Numerical Simulation Study on Miscible EOR Techniques for Improving Oil Recovery in Shale Oil Reservoirs

Shale formations in North America such as Bakken, Niobrara, and Eagle Ford have huge oil in place, 100—900 billion barrels of oil in Bakken only. However, the predicted primary recovery is still below 10%. Therefore, seeking for techniques to enhance oil recovery in these complex plays is inevitable. Although most of the previous studies in this area recommended that CO2 would be the best EOR technique to improve oil recovery in these formations, pilot tests showed that natural gases performance clearly exceeds CO2 performance in the field scale. In this paper, two different approaches have been integrated to investigate the feasibility of three different miscible gases which are CO2, lean gases, and rich gases. Firstly, numerical simulation methods of compositional models have been incorporated with local grid refinement of hydraulic fractures to mimic the performance of these miscible gases in shale reservoirs conditions. Implementation of a molecular diffusion model in the LS-LR-DK (logarithmically spaced, locally refined, and dual permeability) model has been also conducted. Secondly, different molar-diffusivity rates for miscible gases have been simulated to find the diffusivity level in the field scale by matching the performance for some EOR pilot tests which were conducted in Bakken formation of North Dakota, Montana, and South Saskatchewan. The simulated shale reservoirs scenarios confirmed that diffusion is the dominated flow among all flow regimes in these unconventional formations. Furthermore, the incremental oil recovery due to lean gases, rich gases, and CO2 gas injection confirms the predicted flow regime. The effect of diffusion implementation has been verified with both of single porosity and dual-permeability model cases. However, some of CO2 pilot tests showed a good match with the simulated cases which have low molar-diffusivity between the injected CO2 and the formation oil. Accordingly, the rich and lean gases have shown a better performance to enhance oil recovery in these tight formations. However, rich gases need long soaking periods, and lean gases need large volumes to be injected for more successful results. Furthermore, the number of huff-n-puff cycles has a little effect on the all injected gases performance; however, the soaking period has a significant effect. This research project demonstrated how to select the best type of miscible gases to enhance oil recovery in unconventional reservoirs according to the field-candidate conditions and operating parameters. Finally, the reasons beyond the success of natural gases and failure of CO2 in the pilot tests have been physically and numerically discussed

A Systematic Design Approach For Bulk Gel Treatments Based On Gel Volume-concentration Ratio In Field Projects

Controlling excessive water production in mature oil fields has always been a desired objective of the oil and gas industry. This objective calls for planning of more effective water-control gel treatments with optimized designs to obtain more attractive outcomes. Unfortunately, planning such effective treatments remains a dilemma for reservoir engineers due to the lack of methodical design tools in the industry. This paper presents a novel systematic design approach for polyacrylamide-based bulk gel treatments by classifying their field projects according to the gel volume-concentration ratio (VCR) into three design types. In terms of one another, the approach estimates either the gel volume or the gel concentration based on the average gel VCR of each design and formation type. First, field data was collected from SPE papers and reports of US Department of Energy for 65 gel projects conducted between 1985 and 2020. Stacked histograms were then used to examine distributions of field projects according to the gel VCR and the formation type. A comprehensive review of channeling strength indicators in field gel projects was performed to identify the classification criterion and design types of gel treatments. Based on the mean-per-group concept, the average gel VCR was assessed for each design type and formation type to build the design approach. Approximations for the overall gel concentration and correlations for extremum designs were established and included in the approach. The study showed that the gel VCR is a superior design criterion for in-situ forming bulk gel treatments. It aggregates gel treatments into three project groups and ranks them according to the channeling strength. The three project groups have clear separating VCR intervals (3 bbl/ppm) and each of them is mostly dominated by one formation type. The VCR range of each project group represents one design type of the bulk gel treatments. The channeling type is the criterion of grouping and group-wise ranking of gel projects with respect to the gel VCR. In design type I, VCRs/ppm are used to treat pipe-like channeling usually exhibited by unconsolidated sandstones. More balanced VCRs of 1–3 bbl/ppm are designed for fracture-channeling frequently presented in naturally-fractured formations (design type II). Large gel treatments with VCR\u3e3 bbl/ppm are performed to address matrix-channeling often shown in matrix-rock formations (design type III). Prediction results demonstrated that the VCR approach reasonably estimates volumes and concentrations of both single gel treatments and averaged field projects in training and validation samples. Besides its novelty, the new approach is systematic, accurate, practical, and will facilitate the optimization of future gel treatments to improve their performances and success rate

A Novel Numerical Model of Gelant Inaccessible Pore Volume for in Situ Gel Treatment

Inaccessible pore volume (IAPV) can have an important impact on the placement of gelant during in situ gel treatment for conformance control. Previously, IAPV was considered to be a constant factor in simulators, yet it lacked dynamic characterization. This paper proposes a numerical simulation model of IAPV. The model was derived based on the theoretical hydrodynamic model of gelant molecules. The model considers both static features, such as gelant and formation properties, and dynamic features, such as gelant rheology and retention. To validate our model, we collected IAPV from 64 experiments and the results showed that our model fit moderately into these lab results, which proved the robustness of our model. The results of the sensitivity test showed that, considering rheology and retention, IAPV in the matrix dramatically increased when flow velocity and gelant concentration increased, but IAPV in the fracture maintained a low value. Finally, the results of the penetration degree showed that the high IAPV in the matrix greatly benefited gelant placement near the wellbore situation with a high flow velocity and gelant concentration. By considering dynamic features, this new numerical model can be applied in future integral reservoir simulators to better predict the gelant placement of in situ gel treatment for conformance control

Fabrications and Applications of Micro/nanofluidics in Oil and Gas Recovery: A Comprehensive Review

Understanding fluid flow characteristics in porous medium, which determines the development of oil and gas oilfields, has been a significant research subject for decades. Although using core samples is still essential, micro/nanofluidics have been attracting increasing attention in oil recovery fields since it offers direct visualization and quantification of fluid flow at the pore level. This work provides the latest techniques and development history of micro/nanofluidics in oil and gas recovery by summarizing and discussing the fabrication methods, materials and corresponding applications. Compared with other reviews of micro/nanofluidics, this comprehensive review is in the perspective of solving specific issues in oil and gas industry, including fluid characterization, multiphase fluid flow, enhanced oil recovery mechanisms, and fluid flow in nano-scale porous media of unconventional reservoirs, by covering most of the representative visible studies using micro/nanomodels. Finally, we present the challenges of applying micro/nanomodels and future research directions based on the work

A Comprehensive Review of Experimental Evaluation Methods and Results of Polymer Micro/nanogels for Enhanced Oil Recovery and Reduced Water Production

In recent years, polymer micro/nanogels which are re-crosslinked polymers with 3D networks, have attracted a lot of interest in Enhanced Oil Recovery (EOR) field. In size of micro/nanometers, these gel particles are designed to be conformance control agents for in-depth fluid diversion, and various experimental research have been undertaken to investigate the possibilities of applying micro/nanogels in oilfield. However, it is still unclear that how to utilize micro/nanogels to their full potential in oilfield because the transport mechanisms and EOR mechanisms of micro/nanogels are not well studied currently. By reviewing experimental evaluations and corresponding results of micro/nanogels, including evaluation of particle physiochemical properties, transport, and potential EOR mechanisms, the review aims to discuss the evaluation of micro/nanogel particles, transport issue in many experimental designs and the debates of EOR mechanisms. Finally, we present the current challenges of micro/nanogels application and recommend the future research directions based on the review

Pattern Recognition for Steam Flooding Field Applications based on Hierarchical Clustering and Principal Component Analysis

Steam flooding is a complex process that has been considered as an effective enhanced oil recovery technique in both heavy oil and light oil reservoirs. Many studies have been conducted on different sets of steam flooding projects using the conventional data analysis methods, while the implementation of machine learning algorithms to find the hidden patterns is rarely found. In this study, a hierarchical clustering algorithm (HCA) coupled with principal component analysis is used to analyze the steam flooding projects worldwide. The goal of this research is to group similar steam flooding projects into the same cluster so that valuable operational design experiences and production performance from the analogue cases can be referenced for decision-making. Besides, hidden patterns embedded in steam flooding applications can be revealed based on data characteristics of each cluster for different reservoir/fluid conditions. In this research, principal component analysis is applied to project original data to a new feature space, which finds two principal components to represent the eight reservoir/fluid parameters (8D) but still retain about 90% of the variance. HCA is implemented with the optimized design of five clusters, Euclidean distance, and Ward\u27s linkage method. The results of the hierarchical clustering depict that each cluster detects a unique range of each property, and the analogue cases present that fields under similar reservoir/fluid conditions could share similar operational design and production performance

A Dual-Porosity-Stokes Model and Finite Element Method for Coupling Dual-Porosity Flow and Free Flow

In this paper, we propose and numerically solve a new model considering confined flow in dual-porosity media coupled with free flow in embedded macrofractures and conduits. Such situation arises, for example, for fluid flows in hydraulic fractured tight/shale oil/gas reservoirs. The flow in dual-porosity media, which consists of both matrix and microfractures, is described by a dual-porosity model. And the flow in the macrofractures and conduits is governed by the Stokes equation. Then the two models are coupled through four physically valid interface conditions on the interface between dual-porosity media and macrofractures/conduits, which play a key role in a physically faithful simulation with high accuracy. All the four interface conditions are constructed based on fundamental properties of the traditional dual-porosity model and the well-known Stokes-Darcy model. The weak formulation is derived for the proposed model, and the well-posedness of the model is analyzed. A finite element semidiscretization in space is presented based on the weak formulation, and four different schemes are then utilized for the full discretization. The convergence of the full discretization with the backward Euler scheme is analyzed. Four numerical experiments are presented to validate the proposed model and demonstrate the features of both the model and the numerical method, such as the optimal convergence rate of the numerical solution, the detail flow characteristics around macrofractures and conduits, and the applicability to the real world problems

Proton pump inhibitors may enhance the risk of digestive diseases by regulating intestinal microbiota

Proton pump inhibitors (PPIs) are the most used acid-inhibitory drugs, with a wide range of applications in the treatment of various digestive diseases. However, recently, there has been a growing number of digestive complications linked to PPIs, and several studies have indicated that the intestinal flora play an important role in these complications. Therefore, developing a greater understanding of the role of the gut microbiota in PPI-related digestive diseases is essential. Here, we summarize the current research on the correlation between PPI-related digestive disorders and intestinal flora and establish the altered strains and possible pathogenic mechanisms of the different diseases. We aimed to provide a theoretical basis and reference for the future treatment and prevention of PPI-related digestive complications based on the regulation of the intestinal microbiota

Evaluating the Performance of Hydraulic-Fractures in Unconventional Reservoirs using Production Data: Comprehensive Review

Understanding the performance of the reservoir productivity in the post-stimulation conditions has recently gained an extensive emphasis from the specialist researchers and operators. Although there have been different tools used to evaluate the fracturing process and to predict the well performance, using production data as an indirect tool to calibrate the fracturing design and to forecast the reservoir performance has been considered the most potential technique. However, different methods with a high ambiguity have been used in this area of research over the last decade. Therefore; developing, screening, and specializing different methods and techniques to diagnose and evaluate the post-fracture reservoir performance by using flowback data has a significant priority. Determining the performance of hydraulic fractures from flowback data is considered the actual calibration to estimate the effective volume, length, height, conductivity, and width of hydraulic fractures. This paper presents a comprehensive review on most of the approaches, which have been recently introduced in this area of research, including their applicability, pros and cons. Furthermore, this study explains how each method can be valid at a specific time range. The potential tools, which could be more successful to be used in this direction of research, have been extensively discussed and recommended