• Korean Journal of Mineralogy and Petrology
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• v.34 no.4
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• pp.209-218
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• 2021

Studies of pore structure in shale gas reservoirs are essential to increase recovery rates, which is in the spotlight concerning unconventional resources. In this study, the distribution of pores in shale gas reservoir sample were observed using Scanning Electron Microscope Particle Analysis (SELPA), which is appropriate to analyze the distribution of particle or shape for sample in large area. A sample from the A-068 borehole drilled in the Liard Basin was analyzed; calcite is the main mineral. The pore size ranges from tens of nanometers to hundreds of micrometers and the contribution of each pore size to overall sample porosity was determined using SELPA. The distribution of pores was determined by observing the surface in the same area at magnifications of ×1000, ×3000 and ×5000. Pores less than 100 nm were observed at high magnifications and confirm that small-scale pore distribution can be analyzed and identified rapidly using SELPA. The method introduced in this study will be useful to understand pore structures in unconventional reservoirs.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.169-179
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• 2013

Well testing in unconventional reservoirs, such as tight or shale gas formations, presents considerable challenges. It is difficult to estimate the reservoir properties in ultra-low permeability formation because of poor inflow prior to stimulation and excessive test duration. Moreover, radial flow may not develop in hydraulically fractured horizontal wells. For these reasons, the cost of test is high and the accuracy is relatively low. Accordingly, industry is turning to an alternate testing method, diagnostic fracture injection test (DFIT), which is conducted prior to the main hydraulic fracture treatments. Nowadays, DFIT are regarded as the most practical way to obtain good estimates of reservoir properties in unconventional reservoirs. Various methods may be used for interpreting DFIT data. This paper gives an explanation of those methods in detail and examines three actual field data. These show how various analysis methods can be applied to consistently interpret fracture closure pressure and time, as well as before and after closure flow regimes and reservoir properties from field data.

• Geophysics and Geophysical Exploration
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• v.15 no.1
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• pp.39-46
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• 2012

Recently, stratigraphic reservoirs are getting more attention than structural reservoirs which have mostly developed. However, recognizing stratigraphic thin gas reservoirs in a stacked section is usually difficult because of tuning effects. Moreover, if the reflections from the brine-saturated region of a thin layer have the same polarity with those from the gas-saturated region, we could not easily identify the gas reservoir with conventional data processing technique. In this study, we introduced a way to delineate the gas-saturated region in a thin layer reservoir using a spectral decomposition method. First of all, amplitude spectrum with the variation of the frequency and the incident angle was investigated for the medium which represents property of Class 3, Class 1 or Class 4 AVO response. The results show that the maximum difference in the amplitude spectra between brine and gas-saturated thin layers occurs around the peak frequency independent of the incident angle and the type of AVO responses. In addition, the amplitude spectra of the gas-saturated zone are greater than those of brine-saturated one in Class 3 and Class 4 at the peak frequency while those of phenomenon occur oppositely in Class 1. Based on the results, we applied spectral decomposition method to the stacked section in order to distinguish the gas-saturated zone from the brine-saturated zone in a thin layer reservoir. To verify our new method, we constructed a thin-layer velocity model which contains both gas and brine-saturated zones which have the same reflection polarities. As a result, in the spectral decomposed sections near the peak frequency obtained by Wigner-Ville Distribution (WVD), we could identify the difference between reflections from gas- and brinesaturated region in the thin layer reservoir, which was hardly distinguishable in the stacked section.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.419-426
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• 2020

Understanding the pore structure including pore shape and connectivity in unconventional reservoirs is essential to increase the recovery rate of unconventional energy resources such as shale gas and oil. In this study, we found analysis condition to probe the nanoscale pore structure in shale reservoirs using Focused Ion Beam (FIB) and Ion Milling System (IMS). A-068 core samples from Liard Basin are used to probe the pore structure in shale reservoirs. The pore structure is analyzed with different pretreatment methods and analysis condition because each sample has different characteristics. The results show that surface milling by FIB is effective to obtain pore images of several micrometers local area while milling a large-area by IMS is efficient to observe various pore structure in a short time. Especially, it was confirmed that the pore structure of rocks with high content of carbonate minerals and high strength can be observed with milling by IMS. In this study, the analysis condition and process for observing the pore structure in the shale reservoirs is established. Further studies are needed to perform for probing the effect of pore size and shape on the enhancement of shale gas recovery.

• Journal of the Korean Institute of Gas
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• v.17 no.2
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• pp.9-20
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• 2013

Depleted gas reservoir has been already explored and its geologic data, along with its reservoir properties, are already known through seismic exploration and drilling. Therefore it would be less difficult to develope a gas storage from depleted gas reservoir. Cushion gas which remains in the reservoir to maintain pressure affects withdrawal rate of working gas in underground gas storage. In this study, we attempted to investigate the relationship between cushion gas and withdrawal rate using a commercial simulator. From the analyses of the results, it is found that the minimum limit for a cycle of 5-month injection and 5-month withdrawal is 10 wells with 50% cushion gas, and 12 wells with 60% cushion gas for a cycle of 7-month injection and 3-month withdrawal.

• Geophysics and Geophysical Exploration
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• v.7 no.2
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• pp.109-116
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• 2004

Petroleum reservoir characterization is a process for quantitatively describing various reservoir properties in spatial variability using all the available field data. Porosity and permeability are the two fundamental reservoir properties which relate to the amount of fluid contained in a reservoir and its ability to flow. These properties have a significant impact on petroleum fields operations and reservoir management. In un-cored intervals and well of heterogeneous formation, porosity and permeability estimation from conventional well logs has a difficult and complex problem to solve by conventional statistical methods. This paper suggests an intelligent technique using fuzzy logic and neural network to determine reservoir properties from well logs. Fuzzy curve analysis based on fuzzy logics is used for selecting the best related well logs with core porosity and permeability data. Neural network is used as a nonlinear regression method to develop transformation between the selected well logs and core analysis data. The intelligent technique is demonstrated with an application to the well data in offshore Korea. The results show that this technique can make more accurate and reliable properties estimation compared with previously used methods. The intelligent technique can be utilized a powerful tool for reservoir characterization from well logs in oil and natural gas development projects.

• Journal of the Korean Institute of Gas
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• v.2 no.4
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• pp.73-78
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• 1998

This paper considers the applicability of a pseudosteady-state approach to the long-time behavior of real gas flow in a closed reservoir. The method involves a combination of a linearized gas diffusivity equation using a normalized pseudotime and a material balance equation. For the simulation of field-scale problems with multiple wells of differing production rates over extended production periods, the pseudosteady-state equation was solved successively for each flow period. Results from this study show that the approach provides a fast and accurate method for modeling the long-time behavior of gas reservoirs under depletion conditions.

• Journal of the Korean Institute of Gas
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• v.18 no.2
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• pp.1-9
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• 2014

To develop a coalbed methane(CBM) reservoir, it is important to apply production methods such as drilling, completion, and stimulation which coincide with coal properties. However, the reliability of the selected resulted in most of CBM field is not enough to accept because the selection of production method has been done by empirical decision. As the result, the empirical decision show inaccurate results and need to prove using simulation whether it was true exactly. In this study, the intelligent system has been developed to assist the selection of CBM production method using artificial neural network(ANN). Before the development of the system, technical screening guideline was analyzed by literature survey and the system to select drilling and completion method, and hydraulic fracture fluid was developed by utilizing the guideline. The result as a validation of the developed system showed a high accuracy. In conclusion, it has been confirmed that the developed system can be utilized as a effective tool to select production method in CBM reservoir.

• Economic and Environmental Geology
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• v.46 no.4
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• pp.279-289
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• 2013

The most critical factor in developing coalbed methane(CBM) reservoir is absolute permeability. Both productivity and economics of the CBM depend on the absolute permeability. The methods to estimate it are core analysis and well test. However, absolute permeability determined by core analysis cannot be a good representative of CBM reservoir. Therefore, it is generally estimated by well test. In this study, well test methods applicable of CBM reservoir were classified with their characteristics. Merits and demerits of each well tests were also analyzed. Based on those parameters, design considerations and procedures of well test were derived. After each well tests was performed, the procedure of well test interpretations to estimate reservoir properties such as absolute permeability and skin factor was presented.

• Journal of the Korean Institute of Gas
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• v.24 no.4
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• pp.62-72
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• 2020

This study presents a methodology of history matching to evaluate the productivity of shale gas reservoir with high reliability and predict future production rate in the Horn-River basin, Canada. Sensitivity analysis was performed to analyze the effect of physical properties of shale gas reservoir on productivity. Based on the results, reservoir properties were classified into 4 cases and history matching were performed considering the classified 4 cases as objective function. The blind test was conducted using additional field production data for 3 years after the history matching period. The error of gas production rate in Case 1(all reservoir parameters), Case 2(influenced parameters for productivity), Case 3(controllable parameters), and Case 4(uncontrollable parameters) were 7.67%, 7.13%, 17.54%, and 10.04%, respectively. This means that it seems to be effective to consider all reservoir parameters in early period for 4 years but Case 2 which considered influenced parameters for productivity shows the highest reliability in predicting future production. The estimated ultimate recovery (EUR) of production well predicted using the Case 2 model was estimated to be 17.24 Bcf by December 2030 and the recovery factor compared to original gas in place (OGIP) was 32.2%.