulties to the current well test interpretation, so it is important to find a valid interpretation method for changing well storage reserves data. This paper proposed an automatic well test interpretation method based on one-dimensional convolutional neural network (1D CNN) for circular reservoir with changing wellbore storage. Compared with two-dimensional convolutional neural network (2D CNN), 1D CNN significantly reduces the computational complexity and time cost. The CNN takes pressure change and pressure derivative data of the log–log plot as input and reservoir parameters as output of network. This method applies two 1D CNNs respectively to fit two types of reservoir parameters, one type includes CDe2s, CαD, and CϕD and the other type is boundary distance R. In addition, the training samples of the two networks are different according to different parameters. The two-network approach reduces the difficulty of extracting curve characteristics and improves interpretation ability. The effectiveness of this method is proved by the field data in Daqing oilfield. The method greatly improves the working efficiency of well test interpreters and can be widely used.

Well Test Analysis of Inclined Wells in the Low-Permeability Composite Gas Reservoir Considering the Non-Darcy Flow

The application of traditional well test interpretation methods cannot comprehensively consider characteristics of stress sensitivity and non-Darcy flow for low-permeability composite gas reservoirs, which makes it difficult to obtain real reservoir parameters. Based on the micro-mechanism analysis of stress sensitivity and non-Darcy flow in low-permeability gas reservoirs, the flow motion equation was improved. Thus, a mathematical model was established which belongs to the inclined well in the composite gas reservoir with a conventional internal zone and low-permeability external zone. Applying the finite element method to solve the flow model through Matlab programming, the equivalent pressure point was selected to research the pressure distribution of the inclined well. On this basis, the bottom hole pressure dynamic curve was drawn, the flow process was divided into seven stages, and the parameter sensitivity analysis was carried out. Finally, the advanced nature of the new model applied to the interpretation of the well test model is compared by conventional methods. The non-Darcy flow can cause the gradual upward warping of the bottom hole pressure dynamic curve in the later stage, and non-linear enhancement leads to an increase in the upturn through the simulation test. When the inclination angle is greater than 60°, early vertical radial flow and mid-term linear flow gradually appear. A decrease leads to a shorter duration of the pseudo radial flow in the internal zone and the radius of the internal zone. The conduction coefficients ratio of internal and external zones affects the pseudo pressure derivative curve slope in transition phase of pseudo radial flow in the internal and external zones. A comprehensive consideration of the low-permeability composite gas reservoir flow characteristics can improve the fitting degree of the pressure curves. Not only that, but it can also solve the strong diversification of reservoir parameters. Results have a guiding significance for low-permeability composite gas reservoir development and pressure dynamic evaluation in inclined wells.

A New Method for Evaluating Gas Well Boundary Characteristics

In evaluating the reservoir physical properties and boundary characteristics of gas wells, the well test interpretation method is mainly employed currently to obtain K, KH, S and boundary characteristics of the reservoir. This method requires a test system for gas wells and a pressure gauge to record the data of flowing bottom hole pressure (FBHP) at the middle depth of the gas reservoir, with long testing time and high cost. Therefore, productivity testing and test pressure recovery data are only performed for some gas wells, and we cannot get reservoir physical property parameters by well test interpretation. It is considered that this method can better meet the needs of practical work, and has high popularization and application value.

Pressure build-up test application in reservoir boundary structure determination

The design of highly efficient field development systems, their control and management require reliable information about the reservoir properties and structure of productive deposits. Among the most common and informative methods of obtaining information is well testing with the help of pressure build-up curves (PBU). The latter make it possible to study the structure and parameters of the farfield at a considerable distance from the well (tens and hundreds of meters), which allows to make informed decisions in the process of field development. Therefore, the use of PBU test interpretation methods in order to obtain maximum information is extremely relevant for hydrocarbon recovery processes. Well testing under nonequilibrium filtration conditions is one of the powerful tools for assessing the reservoir parameters, the structure of the farfield and assessing the well potential. The use of modern software tools for well test results interpretation allows to obtain much more information from the classical results, to clarify the structure of the field and the parameters of productive reservoirs. The aim of this work is to generalize the world experience of the farfield influence on the character of PBU and its derivative during well testing under nonequilibrium filtration conditions. The study has been conducted using the KAPPA Saphir software package, licensed for use by IFNTUOG for educational purposes. The above methods of PBU interpretation can be used to determine the farfield parameters and structure. On the basis of those one can make effective decisions on field development managing and during 3D geological models creation.

Static Load Test interpretation methods of pile base capacity approximation for design of wind turbine deep foundation

The bearing capacity of a pile is mainly assessed from a static load test, which is widely considered as the most reliable method of pile testing. The test provides important information about pile behaviour in a subsoil, but often for more precise data it should be performed on additionally instrumented piles. With specially prepared pipe piles static load tests can be performed with a load applied only to a pile base. The results of this test allow on an evaluation only of pile base bearing capacity, although it often requires an application of some of the methods dedicated to analyse the static load test results. In paper some of the methods for evaluation bearing capacity of a pile from a static load test are introduced. Evaluation of pile base bearing capacity by different methods was compared using results of static load tests with a load applied only to the pile base. A discussion of results and future recommendations were also presented.

Automatic well test interpretation based on convolutional neural network for a radial composite reservoir

Abstract An automatic well test interpretation method for radial composite reservoirs based on convolutional neural network (CNN) is proposed, and its effectiveness and accuracy are verified by actual field data. In this paper, based on the data transformed by logarithm function and the loss function of mean square error (MSE), the optimal CNN is obtained by reducing the loss function to optimize the network with “dropout” method to avoid over fitting. The trained optimal network can be directly used to interpret the buildup or drawdown pressure data of the well in the radial composite reservoir, that is, the log-log plot of the given measured pressure variation and its derivative data are input into the network, the outputs are corresponding reservoir parameters (mobility ratio, storativity ratio, dimensionless composite radius, and dimensionless group characterizing well storage and skin effects), which realizes the automatic initial fitting of well test interpretation parameters. The method is verified with field measured data of Daqing Oilfield. The research shows that the method has high interpretation accuracy, and it is superior to the analytical method and the least square method.

Transient transfer shape factor for fractured tight reservoirs: Effect of the dynamic threshold pressure gradient in unsteady flow

AbstractIn fractured tight reservoirs, the seepage capacity of the matrix is poor, and fluid migration mainly depends on matrix/fracture transfer. An accurate understanding of the matrix/fracture flow is the basis of well tests and numerical simulations for tight reservoirs. In this paper, the unsteady flow equation for tight reservoirs is deduced based on the boundary layer theory, which can reflect the effect of the dynamic threshold pressure gradient, and the theoretical flow equation is verified by seepage experiments. Based on the study of the flow equation, the approximate semi‐analytical solution of the matrix/fracture unsteady transfer shape factor and the transfer function for tight reservoirs are established considering the early stage of matrix/fracture transfer (pressure does not propagate to the matrix center) and the late stage of matrix/fracture transfer (pseudo‐steady state). The results show that the shape factor of the tight reservoir is mainly affected by three factors (minimum threshold pressure gradient, static boundary layer thickness, and sensitivity coefficient of the fluid boundary layer), and the theoretical curves show that the intermediate transfer enters the pseudo‐steady state when the dimensionless time reaches approximately 0.14. The higher the minimum threshold pressure gradient is, the larger the transfer shape factor. The larger the static boundary layer thickness is, the larger the transfer shape factor; additionally, the larger the sensitivity coefficient of the fluid boundary layer is, the faster the change rate of the shape factor. Finally, the transfer shape factor is applied to a well test interpretation. Examples prove that the fitting accuracy of the new curve type is improved by 34.2% compared with the curve type for the conventional well test interpretation method.

The application of cone penetration test direct method in Jakarta

There are several methods to estimate the bearing capacity of pile foundation using cone penetration test (CPT). Hence, it is interesting to evaluate which method that suitable for a certain location. In this study, 55 piles histories in Jakarta, which consisted of bored piles and driven piles, are used in order to determine the bearing capacity using the following methods: Schmertmann, de Ruiter and Beringen, LCPC, Aoki and De Alencar, Penpile, Price and Wardle, Philipponnat, and Wesley. The pile capacities will be compared to the measured pile capacities from the bearing capacity from loading test: static pile load test which interpreted by Chin method and Decourt method, and the results from PDA testing. The statistical analyses used in this paper are the best fit line, mean and standard deviation, and log distribution with 20% of accuracy. Result shows that LCPC method is the most suitable direct method used in studied location as it has the best agreement among the methods mentioned; the cone penetration test direct method is more suitable used for driven pile; and the safety factor for Chin and Decourt loading test interpretation methods are 2.7 and 2.57 respectively according to Wesley direct method.

Application of Well Test Interpretation in Oilfield Based on PDA Method in Tight Gas Reservoir

The reservoir characteristics of tight sandstone gas reservoirs are characterized by low porosity and low permeability, which brings difficulties to the conventional pressure recovery well test in oil fields. The lower porosity and permeability greatly extend the test time. Radial flow was not detected when the oil well was shut down for more than one month. The well test curve showed strong multi-solution characteristics and could not obtain accurate formation parameters. In this paper, based on the characteristics of tight gas reservoirs, the well test interpretation method (PDA method) is applied to the application of production data. A set of explanations for using the production data to explain tight gas wells and carrying out capacity evaluation and prediction are proposed. The interpretation of the production data of 1 is compared with the interpretation results of the pressure recovery test of the well. The two methods have good consistency, and the multiple interpretation methods can better reduce the multi-solution of the well test interpretation, and verify the PDA. The feasibility of the method applied on tight gas wells, and finally the correctness of the method was verified by the capacity prediction method.

Comprehensive Well Test Interpretation Method, Process, and Multiple Solutions Analysis for Complicated Carbonate Reservoirs

Abstract The main characteristic of the complicated carbonate reservoirs is notably strong heterogeneous, leading to a high uncertainty in formation parameter evaluation. The most reliable method for obtaining the dynamic parameters is well test interpretation. However, the well test curve shows similar characteristics for multi-layers reservoirs, dual-medium reservoirs, and carbonate reservoirs with lithology mixed sedimentation lithology. Sometimes the well test fitting result under the mentioned three kinds of models is satisfied, but the interpretation result is quite different. In order to reduce the parameter evaluation multiplicity, the synthetic identification and evaluation method for obtaining the physical parameters of the complicated carbonate reservoir was proposed, based on completion types, core analysis, lithology analysis, and well test results. The evaluation method distinguishes the different carbonate reservoir characteristics from similar well test responses by summarizing and classifying the completion method, reservoir fracture characteristics, and production logging test (PLT) results. The reliability of the proposed method is verified by an application of actual carbonate reservoir parameters evaluation. The proposed method can distinguish among multi-layers reservoirs, dual-medium, and complicated reservoirs with mixed sedimentation lithology whose main characteristic is that concavity existing in the pressure derivative curve. If the well test match results were satisfied enough which lead to the proposed method and process was ignored, the interpretation results and production performance prediction may deviate largely from the actual situation.

Harmonic Pulse Testing for Well Monitoring: Application to a Fractured Geothermal Reservoir

AbstractHarmonic Pulse Testing (HPT) has been developed as a type of well testing applicable during ongoing field operations because a pulsed signal is superimposed on background pressure trend. Its purpose is to determine well and formation parameters such as wellbore storage, skin, permeability, and boundaries within the investigated volume. Compared to conventional well testing, HPT requires more time to investigate the same reservoir volume. The advantage is that it does not require the interruption of well and reservoir injection/production before and/or during the test because it allows the extraction of an interpretable periodic signal from measured pressure potentially affected by interference. This makes it an ideal monitoring tool. Interpretation is streamlined through diagnostic plots mimicking conventional well test interpretation methods. To this end, analytical solutions in the frequency domain are available. The methodology was applied to monitor stimulation operations performed at an Enhanced Geothermal System site in Pohang, Korea. The activities were divided into two steps: first, a preliminary sequence of tests, injection/fall‐off, and two HPTs, characterized by low injection rates and dedicated to estimate permeability prior to stimulation operations, and then stimulation sequence characterized by a higher injection rate. During the stimulation operations other HPT were performed to monitor formation properties behavior. The interpretation of HPT data through the derivative approach implemented in the frequency domain provided reliable results in agreement with the injection test. Moreover, it provided an estimation of hydraulic properties without cessation of stimulation operations, thus confirming the effectiveness of HPT application for monitoring purposes.

Technical Application of Petroleum Logging Instruments in Marine Logging

Abstract To solve the problem of offshore oilfield development, based on the newly introduced pulsed neutron oxygen activation logging instrument, the application research of test design and interpretation method was carried out and applied to actual production. The structure, technical indicators and logging principles of pulsed neutron oxygen activation logging tools were introduced. The test design under different well conditions was studied, including general positive and negative injection, oil sleeve injection, single oil pipe configuration and multitubing configuration. A large amount of field test data was collected and analysed technically. A set of effective interpretation models was proposed. The corresponding interpretation software was developed. A set of test design methods and operating specifications for different well conditions were developed. Based on the conventional interpretation method, the peak selection, the double-tuber peak identification and the carbon dioxide flooding interpretation method were added. The results show that the test design and interpretation methods were applied well through a large number of field tests and production applications. Therefore, pulsed neutron oxygen activated injection profile logging technology is successfully applied in offshore oil fields.

Interpretation of the DMT in Silts

This paper describes a proposed testing procedure and interpretation method for the characterization of silts using the flat dilatometer test (DMT). This method aims to compensate for errors that are introduced by the partial-drainage conditions that take place around the DMT blade. In transient soils, the after-installation DMT readings change continuously with time because excess pore pressure dissipation. By monitoring the variation in A-readings, it is possible to extrapolate the results back to the origin to estimate an equivalent undrained A0 value. In addition, in seeking to obtain a closed-form solution for the membrane expansion problem in the elastic regime, a simple correction is introduced in the analysis where the B-reading is expressed in terms of average mean stresses that take place prior to expansion. Preliminary results in clay demonstrate that the method is effective and can be introduced in practice with minimal costs by considering simple adaptations to procedures originally developed for clay.

Evaluation of Becker penetration test interpretation methods for liquefaction assessment in gravelly soils

The Becker penetration test (BPT) is the only tool available for characterizing gravelly soils with a probe diameter that is meaningfully larger than that of the standard penetration test (SPT) and the cone penetration test (CPT). Measurements on the BPT system during operation provide information on how penetration is controlled by the driving energy and frictional resistance along the shaft. This has led to development of the instrumented Becker penetration test (iBPT), which uses measurements of force and acceleration obtained directly behind the drill string tip to compute the residual energy and displacement induced by each hammer blow. These measurements are used to produce a continuous profile of normalized blow counts that are repeatable, unaffected by varying driving energy or accumulated shaft resistance, and can be used to directly estimate equivalent SPT N60 blow count values as per DeJong et al. and Ghafghazi et al. in their 2017 studies. The measurements obtained also enabled evaluation of previously developed methods by Harder and Seed in 1986 and Sy and Campanella in 1994. This evaluation revealed that the hammer energy normalization approaches employed by Sy and Campanella and especially Harder and Seed are not robust across the broad range of conditions observed. The predicted equivalent SPT N60 values by Harder and Seed and Sy and Campanella methods are influenced by the shaft resistance magnitude as both methods are based on above-ground field measurements. Estimated N60 values produced by the two methods can be inconsistent with each other, with N60 values produced by the iBPT, and with measured N60 values obtained directly from SPT (where values are obtained in the absence of gravel).

Research on Well Testing Interpretation Method of Polymer Flooding Considering Variety of Polymer Concentration in Reservoirs

Combining the oretical analysis and actual production data statistics, the paper found that concentration of polymer solution at a point in the stratum had exponential relation with the distance away from injectors. Based on viscosity model considering shear degradation and polymer concentration, a non-Newtonian power-law fluid well test interpretation model is built. Then well test interpretation chart of polymer flooding is proposed by numerically resolving the new model. Example analysis shows that the polymer flooding well test interpretation method and chartprovide a theoretical and technical support for explaining reasonably formation parameters under conditions of polymer flooding and quantitatively evaluating the effects of polymer flooding.

Pressure-transient analysis of CO2 flooding based on a compositional method

To find a reliable and inexpensive method to estimate miscibility and other reservoir parameters, as well as to monitor the CO2 flood progress, this paper proposed a transient flow model based on a compositional model that considers the wellbore storage effect, skin factor and multiple-contact processes. The model solution is obtained with the finite volume method and by performing pressure transient analysis. The results demonstrate that the pressure derivative curve of the swept area radial flow rises first and later declines slightly; the pressure derivative curve of the unswept area radial flow rises first and later becomes flat. The CO2 flood front can be recognized when the derivative curve begins to rise after it declines slightly in the swept area radial flow regime. A numerical well test interpretation method can be established based on the model used in this paper to estimate the permeability, miscibility, and formation damage and to monitor the CO2 flood progress.