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Journal of Petroleum Science & Engineering
Elsevier Science B.V.
Journal of Petroleum Science & Engineering

Elsevier Science B.V.

0920-4105

Journal of Petroleum Science & Engineering/Journal Journal of Petroleum Science & Engineering
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    The effect of grain size, porosity and mineralogy on the compressive strength of tight sandstones;; A case study from the eastern Ordos Basin, China

    Yu QiYiwen JuKun Yu
    16页
    查看更多>>摘要：To better understand how textural properties and mineralogy control compressive strength, this work performed the grain size analysis, porosity measurement. X-ray diffraction, microscopic observation, and mechanical tests on deep-buried reservoir sandstones in the eastern Ordos Basin, China. The results suggest that uniaxial compressive strength (UCS) declines with increasing grain size. Meanwhile, the UCS is reduced by grains >250 μm and enhanced by grains <250 μm. Sandstones with higher fractal dimensions are poorer-sorted and have platykurtic distribution, while those with low fractal dimensions are better-sorted and show leptokurtic distribution. The former tends to have larger UCS than the latter because they have more smaller grains to distribute the load over larger grains. Both the UCS and confined compressive strength (CCS) exponentially decline with porosity. Internal friction angle and influence coefficient decrease with increasing porosity, suggesting that the compressive strength of low-porosity sandstones is more sensitive to the variation of confining pressure. With regard to mineralogy, there is a weak negative relationship between UCS and quartz content. It is because textural properties control the UCS, dominating over the effects of mineralogy, or alternatively stress concentrations and the initiation of cracks preferentially occur in brittle quartz grains rather than softer materials.
      原文链接:
    • NSTL

    Evaluation of different machine learning frameworks to predict CNL-FDC-PEF logs via hyperparameters optimization and feature selection

    Auref RostamianEhsan HeidaryanMehdi Ostadhassan
    22页
    查看更多>>摘要：Although being expensive and time-consuming, petroleum industry still is highly reliant on well logging for data acquisition. However, with advancements in data science and AI, methods are being sought to reduce such dependency. In this study, several important well logs, CNL, FDC and PEF from ten wells are predicted based on ML models such as multilinear regression, DNN, DT, RT, GBoost, k-NN, and XGBoost. Before applying these models, depth matching, bad hole correction, de-spiking, and preprocessing of the data, including normalization, are carried out. Three statistical metrics, R2, RMSE, and PAP, are applied to evaluate the models' performance. Results showed that RF, k-NN, and XGBoost are superior to others. While hyperparameters of the best models are optimized by GA, results from optimization demonstrate that each models' performance in predicting different logs can be improved by at least 1.5%. Furthermore, these models are evaluated for feature selection, done by GA, presenting that preserving all data in proposed models will improve the performance to the highest degree while reducing the number of features will deteriorate their performance. Comparison of performance measures for different combinations exhibited that the prediction of CNL-FDC-PEF logs with fewer inputs could be possible with relatively satisfactory outcomes. This study was innovative in incorporating all possible steps that can constitute a comprehensive ML model to improve well log data prediction. Moreover, it confirms that such methods will benefit us by reducing operational costs, time, and risks of tool failure in the wellbore by running a fewer number of well logs when data acquisition can be replaced by a comprehensive ML predictive model.
      原文链接:
    • NSTL

    Gas content evolutionin western Guizhou and differential occurrencein China of Permian shale with type III kerogen

    Xiaoguang YangShaobin Guo
    13页
    查看更多>>摘要：Permian organicmatter(OM) in China mainly comes from higher plants rich in type III kerogen. Exploring gas content evolution and occurrence mechanisms is of great significance for shale gas exploration. Shales of western Guizhou in China were collected from wells and subjected to experiments under formation conditions (e.g. thermal simulation, Rock-Eval pyrolysis, X-ray diffraction and CH4 isotherm adsorption). A thermogenic gas generation model was established based on the logistic model, a hydrocarbon expulsion model was established based on the hydrocarbon potential method, and an adsorbed gas volume model was established based on temperature, pressure and total organic carbon(TOC). Various gas content of shale with type III kerogen were calculated in a special geological history. The differences of shales between the western Guizhou and the northeastern Ordos Basin in China were compared in terms of gas generation, expulsion and adsorption capacity. The results showed that the gas generation capacity of the western Guizhou samples was stronger because of the higher TOC and hydrogen index (HI). Limited differences in hydrocarbon expulsion efficiency were observed between the two areas. The source area of the samples had no significant effect on the adsorption capacity. Due to its high TOC, low geothermal gradient, high pressure gradient and suitable burial depth (500~(-1)500 m), the shale in western Guizhou has a stronger adsorption capacity. Obvious differences in the free gas volume and proportion in different areas were observed and should be analyzed separately in combination with the TOC, HI, geothermal gradient, pressure gradient and depth.
      原文链接:
    • NSTL

    Impact of capillary pressure and flowback design on the clean up and productivity of hydraulically fractured tight gas wells

    Martin VerdugoFlorian Doster
    14页
    查看更多>>摘要：This work analyses the impact of capillary pressure and flowback operational variables on hydraulically fractured tight gas wells with the objective of understanding the clean-up process at reservoir level and its impact on future well performance. Through numerical reservoir simulation, different scenarios were investigated, varying capillary pressure, flowback duration, shut-in duration and drawdown. These scenarios are interpreted with rate transient analysis. The results of this work show the ambivalent effect of capillary pressure in terms of facilitating imbibition but also holding back water close to the fracture. The novelty of this work consists in the findings that for lower capillary pressures, short shut-in periods lead to a better well productivity while for higher capillary pressure extended shut-in periods are better for well productivity. It was also found that drawdown can be used to minimize fracture face relative permeability damage and as shut-in period extends, flowback should be performed at smaller drawdowns.
      原文链接:
    • NSTL

    Adsorption of gases on heterogeneous shale surfaces: A review

    Kawthar Adewumi BabatundeBerihun Mamo Ne gashShiferaw Regassa Jufar
    14页
    查看更多>>摘要：Many studies tied to adsorption on heterogeneous surfaces have been reported in the literature. However, finding an adsorption model that accurately describes the sorption mechanism in gas shales remains a challenge. This is due to the complex surface heterogeneity and the presence of multiple components in the formation. Modelling and simulation at reservoir conditions for adsorption studies are also computationally expensive. An optimized adsorption model is therefore essential because it can lead to an accurate estimation of the adsorbed gas amount and ultimately improve the production process. This work presents a review of the adsorption models that have been used in characterizing shale formation. Moreover, the mechanisms and factors that control adsorption in shale formation and their interaction are also analyzed. As observed from the current review, Langmuir is the most used adsorption model. However, like other existing models, it does not adequately represent the sorption phenomenon in shale formation where surface heterogeneity and the presence of multi-component are eminent. There has thus been works to improve and enhance it for use in shale formation. On the other hand, the advancement of molecular simulation presents an opportunity for better representation of the sorption mechanism.
      原文链接:
    • NSTL

    Performance evaluation of analytical methods in linear flow data for hydraulically-fractured gas wells

    Atheer DheyauldeenHuda AlkhafajiDheiaa Alfarge
    10页
    查看更多>>摘要：Hydraulically fractured wells drilled in unconventional gas reservoirs are often produced with significantly high fixed drawdown to increase production. However, such unconventional gas wells exhibit extended periods of linear flow regime which could last for several years. Linear flow regime results from the fluid flow throughout Infinite-Conductivity Hydraulic Fractures (ICHFs) and Finite-Conductivity Hydraulic Fractures (FCHFs). This makes the analysis of linear flow regime of great importance to estimate parameters like fracture half-length, fracture width, fracture permeability and other parameters. Since the fracture half-length is an essential parameter for history matching and forecasting, it should be properly estimated and predicted. In this study, two analytical methods for analyzing linear flow were used to estimate the fracture half-length in hydraulically fractured gas wells producing from ICHFs and FCHFs under constant pressure conditions (fixed drawdown). The analytical methods compared are square root time and inverse production method. The investigated two analytical methods were compared along with the use of five different correction methods. The correction methods applied on the analytical solutions are those proposed by Ibrahim and Wattenbarger (2006), Nobakht and Clarkson (2012), Behmanesh et al. (2017), Chen and Raghavan (2013) and mean pressure. The comparison was done by conducting sensitivity analysis in term of initial pressure, flowing bottom hole pressure, reservoir temperature, permeability and dimensionless fracture conductivity. The study demonstrated that for ICHFs, both analytical methods provide close estimates of fracture half-length with the best results coming from the use of correction techniques of Nobakht and Clarkson (2012) and Behmanesh et al. (2017). For FCHFs, the inverse production method performed better than the square root time technique with the use of Chen and Raghavan (2013) and Ibrahim and Wattenbarger (2006) corrections. However, the inverse production methodology seems to be more sensitive than square root time to the change level in initial pressure and permeability. Moreover, it is shown that the square root time methodology generally overestimates the value of fracture half-length for FCHFs except some of the cases where the mean pressure is used. The results of this study provide general guidelines on the most accurate methods with their correction ways that can help to better analyze linear flow data in fractured gas wells. Also, this research can serve as selection criteria to choose the best analytical production methods to evaluate the performance of hydraulic fractures according to the well and reservoir properties.
      原文链接:
    • NSTL

    Well production forecast in Volve feld;; Application of rigorous machine learning techniques and metaheuristic algorithm

    Cuthbert Shang Wui NgAshkan Jahanbani GhahfarokhiMenad Nait Amar
    13页
    查看更多>>摘要：Developing a model that can accurately predict the hydrocarbon production by only employing the conventional mathematical approaches can be very challenging. This is because these methods require some underlying assumptions or simplifcations, which might cause the respective model to be unable to capture the actual physical behavior of fuid fow in the subsurface. However, data-driven methods have provided a solution to this challenge. With the aid of machine learning (ML) techniques, data-driven models can be established to help forecasting the hydrocarbon production within acceptable range of accuracy. In this paper, different ML techniques have been implemented to build the models that predict the oil production of a well in Volve feld. These techniques comprise support vector regression (SVR), feedforward neural network (FNN), and recurrent neural network (RNN). Particle swarm optimization (PSO) has also been integrated in training the SVR and FNN. These developed models can practically estimate the oil production of a well in Volve feld as a function of time and other parameters;; on stream hours, average downhole pressure, average downhole temperature, average choke size percentage, average wellhead pressure, average wellhead temperature, daily gas production, and daily water production. All these models illustrate splendid training, validation, and testing results with correlation co-effcients, R2 being greater than 0.98. Moreover, these models show good predictive performance with R2 exceeding 0.94. Comparative analysis is also done to evaluate the predictability of these models.
      原文链接:
    • NSTL

    Gradient descent algorithm to optimize the offshore scale squeeze treatments

    Vahid AzariOscar VazquezEric Mackay
    12页
    查看更多>>摘要：Scale deposition is one of the serious oilfield chemical issues which may lead to a range of downhole and production problems, including the reduction of well productivity index. Scale Inhibitor (SI) squeeze treatments are one of the most common techniques which are applied to prevent downhole scaling in production wells. A treatment typically consists of four stages, (i) a preflush, to condition the rock surface;; (ii) a main treatment, where a batch of high concentration inhibitor is bullheaded into the formation;; (iii) an overflush, to displace the scale inhibitor slug deeper into the near-well formation, and (iv) a shut-in stage to allow further inhibitor retention before putting the well back on production. During this backflow period, scale inhibitor is released from the rock surface into the produced water, and the scale deposition is prevented if the inhibitor concentration is above some specified Minimum Inhibitor Concentration (MIC). Due to logistic constraints in offshore wells, it is often required that the scale protection afforded by a squeeze treatment should last for some fixed design lifetime until the next treatment becomes available. For example, in the North Sea sector, well operations are often based on an annual treatment design. This paper presents a methodology to optimize the squeeze treatment design for a fixed target lifetime and this is applied for two offshore well squeeze treatments. This approach allows us to account for the operational constraints in the squeeze optimization process to treat a fixed volume of produced water, while minimizing the inhibitor neat volume and the total pumping time. A sensitivity study was performed on the inhibitor concentration, where the results showed that deploying a smaller inhibitor slug but with higher concentration is more effective than a larger slug with lower concentration, assuming a fixed volume of inhibitor and injected water. Therefore, it is recommended that the inhibitor is deployed at the maximum possible concentration, while avoiding the potential for any formation damage. Considering the same inhibitor slug (volume and concentration), this study suggests that the squeeze lifetime continuously increases with the overflush volume. This implies that the lifetime function is differentiate with respect to the overflush, and thus a gradient-based optimization algorithm, specifically the Gradient Descent (GD) may be applied to find the exact overflush volume resulting in the target lifetime. Employing this procedure for a wide range of main treatment volumes allows us to calculate the squeeze "Iso-Lifetime" curve which represents all the possible squeeze designs for the target lifetime. Thereafter, from the iso-lifetime designs, the CPB value (total cost of squeeze per treated barrel of water produced) can be minimized to find the most optimum squeeze design. This approach is shown to result in the optimum scale inhibitor squeeze treatment strategy in the long-term.
      原文链接:
    • NSTL

    Characteristics and origins of the modal pore throat structure in weakly cemented sandy conglomerate reservoirs

    Xinyu ZhongLinyu LiuHongmei Wang
    13页
    查看更多>>摘要：The pore throat structure of sandy conglomerate reservoirs is more complex than that of conventional sandstone reservoirs. At present, research on the modal pore throat structure of sandy conglomerate reservoirs mainly focuses on tight reservoirs with diagenesis controlled, while research on weakly cemented reservoirs is limited. Taking the newly discovered Cretaceous Guyang Formation reservoir on the western edge of the Hetao Basin as the research object, the modal pore throat structure of this weakly cemented sandy conglomerate reservoir is studied. The penological and pore throat characteristics are studied by performing various tests. Based on the inflection points of the multifractal curve of the pore throat radius of the studied sandy conglomerate reservoir, the pore throat structures of a sample are divided into three types;; macrothroats, mesothroats and microthroats. The pore throat structures of every sample are composed of these three pore throat structures. The heterogeneity at the microscale is controlled by the proportions of these three pore throat types. Based on the proportions of macrothroats, mesothroats and microthroats, the modal pore throat structures of the studied sandy conglomerate reservoir are analyzed for the first time. The modal pore throat structures of the corresponding samples are characterized into unimodal, bimodal and multimodal structures. When the pore throat structure of the sandy conglomerate reservoirs of the Cretaceous Guyang Formation in the western margin of the Hetao Basin includes more microthroats, it is more homogeneous, resulting in a poorer reservoir quality. The fundamental reason for the development of the modal pore throat structure is the mixed deposition of grain sizes, and the modal pore throat structure is controlled by the combination of macrothroats, mesothroats and microthroats.
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    • NSTL

    Appraisal campaign selection based on the maximum value of sequential information

    Andre Luís MorosovReidar Brumer Bratvold
    13页
    查看更多>>摘要：Field development projects generally demand large investments which are subject to geological uncertainty, hence projects can beneft from geological information obtained from appraisal wells before large capital commitment. But “how much data is enough”? Value erosion occurs both in over-appraisal or under-appraisal of the feld and the value of information rationale is ideal to determine the right amount of data. But examples from the literature are case-specifc and often limited to simple assessments with a small number of alternatives and outcomes. We propose a general method to select the appraisal campaigns based on the value that spatial geological data adds to the development plan. It regards the appraisal campaign as a sequence of wells that will acquire geological data and optimally supports the next acquisition on a well-by-well basis. This approach is compelling for replication in any case because drilling wells is part of every development project. The method is demonstrated in a synthetic example with 8 candidates from which the appraisal campaign must be selected and is observed up to 65% improvement in the development project expected value. Its application provides a tailored solution different values of discount factor and information cost, which are grouped in a solution map. Results clearly show how much data should be acquired considering different circumstances and sensitivity analysis in the value function show value-adding robustness. Given the potential benefts of the appraisal selection method presented here, the modeling of spatial geological dependencies through probabilities is encouraged and future work could explore the use of subsurface fow-simulations to enhance the accuracy of the estimations by considering value coupling.
      原文链接:
    • NSTL