查看更多>>摘要：One of the crucial steps of geological object exploration is interwell correlation. The correlation matches similar parts of different wells helping to construct geological models and assess hydrocarbon reserves. Today, a detailed interwell correlation relies on manual analysis of well-logging data: a process prone to significant time consumption and subjectivity. Alternative automation attempts include rule-based, classic machine learning, and more recent deep learning methods. However, most approaches are still of limited usage and inherit cons of manual correlation. We propose a method based on a deep learning model to solve the geological profile similarity estimation. Our similarity model takes well-logging data as input, constructs well representations and uses them to provide the similarity of wells. The developed algorithm enables extracting patterns and essential characteristics of geological profiles within the wells. We follow an unsupervised paradigm that allows us to utilize large pools of logging data available in the industry and does not rely on subjective labelling. For model testing, we used two open datasets originating in New Zealand and Norway. Our data-based similarity model has decent quality. For example, the accuracy of our model is 0.926 compared to 0.787 for a widespread gradient boosting baseline. The selected representation learning approach also provides high extrapolation capabilities to work for formations other than those used during training and start to work for limited amounts of available data, the experiments show.
查看更多>>摘要：Drilling operations in recent years have gone into much deeper depths to meet the global demands. Therefore, it becomes important that the well integrity is tained throughout its life and in that respect, well cement plays an important role. For the proper application of the cement in the well, it is important to have a MKr understanding of its mechanical properties. The study will focus on the techniques to perform Unconfined Compressive Strength (UCS) tests according to API Standard (cubes) and cylinders having a length to diameter ratio of 2. Moreover, a review of ASTM and British standards for the UCS is given. This paper shows the results of more than 100 tests conducted on cement cubes and cylinders. It was observed that variation in the results existed in the UCS when cubes are compared with the cylinder, which raises the importance of the development of the new standard. The results showed the high compressive strength of the cube as much as 50% and 35% for the sample cured at high and room temperature respectively. Moreover, no correlation existed between the cylinder cured at high temperature and UCS or UPV. Whereas the cube sample was able to give a logarithmic or exponential correlation for all the testing scenarios. Hence a better understanding of the cylindrical sample is needed and the data from this research can help to compare the results from these two geometries.
查看更多>>摘要：There are many RTA (Rate Transient Analysis) methods available to analyze wells producing from unconventional formations. The approach of Agarwal (2010) is one of the RTA techniques which have gained an increasing interest due to its simplicity, flexibility, and wide range of applications. In this study, the approach of Agarwal (2010) was adopted to analyze not only single well systems but also multi-well systems by using three different equations. These equations were then integrated with the principle of superposition rate rather than conventional superposition time. By using two field cases, the accuracy of the proposed approaches was validated with current analytical methods and reservoir simulation. The first case represents a multi-well system in which the wells producing with a fixed flowing pressure were put on production at the same time. The operating conditions were then relaxed in the second case by allowing the wells to have different production starting times and varying production profiles. Additionally, this work examined in details the ability of the superposition rate function in converting various production behaviors to their equivalent constant rate solutions. This research clearly shows the advantage of the superposition rate solution over the traditional superposition time function (material balance time) in maintaining the data order in time. Such an advantage makes it easier for the analyst to observe the production changes in well performance in real normal time. Several case studies were used to show how Agarwal (2010) can be utilized to extract different information from boundary-dominated flow period which are useful in the evaluation of reservoir compartmentalization and the effectiveness of infill drilling campaigns. In addition to that, the application of Agarwal (2010) in terms of frac hits evaluation and refracturing operations encountered during the transient flow period was also examined.
查看更多>>摘要：A strange phenomenon happens all the time that the obtained permeability by the conventional finite-conductivity model (FC) is much larger than the actual value in tight reservoir. The conventional pressure-transient analysis models of vertical-fractured wells regard fracture as a regularly non-uniform flow rate. However, due to fracture bending, irregular proppant filling, proppant crushing, and inadequate fracturing fluid backflowing, the fracture may show an irregular flow rate in different fracture segments. An additional horizontal line or concave curve appears on the pressure derivative curve by considering the irregular flow rate in the fracture. In the past, the concave curve would be regarded as an error from field data, and the horizontal line on the pressure derivative curve would be regarded as the quasi-radial flow regime. If the horizontal line is recognized as the quasi-radial flow regime in tight reservoir, the interpreted permeability will be magnified many times. In this work, we proposed a multi-segment irregular non-uniform flow model with changing wellbore storage effect (MINFC) to characterize the pressure response of irregular fractures better, making the pressure response in the fracture more realistic. The MINFC model can correct the magnified permeability and diagnose the partial closure fracture location, length, and flow rate. Green function and Newman product method are applied to obtain the bottom-hole pressure behavior. The results demonstrate that the pressure derivative curve is not a line with a slope of 0.5 in the irregular fracture flow regime but a horizontal or concave curve. Sensitivity analysis demonstrates that the location and length of the irregular proppant filling will affect the duration of the horizontal line. In conclusion, the reservoir permeability and fracture half-length obtained by the MINFC model are closer to the actual value. The locations of irregular proppant filling and low flow rete are quantified so that researchers can take steps to improve fracture performance. Finally, the comparison between the MINFC model and the finite-conductivity model verifies the MINFC model's accuracy. The MINFC model matches field data to verify its practicability.
查看更多>>摘要：The carbon capture and storage (CCS) process significantly contributes in reducing the atmospheric emissions of carbon dioxide (CO2). During the implementation of the CCS technique, the pipeline corrosion occurring due to the supercritical (SC) CO2 is a major concern. The corrosion of the steel pipelines is caused by contamination of water that reacts with the CO2 gas leading to the formation of corrosive species carbonic acid (H2CO3). To address to this issue, the strategies used are (i) use of corrosion resistant alloys (CRAs), (ii) corrosion inhibitors, and (iii) the protective layers of iron carbonate (FeCO3). One of the most important methods is the application of chemical additives to the corrosive medium that dissolve in the environment and adsorb on the target metallic substrate, thereby impacting corrosion mitigation. This article aims to overview the various organic corrosion inhibitors commonly applied in the SC CO2 corrosion. The requirement of greener inhibitor alternatives is emphasized, and some of the potential research aspects are conceived of. The mechanism of SC CO2 corrosion, factors affecting and chemistries of inhibitors, and their shortcomings are discussed. This review also discusses the application of computational methods in predicting the inhibitive performance. This is a critical, timely, urgent, and insightful review, identifying successes and shortcomings on the inhibitors available for SC CO2 medium, and pointing to potential avenues for further investigation.
查看更多>>摘要：Formation and deposition of mineral scales pose a serious threat to the safety and integrity of oilfield operations. Scale inhibitor chemicals have been widely employed to control scale threat and enhance production efficiency. The inhibitor-formation mineral interaction together with inhibitor transport behavior play significant roles in the design and optimization of oilfield inhibitor treatment. However, limited studies have been reported to investigate the principles dictating the inhibitor-mineral interaction under both equilibrium and dynamic conditions. Moreover, there are few studies focusing on the inhibitor transport at a lower inhibitor concentration. In this study, a systematic evaluation of the physicochemical nature of inhibitor-formation mineral interactions was conducted with a focus on lower inhibitor concentrations (below 50 mg L~(-1)) by adopting two common oilfield inhibitors of diethylenetriamine pentamethylene phosphoric acid (DTPMP) and phosphino-polycarboxylic acid (PPCA). The formation mineral employed in this study is calcium carbonate (calcite). Both equilibrium and the kinetics aspects of inhibitor sorption behavior have been studied experimentally via static batch and dynamic column apparatus. It was found that the adsorption capacity of calcite for DTPMP is higher than that of PPCA. Laboratory fixed-bed column transport experiments were carried out at different physicochemical conditions of initial inhibitor concentration, ionic strength, temperature, flow rate and calcite particle size. Results indicate that an increase in both DTPMP and PPCA concentration can expedite inhibitor transport and a high initial DTPMP concentration could significantly affect the retention of DTPMP in the calcite porous medium. Ionic strength can result in a higher transportability in calcite medium for both inhibitors. Change in temperature has no significant impact on inhibitor transport. The flow rate has a considerable influence on the dispersion coefficient due to elevated mechanical dispersion at a higher flow rate for DTPMP. The calcite particle size can also impact inhibitor adsorption due to the change in surface area. Furthermore, adsorption of PPCA can subject the calcite surfaces more hydrophilic than DTPMP, which can affect the mobility of inhibitor in calcite medium. Atomic force microscopy characterization results confirmed that the wettability of calcite was increased through adsorption of DTPMP and PPCA inhibitor. This study provides deep insights into the sorptive behavior and transportability of DTPMP and PPCA inhibitors in calcite porous medium.
查看更多>>摘要：CO2 as pre-fracturing fluid technology, with dual advantages of CO2 fracturing and water fracturing, has broad application prospects in the development of unconventional oil and gas, and it is also one of the important ways of carbon utilization and carbon storage. In this paper, an accurate experiment was designed first time to explore the replacement capacity of CO2 under different discharge pressure gradients using cores with different sizes. The fracturing fluid flowback law and enhance oil recovery ability were also studied by the self-designed experiment. Before the test, the core was split axially from the center and the core fracture was filled with mixed 40-70 mesh quartz sand and AB glue to simulate the actual formation fracture. Then a dual-permeability compositional model was established to explore the field scale fracturing fluid flowback. The performances of slickwater fracturing and pre-CO2 fracturing were compared. The effects of flowback pressure gradient, CO2 injection volume, and soaking time on the flowback efficiency and oil recovery were also analyzed. The results show that the efficiency of CO2 replacement of oil increases with the increase of flowback pressure difference and is 15% higher than that of slickwater. CO2 pre-fracturing can significantly improve the flowback efficiency of slickwater and enhance oil recovery. As the pressure gradient increases, the flowback efficiency of slickwater increases, which shows that the flowback pressure gradient needs to be higher than 10 MPa to achieve economic output. With the proportion of CO2 injection increased from 20% to 58%, the CO2 flowback efficiency increased from 37.5% to 44.1%, and the oil recovery factor increased from 11.2% to 14.7%. With the increase of soaking time, slickwater imbibed into matrix pore throat according to the capillary force, meanwhile, CO2 diffused into deep formation. The degree of slickwater and CO2 backflow decreased accordingly. Considering the pressure change, stimulation effect and flowback efficiency during the soaking period, the optimal soaking time is 6 h in experiment and 15 d in field production. This study is expected to provide theoretical guidance for CO2 pre-fracturing in tight oil reservoirs.
查看更多>>摘要：Matrix acidizing is one of the most viable options for opening up the clogged tortuous passages in near wellbore region which would lead to improved crude oil production. Nonetheless, the incompatibility of stimulation and reservoir fluids may result in further formation damage i.e., acid sludge. Sludge formation is a highly complex process in which the role of crude oil components is not well understood. In this study, the effect of aromatic and paraffinic components of crude oil on acid sludge formation has experimentally been investigated. For doing so, synthetic oil was used to isolate the impact of individual components of crude oil. Furthermore, the influence of polarity of solvents including DMF, acetone, THF, dichloromethane and toluene was discerned as well as type and concentration of asphaltene and different ratios of acid to synthetic oil mixture. The results showed that a paraffinic synthetic oil would be more susceptible to sludge formation than the aromatic one. Increased polarity of solvents from 2.4 for toluene to 6.4 for DMF resulted in more sludge formation from 15 to 231% and 42-175% for the same synthetic oil but for two asphaltenes, respectively. Acid to mixture ratio (AMR) showed to have a considerable implication on sludge formation. Increasing asphaltene concentration from 5000 to 15,000 ppm caused the increment of 1-3% in sludge content. This implied that asphaltene concentration in the synthetic oil had no considerable effect on the acid sludge formation in the absence of the other constituents of crude oil such as resin.
查看更多>>摘要：Rock formation is subjected to acid stimulation to increase oil reservoirs productivity. Acidizing of sandstone rocks is a common method to remove damage and recover the oil flow to the wellbore. A matrix acid stimulation will always require additives depending on mud acid (HF/HCl) components, which cause non-Newtonian fluid behavior. In this study, the 3-D mathematical model of sandstone matrix acidizing in radial flow has been presented by a modified two-parameter model to consider non-Newtonian fluids and temperature effects. To this end, the Carreau-Yasuda equation has been employed to predict dissolution patterns created by non-Newtonian reactive fluids in sandstone formations. Meanwhile, the energy equation has been solved in the porous media to estimate the temperature in each time step, which affects the dissolution patterns in matrix acidizing. Three main phenomena are involved in dissolution patterns: surface reaction, diffusion and convection. Acidizing simulation indicates the acid-rock reaction constant in the formation network is temperature sensitive, and increases exponentially by increasing the reservoir temperature. In this work, the effects of various heterogeneity magnitude and porosity in the porous media, injection rate, reaction rate constant, power-law index (n) and temperature are considered by the various presented dissolution patterns of sandstone acidizing. The results show that, to reach a certain penetration length, the pore volume (PV) of injected acid decreases sharply with reservoir temperature, but after the critical temperature, it decreases slowly. The model discretized the Darcy, mass and energy balance equations by finite difference method and pore evaluation by Karman-Cozney correlations, and then employed the Tri-Diagonal matrix algorithm (TDMA) method to achieve the solution of the model and analysis of dissolution patterns in various acidizing regimes and Theological properties. All mathematical estimations including Darcy correlations, mass and energy balance and pore evaluation have been solved in FORTRAN program by parallel processing to accelerate 3-D calculations.
查看更多>>摘要：Granular lost circulation materials (LCMs) are used to control fluid loss in naturally fractured thief zones Rapid and automated identification of their optimal particle size distribution (PSD) is highly desirable. This paper proposes a PSD selection method for LCMs based on a PSD representation algorithm and the Monte Carlo method. The PSD representation algorithm describes the cumulative and compositional PSD curves of LCMs according to a piecewise cubic Hermite interpolation algorithm. Comparison with measured PSD data shows that the representation algorithm is more accurate than other commonly used PSD models in describing both homogeneous and mixed LCMs, and the relative errors are all within 10%. The Monte Carlo method is adopted to simulate LCMs with various compositions and select ones with PSDs that meet a proposed selection criterion. Experiments show that the PSD curves of the LCMs were all within the upper and lower bounds specified by the selection criterion. Plugging experiments show that LCMs with the recommended compositions can effectively enter fractures, and the fluid loss is less than 200 mL for half an hour under the pressure difference of 7 MPa. The proposed selection method can be used for the rapid and automatic design of granular LCMs used in fractured thief zones.
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