Journal of Petroleum Science and Engineering最新文献

The cement sheath interface is an important component of the wellbore barrier system. A mismatch between the interfaces of the cement sheath may result in leakage. This paper presents a method for assessing cement sheath interface adaptability based on the Dundrus composite parameter method, and the corresponding test flow for evaluating cement sheath integrity is provided for verification. According to the calculation results, stress concentrations are more common at the first interface of the cement sheath. The second interface is relatively unaffected by stress concentration under the same working conditions as the first interface. Stress concentration at the interface can be effectively alleviated by increasing the elastic modulus of the cement sheath or decreasing the Poisson's ratio. However, if the elastic modulus of the cement sheath increases, the cement sheath will be more susceptible to plastic deformation, and the strength coefficient of the singular stress field at the interface will decrease by approximately 10%. As a result, reducing the Poisson's ratio of the cement sheath effectively reduces stress concentration at the interface end. Especially in sandstone formations, the strength coefficient of the singular stress field at the interface can be reduced by 63% at most, resulting in a good interface adaptability. As a result of the above calculations, three groups of cement slurries with different mechanical parameters were selected and tested. As expected, the test results confirmed the applicability of the method. In light of the above results, cement slurry engineers should factor in the stress singularity effect when designing cement slurry systems. To prevent plastic deformation, high-strength and low-elastic cement should be employed, and the Poisson's ratio should be appropriately reduced in order to prevent interface stress concentration, thereby ensuring the integrity of the cement sheath in an increasingly harsh downhole service environment.

There is a need to develop computationally efficient models for oil and gas production from naturally fractured reservoirs. In this paper, we present an efficient, integrated fracturing-production simulator by combining a boundary element method (for fracture propagation) and a general Green's function solution (for fluid flow) that eliminates the need to discretize the matrix domain. First, the model is validated against analytical solutions and then compared with a fully numerical model. A comparison of results and computation time shows that our simulator significantly reduces the computation cost without any significant loss in accuracy. The simulator is then applied to investigate the effect of cluster spacing and pumping schedule on production from a hydraulically fractured horizontal well in a naturally fractured reservoir. The results show an optimal cluster spacing that can maximize the contact area between fractures and reservoirs while maintaining the highest production rate. Based on the chosen optimal cluster spacing, we observe that changes in the pumping schedule can have an impact on the production rate due to changes in the created fracture network.

Aiming at casing damage in the salt rock, the creep characteristics of the salt rock in the southeastern China are investigated by triaxial creep test. Based on the experimental results, an unsteady creep model which can describe the creep and steady stage of the salt rock is set up combined with the Kelvin model and the Heard model by the deviation stress. The unsteady creep model was used to calculate the radial displacement of the wellbore based on ABAQUS platform. The results show that the higher casing pressure can effectively reduce the creep displacement of the rock, and the higher horizontal principal stress and the overburden pressure can increase the formation deviation stress, thus increasing the creep displacement of the salt rock. The maximum displacement of the casing caused by the formation is 25 mm by a string simulation device. The elastic modulus of the cement is effectively reduced by adding hollow ceramic particles to the cement, so that the strain energy added to the wellbore system by the formation radial creep can be fully absorbed by this cement sheath. Combined with the numerical simulations and the cement tests with the addition of hollow ceramic particles, a casing deformation prevention method is finally established in this paper.

As an important tool for tripping of a drill-string, a drill-pipe (DP)-slip system directly affects both the service life of a DP and the target depth it can reach. In this paper, a finite element (FE) model programmed in ABAQUS is used to simulate interactions within a DP-slip system. For this model, materials, geometric dimensions, loads, and boundary conditions were determined from an actual DP-slip system. A special attention has been paid on the stress field of the slip insert and the DP focusing on the geometric parameter optimization of the slip insert with regards to the stress distribution, wherein factors like a longitudinal groove number in slip insert, a number of slip inserts, and a number of row spacing of slip inserts are considered. Numerical results show that the circumferential stress distribution and stress distribution in the direction of DP axis change for both the DP and slip insert and that the stresses of the inner surfaces are higher than that of the outer surfaces. Effects of geometric parameters of the slip insert on the stress distributions of both DP and slip insert are studied and the corresponding optimized values are obtained, which can be used when designing slip insert tools.

Weighting materials such as hematite are used to increase the density of cement slurries for different applications. Density variation (DV) across the cement column due to heavy particles sedimentation is a critical problem that results in disruption in hardened cement properties such as porosity and strength. In this work, two heavy-weight cement systems using Micromax and hematite were evaluated in terms of rheological properties, fluid loss, compressive and tensile strength, petrophysical properties and dynamic elastic properties. This study especially focused on the sedimentation problem associated with using hematite as a weighting material in well cementing. Different advanced techniques such as scanning electron microscope (SEM), nuclear magnetic resonance (NMR), and computerized tomography (CT) scan were used to investigate the potentiality of using Micromax to solve this problem. NMR, and CT-scan confirmed the results of the conventional method of DV that showed that the Micromax-weighted cement is more homogeneous with only 1.4% DV vertically along the samples. The Micromax-based system had lower porosity and permeability as compared to the hematite-based system. The Micromax-based cement was more flexible than the hematite-based system in terms of the elastic properties. Both cement systems showed a very similar performance regarding rheological and fluid loss properties. Micromax proved its potentiality to minimize the sedimentation problem encountered while maintaining the other recommended cement characteristics.

Catalytic methane conversion (CMC) could be realized in situ in gas reservoirs. Through this process, a new environment-friendly energy carrier - hydrogen-can be generated inside the hydrocarbon field's porous medium. This method can become a new low-carbon, cost-effective method for hydrogen production. For this purpose, the catalyst has to be delivered into the reservoir, and the temperature inside the active zone of the reservoir has to be raised. The effective way to increase the temperature directly inside the reservoir is by injection of air and combustion of saturating liquid hydrocarbons. This research investigates the CMC process at conditions achieved in the reservoir due to oil in situ combustion (ISC). Numerical and physical modeling of in situ hydrogen generation from methane was performed using forward wet ISC of oil to heat the reservoir. The results of the unique experiment on a crushed oil-saturated core-packed model with different inlet flow rates of air, steam, and methane in the combustion tube (CT) are presented in the current study. The experiment consisted of four parts with different regimes and operational parameters: forward ISC of oil, steam methane reforming (SMR) at 450 °C and 8.9 MPa, SMR at 550 °C and 8.9 MPa, SMR at 550 °C and 2.3 MPa. The combination of these processes has led to the generation of hydrogen and methane conversion rates of up to 40% (during the combustion stage). Comparatively, low hydrogen yield was observed within the experiment, possibly due to the secondary reactions. However, irreversible reduction of oil viscosity, density, sulfur, and asphaltenes content was achieved within the experiment. The influence of catalyst and generated hydrogen on oil quality is one of the additional positive effects of in situ hydrogen generation. The numerical simulation of the experiment was performed for further study of the optimal hydrogen generation conditions. The proposed kinetic model consisted of ISC reactions and hydrogen generation reactions. The primary purpose of this experiment was to validate the principle study of the possibility of in situ hydrogen generation and simulate the processes in the core model physically and numerically.

Understanding the effects of temperature and pressure on the supercritical CO₂ degradation of wellbore cement with NaCl content is essential for cementing oil wells in Brazil's deepwater pre-salt basin. The behavior of the cement paste used in cementing oil wells in this environment is very complex, with significant amounts of CO₂ and a thick salt layer that requires a high demand on special wellbore cement capable of adequately sealing and assuring stability to the oil wells. For these reasons, the objective of this study was to investigate the effect of NaCl in cement on oil wells exposed to supercritical CO₂ simulating pre-salt reservoir conditions. Cement slurry samples were prepared using Class G Portland cement (API 10 A), NaCl, water-to-cement (w/c) ratio of 0.46, and deionized water with (0 and 10% NaCl content). Supercritical CO₂ experimental runs were carried out under different conditions for 7 h. Before and after exposure to CO₂, the material was characterized by multiple analytical techniques. The results indicate that salt under temperature and pressure and the scCO₂ environment accelerates the carbonation process by decomposing the hydrated product, increasing the CaCO₃ content. In this scenario, investigations of the effect of adding NaCl to cement pastes are limited.

The mineralogical brittleness index (MBI) of organic-rich shale formations is one of the key parameters to identify the optimal production well locations and optimize hydraulic fracturing. Since we as a community don't understand the exact physical relationship between the MBI and seismic properties from well logs, we have used traditional approaches like the log-based brittleness index (LBI) and the elastic brittleness index (EBI) to quantify the rock brittleness from seismic data and well logs. The LBI method is easy to use but is empirically derived from the porosity and sonic logs. On the other hand, the EBI method is dependent on the average values of Young's modulus and Poisson's ratio but is not physically meaningful in practice. Therefore, we develop a deep learning approach to obtain a more reliable MBI model from seismic properties and enhance the interpretability with Shapley values. First, we analyze the statistical relationship between the MBI and eight seismic properties from well logs and distinguish the influential input variables for the MBI prediction, such as bulk density, Young's modulus, and Poisson's ratio. Second, we find a multivariate linear regression (MLR) model with three input properties and quantify the relative statistical contribution of each input based on Shapley values. Third, we use a deep neural network technique to derive the nonlinear estimation model with a better fit to the MBI data than the traditional methods. We test and verify our approach on field log and core data from the Wolfcamp shales in the Permian Basin, Texas. In conclusion, this workflow can provide a more interpretable and accurate MBI estimation from seismic properties to enhance unconventional shale reservoir characterization.

Acidizing is a well-stimulation operation that consists of injecting a reactive fluid into the rock formation. When in carbonate rocks, the dissolutions create conductivity channels called wormholes. The pattern formed depends on the flow rate, thermodynamic conditions, and several rock-fluid interaction parameters. Despite acidizing operations being well-known, several factors or conditions affecting wormhole formation are not thoroughly tested in the laboratory. We observe a difficulty in the literature to summarize the main aspects involved in wormhole formation. At the same time, understanding how each parameter could affect the wormholing process can help to optimize the acidizing design, maximizing the financial return. Therefore, this review article discusses the main studies about the parameters affecting the wormhole's formation: acid concentration, reaction rate, flow rate, temperature, core sample dimension, and heterogeneity. The main idea here is to provide a resume of the most relevant works founds in our literature review and a reference base for researchers interested in carbonate acidizing. The pore-volume-to-break-thought (PVbt) plotted as a function of the flow rate is the most common approach to evaluate the dissolution pattern observed for each reactive fluid-rock combination. However, PVbt should be seen more comprehensively as a consequence of advection-diffusion-reaction balance. Other essential aspects that need to be considered to obtain a significant representation of the PVbt plots are sample geometry and the initial rock saturation.

A large body of experimental research supports the effectiveness of Low Salinity Water Injection (LSWI) for enhanced oil recovery from carbonate reservoirs in laboratory scale. Development of robust predictive smart models connecting effective parameters controlling this complex process to Final Recovery Factor (RF_f), as the target parameter, is of a paramount importance. The main objective of this research work is to develop intelligent models using Artificial Neural Network (ANN), Support Vector Machine (SVM), Decision Tree (DT), Random Forest (RF), and Committee Machine Intelligent System (CMIS) to forecast performance of LSWI in carbonates using experimental data reported in the literature. Random Search (RS) and Anneal (AL) algorithms were used for optimization of hyperparameters. After data collection from 47 reliable coreflooding studies (582 data points), a rigorous data preprocessing was conducted to ensure quality of the database. Features selection process was used to determine the main parameters controlling LSWI performance in carbonates: brine permeability (K_b), core diameter (d), porosity (Φ), and residual water saturation (S_wi) of the core, HCO₃⁻ concentration, and salinity (S) of the connate brine, the salinity (S) of the injected brine, and initial recovery factor (RF_i) which were used for development of the models. We considered initial oil recovery (RF_i) in this research work, which was not considered in previous works reported in the literature. The applicability domain analysis showed that training and testing response outliers were zero and 9, respectively, indicating acceptable quality of the database. Performance of the developed smart models was analyzed and compared using statistical and graphical error analysis methods. The best performance was obtained for the RF model with Root Mean Square Error (RMSE) of 2.497 and 5.757 for training and testing datasets, respectively, which exhibits a very good agreement with the experimental data.