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Journal of Petroleum Exploration and Production Technology
Journal Prestige (SJR): 0.344  Citation Impact (citeScore): 1 Number of Followers: 2  Open Access journalISSN (Print) 2190-0558 - ISSN (Online) 2190-0566 Published by SpringerOpen  [229 journals]
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- Evaluation of the wellbore drillability while horizontally drilling
sandstone formations using combined regression analysis and machine
learning models
Abstract: The rate of penetration (ROP) is an influential parameter in the optimization of oil well drilling because it has a huge impact on the total drilling cost. This study aims to optimize four machine learning models for real-time evaluation of the ROP based on drilling parameters during horizontal drilling of sandstone formations. Two well data sets were implemented for the model training–testing (Well-X) and validation (Well-Y). A total of 1224 and 524 datasets were implemented for training and testing the model, respectively. A correlation for ROP assessment was suggested based on the optimized artificial neural network (ANN) model. The precision of this equation and the optimized models were tested (524 datapoints) and validated (2213 datapoints), and their accuracy was compared to available ROP correlations. The developed ANN-based equation predicted the ROP with average absolute percentage errors (AAPE) of 0.3% and 1.0% for the testing and validation data, respectively. The new empirical equation and the optimized fuzzy logic and functional neural network models outperformed the available correlations in assessing the ROP. The support vector regression accuracy performance showed AAPE of 26.5%, and the correlation coefficient for the estimated ROP was 0.50 for the validation phase. The outcomes of this work could help in modeling the ROP prediction in real time during the drilling process.
PubDate: 2023-07-01
- A novel material-balance approach for estimating in-place volumes of gas
and water in gas reservoirs with aquifer support
Abstract: Applications of the traditional static material-balance method in gas reservoirs become a challenge with production maturity due to variability in aquifer influx, infill drilling, and production-operational changes in offset wells, among others. Besides, some existing modeling approaches involve a trial-and-error method, making the solution outcomes nontrivial. This study proposes a new methodology for analyzing production data involving water-drive gas reservoirs. The main findings of this study include the following: (1) A straight-line plot that yields gas and water in-place volumes, (2) A modified-(pav/z)* plot exhibits a straight-line with an x-intercept of gas initially-in-place, similar to that in a conventional-(pav/z) plot, (3) A new definition of degree of aquifer support that is quantifiable using production data. Synthetic data verified the proposed modeling approach, whereas a field dataset provided validation.
PubDate: 2023-07-01
- Improving reservoir permeability by electric pulse controllable shock wave
Abstract: Controllable shock wave (CWS) parameters such as amplitude, operating area and number of operations are easy to control and have received extensive attention as a potential new technology for reservoir permeability enhancement. Based on the continuous-discontinuous element method (CDEM) and considering the coupling mechanism of reservoir deformation, failure, pore seepage and fracture flow, a multiphysical field coupling model of reservoir permeability enhancement under CWS is proposed. Under the fluid–solid coupling condition, the formation and development dynamic process of reservoir fractures are obtained, and the change of reservoir permeability is also obtained. The compression fracture zone, tensile fracture zone and undamaged zone are formed around the wellbore. After repeated impact, the number of fractures is more sensitive to tectonic stress, the fracture aperture is more sensitive to reservoir strength. Different from hydraulic fracturing, a large number of fractures in different directions will appear around the main fracture after repeated impact, forming a complex fracture network similar to spider web, which may be beneficial to improve reservoir permeability. The permeability of reservoirs with different tectonic stresses and strengths increases nonlinearly and monotonicly with repeated impacts. Based on CDEM, the change of reservoir permeability with tectonic stress, strength and impact times is obtained, which is a nonlinear monotonic three-dimensional relationship. Based on that relationship, the parameters of CWS can be controlled to predict the change of reservoir permeability, such as peak pressure, duration, impact times, etc. Therefore, it can optimize the reservoir fracturing scheme and improve the reservoir fracturing efficiency, which has considerable practical significance in engineering.
PubDate: 2023-07-01
- Superstructure optimization of subsea processing layouts
Abstract: As the oil and gas industry expands the use of subsea processing, the complexity of subsea layouts increases, making manual design processes cumbersome and suboptimal. Here we propose a method to support subsea field design where optimization is performed on a model of the subsea system, to maximize the net present value of the project. The proposed mixed-integer nonlinear (MINLP) model is solved to compute a global optimum design considering constraints in production, equipment duties and cost, and reliability and maintenance aspects. The subsea layout, equipment capacity, oil and gas production rates, and system pressures are optimized. The method was applied on a synthetic field based on the Goliat field in the Barents Sea. The method successfully finds the best designs, while the second and third-best layouts give general insights for subsea processing layout optimization.
PubDate: 2023-07-01
- PTA-metrics for time-lapse analysis of well performance
Abstract: Monitoring of a well and the surrounding reservoir performances is a crucial component in evaluating on-going and planning future well and field operations. This is carried out at all stages of a well life-span: from exploration to production and, sometimes, after abandonment. Despite tremendous progress in reservoir simulations, simple and fast techniques for well-reservoir performance evaluation are still demanded in the industry, especially in the context of the vast amount of permanent well monitoring data continuously accumulated. Such techniques are of special interest for on-the-fly well monitoring to detect and alarm about deteriorating performance issues. Installation of permanent pressure gauges in many wells motivated development of time-lapse Pressure Transient Analysis (PTA), capable of revealing and monitoring of different factors governing well performance and reservoir production. The paper describes PTA-based metrics introduced in the context of automated interpretation of time-lapse pressure responses and their derivatives. The paper begins with a review of time-lapse PTA applications in the oil and gas industry and examples of patterns formed by the time-lapse pressure transients and their derivatives in the log–log scale. Then, integral-based PTA-metrics for well-reservoir performance analysis are introduced. The metrics enable to distinguish between reservoir and well-reservoir connection contributions to a well’s performance using the Bourdet derivative, while avoiding the need for selecting and matching of a well-reservoir model. The metrics were further tested with synthetic well models and field cases. The testing demonstrated high accuracy of the metrics for the cases of vertical wells with stable transient patterns. Testing for the horizontal well cases has confirmed reliability of the metrics for the stable patterns, while change of the patterns may reduce the metrics reliability. Model independence and using only pressure and rate measurements as input data are the main advantages of the metrics for integration into automated interpretation workflows and on-the-fly analysis intensively developed in the industry.
PubDate: 2023-07-01
- A comprehensive methodology for reservoir cut-off determination
Abstract: The main objective of net pay determination, as an important step of any reservoir study, is to exclude non-reservoir intervals so that better results are obtained from reservoir characterization, hydrocarbon in-place calculations, and dynamic flow simulation of the reservoir. This study is a comprehensive presentation of the most applicable methods available for net pay determination, highlighting their strengths, limitations, and their input data, and presenting a new procedure to prepare the input data, determine the reservoir net pay, and validate the final results. These methods include conventional best-fit line and quadrant methods in a porosity–permeability cross-plot, Worthington method, rules of thumb, cumulative hydrocarbon column plot, and production constraints. This study, unlike previous ones, presents a stepwise methodology to reach the correct answer considering both rock and fluid properties. The necessity for the definition of net pay is discussed in the current study in the first step. Determination of net pay and the net-to-gross ratio is done by definition of some cut-off values for petrophysical properties such as porosity, water saturation, and shale volume. The new procedure presented in this study as a flowchart to determine pay zone uses different methods to determine cut-off values. The sequential and systematic use of all these methods gives a consistent and more reliable answer. The key steps to determine net pay is to find the porosity cut-off based on a porosity–permeability cross-plot and a pre-defined limiting value for permeability and then to use this value to find the shale volume and water saturation cut-offs using their cross-plots versus porosity. To take into account the fluid properties effect, a mobility cut-off is used as the starting point instead of permeability. Cumulative hydrocarbon column plots are used as a sensitivity tool to determine what percentage of the hydrocarbons will be discarded by any cut-off value. Finally, the determined net pay should be validated using the results of production logging and wireline formation tests. The proposed methodology was applied to a real field to determine its net pay. Porosity and water saturation cut-offs were calculated to be 2% and 55%, respectively, and due to the clean nature of the reservoir, a shale volume cut-off was not necessary. Simultaneous application of porosity and water saturation cut-offs discarded 6.3% of the hydrocarbon column for the field example.
PubDate: 2023-07-01
- Garau Formation as an unconventional hydrocarbon resource in southwestern
Iran: a geochemical investigation
Abstract: Due to the growing need for hydrocarbons and the limited conventional resources, paying attention to unconventional oil and gas resources is essential. The upper Jurassic-Lower Cretaceous in western and southwestern Iran contains the most crucial source rocks of the Zagros sedimentary basin. One of the richest source rocks is the shaly Garau Formation. Owing to geochemical and geological characteristics, the Garau Formation, with Neocomian to Coniacian age and periodicity of radiolore black limestones with black pyrite bituminous shales, ammonite, and chertite shale, is the suitable potential sweet spot as oil shale and gas shale. In this study, a comprehensive regional study was conducted on the entire Garau Formation basin using Rock–Eval parameters and organic matter maturity data. In addition to investigating the hydrocarbon generation potential of the Garau Formation as a source rock, the prospect of this Formation as oil and gas shales in the entire Garau basin was investigated. For this purpose, 31 fields in 5 important sub-basins of Zagros, including East Lorestan, West Lorestan, Izeh zone, Dezful Embayment, and Abadan plain were investigated. The study showed that total organic carbon varies between 0.17 and 24.6, and more than 75% of total organic carbon had values greater than 1. By examining the quantity, quality, and maturity parameters and considering the necessary thresholds, it was found that East Lorestan and West Lorestan have the conditions for oil and gas shales. The highest quantity and best quality of organic matter are related to Eastern Lorestan. By moving west and south of Garau Basin, the quantity and quality of organic matter decrease, and the hydrogen index proves the results. Vitrinite reflection studies indicated that the lowest and highest levels of organic matter maturity belong to East Lorestan and West Lorestan, respectively. Therefore, the northeast of Garau Basin (Eastern Lorestan) has the potential for oil shale, and the northwest of the Basin (Western Lorestan) has the potential for gas shale.
PubDate: 2023-07-01
- Numerical approach on production optimization of high water-cut well via
advanced completion management using flow control valves
Abstract: With the development of smart downhole control devices, such as the electric flow control valve (FCV), research on completion optimization using FCV control is gaining traction for successful field production management. Applying and verifying its applicability to actual assets with uncertain production issues occur are important. This study focuses on managing downhole devices to optimize fluid production in an actual onshore oil field in Alberta, Canada. The target field has been in production operation for over 20 years, and water flooding was used in the early stages of production to maintain reservoir pressure. However, according to the flow characteristics of the field, water injection caused a high water-cut issue due to water channeling. To mitigate the problem, proactive and reactive strategies were investigated to optimize FCV control. Additionally, the effect of completion optimization was estimated considering both the field-level economic value and the fluid production behavior at the device level. In most optimization cases, the cumulative water production could be reduced compared with the base case without valve control. Notably, the flow-balancing strategy increased the revenue of the target field by approximately 23 MM$ by maximizing oil production and suppressing water production. However, reactive and streamline-balancing strategies, which directly control and delay water production, undermined the economic value due to the decrease in oil production. The findings imply that FCV control strategy of suppressing only water production for the field with high water-cut could not be the optimal solution considering the reduction in oil production and the field’s revenue. The results of this study could be used as a reference to optimize downhole devices when applying water flooding in fields where high water-cut is expected.
PubDate: 2023-07-01
- Performance forecasting of hydraulically fractured horizontal wells using
dynamic-drainage-area concept with correct distance of investigation
Abstract: Performance forecasting of multi-fractured horizontal wells (MFHWs) completed in tight/shale oil or gas reservoirs is of great significance in the development of unconventional resources. Dynamic drainage area (DDA) concept has emerged as a production forecasting methodology for unconventional reservoirs. This paper investigated the DDA method and derived correct expressions of distance of investigation (
DOI ) for both constant production rate and constant bottom-hole pressure cases by integrating material balance and deliverability equation within the range of
DOI . The modified DDA method with correct
DOI coefficients provided in this paper permits direct calculation of dynamic performance at arbitrary time steps before the end of transient linear flow. At the same time smooth production forecasting of MFHWs from transient linear to boundary-dominated flow is realized without modification by extra coefficient. Hybrid models such as DDA plus dual-exponential and DDA plus hyperbolic are presented, which can be applied quickly and easily to MFHWs in unconventional reservoirs as alternatives to complex numerical simulation. Meanwhile, average pressure in the range of DDA can be readily obtained with correct
DOI coefficients, avoiding complex iterative calculations. The reliability and practicability of this solution have been demonstrated by synthetic and field cases in this work.
PubDate: 2023-06-01
- Prior assessment of CO2 leak rate through cracks sealed by nanoparticle
gels
Abstract: The leakage of hydrocarbon fluids through cracks in the annular cement and CO2 storage is a major concern to the Petroleum Industry. A significant risk is posed when repairing leakage in a micro annuli channel with smaller apertures. A low-viscosity sealant that can generate a long-lasting resilient seal is desired. The solution to sealing these channels might lie in a novel application using nano-silica Gel. In this study, laboratory tests were carried out to examine the capabilities of nano-silica gels to seal the cracks. Analyzing its rheological property, the gel strengths of nano-silica gels were found to increase with an increase in nano-silica concentration. Additionally, it was discovered that as the concentration of nano-silica increases, the sealing and leakage pressures, defined as the pressures before and after water breakthrough, respectively, increase as well. With a typical 15% concentration of nano silica in gel, a sealing pressure gradient of 80.2 psi/in and a leakage pressure gradient of 30 psi/in at a leaking rate of 1 cc/min were noted. To validate the validity of the experimental results, a mathematical model was developed to predict the leakage rate of sealed fractures. The model suggests that the young’s modulus of sealant is a key property of nano-sealants and further investigations are needed to validate the mathematical model for quantitative use. This study suggests a novel strategy for enhancing cement zonal isolation and reducing cement failure in oil and gas sector.
PubDate: 2023-06-01
- Cutting mechanism of a special 3D concave-shaped PDC cutter applicable to
the Weiyuan shale
Abstract: The Weiyuan shale gas field faces problems of long drilling cycles and high development costs. Improving the drilling efficiency of polycrystalline diamond compact bits in shale formations will significantly reduce the overall well cost and duration. Previous applications have demonstrated that conventional PDC bits on the market cannot meet the demand for drilling acceleration. In this work, a new three-dimensional concave-shaped PDC cutter was proposed to improve drilling efficiency. The special 3D concave-shaped cutter has two symmetrical curved ridges on the concave surface and a circular plane at the center. The cutting mechanism of the new 3D concave-shaped cutter has been studied by laboratory experiments and numerical simulations. The research data revealed that, compared with a flat cutter, the tangential force of the original 3D concave-shaped cutter was reduced by 1.4%–35.0%, the axial force was reduced by 6.7%–37.6%, and the mechanical specific energy (MSE) was reduced by 1.6%–35.59%. Simulations showed that the shear action of the 3D concave-shaped cutter was divided into two continuous parts, with the sides and the center surface being stressed successively, which is helpful for extending shear cracks, forming trilobal cuttings, and improving cutting efficiency. With the special 3D concave-shaped cutter, an 8½-inch drill bit was designed and manufactured and tested on the Longmaxi shale in the Weiyuan block. Through field tests, we further compared the performance of the 3D concave-shaped cutter PDC bit with that of the flat cutter PDC bit. The 3D concave-shaped PDC bit had a 41.8% better footage and 22.6% better rate of penetration (ROP) in field test.
PubDate: 2023-06-01
- Estimating electrical resistivity from logging data for oil wells using
machine learning
Abstract: Formation resistivity is crucial for calculating water saturation, which, in turn, is used to estimate the stock-tank oil initially in place. However, obtaining a complete resistivity log can be challenging due to high costs, equipment failure, or data loss. To overcome this issue, this study introduces novel machine learning models that can be used to predict the electrical resistivity of oil wells, using conventional well logs. The analysis utilized gamma-ray (GR), delta time compressional logs (DTC), sonic shear log (DSTM), neutron porosity, and bulk density. The study utilized a dataset of 3529 logging data points from horizontal oil carbonate wells which were used to develop different machine learning models using random forest (RF) and decision tree (DT) algorithms. The obtained results showed that both models can predict electrical resistivity with high accuracy, over 0.94 for training and testing data. Comparing the models based on accuracy and consistency revealed that the RF model had a slight advantage over the DT model. Based on the data analysis, it was found that the formation resistivity is more significantly impacted by GR logs compared to DTC logs. These new ML models offer a low-cost and practical alternative to estimate well resistivity in oil wells, providing valuable information for geophysical and geological interpretation.
PubDate: 2023-06-01
- Experimental simulation of wormhole sanding cavity pattern and microscopic
mechanism in heterogeneous weakly-cemented sandstone
Abstract: Sand production has been a shared problem in the development of weakly-cemented sandstone oil reservoirs. Sanding simulation and prediction are of utmost importance for the production optimization of this type of reservoir. For a long time, research on sand production has been centered on “what is produced from the formation,” such as the size and rate of produced sand. However, “what is left inside the formation,” which is the structural change of the rock after sanding, is also another intriguing and important topic for the management of sand-prone reservoirs. Some related studies have been carried out, and they have proposed that wormhole-like pore throat will appear after sand production, but the precise morphological description and formation mechanism are still lacking. A series of sanding simulation experiments are performed to deepen the understanding of the sanding cavity pattern and its mechanism. The experiments are carried out using a visual sanding simulation apparatus. Through this, the complex wormhole sand production patterns are found and classified into single-branch wormhole cavity patterns and multi-branch wormhole cavity patterns. The extension processes of those different patterns are also demonstrated. Besides, this work discusses the change in the reservoir flowability performance in wormhole sanding mode, and the near-well flowability might be improved by actively inducing weakly-cemented sandstone to create a bigger aperture wormhole sanding pattern. Through the visual microscopic system, the sand competitive detachment mechanism that induces wormhole extending is revealed, along with the cavities concurrent extension mechanism that induces multi-branch wormhole extending. Moreover, this work discusses the microscopic detachment forms which help explain the sand-produced rate from weakly-cemented sandstone. This work enhances and creates a novel understanding of the sanding patterns and mechanisms in weakly-cemented heterogeneous reservoirs, which is beneficial to providing direct guidance for sand production prediction and sand control optimization.
PubDate: 2023-06-01
- Study on influence of failure mode on fracturing performance of fractured
reservoir
Abstract: Reasonable volumetric fracturing effect evaluation is the key to effective stimulation of fractured reservoir. Traditional fracturing effect evaluation is mainly conducted by the SRV (stimulated reservoir volume), fracture length, fracture width and other indicators, ignoring the influence of failure mode on fracturing performance. In this paper, the different fracture modes including main fractures, branch fractures and self-supporting fractures contained in the fracture network and their contributions to fracturing effect were studied in depth by numerical simulation. The results show that the main fracture formed by tensile failure has the largest width but simple shape and relatively small distribution range, while the branch fracture has a slightly smaller width but effectively expands the main fracture. Although the self-supporting fracture by shear failure is not connected, it can still improve the overall flow conductivity. The angle and number of natural fractures in fractured reservoir have a significant effect on fracture network scale and fracturing effect. When the number of natural fractures is larger, both of the number and proportion of branching fractures and self-supported fractures are larger, although the isolated self-supported fractures account for a larger proportion, the overall flow conductivity of the final fracture network is stronger. When the angle of natural fractures is larger, the natural fractures in uniform stress field are easier to be connected by hydraulic fractures and the final fracturing effect is better. The research methods and results have a certain guiding significance for the evaluation of volumetric fracturing effect in fractured reservoirs and are conducive to the reasonable selection of favorable fracturing areas and engineering parameters.
PubDate: 2023-06-01
- Application of machine learning algorithms in classification the flow
units of the Kazhdumi reservoir in one of the oil fields in southwest of
Iran
Abstract: By determining the hydraulic flow units (HFUs) in the reservoir rock and examining the distribution of porosity and permeability variables, it is possible to identify areas with suitable reservoir quality. In conventional methods, HFUs are determined using core data. This is while considering the non-continuity of the core data along the well, there is a great uncertainty in generalizing their results to the entire depth of the reservoir. Therefore, using related wireline logs as continuous data and using artificial intelligence methods can be an acceptable alternative. In this study, first, the number of HFUs was determined using conventional methods including Winland R35, flow zone index, discrete rock type and k-means. After that, by using petrophysical logs and using machine learning algorithms including support vector machine (SVM), artificial neural network (ANN), LogitBoost (LB), random forest (RF), and logistic regression (LR), HFUs have been determined. The innovation of this article is the use of different intelligent methods in determining the HFUs and comparing these methods with each other in such a way that instead of using only two parameters of porosity and permeability, different data obtained from wireline logging are used. This increases the accuracy and speed of reaching the solution and is the main application of the methodology introduced in this study. Mentioned algorithms are compared with accuracy, and the results show that SVM, ANN, RF, LB, and LR with 90.46%, 88.12%, 91.87%, 94.84%, and 91.56% accuracy classified the HFUs respectively.
PubDate: 2023-06-01
- The effect of forces affecting the spread of oil droplets on a rock
surface
Abstract: A better understanding of the main forces that affect oil droplets is expected to play an important role in enhancing oil recovery from reservoirs. The effects of the various forces on an oil droplet on the top of a rock surface or hanging from the bottom of a rock surface are analysed. The results proved that increasing the mass of an oil droplet creates a favourable condition for interaction between the displaced and displacing fluids, which prevents the displacing fluid from bypassing the oil droplets. The results show that the mass of an oil droplet plays an important role in initiating its movement if the gravity force is greater than the capillary force. This study provides a sound understanding of the main forces affecting oil droplet movements and opportunities for future enhanced oil recovery projects.
PubDate: 2023-06-01
- Determining the drilling mud window by integration of geostatistics,
Abstract: Accurate knowledge of pore and fracture pressures is essential for drilling wells safely with the desired mud weight (MW). Overpressure occurs when the pore pressure is higher than the normal hydrostatic pressure. There is a challenge regarding the pressure studies domain in an oilfield in SW Iran, where lack of geo-mechanical data limits exact mud window calculation. Also, the reservoir generally consists of carbonate rocks and contains no shale interbeds, so mechanical stratigraphy based on Gamma ray could not be applied. This study is to provide safe drilling considering MW to prevent the flow or loss in the vicinity of the new wells in the studied field. In this research, the formation pressures and mud window models are determined by combining geostatistical, intelligent, and conditional programming models and compared with real data. The conditional programming was also used to correct small out-of-range data. The highest correlation between the final effective pressure and velocity cube was observed in lower Fahliyan Formation with 0.86 and Ilam with 0.71.The modeled MW difference ranged between 2.5 and 30 PCF. Also, the maximum modeled MW is 150 PCF in the upper Fahliyan Formation. Heavy mud of more than 130 PCF is suggested for drilling the Khalij member and continues to the end of stratigraphy column. Best observed correlation comparing the drilled and modeled MW, especially achieved in the Fahliyan reservoir Formation with more than 100 PCF and the Ilam Formation with 80–100 PCF. Finally, 3D formation pressures are presented and recommended for further safe drillings.
PubDate: 2023-06-01
- Quantitative characterization of igneous rock thermal effect on sandstone
reservoir reconstruction based on heat conduction
Abstract: The X oilfield is the first sandstone reservoir under the influence of igneous rock, which is discovered and put into development in Bohai Sea. Compared with the conventional sandstone reservoir, the oilfield is affected by magmatic activity, the reservoir heterogeneity is serious and the micro pore structure is complex, which results in the poor correlation between mobility calculated by traditional methods and specific oil production index. In order to predict oil well productivity and guide oilfield well location deployment, the quantitative transformation of sandstone reservoir affected by igneous rock is studied in this paper. According to the distribution mode of igneous rock in the reservoir, a permeability model of quantitative characterization for sandstone reservoir permeability is established, in which the influences of heat conduction, reservoir skeleton deformation and stress sensitivity are considered, and then the igneous rock influence on the ground temperature field of surrounding rock is simulated by ANSYS software. According to the relationship between porosity and permeability, the quantitative transformation effect of igneous rock thermal effect on sandstone reservoir is quantitatively characterized. The reservoir temperature field variation law, different baking types and igneous rock thickness influence on the transformation degree of sandstone reservoir are analyzed. Finally, the X oilfield is taken as an example to verify the research method, and the second batch of wells location deployment is successfully guided. The results show that the thermal effect of igneous rock reduces the permeability of reservoir, and the temperature of reservoir increases first and then decreases with time, the rising speed is faster than the falling speed, with the increase in distance from igneous rock, the maximum temperature of reservoir shows a downward trend, in the case of baking on both sides, the heat of igneous rock is greater, which makes the temperature of surrounding reservoir rise more, and the transformation effect on reservoir is more obvious. The influence range of igneous rock thickness on permeability is basically the same, but with the increase in thickness, igneous rock has a greater influence on surrounding rock. The research example of the X oilfield shows that the existence of igneous rock reduces the reservoir physical properties of development wells by 1.2–5.9 times. The correlation between igneous rock physical properties and specific oil production index corrected by this method can reach 0.9478. By avoiding igneous rock, the comparative production of the second batch of development wells is 1.5 times that of the first batch of development wells.
PubDate: 2023-06-01
- Condensation distribution and evolution characteristics of water vapor in
annulus of flexible riser
Abstract: Water vapor penetrating an annulus causes condensation and corrosion and endangers the safe operation of the flexible riser. However, in current studies, the condensation of water vapor in the annulus is modeled based on the film condensation hypothesis, which assumes that the metal material is uniformly corroded. This assumption differs from the true corrosion incidents, which are usually initiated by localized corrosion. To further study the condensation law of water vapor in a flexible riser annulus, the evolution of water vapor condensation on the wall surface of a sapphire reactor was evaluated using an annular condensation experimental device. A water vapor condensation growth model was established to analyze the condensation law and its influencing factors. The results show that the maximum radius of condensate droplets on the annular wall surface is approximately 0.48 cm, the average radius of droplets is approximately 0.35 cm, and the volume of condensate that can be accommodated in the 18 × 18 mm simulation area is approximately 0.5 cm3. After the droplet reaches the departure radius and falls off a surface, the time of recondensation is faster than that of the first condensation. The condensation surface coverage increases rapidly in the early stage and then gradually slows down. After stabilization, the maximum coverage can reach 80%. Parameter analysis suggests that the number of fixed nucleation points on the condensation wall affects the time to reach the departure radius and the increasing rate of surface coverage. However, the number of fixed nucleation points has minimal influence on the departure radius and coverage outcomes. The findings of this study establish a theoretical foundation for predicting dropwise condensation behaviors in annulus of pipelines and developing corrosion protection strategies that modify the wall contact angle or structure.
PubDate: 2023-05-27
- Factors affecting casing equivalent stress in multi-cluster fracturing of
horizontal shale gas wells: finite element study on Weirong Block,
southern Sichuan Basin, China
Abstract: Multi-cluster fracturing technology was often used in horizontal well reservoir reconstruction to achieve production increase, which also affected casing equivalent stress distribution. This paper focuses on multi-cluster fracturing and establishes a fracturing model in line with the reality. The three-dimensional finite element model of multi-cluster fracture-formation-cement sheath-casing was proposed, the influence of cluster spacing and fracturing cluster number on casing equivalent stress was studied. On this basis, a single segment 8-cluster three-dimensional finite element model was developed. The influence of rock elastic modulus, casing inner wall pressure, geostress change and elastic modulus of cement sheath on casing equivalent stress was simulated from two aspects of uniform and non-uniform extrusion of wellbore. Actual data was used and analyzed for the fracturing section of a well in Weirong Block, southern Sichuan Basin, China. The results showed that the casing equivalent stress decreased with the increase of fracture dip angle. The casing equivalent stress increased with the increase of cluster spacing; however, it decreased with the increase of rock elastic modulus. The casing equivalent stress increased with the increase of casing wall pressure. Also, the cracks extrude the casing evenly did not affect the change on casing equivalent stress. It was also found that, when casing was uniformly squeezed by multiple fractures, the difference of ground stress had little effect on casing equivalent stress, while non-uniform extrusion had greater effect on casing equivalent stress. Further, when there was no wellhead pumping pressure, the casing equivalent stress increased with the increase of the elastic modulus of the cement sheath, and decreased on the contrary. The elastic modulus of rock was lower than that of cement sheath, and the casing equivalent stress increased with the increase of the elastic modulus of cement sheath, and decreased on the contrary. The research results had certain guiding significance for the prevention and control of casing damage in fracturing section.
PubDate: 2023-05-02
